Archive for the 'Beyond Unboxing' Category


Beyond Unboxing: The Great Cambridge Chainsaw Massacre; Ryobi RY40511 Cordless Chainsaw

Jun 23, 2014 in Beyond Unboxing, Reference Posts

Hello everyone,

I’ve decided that I need a career switch. After 2-3 years of being a shop ninja, I’ve decided to move on and become a…

…Chainsaw murderer. I’ll see you shortly.

This is probably the shortest turnaround time for a Beyond Unboxing post ever. Around 2 in the afternoon on Sunday, I received a tip from Shane and the motley crew at Freefly about this device and how it might be worth looking into.  An hour later, I was blitzing down Storrow Drive heading due west towards the Home Depot in Watertown, MA on a war path to obtaining one. Just to check it out. And an hour after that, it was parted out completely on my shop bench.

Why the hell do I find tearing apart consumer products so amusing? Probably because I know both how the sausage is made as well as how the sausage will be cooked and eaten. As with other Beyond Unboxing posts, the focus is how to divert these products into small electric vehicle or robotics applications, in the context of teaching newbie builders and hackers to be resourceful and to see parts everywhere.

From the past few years in meddling with lithium ion batteries and brushless motors, I’m always giddy to see them used in more and more tools and common implements, but they’ve been primarily in the domain of the ultra-high-end until recently: Spending $300-400 on a drill for parts, to me, is not really worthwhile when you can engineer around the same problem using other commercial parts, or even custom-made ones, for much less. This is part of the appeal of things like mini-jasontrollers and angle grinder gearboxes: To duplicate the functionality would imply spending an order of magnitude or more, and the chopped up commercial product would be workable for all but the most stringent and demanding of applications (Former students, I’m counting on you to put T-nuts and Jasontrollers in space).

I’m glad to see these lithium ion and brushless systems coming down in price and going up in power. The advent of the Inexpensive Chinese Brushless Motor has been beneficial to many industries. First they started small with compact drills and drivers, then moved up to saws, and now bigger power tools whose domains were previously dominated by gas engines. Once you get to things with power levels in the hundreds and thousands of watts, you can ride them. Perhaps the advent of this tool is the closing of a circle of life for vehicle builders: Years ago, kids would build shoddy vehicles powered by gasoline engined chainsaws and leafblowers. Now, they can finally do so with electric. And have it not suck.

Here’s what’s inside a Ryobi model RY40511 “40v” cordless chainsaw. I’m surmising I know (directly or through only 1 or 2 degrees of separation) the intern who first conceived this and put it together, because as you’ll see, the hardware is quite familiar….

First off, this is what the box looks like. GAS-LIKE POWER! I can’t believe you guys trademarked that. I mean, it’s basically in the vein of “polypropylene-like” modeling resins for expensive-ass 3D printers (sorry, Objet!) or “fat-like” additives for greasy fast food.

…and would it kill you to use a longer box?! What is this, Minecraft? How many of these get bent up and broken in shipping?

Putting a picture right on the box of an outrunner. Damn, I wish I paid more attention to the aisles of Home Depot now! Maybe I could have gotten on this months before!

Step 1: unboxing. This is pretty much one of the only normal pictures this post will contain, so savor it. Included is the saw unit, a battery, and a charger.

The battery in all its glory. I’d wager by the oblong shape of things, it’s an 18650 pack made with 1.5-1.8Ah “power” cells laid flat in a “W” pattern. You’ll see later that this wasn’t a bad guess – being a little familiar with the state of the industry helps (and some math: 55Wh / 40V is about 1.4, figure in some overhead).

The battery has two terminals besides the + and – called T1 and T2. Most lithium packs have a connection to the battery management system or similar, and this format varies by manufacturer.

While I was plotting the deconstruction of the saw, I put the battery on its charging dock. It’s a fast charger – 1 hour or less.

I’m extremely happy that lithium ion power tools are becoming the norm, because that means an end to the era of those irritating as fuck “Revive your battery!!!” kits and guides sold by industrial charlatans all over eBay and the like, because those clutter up every possible search you can make with power tools terms. That only “works” for nickel cells (it’s called Zapping, and it doesn’t actually fix much in the long term), and if you tried that with a lithium battery, congratulations on your newly made IED.

Taken out of the box. Where a 40-50cc gas engine would go is a big hollow battery cavity.

Hmm, weird. The tabs inside the tool would only connect to what is called T2. This will come into play later.

And here is the whole device. It weighs about 10 pounds without the battery, which is way lighter than a gas powered saw. Chain bar oil container at the front, variable squeeze handle at the back. I liked how it felt – it’s definitely designed from the ground up to be an electric saw, and not a crude rush to market retrofit of a gas saw.

That’s all the generic unboxing post you’ll get from me.

Break out the wrenches and hex keys! The majority of the body screws on this thing are T25 torx. First to come off is the chain cover, with four screws.

The two M8 nuts come off also, and the drive sprocket and tensioner assembly are revealed.

The chain and bar assembly come off easily once the nuts are removed.

To remove the drive sprocket and flange, you’ll need a snap ring plier, or some tiny screwdrivers and a bucket of patience. Retaining rings used to be my most hated component when it came to taking something apart in my middle school and high school years, because I didn’t have retaining ring pliers!

But now I love them. Welp.

The smaller case screws take T20 torx. There’s three on this side of the saw.

However, I found that the side plates were keyed into the gray top. There’s more T25 screws on the top plate, and then it lifts off pretty easily:

…to reveal the Jasontroller… uhhh, okay, Jasontroller. Two 470uF bus capacitors and discrete FETs, two per leg of the three-phase bridge, is all I can see at this point. The FETs are Alpha-Omega (what kind of semiconductor company name is that!?) AOT470 type – kind of low end of the market, but they’ll get the job done I suppose.

The board is actually quite well designed and marked. Hell, everything is labeled already! Even the motor hall sensors and the trigger switch wiring harness. The ‘throttle’ is 5 pins labeled S, S-, S+, -, and +. The “communication” wire leads to terminal T2 on the battery.

If I had to guess, this assembly contains a “throttle switch” that tells the controller you’ve hit the trigger (before the signal changes), and the S, -, and + are what would be a 3-pin Potentiometer sensing element or Hall sensor sensing element. I haven’t verified this on the actual throttle, by the way, but it makes sense.

Back to the saw! This assembly in front of the motor appears to be a bar oil pump driven from the motor, or perhaps feeding the motor. It has to come out for the motor to be removed. Two T25s screw it into the motor.

But that wasn’t all. To remove the motor, I had to be able to take the other half of the plastic shell off. This took a longer T25 bit than I had in the form of that green set. It was 5:45 PM on Sunday.

I’m proud of the Commonwealth of Massachusetts and the City of Boston for not supporting the usage of speed cameras, and of Mikuvan for not…. uhh, exploding. The closing staff at HF were waiting for me at the front door when I pulled in. Thanks guys!  This is a T-handle Torx set, 42926.

(The observant would note that the local Home Depots close at 9pm, but…)

With my newfound long-reach Torx set, the case screws come off.

The goods are within sight. Check out that motor – it’s like a pointier, more gritty version of a Hobbyking outrunner!

Hell, it even says the size on there. However, this motor house, whoever they are, seems to label their motors properly: By stator diameter and stator length! Hobbyking would actually call this, in all likelihood, a 63-54 type motor. The can length compares.

The motor is attached to the controller through these terminal block things. I guess they wanted something to distinguish them from an R/C outrunner. Should have used 4mm Bullet connectors!

The motor sits over a Hall sensor board. This board uses 120-degree oriented Hall effect sensors, but what is interesting is that they’re surface mount devices, and oriented vertically. Having a custom motor without a nosecone, unlike the R/C outrunners, would let you do that. Having the sensors in such close proximity to the magnets’ ends, not sensing through a steel can, surely contributes signficantly to their ability to not drift significantly out of time at high speeds (That video is the reason why we made those Hall sensor boards slotted and adjustable).

Removing those two T25 screws on the oil pump reveals the pump mechanism. Now, this thing is clever. So I’ve never taken apart a chainsaw before this point, so I’m not sure if this is in common use, but it’s cool anyway. The little gear inside the pump body is engaged by a helical spring slipped over the motor shaft (more visible in later pictures). This spring is a slumlord worm gear, meshing with the pump’s own gear.

I didn’t get a picture of the right side of the pump where it connects to the black rubber tube, but it’s a lobe looking thing that acts like a one-rotor gear pump. It’s enough to squirt a little chain bar oil onto the blade steadily, nothing special.

Continuing the motor removal with 3 more T25 screws:

And the system is out! I love this motor. Not only does it have a big fan cast into the end, but it has a normal shaft. It’s 12mm diameter, 10mm across flats. You can straight up slam a belt cog or chain sprocket over this and use the flats with some giant set screws and be done with it. Or, you know, just use the friggin’ chain and make a killer ice-racing machine.

I studied the plastic parts for a while. They’re mostly useless for our purposes, but looking at them is a great manufacturing study. The injection molding crew spent some time on this! And imagine those molds being made.

Here’s a close up of the controller. The construction is “jasontroller-like”. The gate drive circuitry is entirely discrete. Hell, the microcontroller is a STM8S, a staple for Chinese motor controllers. I bet this pinswaps for a generic Chinese e-bike controller pretty well.

I decided to take apart the battery next to see what’s inside. They put a bit more effort into this one: It needs a T15 security bit (with the center pin). Luckily, I had such a thing.

Four screws and the lid pops off. Holy crap, that’s a ton of electronic jibba-jabba for a battery. On the left, a big fat current sensing shunt. On the right, the battery management circuitry and charge balancing circuitry. On the very left, edge, buried under the board, were two semiconductors of some sort – I think they might be TVS clamping diodes. I decided against unsoldering each and every cell connection to try and find out, but again, it would make sense.

To lift the battery pack out, there’s two tiny hidden screws on the bottom, right where it says RYOBI. I’m going to guess that placing one of them right under the “O” was intentional.

To find hidden screws, I usually drag a screwdriver in a grid pattern around the tops of stickers and badges until it “sinks”. It is a very common tactic to hide screws under labels, stickers, and those little rubber bumpy feet if your appliance has them. Sadly, not everyone loves giant-ass cap screw heads sticking up every which way on their products like me. I’m a mechano-aesthetic snob.

A close-up look at the power side of the BMS. The 1 milliohm current sense shunt resistor has some little analog filtering passives growing on it which may or may not lead to the “T1″ and “T2″ terminals. Again, to find this out for certain is your job required unsoldering 12 cell tabs, and I wasn’t going to delve in that deep yet.

Again, if I had to guess, these do not (or do not only) lead to the T1 and T2 terminals, but is also used by the BMS to determine if it has to cut off the battery pack current.

BAM! Who was spot on about the battery? Here’s a LG Chem 21865 1.5Ah “power” cell. I say “power” because there’s often 2 ways you can optimize your lithium ion battery: for power or for energy. It all depends on how thin your terminal plates and separator is (the thinner, the more volume is occupied by active anode and cathode material, but the more resistance and hence less ability to dump amps). Most power tools are going to use “power” cells, most cell phones and low drain devices “energy” cells. For instance, in the 18650 (one size smaller) size, 3Ah “energy” cells are becoming common, and these are the next larger size and only 1.5Ah. But as will be seen, they will push current.

(Today when I learned about the world of customizing electronic cigarettes. What the great carbide-tipped fuck? Seriously, it’s like the old adage of racing – “if it moves, race it”: If it’s a electromechanical device, mod it.)

With the saw fully vivisectioned (never before has this term worked so well, since everything is still working!), let’s start doing some science.

The “throttle” is a plunger switch – on the side, it says it’s a Defond model EGA (see page 44 of this catalog). As suspected, it’s an ‘enable’ switch, plus a 3 pin potentiometric element. Which pins are which, I haven’t dug into.

First, the motor running at top speed (it sounds awesome) draws anywhere between 4.2 to 4.4 amps at the battery voltage measured at this instant in time (39.2v).

No-load waveform of the motor, showing voltage (39.2V) and electrical frequency (1,389Hz)

Scoping two of the phases tells me that at full throttle (100% pwm – no switching waveform seen, just the commutation frequency cycling of the FETs), the motor spins at 1,389Hz, or about 12,000 rpm. To get from electrical Hz to mechanical RPM, you take this waveform frequency ( “electrical cycles per second” ), multiply by 60 (“electrical cycles per minute”), then divide by the number of pairs of magnetic poles of the motor. For this motor and many R/C outrunners like it, it’s 14 magnets, so 7 pole pairs. You arrive at 11,905 RPM, with some amount of error nobody cares about outside of an instrumentation course at MIT.

At this speed, with the Hall sensor timing given, the motor’s Kv (“volts per RPM”) is approximately 300: 11,900 RPM / 39v. This is fast for a motor of this size, so to be useful in a vehicle, it will require significant gearing.

I next measured the low end – what the controller will run the motor at if you tell it to do so at the lowest possible speed. What I noticed right away is that there is a speed-dependent cut-out, presumably to prevent saw damage in the event of the chain getting stuck. Let’s find out what this is:

Cut-out speed of the controller, under load, 66 eHz or 500 RPM

Often, these motor controllers will hold the motor spinning down to a lower speed than the minimum speed they will start up at, termed the cut-out speed. For this controller, it was 66 eHz, or roughly 500 mechanical RPM.

By the way, I tested all these speeds by grabbing the motor while it was spinning, wearing leather welding gloves. At one point, the glove started smoking when I did a haul all the way out to about 65 amps. Do not do this. Ever.

If you do, do not grab the pointy fan bit.

Cut-in speed (minimum speed) of the controller, approximately 350 eHz or 3000 RPM

However, the minimum cut-in speed of the motor was about 3000 rpm. This implies the following:

  • The motor must be able to start up with relatively small load and get to this 3000 rpm speed quickly
  • Once there, it will happily be loaded to any degree provided the speed does not fall below 500 rpm.
  • I wasn’t able to accurate characterize the startup torque available during the startup routine, because that required too many hands.

This may ruin the usefulness of this setup for go-karts and related (e.g. no foot-starting available), but should be still useful for scooters (push starts with feet is part of the game). I try to tell people to model controllers/motors with low speed lockout similar to sensorless motors: the motor shouldn’t be able to tell that you are there, and this is accomplished with sufficiently high gearing.

With a 300 RPM/V motor, you need plenty of it anyway!

I was curious about what the T2 pin connection on the saw’s connector led to. Scoping it, I saw something which was basically an analog voltage that varied with the current being drawn. Zooming in close enough to the scope showed the PWM frequency, so I’m pretty sure this is just a straight tap from the T2 terminal of the battery pack, possibly corroborating both tool and BMS having access to the current sensing shunt in the battery.

I couldn’t tell what the sensitivity was, given that I was out of hands. It seemed nonlinear: 4 to 6 amps occupied a 1-volt division, but so did ~20 to ~35 amps (did I say something about the glove smoking… I was dumping 900 watts into myself here). So there may be something else at play.

Next, let’s find out the resistance line-to-line of the motor. This is the determinator of how much the motor can pull, current-wise. Using the 4-wire method, I got that it was about 29 milliohms. Solid – this is on par with an R/C outrunner of similar size.

(The 4-wire method is basically: Two terminals whose ONLY JOB is powering the device under measurement, two terminals whose ONLY JOB is to measure something. This isolates the effects of parasitic resistance in the power wires from the sensing wires.)

By the way, in 2.00gokart, every student characterizes a motor for Kv and R in the fashion just presented.

One last thing I wanted to find out is if the controller was stupid flexible enough to run without the battery and its sensing circuitry. Hey, the absence of the battery current sense line would mean it’s drawing 0 amps all the time so it shouldn’t ever turn off, right!?

The answer was yes, it will run off just any old power supply. No hackery needed. Supply 38 volts, turn motor.

It will in fact run down to 20 volts.


So what do we have here?

The Ryobi 40V cordless chain saw is:

  • A 300 rpm/V, 14 pole, 63xx class, 29 milliohm brushless motor with a 12mm flatted shaft and beefy aluminum mount
  • A controller with Hall sensors, a free plunger throttle (add your own lever/knob), and maybe an irritating speed-dependent cutout that will cause loads slower than 500 rpm to not work.
  • A battery and charger with internal battery management circuit that can dump at least 60+ amps for some time.

Gee, that sounds like a go-kart or scooter to me. Thanks, Ryobi!

I invite anyone else who is curious to pick one of these up and maybe try running it in something. I’d say you would be hard pressed to find matched components of this power level for less than $200, battery included. The downside is that a spare battery is $100+ by itself, but as can be seen, the controller will happily use any ol’ battery. I’m curious to see how the speed-dependent cutout affects real world operation, since I couldn’t get a good handle on how much available torque it has between 0 and 3000 RPM, the controller’s “minimum speed”.

As technology marches on, so the spoils of yesterday’s cutting edge shall become available to the homebuilder/hacker. Hopefully this series will contain some more interesting tools and equipment in the future!


Random Shenanigans to Break In 2014! Beyond Unboxing with Ikea Drills, LandBearShark’s Battery Surgery, More Van Nonsense

Jan 10, 2014 in Beyond Unboxing, Land-Bear-Shark, mikuvan

Happy new year and welcome to Big Chuck’s Automotive Blog! The mission of BCAB is to share and discuss all of our misadventures in being shadetree mechanics. Not only will I post all the questionably sound work on my own wreck, but every week, there will be one story submitted by you, the readers, about any aspect of your life pertaining to your own automotive project or rolling piles of garbage, whichever you would prefer.

I kid.

The way my site visits and interesting search hit terms have been slippin’ lately, though, you’d figure I’d have gone full-time car blog. Luckily, that’s only partially true. It used to be that I got plenty of weird and interesting search hits, site referrals, and the like. I feel like I’m losing my touch there – these days it’s all full of “electric bike” or “electric go-kart” or “How to avoid electric shock installing I’m a hybrid battery” (sic) and stuff. Booooooooooooring. Perhaps I should be glad that I’ve been genericized to that point, such that my content has become more generally relevant. But I do miss the days of the Arduino powered butt massager.

This IAP, I’m watching over MASLAB which is using the IDC classroom and my shop space, while also ordering things and preparing for the next round of 2.00gokart in the spring. MASLAB is historically a ‘shopless’ activity… which means that students break into or ninja the use of whatever shops they can get into in order to finish their robots. This year, they faced difficulty getting their usual space in the EECS department, and several of their core team and students being my former students, I got pummeled with appeals for space. Now, it creates way more work for me (what amounts to an actual full term class’s worth of preparation and shop orientation sessions), but what better way to spoil even more undergraduates? Furthermore, I think it’s better for them that they have official access to much more resources that can be properly used (i.e. under my titanium fist rule) than students trying to steal and beg resources from any space they have access, or “get” access to; which in my mind is patently unfair to those who are also just starting out and don’t Know Somebody – MASLAB is often one of the first “Build a robot” things a lot of freshmen do.

Anyways, I went to Ikea:

I defy anyone to challenge me for the title of “Best Ikea Space-Filling Ratio”. Flat-pack furniture works best with a vehicle which can be 90% modeled in no more than 3 solid modeling features.

Now, none of this is actually mine, since my own life is containerized into a number of typical milk crates, and I wouldn’t touch anything Ikea produces with the most bargain of Harbor Freight allen wrenches. But while on the tour in the most perfectly structured consumerism experience, I naturally gravitated to their tool section. The selection was naturally all custom-commissioned products geared towards assembling only their shit – again, part of the most perfectly structured consumerism experience this side of Buy & Large.

1. Beyond Unboxing: Ikeaworks (FIXA 7.2v drill)

(To quickly skip to the other sections, here’s…

2. Landbearshark’s new battery

3. The Weekly Van Shenanigan: Bodywork, oil pan gasket, and fixing that subyiffer

I spent a little while looking at the FIXA (I keep wanting to say Fixya) power tool series – they have things as interesting as a 14.4v hammer drill and a standard two-speed drill. Ikea being an entity that nominally prides itself on inexpensive low-key quality (as opposed to, say, Harbor Freight, which prides itself on Fuck You), I did expect that these tools would have worked just fine in their intended household lives. It’s like a domesticated goose – all you really need is a guarantee that it will poop everywhere, perhaps not with the flamboyance of a wild Canada goose.

I found their 7.2v drill/driver interesting. This is because it evoked the shape and function of the classic Handiworks mini-drill found at Walmarts back in the Early Noughties. This little thing fueled the rise of the 12lb weight class. For a while, Harbor Freight carried a 7.2v variant which made it into the 2nd and 3rd iterations of my own Test Bot. That was about 2005-2006. Those drills disappeared with an increasing RMB to USD trading ratio, as did most of the low-v0ltage (9.6v, 14.4v) drill/drivers from Harbor Freight.

An overwhelming sense of curiosity and nostalgia drove me to pick up one of these units. I’ll say right away that for $24.99, it may not be worth it in general, even if it were identical to the old Handiworks. However, the package ended up being more compact and a higher ratio – it definitely could be robot-applicable for somebody. So thus begins the Beyond Unboxing of the FIXA 7.2v drill/driver.

The casing is shed with a few Phillips-head screws from one side. No hidden screws here. The first thing I found is that it really IS lithium ion! There are two cells, 1500mAh each, size 18650, of lithium cobalt or lithium manganese chemistry (not LiFePO4). These 1500mAh cells contrast with the modern generation of laptop and other device cells which are typically 2400mAh, likely because they are “power” cells made for industrial use – wider temperature ranges and higher allowed burst currents – than “energy” cells which simply try to provide the longest runtime.

It has a cute little BMS board attached to it that handles both charging and discharge protection. The large FET at the top is connected to a current sense circuit that actually causes the drill to shut off if it’s near stall or suddenly locks up. This manifests itself as suddenly losing power, but it resets once the trigger is let go of. A nice protection to have if you sell your tools to total rubes for sure.

This current sense circuit depends on a sense resistor, which, like the Jasontrollers, can be easily chopped to a lower resistance if somehow you are compelled to do so, God help ye.

Four more screws and the gearbox comes apart. The gearbox is unlike the standard 36:1 or 24:1 drill gearbox. Rather, the gears are somewhat smaller in pitch, 0.6 module by my closest guess (about halfway between 32 and 48 pitch, which is what they look like). What was surprising is that the first stage of the geartrain is all metal. Usually, the first corner to be cut on these is to replace the first stage with nylon gears, ostensibly for noise reduction but we all know really why.

The gearbox is 3 stages of 16:14:45, resulting in a total ratio per stage of 3.8125 and a final ratio of 55.41:1. The final stage has 5mm thick gears, compared to the 4mm thick in the rest of the thing, to handle high torque demands.

The ratio is a little high for my tastes for a robot drivetrain, but for those not aiming to hit 15-20mph, perhaps just a slightly larger wheel will suffice. Remember that I’m clouded by a decade of smashing robots into each other; very few parts which are generally useful make it into the top echelons of the battle-tested.

I wasn’t quite curious enough to take off the chuck, since the left-handed locking screw was better installed than most Harbor Freight drills and I wasn’t in the shop at the time. I suspect that the traditional drill gearbox bellhousing, albeit in a smaller size, is on this one. The drill shaft is also most likely a 3/8″-24 thread like normal, but I won’t speculate more unless I have it taken apart. It has a nominal rating of 400RPM – which, through the gearbox, yields a motor speed of about 22,000 RPM, in line with the typical small drill motor. The motor in question is a 7.2v Mabuchi RS380 knockoff, unlabeled.

2. landbearderp

Remember the Landbearshark video? Well, after that and the additional snowstorm a week ago…

Whoops. I guess I went a little too hard. I noticed something was wrong after the batteries never recovered above 16 volts even after a day of sitting. Both battery packs had cell groups which were either at 0 volts completely, or at severely damaged levels like the 1.38v group above. This was the batteries which caught fire once and also survived months of tumbling in the original Landbearshark, finally having been done in because the rest of the thing worked too well.

Damn. Well, with the potential for more weather in the next few months since this winter has really been making it rain snow, I had to replace the damaged batteries before LBS could work again.

I went digging in my lithium nuclear arsenal, which I obtained after the MBARC class ended and I confiscated all the lipos (with exception of those taken by R/C airplane experienced students). Most of the packs were in the 5S and 6S range, which was good for LBS, but they did not have built-in battery management boards and I didn’t want to add a big balance harness to LBS. However, there were also these:

One of the teams went commercial/industrial and picked up these from Batteryface. These are sold with a “PCM” module built-in, so they don’t need to be externally balance changed. I’ve used these boards a handful of times before in not-my-own applications, and they do work just fine, but I find them a little too wimpy on the discharge: for most high burst current or other high power apps, I prefer running straight battery, because the management board usually introduces more resistance or has built-in current limits.

But LBS is not particularly high power. I could also fit four of them in the space left by the 6S6P A123 pack, netting me much higher energy density: 22.2v 40Ah instead of 19.2v and 26.4Ah. I’d trade the unneeded brute force for ease of use and built-in protection.

Sounds like what these were made for! So in they go.

To get four packs in the space of two, I had to put Y-harnesses on my Y-harnesses. I chopped the discharge leads off my old battery, which had a type of 6mm bullet connector I no longer had on hand, and spliced them to two Deans plugs each. The students added quick disconnect terminals to their batteries, which I cut off and replaced with Deans.


The batteries are mounted to the electronics box with strips of Velcro. Their height is just under that of the box itself, so they shouldn’t be going anywhere.

Suddenly, the wiring looked less nest-like than before. Not because I made it better, but now all the excess runs were the correct length to tuck next to each other! Science.

LBS has yet to make it back outside since the weather has been… “nice”? Test riding around the building showed me that it was very much more responsive. Not only because the voltage has jumped a few from the A123s, but that the batteries must have been damaged for a while and have been sagging more for the same current draw. Hopefully the next bout of winter commuting will put these to the test.

Rewinding before the new year once again, I’ve officially commenced…


It could refer to several things. First, the old magnetic disc drives that used straight iron oxide (rust) to store information; the earliest kinds that went into the “refrigerator” hard drives. Next, the fact that you can’t quite remember something.  Finally, all of the really shitty bodywork I’m about to do to prevent more problems down the line.

I’ve been leery of doing bodywork for a while, despite a slow buildup of arms in the interest of doing so. The past has shown me that I have no patience for making smooth and clean lines or blending paint. However, the recent pressure of winter and its associated wet salt slush has caused me to examine some of the spots in more detail. I’ve determined that there’s some areas where I’m getting close to now-or-never, because the underside and “hidden” rust. Remember these boarding step holes? They’ve gotten bigger:


Soon, they will soon break the outside body lines… and hell if you’re getting me to rebuild external lines. Other trouble spots include the majority of the left underside for some reason – the right side is pretty clean, but the left is all sorts of beat up.

Before tacking the more complex curvature of the step, I decided to practice more on a less visible spot – the left rear corner. Here’s what it looked like in May:

A complex confluence of edges in the corner with quite a few holes and thin areas to patch up. The plan I formulated was to cut away as much of the bad areas near the holes as I could get, then grind or wire brush off the rest. About two weeks before starting on this, I thoroughly coated the interior of the bodywork in the area with that “rust converter” compound and let do its job for a while. Hopefully this will help prevent the interior sheet metal from being a problem in the near future.

Let’s get started. I once again dibbed the corner of the garage for a weekend, though I didn’t need the lift. What I did need was a spot that wasn’t -30 degrees out, so things could actually cure.

When I was using the lift before, I had noticed that the arms block the area I need to work on, regardless of orientation. So I had to use a whole trade of jackstands (the proper collective noun for jacks is a trade) in that area. Since I’ll be violently thrashing on this area for a while, I used not only a stand on the frame, but on the corner of the rear suspension also, kept the floorjack a little pressurized under the differential, and chocked both right wheels in both directions. A little paranoid? Perhaps, but I also prefer to have thickness.

This is what that region has devolved into since that time. The holes have grown a bit, and much of the weaker rust has fallen off. The treatment compound is seen in green.

The excise begins by gently hammering at the panels to loosen up more internal rust. This is item #2 on the list of 3 things Mikuvan does very well: dropping little flakes of rust everywhere. The other two, of course, are emitting black mucuses of various viscosities, and raining bearings.

Maybe I should have done this before spraying the converting compound…

Next up is imprecise angle grinder cutoff wheel excise. The biggest trouble spots went first.

About 1/3rd way through the process. When the angle grinder became too unwieldy to maneuver, I switched to a Dremel with a small cutoff wheel. My goal was to eliminate as much of the obviously rusted metal while retaining features that will help rebuild the area. I cut off a piece of the wheelwell (the right angle upside-down-L cut is center in the picture) to gain more maneuvering space for cleaning the area behind it. After the cutting, liberal application of wire wheels knocked out the rest of the surface rust in the surrounding area.

What I do not have is a picture of the completed surgery, since much of this process was mentally streamed. More of the steel on the inner wall to the left was removed, as was the area with the perforations in the upper left, extending about 4″ towards the front (where the wirebrushed paint starts).

I retained my tactic of using 3 layers of fiberglass cloth (I’m not sure of the weight, but it is pretty heavy) that were nipped from Solar Car.

I decided to split this work into two sessions to make sure I didn’t have to hold onto too many things at once. I patched the outside first and let the glass cure overnight.

The next day, I worked on the inside. To cut the cloth to shape, I just mashed the fabric against the repair area and used a marker to get the rough outline, then cleaned and simplified the marker scratches to a cut pattern. The pattern was used as a template to make two other pieces, each very slightly smaller. The marker dissolving into the fiberglass resin is the cause of the blue outline.

This area looks pretty gnarly because of the untrimmed glass and the fact that I didn’t try to rebuild the down-facing curvature of the original body section.

The day after was cleanup, filling, sanding, and painting. The tattered glass edges were trimmed flat with a Dremel and cutoff wheel first, then the whole area manually sanded with a sanding sponge and then some fine regular sandpaper. I used a small amount of Bondo to smooth the transition between the glass layers and the remaining bodywork, but as the masked area shows, did not attempt to resmooth the surface from where I wire brushed off the paint.

Paint was the same procedure of primer, color, and clear I used on the rear hatch. This took several hours by itself, then I let everything dry overnight once again.

Once the outside was dry enough to put some masking tape on, I sprayed a few coats of underbody coating compound on the inside repair to seal it as well.

Here’s what it looked like as of a day or two ago – it’s gotten a little dirty since:

I make no claims to ever passing auto body school.

Based on my research, a real auto body guy would have removed far, far more metal than I did, and also have remade at least some of that inside corner box section in steel, if not straight up remake the entire sheet metal of the wheelwell area. When I can afford this service, I suppose I’ll have that done…

I’ve learned since that they make this stuff called “spot putty” which helps fill in the very small resin bubbles that are visible; plus that I’m not spamming enough resin onto the top ply to start with, a phenomenon also visible in the rear hatch work. These lessons will hopefully be put to use in repairing the boarding step hole soon, since that is a more visible location (with the door open, anyway).


A quick break from inhaling styrene and toluene led me to try and figure out exactly what the deal was with the “subwoofer-like device” that I touched upon previously. I thought it was barely working, but it turned out to be sympathetic vibration transmitted through the front sheet metal and dashboard components. It was in fact totally out.

I’m sure a normal person would have replaced this with a set of 12″ subs in the back, but I dunno, it’s already there and most likely working anyway. What if it was as simple as some dumb fucker not connecting one of the wires? Wouldn’t I feel foolish for not trying to make use of it at all!?

Besides, the 12″ subs come after the electric drive conversion, as do the tacky underglows and stancing.

It was 20 degrees out, in the middle of winter, in Massachusetts. And here I am, outside, with nothing but flashlights, using an oscillosope and soldering iron to probe the paths that the signals took in an attempt to debug the amplifier board. Consider the frightening possibilities if I had put this much effort into actually studying something.

I ran into a slight metaproblem – it was so cold that my small cheap soldering iron, which travels in the robot service toolbox normally for use in the field at events, froze its power cord off. Literally. It probably deplasticized in the cold and in the process of me unfurling the cord, it broke off.

I borrowed a Weller station from MITERS in the mean time, which seems to use a plasticizer that didn’t also grow up in the South like me.

So if you’re ever stuck debugging the subwoofer amplifier circuit of a generation 3 Mitsubishi Delica, here’s what it is. The whole thing is OEM’d by Matsushita (a.k.a Panasonic). There’s 7 wires leading to the board – three of them are the ground, 12v, and “power on” lines shown, the others are two channels of signals and their return lines.

What the frontend of this amplifier does is add the two stereo channels together, then severely low-pass filters it before sending it to the amplifier power IC. This is all done actively, with op-amps. In fact, the circuit is eerily reminiscent of this generic mono amplifier circuit.

The ENABLE line controls the coil of a little relay that is in between 12 volts and the amplifier chip. Guess which wire was open circuit?

Naw, couldn’t be that someone forgot to wire it up.

(Alternative explanation: The new head unit that came Free With Purchase did not have an external amplifier enable output, so this was left unwired, but that doesn’t explain why someone took the speaker totally out…)

I took the cheap and dumb way out: Jumping the enable pin directly to 12 volts. When I turned the ignition key, I heard the faintest click of a relay and a little pop from the speaker.

Scoping the speaker’s terminals shows this nice waveform coming out. The cutoff frequency does appear to be around 150Hz.

I packaged everything back up after this fairly simple hack, and immediately ran back inside to defrost. Let’s be honest here – this little thing didn’t add that much to the experience; finally some noticeable low end now, but it seems that it saturates (clips) relatively easily. Not that I blame it at all. It was another box ticked off on the checklist of completion.

Oil pan rebuild

Item #4 on the list of things Mikuvan is good at: leaving small droplets of oil wherever it goes.

It’s done that ever since the first start. I’ve always attributed it to a crank seal problem, but recently I started suspecting otherwise, because the symptoms didn’t really line up with just a crank seal issue. If I had a leaky rear crank seal like I suspected, then the oil drops would be coming from very specific, concentrated locations. Same goes for the front seals. I’d at least see a consistent, concentrated ‘shot pattern’ from the two locations in my parking spot… which I assure you is terrifyingly disgusting.

Instead, it just seems like it’s been shitting everywhere. Since I’ve been getting under it more recently, I’ve also been keeping track of the cleanliness of the underside: Every time I look under it after cleaning up all the oil and grime, there’s more of it everywhere. There was no one consistent spot at all – the whole underside near the engine would be wet all the time and spots would appear almost at random. It was less oil leak and more Self-Applying Undercoat.

As the weather got colder, it just started getting ridiculous, and once again I was faced with a now-or-never scenario. I was beginning to suspect the oil pan gasket a few weeks ago when I first began noticing that it was always wet on the outside. Hey, shouldn’t a gasket keep the leaky stuff on the inside?

During the suspension work on the lift, I gave that area a very fine look-over.

This is the forward left side of the oil pan. First, that gasket is pushed out completely and ripped. Second, it’s disgusting.

I figured, once again, that even if it was not the main problem, it could be a contributor or aggravating factor, and that I should at least inspect it. I braced myself for yet another Yak Shaving Session where I end up having to remanufacture the entire assembly. How bad could it be!?

(Always Famous Last Van Words)

I looked at the service manual for a bit and then began disassembling the oil pan screws.

First to come off is the oil level sensor. I have no idea how this is supposed to actually work – and it just barely does. Usually, if I park on a non-flat area, it’ll throw an oil level light; and not knowing how leaky the thing actually is, I check every time, only to find the majority of the time it’s totally fine.

I have no pictures of the pan removal process, since my hands were well-covered in oil, and the whole thing just sort of fell off after I undid the last screws and put a little pressure on it with a scraper. Well, that’s certainly a bad sign. From my Youtube instructional video surfing, you’re almost supposed to use said scraper to cut the whole thing off.

Oil pan removed! This is the first time I’ve ever physically seen the inside of an engine, from the bottom end. Who the fuck thought this was a better idea than a brushless motor?

The fact that oil is everywhere on the alleged gasket sealing surfaces is, again, not a good sign.

So here’s the deal with the gasket. First, on top, there’s a layer of silicone. Not, say, specially formulated gasketing compound, but I swear it was just clear RTV used for bathroom tiles.

Next, there’s a paper/felt sort of gasket, the type that you would buy specifically to fit a model of engine.

And finally, there was another layer of silicone. 

Silicone-on-paper-on-silicone didn’t exactly strike me as a professional repair. I suspect, again, that this was like 5 different dudes’ repair hacks and I am the 6th.

Unlike bodywork, I considered this a blasphemy against the  mechanical gods. I rage-cleaned and stripped the entire pan, paying special attention to the gasket seal surface. I also cleaned up the bottom of the pan some. Luckily, there were no metal particles to be found, but there was a sizeable amount of brown and black sludge; likely from before I was also meticulously keeping track of oil condition.

Here’s a shot down the line of crankpins and big ends. Once again… who thought this was a better idea than twirling a magnet (or a blob of copper and steel) on a stick?

Here’s a picture of a 3-floor building sized engine’s crankcase while we’re at it. It’s only a little bigger.

I didn’t get any pictures of the re-gasketing process, but it entailed borrowing a small amount of this RTV material designed for gaskets and laying it out in a roughly 1/8″ wide bead in the pan’s top groove, around the outside perimeter, and in a circle around the bolt holes. I then let this cure overnight under the influence of a halogen lamp, and retorqued the screws according to specification the next day.

After a week and a half of this, I’ve only seen 3 new oil drops after having placed a white spill mat on the concrete parking spot. They were concentrated around this spot:

I didn’t notice this little vent in the bottom of the transmission bell housing until I was under there looking at it. Under the cover is the torque converter and its crankshaft adapter plate. If I had a crank seal leak, I would have seen the majority of the oil drops originate near here.  It might still be leaky; I have not confirmed its health in either sense. For now, however, the oil-shitting problem seems to have been resolved in the majority.

This concludes the latest Big Chuck’s Automotive Blog entry. Make sure to check back next week as I make even more mechanics and auto body technicians cry!


The Equals Zero Christmas Special: eNanoHerpyBike; or How to Hack Your Cheap 5V BEC to be a 12V DC/DC unit

Dec 30, 2013 in Beyond Unboxing, eNanoHerpyBike, Project Build Reports

Hey everyone! It’s time for another “Did I say later… I mean like now“! Recall this from a few weeks ago:

Going above, beyond, and way further on the highway to collect dumb shit than ever before?

I decided that it was so simple and required so little fabrication that I might as well do it in the post-semester downtime when the students all go home continue to use the shop for their own derpy projects, but luckily they don’t involve my oversight as much. It also presented me with an opportunity to finally use one of the One Thousand Hobbyking Amps ESCs, and I got to try the “mechanical waterjet” on aluminum to test out how well it was able to perform; even though it’s not really meant for that.

So here’s what it is.

Here it is on the dissection table in preparation for removing the existing powertrain.

What it comes with:

  • 12v lead acid battery
  • “80W” generic scooter motor – it metered 0.18 ohms, which means this motor could actually push quite some power. I couldn’t find these on sale anywhere, so they might have been a one-off made for this vehicle by Razor by Unite Motor (which makes OEM motors for Razor)
  • On-or-off controller that was really your finger switch pulsing a relay. Finger-PWM!
  • Roughly 8.5:1 reduction, belt drive. I found this impressive since it means I could easily make use of it for sensorless drive, to which a high gear ratio is crucial.

What it’ll get:

  • 25.9v (7s) lithium battery, from my Nuclear Arsenal
  • Hobbyking “200a” controller. I decided to start with the “Birdie” model.
  • A left over T600-880 motor. It was way too fast for the application, but is the closest hardware direct swap!

The big plastic belt cover comes off to reveal the driveline mechanics. They put quite a lot of engineering effort into these, so I’m sad that these things are no longer being sold. An adjustable sliding motor mount and a real spring-loaded belt tensioner, commanding a quite unconventional 14mm wide 3mm HTD belt (size 549-3M-14). Typical 3mm belts are only 12mm wide. I was only about to find the belts listed specifically for this vehicle, so again it might be a dedicated thing for Razor.

I designed a quick mounting plate that adapts the T600′s 25mm bolt pattern to the 56mm pattern of the original motor:

I was going to lob it at someone in MITERS to sneak onto one of the waterjet cutters, but somehow this felt immoral. One thing I had been itching to try was cutting metal on our Shopbot PRS Alpha. It’s something which has been done in limited amounts and generally very slowly, often on thin material. The Shopbots aren’t metalcutting machines by design – their construction is lightweight aluminum extrusions and little wheel guides on steel rails. This doesn’t lend itself to maximum rigidity or vibration damping.

Here’s where I found out that our machine has a bit of head backlash- look at the oval flattening of the holes. I guess I’ll have to dial it out now.

I drilled and screwed a spare 1/8″ plate onto our cutting bed and sprinkled the area in cutting fluid to keep the cut cool. Another reason why I’m not about to buy aluminum in 4 x 8 foot plates is the lack of a coolant system and chip extraction system – the vacuum next to it isn’t gonna do that for you.  If this becomes a more common practice, I might try to invest in a standalone mist cooler, which doesn’t make a huge lake of coolant and delivers just enough to keep the bit clean and cut area lubricated (Example)

Using a feed and speed calculator, I came up with a conservative feed rate and spindle speed assuming 0.001″ of cut per tooth – pretty light. Using an 1/8″ carbide endmill, I was going to run it at 30 inches per minute at 10,000 RPM.

It broke pretty much instantly.

I’m going to guess that the machine just can’t absorb that level of force and not vibrate, which is weird, but when your bit is brittle and tiny, even a small amount of vibration will destroy it. I began at 50% of that speed (15 IPM) and gradually put it back up to 20. In the picture of the two parts, the left was done at 20IPM and the right at 15IPM, and the right one exhibits better surface finish.

I suspect dialing out the backlash and tightening the axis rollers more will help it, but it seems that slow and steady with a “one flute” cutter wins – check out the work by this crew.

Anyways, the “is this insane” part of the mission is complete with a satisfactory part, so I’m good for now.

The adapter plate and motor installed!

To make an adapter for the 6mm D-flat shaft of the motor to the 8mm D-flat shaft of the pulley bore, I turned a piece of aluminum tubing to a 1mm wall, cut off an arc with a Dremel tool to make it the rough proper circumferential length, and then mashed the pulley and motor and itself together on an arbor press. The 1mm tubing section cold forged into the shape of a D-flat that bridged motor and pulley, and all was good!

I wouldn’t send it into space, but I would totally send it down the hallway.

The slot is to pass the pre-assembled motor and pulley through, because the pulley flange was too large to fit between the mounting holes, and the arbor press installation was pretty much a one-shot thing.

A better view of the motor installation, with the same M4 screws it came with.

Moving onto electronics:

I whipped up this really quick housing to be made from on-hand high density fiberboard. It served two purposes – first, I hate zip tying electronics together (and explicitly ban it in 2.00gokart!), and I was going to actively fan cool the controller, so it needed a “wind tunnel” of sorts. This thing hangs down on the center frame tube and is secured by some circular sectors with matching holes. The fan is mounted to the left (the front), and the controller sticks out the rear. I designed it to cradle the controller by the output wires.

For signal processing, I brutally butchered a small servo tester – cut the LEDs off, cut the mode button off, and cut the potentiometer off. I only used a soldering iron to clear the potentiometer’s pin holes to add my own 3 pin cable. The potentiometer’s voltage output is to be substituted with a typical small EV throttle (example).

These little testers swing from about 900 to 2100us with the pot’s 0-5v output, so with a typical Hall sensor throttle’s 1-4v output, I’m still in a reasonable range to interface with the R/C controller. This is the quickest way to get set up with an R/C power system – more details can be found, of course, in Scooter Power Systems.

The ESCs I got in the Hobbyking vivisection post are all “Opto”, meaning they do not supply power to the receiver and they take signal in through an optocoupler (hence the name).

Well, first off, there’s no optocoupler – in Hobbyking language, these “Opto” ESCs just have all the parts for an onboard 5v power supply taken out for cost reduction.

Smart. Well, there’s always a very small 5V supply – the microcontroller’s own power regulator. It’s too small to run any servos or bright LEDs, but if you only need a few more mA to run said servo tester, then it’s an easy wire jump from the 5V regulator to the red wire of the servo signal cable! In these applications, the regulator is already very heavily stressed (they’re not supposed to be dropping 20+v on their own), so a small auxiliary micro is about the most that can be gotten from it.

Now, to be fair, it’s not true for all of them – most of the higher value controllers, such as my eternal favorite the 100A Sentilon, have legitimate optocoupled signal inputs and isolated grounds. For high current applications, it can greatly reduce noise glitching.

I bunched the old heat sink back on, in a less precarious location (recall that they ship with the heat sinks touching the output solder blobs), and threw a new heat shrink shell around it.

This leftover 4400mAh  7S Thunder Power battery from the DERPA robot fit perfectly in the 12V lead acid tray. It was so perfect that I just used some Velcro cinching straps (not zip ties – never, ever zip tie your lipos) and it sort of hangs out there, oblivious to all that is about to occur.

I needed a 12v rail to drive the cooling fan, which was not going to tolerate 26+ volts straight from the battery. I decided to check if my collection of cheap HV 5 volt BECs was hackable to yield 12v. The answer is yes, and I’ll keep it as a separate section under Beyond Unboxing, so for now, this is the 12v DC to DC converter!

The electronics box was laser-cut from 1/8″ and 3/16″ high density particleboard. This stuff is actually reasonably strong and water-resistant – not like Ikeaboard. I am still on the hunt for a high strength laser-cuttable plastic that isn’t either terribly messy (ABS, PETG) or expensive (Delrin). Or really soft and plushy (Polyethylene). For now, wood was fast and someone left a plate of it without their name anywhere, so it automatically becomes state property.

Here’s where the controller sits.

The 12v DC-DC module and servo tester have been added. That fan is a 40mm harvested server fan – the ones that scream at 10,000+ RPM to move the same air as a big computer case fan, but it’s a server in a room by itself and flatness is more important than being quiet. I whipped up an adapter block and had it 3D printed while the rest of the wiring happened.

A better shot of the fan, as well as a view of the master switching. The male Deans connector is where I jack in the battery; the vehicle is turned on using the “Georgia Tech Switch” that I now use on almost everything that doesn’t matter. It’s also known as a ‘removable link’.

A shot of the completed vehicle! I used left over wiring twizzlers spiral loom from the Electric Vehicle Team to keep the wire bundles neat.

First impressions: It’s very menacing wheels-up when you gun it, but on the ground is a different story. Remember how I said the motor is “too fast”? Basically, the theoretical max speed for this design is 61mph:

  • 880 RPM/V at 25V (assuming some loss in the system) to yield 22000 RPM
  • Reduced 8.5:1 to yield 2588 RPM at the wheel
  • with an 8″ wheel, that results in a ground speed of 61.5MPH

That’s an impressive number to throw around to the uninitiated, but what it means is that at any speed under half of that – or about 30mph – the motor is dissipating more watts in heat than it is giving you in mechanical watts of ass-haul. So, in other words, this thing just pulled 200+ amps and didn’t do that much. The takeoff was still extremely strong, but at the expense of all the wires and the battery being hot within a minute. The controller is only surviving due to forced air cooling.

Despite all this, I rode it home and back a few times for sheer shits. I might even say I love it more than Melonscooter, since it’s so light and nimble. I just had to have a very, very sensitive throttle finger since if I accidentally gunned it, it’s not going to take off without me, but just light on fire.

This stopped being funny within a few hours. I decided that nobody else was ever going to be able to experience the joy of this thing since it would self-eat so easily. And self-eat it did – for some reason, one day Jamison was taking a spin and it made a popping noise and stopped working.

Whoops. Well, it’s time to “downgrade” the motor while I’m at it:

I spent a while on Hobbykong searching for a replacement motor. I decided to try and get the speed down to about 30mph tops – which I assure you is plenty fast enough. I had to juggle which motors were in stock with how much work I wanted to do to replace the shaft (since almost all of these small outrunners have 6mm shafts), with which ones actually had my required RPM/V.

I settled on this 700-class heli motor with 500 RPM/V. It would yield a “max power speed” of 16mph, so you could actually stand a chance at blitzing down the hallway and be able to kill yourself instantly at the end. I also trade an unrealistic top speed for more useable launching torque.

I wanted to do away with the irritating forged sleeve adapter. I had left over 8mm precision shafting, so I turned this replacement shaft on tinylathe and made retaining ring grooves on the right end to keep the pulley on without a set screw (It came with a snap ring on the original motor). The dimensions are otherwise on-the-fly measured directly from the heli motor.

The new motor installation was easy; it shared the same bolt holes as the T600. I replaced the burnt Birdie with the Red Brick.

This thing now really hauls – I can legitimately hand it to someone and have them throw themselves off without potentially destroying anything. Not to mention that it somehow became 100% practical too! The suspension and pneumatic tires means it’s actually very smooth in handling bumps, and a little exciting in acceleration since it compresses and you are not sure if it will keep compressing until you land on your head. Just don’t try to stop. It has 1 brake, in the rear, and your center of gravity makes it lock up if you are even thinking of stopping.

eNanoHerpyBike (because it’s electric and smaller than Herpybike to the left) is up for some test video soon, whenever it stops being disgusting outside. I do have some hallway footage, but this really needs space.

That’s all build-report wise. I said, super simple and minimal fabrication. I’m truly sad that these things are now getting rare.

Beyond Unboxing: Turning Cheap BECs into 12V DC/DC units

Now a little more about the BEC hack. This falls under the category of “you might find this useful if you already have $part but want to do this thing with it”.

You can buy dedicated 12V DC/DC converters for your contraption, but they’re either fairly expensive for the job ($30-100+ dollars) or are a fixed, narrow voltage input and output for industrial use. Good quality R/C BEC (Battery Eliminator Circuit – originally for pilots who didn’t want the extra weight of a receiver battery) are usually wide-range input switching converters, but they’re tuned for 5V.

Update: For thoroughness, and at reader suggestion, here are some examples of where you might be able to get DC/DC converters:

Current Logic is one place I’ve gone to frequently for commercial/industrial modules.

End update!

But since they cost $4-5, a little bit of legwork can turn them into 12V units which will often put out more than enough current – 3 to 5 amps – to run gaudy lighting or auxiliary systems.

I have a pile of these inexpensive 8-40v things specifically for robots and vehicles, so I decided to tear one apart and see which resistor I need to jump to get the output voltage to change.

Inside almost all of these, it’s just a small switching regulator chip, similar to the LM2576 – the design has been genericized to hell and back. This one is by “XL Semiconductor“.

The circuit is pretty much exactly the application note:

Essentially, the converter doesn’t actually “know” what voltage you want it to output. It only decides if the voltage at its feedback pin, measured through the divider R2 and R2, is higher or lower than an internal reference voltage (usually 1.23V). If it’s higher, it’ll lower its output duty cycle percentage to compensate, and if lower, it’ll raise the duty cycle. This is a brick simple, classic DC/DC buck converter.

The feedback circuit is right here. The two resistors that make up the main feedback network are R4 and R2 (the small resistor horizontally displaced to R3′s left).

In this application, R4 is what the schematic above calls “R1″ (the lower half of the divider), and R2 is… well, R2.

R2 is designated 49B (3.16K) and R4 is 01B (1.00K).  Small SM resistors use some god-awful lookup code instead of a numeric ones – here’s a table of them. Let’s see what voltage this yields:

Vout = 1.23v * (1 + (3160 / 1000)) = 5.11V

The way it selects 5v or 6v is by jumping R3 on the board in parallel with R4, reducing the effective value of the low side of the resistor divider,and causing the regulator to sense an artificially low voltage. So it tries to make up for the deficiency by outputting a higher one. The resistor that gets jacked in by the jumper is a 472, or 4700 ohms (4.7K). This results in a net low side resistance of 1.0K || 4.7K, or 824 ohms.

Vout = 1.23v * (1 + (3160 / 824)) = 5.95V

And that’s how you get 6V.

So if I wanted 12 volts, I can do one of two things:

  • Keep lowering the low-side resistance value (lesser R1 in the example schematic, or lesser R4 on this board)
  • Raise the high-side resistance value (make R2 larger).

To do the former, I would need a R1 (slash R4) of:

R1 = R2 / ((Vout/Vref) – 1) = 3160 / ((12.0 / 1.23) – 1) = 360 ohms

To do the latter, I would need an R2 of:

R2 = 1000 * ((12.0 / 1.23) – 1) = 8756 ohms

Now, most of these datasheets recommend keeping R1 to 1-10K ohms for best stability, so the second option is more palatable. I could use a 9.1K resistor in place of the R2 on the board to get about 12.4 volts.

I didn’t have a 9.1K resistor of any kind. And then, only SMT resistors of the utterly incorrect size and value, a 1206 package (the board uses 0603 package, half the dimensions in every way!).

So I’ll just glob it on sideways. Whatever.

This 10K resistor nets me a extra volt or so:

Whatever ¯\_(ツ)_/¯

What is this, science?!

If I put the 5V-6v jumper into the “6v” position, the voltage becomes about 14.8 volts. In other words, damn perfect for charging a 12V auxiliary battery in constant voltage mode. These things automatically enter constant current if the current load exceeds 5 amps, but they heat up and can be damaged quickly. So, float charge only.

Anyhow, I’m doubtful of the utility of this hack for most hobbyists because it requires SMT surgery. Because the external jumper only adds a different resistor, there’s no Clever Jump It With a Different Resistor hack possible – it’ll need to bypass the internal R to ground to get it done. Adding more resistance to the path will make the voltage differential lower.

To avoid SMT work (trust me, it’s not that bad: sharp, clean tip, and a tweezer), you could solder a regular 1/8 watt small resistor directly to Pin 4 of the chip, the feedback circuit, and just solder blob away the smaller feedback resistors.

Regardless, this is presented in the interest of aiding anyone else who might think of this bad idea in their own quest. I’m certainly ordering a bucket more of these things – I can’t believe I didn’t think of this until now.

Beyond Unboxing, Chibi-Mikuvan Miscellaneous Engineering Edition: Inside a 9-Inch Angle Grinder Gearbox; Hobbyking T20 Inrunner Motor

Nov 24, 2013 in Beyond Unboxing

This post will wrap up some more of the components I’m aiming to incorporate into this build. Recall that part of the mission of Chibi-Mikuvan is to use a jumble unconventional parts together as a technology demonstrator of sorts, so I’m exposing the inner workings of a handful of potential part sources not typically seen in public together Previously, I dove into the Motor Controller of 1000 Cool Story Bro Amps, then the Dramatically Over-Engineered Batteries of Doom. This time, the teardowns aren’t as epic or novel, but as usual I figured the more pictures of things, the better. The story now moves to the drivetrain parts; in particular, one way to get a compact 3:1 or 4:1 reduction, and then a few pokes inside the motor I settled on using.

First up:

cheap angle grinder gearboxes

Angle grinders are three things: A way to really quickly embed little abrasive rocks into your face, a fast and powerful motor, a high-speed right angle gear drive, and a doubly-supported output spindle that usually even comes with a little nut to attach deadly centrifugal grenades to. In the past, I’ve personally seen them used on some Battlebots in a weapon application for overhead bar spinners in the “sublight” weight classes (12 and 30 pounds). At one point during my early days, I had the parts of 4 or 5 cheap Chinese angle grinders floating around my combination bedroom & machine shop.

I never said I was smart, that’s just what everyone else says… (Picture from 2004)

Angle grinders tend to also come in two major classes: For parts, or to be used as tools. I’m concentrating on the former here – the so-called “Harbor Freight-class” angle grinders that typically sell new for $20-30, if not even less on discount.

Some time featuring such things as “noise reducing gears”.  (Picture from 2004)

Okay, so I literally haven’t seen a single plastic geared one since then, but the precedent is set!

These days, I assume the Chinese gear-hobbing industry is better established. You can even buy individual grinder gears on eBay nowadays, if you want to build your own housing, and by far they are the cheapest way to get a right angle drive; however, like repurposing car parts, they aren’t sold by tooth counts and equivalent diametrical pitches, but exact model replacements. So to use them, you’d need to do a bit of ‘shotgun designing’. You can even use them to make differentials like God intended. Bear in mind that the steel quality for most of these gears is likely a little on the shady side – I recall being able to machine them easily using my primitive garage tools, so the steel is most likely a low or unhardened medium carbon type.

I specifically picked these out of the back aisles of my mental design warehouse because I was in need of a way to make a very high gear ratio, on the order of 20:1, in a small space and without being too expensive. Spur gears were essentially out of the question right away due to price, even Andymark gears, since at least 3 stages would have been needed. Chain drive was a little more feasible, but still, the cost of support materials like the bearings and shafting to form the intermediate stages was high. I tried to think of clever ways to get a high reduction without causing the material cost to exceed the PPPRS $500 threshold.

And then it hit me! Something I forgot about for many years now seemed like the obvious strategy. I began the eBay hunt and tried to cross-correlate different angle grinder models with their gear tooth counts, but what I found about the smaller 4 to 5 inch disc grinder size was that their ratios were really low (2.5 or 3:1, or thereabouts) because the torque levels needed to drive a small grinding disc were not that much. Ben’s differential build above shows a pretty typical 4 to 5 inch class gearset. This wasn’t going to be sufficient for a first stage, since I was constrained by wheel and sprocket size to no more than roughly 5:1 in the second.

I decided to try a different method of finding out what gears were in which size grinder: Going to my local Harbor Freight and literally taking apart their display models in the aisle, with a screwdriver sourced from their hand tools aisle. The manager was nonplussed, but backed down after I explained that I was actually doing an engineering study and would buy the display model that fit my needs. Sadly, I didn’t have any pictures from this excursion.

I got the 69085 9″ grinder display model (an older version; all of the boxed ones were this new gearbox design) for $30 after some explanation, without any of the frills. My hunch settled on the 7″ through 9″ sizes having bigger gear ratios because the torque needed to swing such a large disc combined with the motors not being that much larger across pointed towards it. So let’s see how this looks inside.

Four longitudinal case screws and four dorsal gearbox screws later, the whole thing sort of falls apart. The motor itself is a hefty universal motor – a brushed DC series-wound motor with laminated stator to enable it to run on AC with less losses.

In my opinion, this motor can be rewound to run effectively at 24-36 volts just by replacing the many turns of thin wire on the stator with a few turns of very fat wire. The stator coils measured 2 ohms, so the stall current of the motor is quite low if used stock at that voltage. The armature resistance was around 0.25 ohms – high, but not the end of the world, and you can find low voltage motors that have a higher resistance easily. Maybe I should just do this instead!

The gearing is already starting to look promising.

The pinion is only retained by a nut on the end of the motor shaft, and as I found out, there’s no other power transmission medium in it except the torque of that nut. To remove the nut, I stuck the rotor in a vise and uncranked it with the appropriate sized wrench. Then, a little rubber mallet coaxing of the gearbox housing popped the shaft out of the gear and input bearing.

Here’s the gearset! A solid 49:12 reduction, or 4.083:1. Why 49 instead of 48? It’s so the teeth wear more evenly. The greatest common divisor of 12 and 49 is 1, and the least common multiple is 588, their products. Not only does this mean that it will take 588 turns instead of 4 for the same two teeth on pinion and gear to meet again, but it also disturbs any potential 4:1 mechanical resonances and harmonics that can pop up, contributing to smoothness.

The gear pitch is somewhere around module 1.5 (or about 16 pitch). The little gear has a plain 10mm more, and the big gear has a 15mm bore.

The output gear is retained axially by a single snap ring (which makes me feel really good about hanging a giant grinding disc off it, I’ll say). Rotation is ensured by a 4mm thick woodruff key. This is the same as the little grinders, just more metal.

Short of machining a custom housing, the most useful form of angle grinder gears is inside the angle grinder gearbox itself. The idea that I settled on is to machine a 10mm shaft that has a standard metric keyway cut into the end, broaching the small gear with that size key to make for a positive power transmission coupling. I’ll retain the threads on the end to lock the pinion in place axially. The nice thing about the pinion is that the right spacing relative to the output gear is attained just by running it against the input bearing – a good move for repeatability.

I’ll probably purchase hardened woodruff keys for both sides because I’m inclined to believe the ones that are included are very soft steel; at least, the “file test” made a huge divot in the output side one, which is the most likely to shear.

I made a ‘important dimensions only’ model of the gearbox for use in the design – it will be released once I validate it.

Full disclosure: All the bodywork on Mikuvan has involved a 4.5″ Harbor Freight angle grinder. It works just fine.

the unnecessarily large inrunner that will beast into it

There’s some pictures that just shouldn’t exist. For instance, this:

No, not the Moxie, but the inrunner that’s almost as big as it. Disclaimer: I have no clue what Moxie Cola is; this was given to me by someone, and I’ve actually been too scared to open it.

That motor is the Aquastar T20, a “1/5 scale” class inrunner for boats. So, I don’t understand the 1/5 scale R/C vehicle class in much the same way I don’t understand model airplane scales that are indicated in percent, like 33% or something. To me, when a radio controlled model gets that big, why don’t you just fucking get in and drive it yourself? A 1/5 scale model car is already a go-kart!

I typically advise people to stay away from inrunners because of their tendency towards extremely high speed (high Kv, or RPMs/volt) and consequently lower torque than an equivalently sized inrunner due to the smaller rotor size. It’s not as optimal a setup for small vehicles, in my opinion – that, and they are far harder to append Hall sensors to unless they already come with it.  However, when they get ridiculously sized, it’s a different story.  This motor is just slow enough that you can build a rideable vehicle using the Burnoutchibi principle: running a fast motor with a very high gear ratio to divide down your own apparent mass, and using a high capacity R/C controller instead of a dedicated EV controller.

This is where my number of 20:1, previously mentioned, came from. With the motor’s wye-terminated speed of 730 RPM/V and running the 28.8v system described previously, it works out to about 21,000 RPM, which isn’t far from what the angle grinder motor would have made anyway. Geared 4.08:1 and then 5:1 externally, the output speed at the wheel is theoretically 26mph. That’s just in “gear 1″.

One of the major reasons I selected this motor, besides straight up motor pen0r (that’s a technical term), is because it can be externally terminated in Y (wye, star) or Delta. The difference is how the windings interact with each other inside the motor – in a motor power system that is otherwise the exact same except for the type of termination, the Y-terminated motor spins 1.7 times slower (actually √3) with 1.7 times more torque. The science of it is more complex and has to do with the windings being placed in series in the Y termination, among other factors (see Mevey Ch. 2 for the rundown). My hub motor instructable of yore assumes you wind in Y.

This means that Chibi-Mikuvan could have two electrical ‘gears’, to contrast with Burnoutchibi’s two mechanical gears. Switching between the terminations without actually pulling wires means I’ll need an additional multipole switch or contactor rig to splice phases and connections. I have a few designs for this, and I’ll also post those once they’re validated. The hypothetical top speed in ‘Delta gear’, as compared to “Y gear”, is around 40mph, though realistically it will be less due to the nonlinear effects of wind resistance. I haven’t really thought about anything going that fast since the LOLrioKart days.

Let’s crack this motor apart:

Well, that was easy. Six faceplate screws and the rotor pops right out after some tugging. This is a 4-pole, 3-phase, 12-slot (or tooth) motor – most inrunner motors are build to be integer-slot like this.

This motor has a shorter rotor than what the can would indicate, with the extra space taken up by a spacer bushing. This is because the Hobbyking version is actually the smaller one. Elsewhere, this motor is called the “X520″, and yes, they make a longer one called the X524 (example 1, example 2, example 3… in case they vanish one by one), if you need an EVEN BIGGER MOTOR PEN0R (that’s a technical term).

The stator windings are very cleanly done up, though they don’t seem to be lacquer-coated for heat resistance. In most industrial motors, they dunk the whole stator in a resin that seeps into the windings and helps secure them at high temperatures and prevents the magnet wires’ enamel coating from coming apart. The whole wound stator seems to be mashed into the can, and that red heavy paper layer is presumably there to prevent it from being mashed too much.

I tried my best to pull the rear cover of the motor off, but the bullet connectors are very tightly press-fit into those plastic pass-throughs. Furthermore, the stator itself is also pressed into the can, so it wouldn’t have done much good. This was as good of a picture as I could get of the distal end of the motor can. You can just barely see where the terminations are brought out and soldered into the bullets.

The rotor length is 50mm…

…and the rotor diameter across the magnets is 27.8mm. The 4 magnets are wrapped in some kind of resin impregnated fiber. Now, it claims to be Kevlar, but I vote dental floss.

The boat variant of the motor has a water jacket, which I think will aid greatly in continuous power dissipation. It’s a very simple ring type one, with no internal turbulation devices or flow channels, so its effectiveness might be limited in comparison to a more rigorously designed one, but the tube structure is easy to make. My only beef is that the inlets are too small to use with regular PC water cooling equipment. The nozzles are 1/8″ ID barb fittings, so 1/8″ silicone or PVC tubing is the best you can do, but most PC stuff is 8mm or even 10mm. I haven’t designed or even thought about parts for the water cooling loop, but it’s something I do want to incorporate because inrunners seem to love to run hot.

The motor has a flatted 8mm shaft, but I almost wish it didn’t, since a flatted shaft makes it more difficult to use a collet or friction grip system to transmit power. I suppose for the application these are intended for, the flat is welcome, but my shaft coupler to run this into the angle grinder gearbox is a simple collet-like system identical to what I keep putting on my 3d printers and battlebots. I call it the “ninja coupling”. I also have just a bad impression of flats coming with my motors because of the nightmare that was aligning the collets on old Deathcopter’s ducted fans – a combination of poor quality collets and the flats on the motors meant that balancing the damn things was basically a crapshoot. In this case, a sturdy and well constrained motor mount would prevent that.

That does it for these parts! The only thing left to do is the Chibi-Mikuvan global engineering update itself, and that will come in due time; plus, I have some update for BurnoutChibi. So now it’s time for….

daily van bro.

I often have to avoid main thoroughfares and their associated never-ending traffic by ‘leaking’ through neighborhood blocks and side streets, where I have a vague sense of where I need to get and just navigate ad-hoc, re-orienting every once in a while by trying to find the Prudential Center. This has shown me a good chunk of the vehicular underbelly of the area, like when you lift up a rock in the woods and about 80 different species of bugs and small mammals all scatter. One day, I found this quite lovely Dodge A100. Along with the Chevrolet G vans, and Ford Econoline gen1, it was part of the American trio of derpy vans from the 1960s.

Maybe these should all be on my hit list too – it’s like Pokemon #800-951 (they’re up to that many now, right?)

Another potent candidate for Vans Next To Things! Here’s a great size comparison – even the “compact vans” were still bigger (which is weird, since Mikuvan is larger than a Greenbrier?)

Incidentally, right up until 2009, you could purchase a new 3rd generation Mitsubishi Delica in Mexico as the “Dodge Van 1000″.

Y’know, I really, really think one of the reasons cab-over vans never caught on in the U.S. was because we kept giving them names like “Van”, or “Van”, or “Van”, or the like. Would you buy that shit? No, but I would totally buy the SUZUKI EVERY JOYPOP TURBO. Or, since we’re American and macho here, the FORD BEASTMASTER GREAT ADVENTURER SRT, perhaps?

Either way, I know what I’m doing if I ever need parts on a greater scale…

Beyond Unboxing: How to Take Apart a Ford Fusion Hybrid Battery While Minimizing Death for You and Onlookers

Nov 13, 2013 in Beyond Unboxing, Stuff

Alright everyone, it’s time to get serious! This is the first of most likely several engineering posts directly relevant to Chibi-Mikuvan (see its introductory post here), in which I’ll delve into the parts that I’m intending on using in the build.

No, I was not kidding one bit.

・ω ・

It’s the hallmark of this whole thing.

Anyways, recall that most of my recent EV-related builds are in the interest of pathfinding and trailblazing. Taking a stab in the dark at a potential useful part for makers and builders and seeing how it works out, some times involving a little bit of science, and possibly incorporating it into my personal go-kart kindergarten. That, and ultimately looking silly. With this build nominally trying to fit under (or at the least, not outrageously around) the PPPRS $500 parts and materials budget, I’m intending to try several new tricks at once, and all of them will be exhibited here.

This post in particular will focus on the one pivotal strategy that I explained in the post-Maker Faire post – cracking apart a second generation hybrid car traction battery and using the internal cell modules. These modules are typically NiMh chemistry; this was before everyone switched to lithium ion batteries this and last year. NiMh lends itself to highly favorable energy density over lead-acid batteries. Being several years and tens of thousands of miles out, you can find these batteries sold by auto recyclers for between $300 to $500. For people looking for huge capacity in less weight, I think the cost per watt-hour of energy of a used hybrid car battery is the best you can get.

In fact, my final cost in this investigation was $300 per 2.15kWh, or $0.139 per Wh. This beats out even Hobbyking lithium polymer batteries at 33-50 cents per Wh (which aren’t allowed in the first place in the series!) and most lead-acid battery options short of ‘found objects’ or purchasing at heavy discount. This is now on record as being possible, which, really, satisfies me even if I don’t end up build my own entry with it.

Someone else can totally take the torch from me right now! I’m certain somebody’s already dropped a hybrid battery into a custom project, but this is where I declare pics or it didn’t happen. Otherwise, feel free to scoop me on actually using these, because I’m sure I’ll never get around to it at this rate.

So here’s how it went down:

Initial reseach

The first step was hopping around on Wikipedia, hybrid owner forums, and Google Images compiling a list of battery candidates. I had a few in mind after a day’s worth of looking around:

  1. Toyota Prius, 2003-2009, or the “Gen 2″. This was the duh option – millions of these are on the road, so their parts are bound to be the most plentiful. The prius battery is a block of 28 “blades” composed of 7.2v modules, each 6.5Ah. The total battery energy of the car is  302V and 1300Wh (total, not useful – there’s a distinction). I was particularly interested in the Prius at first because the 28 blades could be arranged into a 28.8v, 45.5Ah battery by putting four 7.2v modules in series, and seven of those in parallel. 28.8v happens to be near the maximum voltage rating of many inexpensive R/C power system options.Along with the Prius, other same-gen hybrids like the Camry Hybrid and Toyota Highlander hybrid share the power system.
  2. Ford Fusion Hybrid, 2009-2012. This option was familiar to me because the MIT EVT chopped the powertrain out of a 2009 Mercury Milan Hybrid and converted it to full battery electric. The car’s advertised battery is 275V, 2.1kWh. We took apart the large hybrid module about 2 years ago, long before I had any delusions of using it on a small go-kart (since we were, and still are, up to our nostrils in donated A123 cells). I knew already that this battery was composed of 28 9.6v, 8Ah NiMh D cell modules, which can be arranged into a 28.8v  72Ah battery. Similar year Mercury Milans and Lincoln MKZ share the same powertrain.I also briefly looked at the older Ford Escape hybrids (2004 to 2008 years) which used a higher voltage, lower capacity (330v 5.5Ah) 1.8kWh battery, but I did not find many for sale, and the familiarity with the Fusion pack meant I focused on it harder.
  3. Honda Insight and Civic Hybrid, first generation, 2000-2006. I knew little about these except that they had 7.2v, 6.5Ah modules arranged in a 144V battery pack, which means they came in at a clean 1kWh. These are getting rare, however, and I did not find many for sale that weren’t very expensive.

I found an interesting price curve when studying eBay’s listings. Well known hybrids like the Prius commanded high prices because you know people are going to need parts, and will pay for them. Rare hybrids like the Insight command high prices because of the few people who are still keeping them on the road. It was the hybrids that nobody really cared about, like the Civic Hybrid and Fusion Hybrid (and relatives) which seemed even remotely plausible. Since I knew what was coming in the Ford Fusion battery, I decided to focus harder on it, and still keep options open by inquiring about the Prius.


I was aiming to get $300 or less for one of these units. This was the number that I decided would make sense for a PPPRS entry – you take the battery, split it in two to obtain 28.8v and 32Ah so you can have two of them to swap out between, and each battery half will only count for $75 on the budget under their accounting rules: $300 purchase price, $150 budgetary price, and half of that running at any time.

I began by scoping out these batteries on auto yard listing websites such as, to identify potential candidates. The plan was to get a handful of leads, then call the yards themselves pretending to be an instructor for a MIT electric vehicle design team whose students are carrying out a project where they want to utilize a hybrid car battery, and would you happen to have any as-is, repairable, or core return batteries we can use?

Only 10% of that sentence was bald-faced lying through my teeth, so I felt clean!  The hope is that someone would drop their price for such a noble cause. You might call this unethical, but it was also a good probe of how open these yard operators were to the idea of makers and hackers (mis)using their parts, especially young ones. If you weren’t actually going to put it on a car, the yard doesn’t have to worry about a warranty or whether or not the part is damaged or not functional to OEM spec. Even a worn out battery from an automotive perspective is most likely still useful for small vehicles. Hence my emphasis when I called on these packs being rejects in some way.

This was an adventurous roughly 2 weeks. I would call to find they have no stock, but be told to “call back next week in case” – so I did. So many of these were “Call this number and ask for Billy” type situations, which I frankly love. Here is a sample of the text file that I was compiling:

Chuckran’s 508 697 6319  x

Robertson’s (800) 551-7000 x

Linder’s 800 521 8000 ($900 07 Prius ) ($700 09 Fusion) Jesse sent you

D Richards Jack 800 776 0459 $300 ! 10 Fusion

Tom’s 800 255 6656 (left my info)

A-rite Auto 800 874 7116 $700

LKQ 800 500 8733 Candia NH call back next week JC

Bishop’s 860 346 2336 x check later

Goyettes 800 640 7548 fax 508 207 1546 x

Self-Serve Used Auto Parts 1-508-763-4442 Check in a week

Route 128 Used Auto Parts 780-980-0025 (calling back soon?)

I ended up calling 18 yards in increasing distances from Boston, gathering prices and references (When a yard didn’t have stock, I asked for a recommendation on other businesses to call). Several of them led me to each other by accident. The price was slowly falling the further I got from the metro area – this made sense, after all, since I’m sure not only the cost of doing business is higher closer to an urban area, but more cars means more wrecks and more throughout and more people needing their car back on the road; all leading to higher prices. I started breaking into Connecticut and New Hampshire.

Ultimately, my lead came from Burlington, Vermont. So one Friday morning a few weeks ago at 5:30AM sharp, I blasted out of Boston and ended up 45 miles from Canada about 4 hours later, collecting no maple syrup or moose in the process.

Or bears. As I wandered further up I-89, the “_____ Crossing” signs got more and more hardcore. Bears? What’s next, T. Rex?

I must say, if I spent my life here, I’d be a nature hippie too. Burlington is pretty damn beautiful, especially down by Lake Champlain.  I wanted to pull down by the waterfront to get a Vans Next to _____ picture (the VT-NY ferry was a good choice), but the area was blocked off and full of tour buses. I decided against pushing my luck.

The yard itself was about 15 minutes north, in a small town called Colchester:

D. Richard Automotive was the name of the place, and I didn’t exactly look out of placed parked amongst their selection of used cars. A few what the hell is that questions were received from some of the customers and staff, to my amusement. Apparently Mitsubishi vans just never quite diffused evenly throughout the country.

The owner, possibly Mr. D. Richard himself, was very receptive to the idea of student-built EVs using these packs, and I made some idle chit-chat with him about 2.00gokart and the Makersphere while his… Ninjas? Cronies? were retrieving the part from stock. It’s a little far to drive every time something good comes up, but more links in the network, the better!

This is the thing. If they made Hybrid Mikuvans back in the day, I’m guessing the battery will go in a not dissimilar position in the rear. It weighs about 150 pounds (judging by my non-ability to lift it). Check out those bullet connectors.

A four hour drive back home and some Bro Assist got this patient on the operating table. The T-square is to illustrate how big this is – about 20″ wide by nearly 4 feet long. By this time, I was pretty much worn out from driving totally randomly into 3 different states to get a part for a silly go-kart, so I passed out. The following pictures were taken some time after the fact.

That thing above the battery is a cooling fan that pulls air through the cells and exhausts it to the side.

These are the side vents in the case, through which you can see the cell modules.

The fan shroud is held on by a handful of small hex head bolts. Use a 8mm socket (5/16″ works too) to remove them.

Before I totally took the fan shroud off, I decided to have a look at the fan itself, since it’s a brushless fan for long life and greater efficiency. What was it – a really hardcore Hobbyking controller driving it? Could I turn it into a hub motor?!

The fan pops out with the same little bolts, three of them. Under the big white sticker are 4 little Phillips head screws, and after you remove that:

Holy hell, it is a Hobbyking controller! A really, really hardcore one…

This thing appears to have its own DC-DC converter in line with the power input. Judging by the 35V output capacitor, it probably modulates the speed of the fan only through this DC voltage, either raising it past 12V or lowering it, commutating the phases fully on or fully off at all times. This architecture is called a current-fed inverter, and it saves you from having to PWM all the 3 phase bridge FETs, cutting some losses and complexity.  I would have literally lobbed a HK controller in this, startup beep and all. I guess this is why I am not working for a car company.

(If I had it my way, everything would have a V8 made of Melons in it.)

Once you pop the retaining ring on the back side off, the rotor dismounts:

It’s a copier motor.

I literally burst out laughing uncontrollably when I found it. It is the exact same dimensions as a typical 68mm copier motor I’d harvest from some poor Xerox to use in a scooter hub motor. Hey, this winding might even be fine as-is for a hub motor, since it’s a fairly high voltage motor!

Some larger Torx screws also hold the lower fan shroud on. A T25 Torx bit is the proper way to attack these. With the fan shroud tossed aside, it was time to start cracking the battery itself open.

Here’s where I pause for a second to say:

The following images depict opening up and messing with a 275 volt DC power system. It will be exposed, be unfused, and be extremely dangerous. If you touch the wrong spots, you will commit suicide instantly. If your metal tool touches the wrong spots, it will explode in a plasma cloud and deposit itself on your face. It is your responsibility to educate yourself on proper handling of, and safety-oriented behavior around, high voltage systems.

tl;dr be safe around batteries, kids. These pictures are for your reference and educational value only – I am not here to train HV electricians. As you’ll see, the battery pack is extremely well designed and anticipates service and disassembly, but it makes best practices no less necessary.

Now, onto removing the battery’s shell.

First, I had to remove the various other warts and boxes on the bottom of the battery. These include, from the left to the right, the main contactor set and output connectors, the orange  service disconnect, the battery charge monitor controller, and the battery computer which interfaces with the rest of the car.

These are all held on with nuts on studs, and I used a 12mm deep socket to reach them.

I decided to ruin the resale value of these OEM battery parts by prying them open and looking inside. (Seriously, I could have made $150 on each of these battery controller parts!)

This is the “Battery computer”, as it seems to be called . I’m assuming this takes battery voltage info from the other box (with the HV interfacing hardware) and pipes it to the car’s ECU. I’m not focusing on reverse engineering this stuff, so it’s here for visual stimulation purposes.

 The other box contains the high voltage interfacing hardware – check out that isolation gap! My guess is this has an array of multiplexers and ADCs to sample the battery voltages at the module level. That or a huge string of op-amp subtractors, Hobbyking style, with 400 volt opamps?

Some more prying and biting later:

Looks like the two theories might be combined. On the left board (the first module) are what appear to be several 14-pin, possible op-amp or comparator ICs. The part numbers are all proprietary – even though they feature logos like NXP and Texas Instruments, the etched numbers all seem to be serial numbers of some sort. The myriad passives on top and on bottom suggest to me a possible series of op-amp circuits.  The right board has a shoreline made of optocoupler solid state relay devices, KAQW216 (the chips are marked W216HC5). Most of them seem to eventually pour into (or out of?)  a large Analog Devices chip, an ADUM1401 4 channel digital isolator, surrounded by some quad op amps (AD8554).

Again, I’m not out to decompose the battery management system, since I won’t be using it and it’s surely very proprietary, so this is as far as I’ll go here – component staring and hypothesizing. My fan theory is that the 4 channel isolator turns on the solid state relays in a multiplexer fashion to select groups of cell modules, the top end and low end voltage of which flow into the op amps to be subtracted to get a voltage number; combinations of groups of modules being read will let you deduce the voltage of each individual module if you keep track of what is being read at any one time.

Moving on:

This is the contactor bank of the battery pack. There’s three separate contactors: one for positive, one for precharge (connected to positive), and one for negative. In vehicles, traction batteries are generally fully isolated when the vehicle is at rest. It’s not frame grounded like you would do for a 12V auxiliary system. It’s great to see all the systems my students typically build into a small or medium size vehicle (like the precharge circuitry) because I tell them to, being used on an industrial scale because you neeeed it in order for the system not to grenade instantly.

The set of two contactors at the top left control positive – one of them fills the HV rail through the precharge resistor (the big sand block resistor next to them). The single contactor at the bottom is the negative. The only thing that looks a little cheesy is the great big negative bus bar that spans the entire length of the thing.

Finally, the black hole that the positive busbar disappears into is a Hall Effect current sensor which, again, seems to be a proprietary part. Maybe I will take it apart in more detail and try to extract the functionality later.

Update:  The current sensor is a LEM DHAB-S/34 type, which outputs an analog voltage proportional to current. It has dual sensitivities – one pin for 40mV/A, the other for 10mV/A, so you can monitor low currents and high currents alike while minimizing quantization error and sensor accuracy error.

I decided to remove the back cover first to check if anything else needs to be removed. More 12mm nuts and T25 headed screws hold this on.

The yolk of this egg is beginning to show. Twenty-eight D cell modules, bound together by (non electrical) aluminum bars and plates.

I came around to the front again to disengage the service disconnect. Without this connector in, there is no voltage present on the contactor pack. I had to thread it through its panel hole to release the cells eventually, however. This also meant disconnecting the large ring terminals that fasten the battery to the contactor pack first – they’re at the very top, isolated by a plastic wall to prevent “mishaps”. A 14mm nut holds the terminals together, so I used a deep 14mm socket to extract them.


266 volts from non-isolated negative (before the contactor) to the service disconnect.

After I removed the contactor pack and service disconnect, I needed to remove the handles to gain access to the side plates. These handles are held on by some 12mm hex headed bolts that also retain the upper two sets of structural aluminum bars.

The bottom set of bars have giant Torx screws holding them in – T45 to be precise. I only had this size in a ratchet drive.

And both the side plates pop off…

There it is – the delicious Roe of Fusion at the center. But we’re not done yet – I still need to take apart the pack module by module.

The battery modules are retained by these non-electrical aluminum bars (I keep wanting to call them busbars, dammit!). So really, I could have just removed both top and bottom cover (and contactor pack), then only one side plate removal was needed. I could slide the whole thing around at this point.

Little temp probes that contact the cells at certain distributed locations to get a pack temperature reading.

Some intern had a lot of fun designing this engraving, I bet. This bar is totally something you’d hand off to an intern to do. It’s a straight piece of metal with holes in it! There is no way it’s fuckup-able!

Here’s how the pack comes apart. The moment you take the end module off, the whole pack is split into two, so you can’t even drop something across the primary positive and negative. Furthermore, you can only remove one module at a time: the busbar retainers interlock and are retained by two adjacent modules, so you must necessarily disconnect a whole module and remove it before moving onto the next set.

This construction is quite ingenious and must have taken weeks if not months of engineering committee meetings to come up with. I and everyone present at the first autopsy of this battery have said that it’s best example of design-for-assembly and design-for-service that we’ve seen.

I would never, ever have the patience to design such a system.

The back side of the battery is one solid strip of bus bar endcaps, removed one at a time at your leisure. The module endcaps are M5 threaded, and all the heads are T25. Someone really, really loves T25.

The full disassembly would look like a messier version of this – a small mountain of cell modules being slid out one at a time from the main pack.

The busbars live in snap-in mounts and are 1mm thick copper. On the “front side” of the battery, they simply are friction fit in place – they slide right out.

On the other side, they are retained by little snap fits. Unsnap them to take them out if you want to reuse them.

THIS IS THE BUSINESS END OF THE PACK. To avoid having to deal with this at 275 volts, take apart the pack starting from the right side of the contactor pack, if you’re looking straight at it. That’s the way I have it done here. If you start from the left side nearest to the contactor pack, you get to disassemble 275 volts first. Have fun.

If even one module is removed from the right side, this connection is isolated.

The sticks are made of 4.8 volt strings of D cells, with (I think) a nominal capacity of 8Ah. As you charge and discharge them faster, the useful energy will decrease – I put these on an aggressive 1 hour charge, so they won’t read 8Ah. One that I left overnight on a slow near-trickle ended up at 8250mAh.

Here they are inside. The cells are held off from their cases by rubber insulators; this is so air can flow through the case and around the cells, allowing them to cool or heat using the fan.

I may delve into the contactor pack in a future post. I think it’s quite useful stock and as-is, so I did not take it apart. After all, it’s just contactors with wiring already built in, and a precharge to boot – it doesn’t care if it’s being run at 275 or 27.5V – the coils are all 12 volts.

The contactors are nice – way better than the cheesy relays the students rig up remote-power circuits with in my class (but then again, that’s all they need). They’re Matsushita (Panasonic) type AEVS contactors designed specifically for EVs. It’s hydrogen filled!… wait, isn’t that bad?! Hindenburg Relays!

I’m sure if you had to buy these they’re a hundred dollars or more alone, but you get three of them with purchase of a cheesy old hybrid pack. Limited time offer.

Since I did not need this pack immediately, I decided to not take all the modules apart. Instead, I put the end plates back on so the whole thing is rigid, and it currently lives on a handtruck in the shop. I left the rightmost ‘crossing busbar’ out so there’s nothing 275 volts about it in public.

I made an almost-accurate model of the Fusion Sticks and have uploaded it on my reference page as a Parasolid (x_t) file, which should import into most CAD programs. The dimensions are accurate to 0.1mm for the first inch of length on both sides. There’s a lot of little randomness that sticks up in the middle, including the aluminum structrual bar channels, that I didn’t model since I was planning on mounting them on their ends only in my application. You could, if you’re crafty, just saw the bars in half and arrange the stock copper pieces to your liking on the cells, then redrill the end holes and use the stock endplate and handles.

Each module weighs 3.66 pounds, so this full pack of 28 is 100 pounds. And 2.1kWh! Beat that in lead.

So there we have it – another episode of Charles Takes Something Apart for His Own Amusement at Great Personal Expense Beyond Unboxing! I would actually love to do a series of this just on hybrid car packs, but it might have to wait until I find another one such as a Prius module or Leaf lithium ion module for super cheap (or someone comes and drops one on my desk). Mass produced commercial things always have the potential to be low cost and highly functional, and I think the gradual increase in market share of hybrid and electric cars is a boon for the hobbyist or home builder.