It’s time for SCIENCE!

As promised in my last post about the Jasontroller’s seemingly language-barrier-impeded sentience (it is screaming to be heard, but we (mostly) cannot hear its 16kHz switching frequency?), I have a pile of different Chinese electric bike controllers purchased from several eBay sellers. They were pretty much all purchased about a month or more ago with the goal of eventually exploring this functionality. This perhaps betrays the planning of this post for a long time.

I’m generally more willing to accept the sketchiness of generic Chinese products than most people. There really is no one company, dealer, seller, or support website for dealing with these controllers. They’re made to fit one or several models of electric bikes and mopeds, one-for-one, no questions asked or answered. All of the information on them on the Internet, in the Western electric vehicle hacker world, is pretty much in the form of blog posts, forums, and wikis. This isn’t something I expect to change any time soon, because there are about as many variants of the controllers as models of derpy electric mopeds. Plenty of companies exist that stand by their products and offer support and usage advice, and they are pretty much the go-to if you need something that will undoubtedly work (though this assumption can be a bit challenging at times…). But  half the fun of projects is the hackery, in my opinion, and it never hurts to expand your resource horizon.

So, this post is not intended as a definitive reference on Chinese e-bike controllers. I think I could test a different one every day for more than a year, guaranteed, and still not be through with all the variants. Some of this info might become totally irrelevant if the company turns over or the seller on eBay disappears. The goal is both more immediate: these are specifications that are known to be good RIGHT NOW, but may not be this time of next year, so buy it now; and more general: to elucidate some of the Chinese controller marketing words such that everyone can look out for future variants and understand what goes inside of one, and why they are not bad, per se (You can’t sell millions of abad thing that people have to use day to day…. or can you?!), but that we, weird brushless scooter and go-kart and e-bike guys, use these devices generally far out of their original design specification.

Which, given how much the same commercial, street-legal electric bikes and things are, is likelyvery very narrow. A recurring trend of the lineup is that they pretty much use the same components in various permutations – things which have stood the test of time and probably stochastic layout design selection. I now present…

(more…)

In my continued quest to discover new ways to EV on the cheap for builders, I’ve worked on demystifying several types of sketchy Chinese motor controllers to assess how applicable they are to little electric rideable things. My most recent favorite has been the “Jasontroller” electric bike controller. Like every other generic Chinese electromechanical product – it has no actual real name (the “Jason” moniker started as an inside joke in our EV contingency and is a bit of a satire on companies like Kelly), no well-known company with customer support to back it, nor any real details about hookup and operation.

(Scheduled plug: By the way, I still have alot of stuff for sale!)

Do you guys, like, know eachother?

Most of these generic Chinese e-bike controllers are pretty much the same functionality and firmware-wise, but what appealed to me specifically regarding that model is that it has a reasonably competent sensorless mode, complete with motor current limiting, for driving inertial loads, specifically vehicles. R/C type aircraft and car ESCs just aren’t the same in this regard; more details can be found in my Instructable on the matter. I’ve found that the sensorless mode on the Jasontroller is fine enough for scooters (and their design target, electric bikes) because you can always move just a little to avoid the zero-speed condition that sensorless is worst at. For things where you don’t get to push off, like Chibikart and DPRC, they’re somewhat hopeless. The algorithm is very simplistic and typical of ‘block’ commutation startup – just open-loop power the motor phases until a valid phase voltage waveform is detected. Usually in the case of an inertial load, the slow bobbing of the rotor is not strong enough to cause any significant motion and the startup fails. In the case of a cheap R/C type controller with no current limiting, the controller explodes from having to power a stalled motor.

While the controllers usually do have a Hall sensor connection, the hard part is adding sensors to the motor itself and connecting them correctly. In the past, I’ve accomplished this by both putting them inside the motor as well as outside on 3D printed mounts and cute sensor holder rings. Then, explaining the process of lining up the 3 sensor bits with the 6 internal states of the 3 phase motor usually takes at least half an hour and much confusion – without knowing the way the motor was wound (i.e. you didn’t wind it), there’s 12 possible ways to hook up motors and sensors and some times you have to brute force them all before finding the right one.  Additionally, sensors aren’t optimal at anything except low speed anyway because they suffer from hysteresis-induced timing lag.

Optimally, you’d have a controller that uses the Hall sensor feedback just to kick off. Even if the sensor combo was total bullshit, actively driving the motor in one direction and getting some kind of positive position change is enough to begin ramping the motor sensorlessly up to speed.

What I’ve been kind of hiding is that many of the latest generation e-bike controllers, including the Jasontroller (I have enough of an emotional connection with the thing to name it), has this exact functionality. I’ve never explored it until recently when curiosity got the best of me, and I think this is a total boon for everyone who is building small EVs. It is now my goal to explain how the mode is used and what its limits are. There appears to be some confusion on how the mode is used (example and another), and as a result I haven’t seen it frequently mentioned.

We begin with a picture of the rear of a Jasontroller, where the mysterious Chinese sticker is located.

For your entertainment, I’ve fansubbed the Jasontroller below. I’m not gonna claim perfection with my several-versions-out-of-date Chinese language drivers, but hey, who else is gonna give you an English manual?

All of the Chinese e-bike controllers you can find are probably generally wired the same way. The funny thing is, as amusing as these devices are to me and many other EV hackers, I’m willing to bet that literally millions of people use them on a day to day basis and find them nothing too ordinary. These are generic replacement controllers for electric bicycles, moped, and scooters made and used by the millions in China. To people who have one of those things, it’s like changing windshield wipers or something.

Take note of the “Self Learn” wire in the lower right. The instructions on the bottom are basically how to use the self-calibration mode of the controller.

The magic green (may be other colors on your specific variant) wire is usually embedded in the forest of wires these things come with. It’s terminated in a small snap-on connector.

Basically, the controller recognizes that this pin is connected when you first power on. It attempts to run the motor sensorlessly and captures what the Hall sensor waveform looks like, saves it to memory, and then when throttle is commanded, it will power the phases according to what state the motor is in and what it ‘saw’. You can indicate that the motor is being learned in the wrong direction (by unplugging and reconnecting the self-learn wire once) and it will reverse the direction and record the states again, saving that and associating that direction with “forward”.

Nifty. That’s so much software I can’t imagine ever doing it myself. Luckily, some smart Chinese guy has figured it out (and probably got pirated).

Here’s my Rig of Science that I set up. A 63mm outrunner with my custom Hall holder rig, externally adjustable so I can try and confuse the Jasontroller. The jumper wires that connected the sensor board to the controller was also rearrangeable. Basically, I wanted to see how much bullshit I can feed it and still have the thing work.

The process was basically to train it on a specific sensor arrangement, then swap the sensor combination around and move the board such that the timing is terribly off, and combinations thereof.

What I found was the following:

• If sensors are present and the controller hasn’t been trained before, it will use the factory programmed motor state model.
• The sensors must be 120 or 60 degree space electrically – if there is significant inequality in the spacing, the process incrementally gets worse and worse with spacing error until it just errors out.
• If the sensors are incorrect (do not result in continuous motion) or throw an error for any reason, it will automatically try to switch to sensorless mode.
• Once “trained” for a specific sensor arrangement, it will retain that and use it for any other motor it is connected to until trained otherwise, pursuant to the above rule.
• The sensors are only used for low-speed and stall conditions. There is an audible transition to sensorless mode – the motor sounds “smoother”, lacking the hard-switched sound of the sensored mode.
• Sensored mode does not bypass the internal hardware “speed limit” as a result – the processor is still only capable of running the motor to a relatively modest speed.

There were moments where I got the controller “stuck” in sensored mode, but I can’t consistently replicate the problem. It seems to happen only when the sensors are horrifically off-timing that, I assume, the sensorless algorithm cannot lock in, but why it doesn’t just ditch the sensors at that point is not known to me.

Additionally, another weird symptom that happened several times but I cannot replicate reliably is that if only 2 sensor wires are swapped, it catches on and figures the problem out. The first start is false and runs sensorlessly, but the next start is properly adapted to the new sensor arrangement.

The fuck? Are these things actually sentient and just messing with me instead of vice versa?

Basically, what I found is that if you line up any sensor with a slot (placed in the middle), the controller will figure it out just fine. For any sensor over a slot, there’s a valid combination that will result in motion, maybe not in the intended direction (but that is what the “reverse learn” switch is for, right?). In the above picture, the rightmost sensor is centered over a slot. I don’t have any info on how this motor wound, so which slot it is is completely not known!

If a sensor is not centered in a slot, then the startup gets rougher and rougher with increasing error until it just switches to sensorless. The transition between sensored and sensorless mode also becomes less smooth.

summary

Here’s a video where I demonstrate how to use the auto-calibration as well as illustrating what happens if a sensor is not located over one slot.

conclusion

Suddenly, the Jasontrollers have become alot more favorable to me. I’ve had a few of them die running all-sensorless into an R/C type outrunner because the current limiting circuit is just not fast enough for those motors, which are generally super-low inductance (current changes very quickly).

Not even Kelly controllers can do this sensor auto-recognition thing right now, and they are currently my go-to for when someone asks me what controller to use for their brushless setup. Calibrating sensors and adjusting timing is one of the worst “black box” magic processes that people have to do, and they matter alot in having smooth vehicle operation.

This neat little feature will save alot of time and effort in vehicle construction. All you really need now is a way to mount sensors to the motor.While I now favor external sensors for outrunners due to their ease of adjustment, the controllers having an automatic sensorless switchover after a certain speed means that embedding sensors in the middle of a slot (inside the motor, by taking it apart) is completely reasonable. This would be an option for people who do not have, or want to make, an external sensor-holding jiggie thing.

I’m probably going to try throwing Halls in DPRC‘s 50mm outrunners in order to truly test this hypothesis under load.

Of course, now I also really want to start selling these sensor holders and boards. Perhaps that will be a product line parallel to RageBridge…

Seeds for your melon

In conclusion,

Why should I go to the length of adding sensors to my motor to use this feature?

Most commercial sensorless motor controllers usually fail at zero and low speed because they depend on having a voltage feedback from the motors to determine rotor position, only possible with continuous motor motion. This means you have to be moving before you can move. While this is okay for, say, scooters and bikes because it is totally reasonable to push off with a foot before hitting the throttle, the same is not true of go-karts, robots, wheelchairs, etc. which you cannot really push off without compromising the function of the vehicle. These MUST have a “zero speed” torque on demand.

What should the motor and sensor arrangement be?

The sensors should be spaced 120 or 60 electrical-degrees (both industry standards), mostly because they divide equally into 360 degrees. Incorrect spacing will probably just result in the controller bailing out to sensorless mode anyway. The way to tell is if the motor has very little startup torque or just twitches helplessly. One sensor should be aligned with 1 slot between the windings on the stator and the controller will be able to figure out the rest. This is true for a standard 12-tooth stator with fractional magnet to slot ratio, anyway – other motors are currently not determined. If the sensor is not aligned with the slot, the startup and switchover transition become rough and rougher with positioning error.

Is this really simpler than running a normal, all-sensor-commutated controller like a Kelly?

Oh hell yes. There is no more playing the keep-it-change-it-flip-it game with sensor vs. phase combinations.

So, simpler, and I believe potentially better. Hall sensors introduce significant timing lag at higher speeds, and the optimal sensor position also changes with speed and load. Having the sensors there only for startup solves the low end torque issue, while driving the motor sensorlessly at high speeds effectively means you drive the motor more according to how it wants to be driven at a given speed and current draw.

Note that your shady-ass generic Chinese e-bike controller may be different. I can only account for the controllers retailed by “bobzhangxu” on eBay at the moment. However,

That lead image. Be prepared for a massive Beyond Unboxing post in the next few days where I will attempt to catalog several different shady e-bike controllers and see which ones can perform this training routine! I literally went on eBay and bought 1 of every controller that was under $30 with free shipping or under $40 with shipping. There are 7 in total. The intention is to make an index like my copier motors spreadsheet.

First of all, buy my excess stuff! I’m still periodically adding goodies to the page. There are now MELONS.

As hinted in the Carly Rae Jepsen Wallbanger build report, I tore into a few different types of cordless saws to gauge at how adaptable to robot drivetrains they would be. Cordless drills have been a staple of small robot drives (in the 12-30lb range) for many years, but recently they’ve been getting a little… flimsy. The Sketchy Chinese Drill Co. Ltd. loves to cut corners. Not to say that these are intended as replacements for the drills, but expanding your robot part horizon is always a good thing.

During the week of robot mayhem leading up to Dragon*Con 2012, I binge-purchased 3 different types of cordless saws from the Harbor Freight store near my historical home base of Atlanta. I then proceeded to rip them apart and photograph their remains like the world’s most enterprising and aggressive medical examiner. The 3 tool-like devices I investigated were the 68242 18v cordless jigsaw, the 68240 18v cordless reciprocating saw, and the 67026 18v cordless saw.

Let’s start in the sequence of usefulness. First, we have the jigsaw:

From the same updated “Drill Master” line as the 18v drills I’ve come to love so much, and with a battery which even fits those drills, are these cute little cordless jigsaws. I didn’t check to see if they could, say, actually cut things, but that is not important here.

A few Phillips head screws later, and the case splits in half. Hmm, it’s not too exciting.

There are very few parts that go into making a jigsaw apparently. The crankshaft-like pin on the main gear engages with a stamped slot in the blade holder, which rides in sintered iron bronze guides.

That’s it.

The main gear rides on a roughly 6mm pin…. made of the same plastic the motor mount is made of. Hey, who thought this was a good idea? I was hoping it was at least black-oxide plated steel or something, but nope. Totally plastic.

Maybe this will be useful if you needed a gearset THAT BADLY, but there is also no easy way to couple that gear to anything. The motor is also not very worth pulling, since it’s the same type of generic 550 motor in the drills.

Verdict: Not very useful. Let’s move on!

Next is the reciprocating saw (“sawzall”) from the Chicago Electric line. These use batteries which are of course incompatible with everything else, so I couldn’t try to cut anything with it. Not that I was in the mood to anyway.

Cracking this one apart shows quite a surprising amount of metal. Well, shady cast aluminum, which may qualify as metal under certain tax brackets. I’m interested in what that right angle drive looks like.

The gearbox itself is modular, which is a big plus for this thing. The reciprocation mechanism is housed under the black stamped cover.

It’s a “scotch yoke” mechanism made of a stamping of steel….. welded?! to a precision ground rod. Given my adventures with welding things, neither of these components are likely heat treated. There is at least a real needle roller bearing that is doing the yoking!

A bottom stamping isolates the yoke from the crankshaft gear. I took apart the slider for kicks – the main guide bushing is pretty robust. It’s a solid iron-bronze bushing, which seems to be a Chinese tool favorite ingredient.

Here’s the crankshaft gear – it’s a machined spiral bevel gear sintering (as far as I can tell – the machining patterns don’t match up with any 3D process I know of). As spiral bevelly as it might be, it is not very useful because there’s no way to attach something to it that isn’t a crank pin. The assemble rides on a live shaft supported by ball bearings on one side.

The ball bearing and part of the spiral bevel gear is seen here. Unfortunately, I could not get that shaft out of the bearing at all, and ended up cracking the casting.

My curiosity satisfied for now, I elected to take off the motor.

…certainly not what I expected. So let’s see the thought process here.

“Hey 李小龙, what motor do you think we should put on this saw?”

“Not sure, 刘少奇… They want this to cost $0.45 less, but I’m kind of out of options from the motor factory. We’d need a custom shaft to couple to the gearbox and they will charge more for that”

“What if you just took the motor from the 18v cordless nose hair picker? It’s the same size as the motor we need for this.”

“They supply that with a gear already on it though.”

“So? Make a fucking adapter that goes to the gearbox we need that has a  cutout of the gear in it.”

I’m really betting it went down kind of like that. That’s what I’d do, anyway.

Anyways, the input pinion has a negative gear that fits onto the motor’s gear. I guess it’s a variant of a spline transmission, but it’s so Chinese.

The combination of nonremovable specialized output gear and nonremovable input…. thing has led me to give this thing a verdict of not very useful either save for maybe making a pokey-spike weapon for your robot or something.

Now, if the existence of CRJW is any indication, here’s the useful thing!

A cordless circular saw should consist at most of a motor, a gear, and a switch; two of those are interesting to me. This model, by the way, is from their third (out of like 5) line of battery-incompatible cordless tools!

Full disclosure: A little while back, I bought a Grizzly 18 volt cordless saw second (or third) hand for like $5, which led me to take it apart and discover what’s inside. So really I knew the conclusion coming into this teardown, but for the sake of informing everyone else, I’m doing the other two saws anyway. Additionally, the Grizzly saw seems to be a 2004 era vintage, so I wanted to check on the quality decline between then and now (the drills have gone downhill a whole bunch…).

Off the trimmings come! The metal nosecone of the gearbox poking out from the plastic is a good sign.

The cordless circular saw also uses a 700-class DC motor like the reciprocating saw.

And here is the assembly that was shown in CRJW’s build report!

The metal casting looks fairly stout, but it’s just an awkward shape. However, this gearbox is useful as-is. The shaft is supported in a ball bearing that is in the metal cone, so if you bolted it to a bulkhead or side plate in a robot it could be an immediately swappable part.

Inside the gearbox is this sintered assembly that consists of the spindle lock (for changing blades) and a solid ring gear/output shaft bushing assembly. I can tell that they are two different sinterings, but I wouldn’t be surprised if they were somehow the same material!

Here’s the gearbox split apart into components. As discussed in CRJW’s build report, the ratio is 5.2:1, single stage, using gears of (roughly) module 0.8 (about 32 pitch, but larger) that are 6mm in face width. All metal. Questionable metal, but better than that 1-stage-of-nylon, 1-stage-of-questionable-metal bullshit in the drills!

The output speed at 18 volts is about 3800 RPM.

So do I like these? Absolutely. They can be useful under certain circumstances – I think that they are far too fast for drive (CRJW may or may not disprove that), but in a situation where you have 2 motors and 4 wheels and can link them with chain or belt, a small amount of external reduction is reasonable. They are certainly more useful than the previous 2 saws, and I believe the gearbox is quite durable.

I’m satisfied with CRJW’s use of 2 plates to mount the plastic ring gear holder by itself, without the weird casting. The total weight of the gearbox assembly is about 18 ounces without the casting. I don’t anticipate using these on a robot quite yet, but I now have about 6 different saw motors and so have an option of it if I needed. Besides this HF version, I took apart the Grizzly and a “Speedway” brand saw (formerly retailed at homier.com which seems to have gone under) and they all have this same style of gearbox.

As a comparison, I also bought this Ryobi 18v saw secondhand. Ryobi is marginally more legitimate than a Chinese generic tool manufacturer, so I was expecting some custom hardware in this.

Ryobi is well known for making nicer 18 volt drills but whose chucks are patently impossible to remove – often needing to be cut off!

Long story short – no.

The gearing is spur instead of planetary, which, while it isn’t THAT terrible on its own, is integrated into the molded plastic case! The ball bearing in this case is just pressed into the plastic. As long as I’m not actually using the tool for the purpose it was intended, I’m gonna stick with the shady generic-brand import with their modular gearboxen. I’m wondering if the generics will move towards this design in the future too..

So here ends the lesson on cordless saws! I hope it spawns at least one retardedly fast robot besides the Carly Rae Jepsen Wallbanger!

About 2 months ago exactly, I commissioned a Replicator for our research group because I at that point was clearly never going to get anywhere with my plastic-pooping EZ-Bake oven. Several weeks (about 8, actually) passed, a few seedlings did some burnouts in a parking garage, I allegedly invented Mario Kart (again), and a bunch of other stuff happened and I kind of forgot about it.

Then this showed up.

Oh dear. Well, I’d gotten cryptic emails a while back regarding awaiting some kind of special shipment…

Alright, it’s time for another episode of BEYOND UNBOXI…well, I guess i’m only unboxing it right now, so nevermind.

With the top layer of packing material removed, I SEE THE THING. Glossy printed setup manual and cut-to-shape cardboard packing structure? Makerbot is getting so legit that it’s still funny because it’s awesome.

THE THING. GUYS. IT’S THE THING.

The whole process of unpacking it speaks to how much effort was put into packing it in the first place – there’s alot of well fitting custom packing material. I guess if you’re shipping a completed and tested machine there’s no other choice. The platform is all pre-coated with Kapton and there’s a free roll of it included.

I presume the little calibration dongle was made using the machine itself before shipment.

The level of engineering in this thing is leaps and bounds over the Cupcake and even the Thing-o-Matic, as far as I can tell by eye (and by jiggling axes). Injection molded brackets and bearing holders! It looks like the focus has shifted way from ‘kitting’ to integrated, tested machine – which, IMO, is probably better. As my past adventures in designing for easy lasering and waterjetting, and DPRChibikart’s build process is showing again, there’s alot of optimization potential and performance you sacrifice by restricting your build to a certain process or making it so generalizable that anyone can put it together. For silly vehicles, my view is that alot of these compromises are acceptable because there’s invariably many solutions to the same problem; I don’t think the same is true for machine design, especially machines relying on precision and repeatability.

Anyways, this new gantry seems rock-solid and ripe for serious overclocking.

OH, DID I MENTION IT’S NOW A GANTRY HEAD

One of the things I didn’t like about MaB from the start was the fact that I hurried through the design and just kind of copied and pasted what everyone else had going on at the time. The moving bed design really sucks because the axes have significant inertia and you accelerate the workpiece itself, which is bad if it’s remotely heavy.

The little details are great, like these integrated spool holders and all the cable snaps.

It even comes with allen wrenches. Guys, this is just like IKEA.

(The little black things are rubber edge bumper stock cut up to make convenient legs for the machine)

With two screws, the dual head extruder pops on. We went ahead and sprung for the twin head (can you say profit margin?) in case fully integrated support material becomes a thing in the near future, which I am positive it will. Right now, you still have to “merge” two separate STL geometry files within the software (ReplicatorG) to use the dual extrusion feature. More legwork on your end, but legitimate dual material is possible right now, such as ABS + PLA or similar.

Because I think we’re mostly going to be making machine parts and robot dong(les) with it, I’m more interested in integrated streamlined support material deposition than the ability to print a blue and green world. That would make this thing roughly 90% of a Stratasys uPrint at 10% of the cost.

If Makerbot were steampunk, this would be a cast-iron or forged brass badge with THE REPLICATOR MAKERBOT INDUSTRIES BROOKLYN N.Y. U.S.A. in fat script or squared off block letters arranged in circular outline. Or if it was really hardcore, just straight across with no stylization whatsoever because your machine is too badass for cute logos.

Because old machine badges are awesome.

After setting it up and powering on, the machine has a first-startup script that tests the extruder and helps you level the build plate (which is fully retracted for shipping). It also changes colors as it heats up – the ‘underglow’ is blue for cold plate or extruder, gradually fading to red when it is fully heated.

Well, technically that’s the opposite of what a black-body radiator (“heat source”) would do, but just like conventional current vs. electrons, who’s gonna argue…

IT’S POOPING

IT’S POOPING

I tried one of the dual extruder files that were included on the SD card (whose slot I searched on all 5 sides of the machine which did not have the SD card slot) just to see if I did the levelling thing right.

While I guess I did, the actual level that this sets seems to be too high. This file was the fish looking thing, and it didn’t end very well. Any other Replicator owners notice this? When printing the bottom most raft layer, I’m used to seeing the head mashing a thick track of plastic into the build plate – with the ‘one paper thickness’ first-run platform height, it seems to be nearly .5mm too high, and even the base layer sort of just squirts onto the surface but doesn’t get spread out at all.

I kept adjusting all of the leveling screws until the ABS trace was more like what I was expecting. This involved moving the plate up at least another full turn and a half, or something like .75mm if I estimated the screw pitch correctly – I was afraid that the nozzle was going to plant into the build surface, but it seems to have a preset altitude.

The RepG software is infinitely easier to use this time around. This is the first time I’ve used the “Print-o-Matic” feature in person, and I must say it makes the user experience more intuitive.

It looks like the default infill is scribbly hexagons.

I swore I would make no setting or hardware changes to the machine to appraise it for its out-of-box funcationality, but I couldn’t resist. The default full-fill setting extrudes using only one axis – either X or Y. I’ve historically favored the ’45 degree’ method which ensures both axes move simultaneously to draw a fill line, because it forces any axis inconsistencies to average out through vector addition – keeps things symmetric. Therefore, I changed the “infill direction” to 45 degrees instead of 90. It’s like printing X’s instead of +’s.

So that’s two things I’ve deviated from so far – platform trim height 0.75mm closer to nozzle after the levelling script has run, and infill direction to 45 degrees. Not bad yet…

Alright, so let’s make that three.

I’m still not sold on the whole “hot kapton tape” surface, unfortunately. It’s included with the machine, it looks great, but I just couldn’t get it to stick well at all. I tried cranking the platform temperature to 110, then 115 celsius, but the results were not much different (two 6%-bunnies died for this cause). Maybe it’s just extra cold up in Boston or something  – MaB had never fared well during winter either, and the shop was about 55 degrees that day due to leaky windows and a friendly cold front.

So I did the THIS IS HOW I DID IT IN MY DAY thing and dumped some blue tape onto it. Sorry Makerbot D:

Quantiatively speaking, I could get about 6mm of bunny out of the blue tape before signs of raft warping showed up, whereas the raw Kapton gave up after what seemed like only 4-5mm. I let two half-bunnies print to see at what point the prints fell off – the blue tape bunny detached around 60% whereas the raw Kapton bunny only made it to 45%. This was all during the chilly evening, so I’m sure ambient temperature played a role as well, but an equal role for both.

Yes, I watched this thing print bunny asses for about 4 hours. In the name of Science, I swear.

Alright, after the aforementioned minor finangling, the FIRST CALIBRATION BUNNY! The effects of the less than warm room (which is also pretty drafty) can be seen in some of the split layers. Extrusion settings for this run were bone stock, though, and the results are impressive. There was absolutely no tuning of extruder settings or making 10 calibration cubes to reach this stage.

To alleviate the breeze problem, I might consider walling off the sides and front (with a door in the front) like some people have. Breezes and incidental wind gusts are what do the most damage to these unshielded prints, and just the turbulence of you coming up to stare at it will generate a puff of cold air. I’m not inclined to try and turn it into an oven because some of the internal major structure is made of ABS plastic, and to stress-relieve ABS being held up by ABS will not end well.

It’s not my machine to hack, technically, but maybe if I plan it well and make it reversible I can make aluminum replacements for the ABS moldings and then heat the interior up to 50-60C.

Also, it’s been christened Fatbot, because it’s pretty wide.

I’m going to harp a little more on the development of the direct-drive stepper motor controlled extruder and its associated control hardware/software from even a year and a half ago to now. This amount of detail on the tip of the ears is phenomenal, and done without support structures. This just about beats the uPrint machines we have already in terms of finish quality. That’s a ~2.5mm long single line at the very tip.

So to recap… I think this contraption is awesome. But I’m not so sure on some of the very fine details that I took note of immediately which novice buyers and users might miss on – such as the seemingly extra low build platform and the inconsistency of hot Kapton. Any machine can be made to work much better once nudged enough, and while I didn’t have to nudge it as much as MaB, I’m wondering how these tests would have ended up if anyone else in this lab space – who don’t necessarily follow the hobby 3D  printer scene – were the one unpacking and testing.

There is a Calibration Naked Lady printing right now, overnight, without supervision (just like the manual told me not to do). We’ll see how it is in the morning!

Whoa, it’s back! Another episode of Beyond Unboxing, the series of random curiosity-driven posts by me which has so far shown light (literally speaking) on the inner workings of a few shady motor controllers. This time, I explore what is going on inside a commercially available generic lithium ion based “lead-acid replacement” – a battery made of a bunch of lithium iron phosphate cells hiding inside the shell of a standard-size lead-acid battery, with (or….without?) a battery management system to make them act like a plain lead acid battery.

Why would you want such a thing? Reduction of weight, longer lifecycle and shelf life (1500-2000+ charge cycles compared to 500 or less), no lead or acid, and higher power density and efficiency under high discharge loads, among other things. First, a little bit of philosophizing and rationale, though:

I’m looking at them as a possible prepackaged lithium ion battery solution for hobbyist & amateur electric vehicle construction – it’s a solution that is less white-hair inducing to suggest to people than “Oh, you buy this shady hobby lithium ion battery with no hard shell or output protection and use this rather complex multi-purpose charger to charge it, occasionally making sure to use the ‘balance’ function so your battery doesn’t explode”. While that solution is perfectly workable for someone with some technical ability or experience in the field, a plug-and-play solution can reach a wider audience.  I can reasonably assume that the people I see day to day in the engineering departments can handle such instructions as “use this battery charger on this setting and don’t plug it in backwards”, for instance, but from experience with the average curious audience member at the Maker Faires who wants to build a vehicle, it is not something I would suggest immediately without gauging their technical experience more.

Batteries are one of the last finicky items on the list of cheap & repurposed EV parts that we have compiled here over the years – I consider the problem of motors and controllers to be well-solved, especially with things which are coming down the pipe locally, but the answer to “What battery do I use?” has always been sort of difficult. The first response is the one stated above – hobby equipment and soft, plushy lithium pouch cells. Workable? Absolutely. Unforgiving if you are an idiot or just don’t pay attention for a second? Definitely. The second class of answers usually centers on chopping power tool batteries, e.g. DeWalt 18v XRP or 36v lithium ion batteries, which are nice because they already come with the charger for the hapless drill or saw you are about to dissect.

For example, the DeWalt DC9360 36v pack, popular with electric bicycle hackers, is only 2.3Ah and $150 (about $2/Wh), not including charger, but you either have to find an interface for the proprietary DeWalt drill connection or modify the battery/solder discharge leads yourself. They are by far the closest to plug-and-play generic battery solutions I’ve seen yet, though. In terms of modern Li battery solutions for small vehicles, there’s a clear trend between cheapest but highest user experience required (hobby and R/C batteries, chargers), and most expensive but plug and play.  There’s always the classic fallback of nickel cadmium or nickel metal hydride batteries – easy to charge, easy to use. But as it turns out, a good NiMH pack is actually as expensive, if not more expensive, than a lithium battery of the same watt hours these days. It would seem that the magic Chinese manufacturing cloud has largely moved towards producing cheap lithium.

Now, the other big question is, do I really want everyone to be scurrying around on Chibikarts? Probably not, but one step in pushing the construction of electric vehicles as a…… vehicle…. for engineering design education (I’m going to use that pun so much it’s somehow going to end up in my thesis, just watch…) is making sure that more people can do it, and there exist many different starting points and “upgrade paths” as you go. It’s similar to what happened to the robot fighting/combat robots community that I’ve been part of since the beginning of it all for me over 10 years ago: Starting out as a niche sport for people with tons of money and expertise with access to expensive tools, and gradually having commercial solutions and clever hacks for common problems emerge and letting more builders participate.

Anyways, rant over. Onto the relevant subject matter.

A product exactly like this, the A123Systems ALM12V7 module, is what powered this year’s 2.007 EV section to victory:

They are pretty awesome, I’ll admit. Externally accessible ATO fuse, automatic charge cutoff, automatic discharge cutoff too. These were pretty much foolproof, and fainted like Pokemon when the fuse blew or they were overdischarged. Really, that was the word we settled on describing it – when the battery shut off its outputs due to undervoltage or fuse tripping, a brief application of charging voltage would wake them right back up.

But what I found disappointing about them is that nobody else can get them. We were lucky to get them as a sponsorship / donation, but just typing “ALM 12v7″ into Google shows alot of press releases, datasheets, and articles, but no product. This is consistent with A123′s (and most American companies’) position of not dealing with the public directly, something which kind of irks me a little – no matter how much I love the fact that they are an MIT-affiliated battery company that regularly throws prototypes and QC line rejects at us for our own consumption, it’s not reproducible in a setting which is not us. Kind of hard to test your hypotheses then, huh?

They are not the only producers of these lead acid replacements, though. In fact, here’s a whole page of them.  And another.  And that’s just two of my favorite shady Chinese back-of-the-truck battery dealers, out of many! It’s my firm opinion that A123 has already lost the game here – when the 12V7 finally hits the market, they will be seen as just another player in the game, not the player or the leader.

As with all Chinese products, I viewed the generic SLA replacements with a healthy skepticism. I’ve already observed how the A123 modules behave under “out-of-spec” charging and discharging conditions, but I also understand some of the engineering and testing that went into them. The Chinese modules? Not so much. Thus, even though I knew of their existence for a long time, I hesitated recommending them to people. For all I know, they could be just cells in a box.

I was lucky enough to come upon some “class droppings” recently, in the form of these guys:

As far as I know, a 2.009 team purchased 2 of these units for a project last fall, but they were unused. They were found sitting in the Course II teaching laboratory and conveniently hijacked to run the 2.007 tables this year for a little while. Afterwards, they were moved back to the graduate student nest. My interest in them fell to a low point after finding out they were pretty well sealed – the A123 brick prototypes we got last year still had removable shells for testing purposes – and I just figured these were the same thing inside, or somehow knocked off of A123.

Renewed interest in their internals came during a battery search for a new variant of Chibikart (to warrant its own discussion later). So, last night, I decided to crack one open just to see what was going on.

The module above is sold by K2 Energy, which I can’t quite tell from their website if they’re a front for a shady Chinese operation or not, but who cares?

update!

A representative from K2 Battery actually wrote to me in response to the above:

“K2 is a Nevada corporation founded by myself and 5 other partners in 2006.  Most of the technical group, myself included, came to K2 from other battery companies, where we had been developing and manufacturing phosphate-based cathode materials.” -K2 Battery dude

Well there you have it!

end update!

The funny thing about it is, if I search ‘K2 lead acid replacement” or “K2B12V7EB” , the only things that show up are places selling them! It’s kind of a negative A123 problem – I can’t find anyone who’s used them in depth, dissected them, dissed them in general, or anything. They exist. In product form. That’s definitely a sign that something needs poking internally.

It’s interesting to note that these come in two forms – there’s an “EB” version which, according to the short shopping site blurbs, has an internal BMS, and the “E” version which does not. Presumably the latter is literally the box of cells of legend, but here I had an EB version, so it was a chance to see just how BMS-y it was.

I had Shane randomly select one (of two…) to be sacrificed to the scooter gods. Next was figuring out how to crack them open – I didn’t want to do that literally, since I did want to use them as batteries. I settled upon a more dramatic but significantly cleaner solution:

If there is one image which I should not post on the Internet, it is this one. Please, everybody, do not mill your batteries.

I positioned a thin slitting saw right on the green-black plastic seam which is cemented together very thoroughly. I made sure to do very light and shallow passes, poking with a screwdriver each time to see if I broke through the welds – if the top moved, then it was a sign to stop increasing the cut depth and move on to another side.

Whatever they make the casings out of, it smells positively disgusting. Also, the case is thick. Like well over 2mm thick!

After all four sides, the lid is popped off… and we have…

…

……

Well that was anti-climactic.

It’s cells. In a box.

With what appears to be a generic “PCM” board glued to the underside of the lid. These boards are sold throughout the Inexpensive Chinese Battery Markets (YES, ANOTHER USE FOR “ICBM”!) to append to your own battery packs. In my adventures in EV design at the MIT Media Lab, I’ve had the joy? of using them for a few different custom packs.

They function primarily as output limiters – the 3 bars of metal soldered to the board are current sense shunts – and will turn off the output FETs if the voltage becomes too low or the discharge current becomes excessive. These are nominal 25 amps, peak 40 amps (according to manufacturer datasheet). They also usually perform low-current charge balancing if any of the cells become out of line by a certain amount – purely voltage-differential triggered. As far as I can tell, they also do not limit input current – presumably because the shunt is only set up as a single-sided measurement so the simple logic cannot handle negative voltages. As black-box devices to append to your battery for some semblance of failsafe behavior, they are more than adequate.

These boards, though, seem to have the FETs back-to-back – the Source leads of the row of devices goes to both the negative output terminal and the shunts. So it very well could be more sophisticated – I didn’t take the opportunity to disassemble the board, since it was plastic-welded in place and I accidentally stripped two of the screws trying to get them out.

So I guess it’s not just cells in a box…but that still doesn’t say anything about the “E” version. Now I kind of want to get one, but also don’t feel like dumping $100 on cells in a box.

(By the way, this is my favorite PCM board by far – the 100 amp model. It really shows the Chinese design paradigm of “CTRL-C CTRL-V” well.)

Well there it is. I do like this arrangement of cells, though – it’s almost like there’s enough space in the case, with the cells laying down and the BMS board in the otherwise wasted space of the lid, to add another row of paralleled cells for more capacity…

….oh.

i see what you did there.

There is a plastic insert that is conveniently one-cell in height. I wonder why?

There is a “10Ah” model which is oddly enough the exact same dimensions despite it having 50% more cells. Could it be that it’s just rows of 3 paralleled cells instead of 2, and the insert is not used?

Nah. Couldn’t be.

A better view of the board, for anyone who wants to do some armchair trace-guessing. In keeping with the tradition of posting FET datasheets, here’s the AOD4184, which is pretty reasonable I suppose since 6 devices are used in parallel to share the output current.

My assessment of these modules:

I’m going to guess that anything which looks superficially similar will use a similar setup inside (The Law of Chinese Packaging Inertia), just with different PCM boards. The rudimentary charge-balance and output protection these devices offer is reasonable if the battery is similar in voltage to the lead-acid systems they are designed to replace. Most common non-automotive SLA chargers do a rough constant-current constant-voltage charge profile anyway – the former is called  “fast charge” and the later “float charge”. With 4 cells being 12.8v nominal and 14.4v charging, that’s pretty damn close to a 12v SLA setup. 24v systems are similar, with the nominal voltage being 25.6 and peak voltage being 28.8v – most 24v SLAs charge at 28 volts.

Some of them come with a “2 maximum modules in series” specification and it’s clear why that’s the case. A “36v” system made of these would actually be 38.4v nominal and 43.6v charging – the deviation from SLA nominal voltages gets more severe with each added cell. There is also a potential for inter-module imbalance. As some 2.007 students have already found out, the modules themselves can take on different levels of charge and during heavy use, one will fall under its minimum voltage and shut off. It is exactly like the inter-cell balance problem, just more meta. The way around this would be to make sure the packs are at the same level of charge (e.g. full) before connecting them in a string. Real SLAs and Ni cells will all suffer from this problem too, so it’s not necessarily any worse. With the output protection circuitry, I think it is manageable, but over charging is still a concern. I haven’t tested to see if these generic modules shut off on overcharging yet.

In terms of Wh / $, it’s expensive but not terrible – on par with the DeWalt DC9360, but more general purpose. The K2 “EB” module sells for $140 and at 82 Wh that works out to be about $1.70 per Wh. The “10Ah” version is in fact a better deal overall at $1.40/Wh. For a 24v 7Ah battery system with decent plug-in-wall charger (6+ amps), it would run about $350 and charge in an hour. If you don’t mind waiting all day, then generic 24v scooter chargers are like $20. As a reference, two of these 8.4Ah Hobbyking LiFe packs would run $160 (That’s only $0.75 per Wh… damn you Hobbking), and a charger which can handle 8 cells starts at $45 or so. But you will need a 12v power supply which can handle the wattage (example – $40). So the hobby solution is certainly still the cheapest for those who can accept its lesser level of integration and can properly secure the battery from damage.

Perhaps most importantly, the modules do have a (very) tough shell and rectangular brick form factor. It’s way better than watching someone zip tie a soft-pouch pack to a bicycle frame. I did a little bit of further shopping on BatterySpace, and found that I could buy the parts for my own 8-cell, 12.8v 6.6Ah pack with a 30 amp PCM board for about $100. However, then I would spend several hours putting it together and then still not have a cute box in the end to put it in. So certainly I could buy the parts for much less, but the balance of the $140 price is made up in convenience.