Archive for April, 2013

 

Operation MIKUVAN; Or, Why I Bought 3000 Pounds of Steel off Craigslist and Went to Pennsylvania to Pick It Up

Apr 30, 2013 in Stuff

Hello everyone. I just bought a van.

 

Okay, strictly speaking, it’s currently a “van shaped object”, since it doesn’t run. So, more accurately, I just bought another potentially never-ending project.

Before I reveal the details of what transpired this past weekend, I’d like to plug one of my MITERS compatriot’s robotic shindig coming up this weekend, Hexacon 2013 at MIT. Organized and hosted by Nancy of Orange Narwhals fame, this event will feature everything that has 6 legs (plus or minus a few) and is robotic (or can pretend to be so). If you’re in the Cambridge or MIT area, come on by. It’s being hosted about 50 feet from my desk nest midden in the International Design Center space.

Hexa-van?

Anyways, before everyone asks the obvious question of “How the hell did you pick this one, of all possible cars on the planet?”, let me explain the backstory a little. Raise your hand if you’ve ever seen these things on the internet:

If you haven’t before, you’re welcome.

Basically what is going on here is a Japanese pokemon “vanning” show. While U.S. van culture appeared to have died out by the time the 1980s rolled around, the movement picked up speed in Japan in the 90s. The digimon vans above are all 90s model Toyota Hiaces, a vehicle not sold in the U.S. for using the driver as a crumple zone. I’m not in tune with the Japanese internet (only some parts of it, and not the automotive bits) enough to know whether or not this still happens, or like most things about Japan that get crossposted to the North American imageboard market, actually stopped 10 years ago and we’re just watching badly dubbed reruns. Whatever the case, even if these kinds of Flamboyantly Gay Decepticon mods have died out, “VIP style” and other less ostentatious mods are still common.

Many of these get pretty ridiculous and they’re often adorned with the images of singers, characters, or the odd politician or two.

Popular features tend to include fake Testarossa style side strakes, side hatches, extended front and rear lips, cowlings and visors, an enormous rear plume, and those weird antenna things sticking out the front that look like curb feelers for rooftops. I’m not even sure you could move 5 feet in that in Boston without being stuck in a pothole.

I was introduced to these things some time in high school while reading then still-embryonic car blogs, and as I tend to do to extraordinary mechanical things, immediately fell in love with them. Sadly, if you are looking for more, I can no longer help you. All of the gallery links I bookmarked in high school have disappeared from the Internet. Short of speaking Japanese yourself, searching for “バニング” on Google Images (it being the katakana syllabic representation of “vanning”) will probably lead to the most returns.

Anyways, the plan for my van is not to completely dress it out. It comes from before the era when CAD programs supported things like fillets and lofts and G3 continuity surfaces. I think it has to retain the somewhat Brutalist, built-on-the-fly aesthetic, maybe like of like melonscooter. As of right now, all of the electrical accessories work but the engine doesn’t start. It cranks, and seems to try really hard, but something is just not going puff. I’m not historically a “car guy”; the only car I’ve driven in the time before nearly-new rentals and shared-used cars was pretty tame and reliable, so I hope to use this to pick up a few skills and learn some new things (some of the gory debugging details are forthcoming). I would like to get it running, even if rudimentary and completely emissions-destroying.

The ultimate plan for it is going full electric.

Yep. I’m doing it. There’s no turning back now.

I’ve always thought that it would be fun to have an electric car, even if they are less practical than a fuel vehicle at the moment. I like EVs. For a long time now, I’ve been sort of halfheartedly wanting to do a conversion, but the price of parts has always been the killer to that ambition. Even for the most basic conversion with lead batteries and DC motors, you probably won’t get away with under $7-8,000 (if you bought all the parts), not including the vehicle, and it will be extremely stripped down. AC and lithium systems will easily cost 5 figures (if you bought all the parts).

Emphasis on if you bought all the parts. I’m lucky to be surrounded by some ne’er-do-well friends who bought out the remains of failed electric car companies or worked at battery companies designing lithium ion battery modules (and abandoned ship before they went full Titanic and now run nuclear reactors). Stationed in the next lab cluster down the hall is an electric vehicle club bored of full size cars and now totally into bicycles and motorcycles, with their attendant spare and unused parts. Downstairs is an auto shop with a 2-post auto lift (and 19″ giga-lathe among other toys). But most importantly, I now have a real parking spot in the basement garage of the apartment complex I currently reside in (and which I pay a fee for it in the rent anyway, so why not?). The alignment of circumstances means #yolo the time is right.

Operation MIKUVAN

This story starts a few weeks ago through a combination of peer pressure and realizing that the stars of electric hoonage were lining up. If you’ve ever had friends offer you narcotics or alcohol, it’s like that except 150kW induction motors, inverters and LiFePO4 battery modules. Don’t make my mistakes, kids.

My derpy Japanese van fandom took a back seat (…) to other interests in the intervening years between high school and now, but I always thought about it from time to time. Living in the extremely dense Cambridge-Boston area means I never need a car (and if I do, all sorts of rental car agencies abound). Hence, any car I buy would have to be worth driving to justify the expense of parking, insurance, fuel, etc. Did I say fuel? My grad student income at the time was also (of course) insufficient to take on any kind of project like this. These days, being a shop instructor pays better – not the most glorious job, of course, given the mixed income priorities of our current economy, but I like the environment and interacting with the students.

So recently, every once in a while, I’d breeze the local Craigslists to see if there were any easy catches nearby. I always passed them up since I couldn’t ever justify throwing down a thousand plus dollars. The last cab-over style vans imported into the U.S. were sold in 1989 and 1990, so anything I could get from the Northeast would probably be more rust than van. I also checked southern cars around Atlanta, ones I could potentially get and then immediately stuff in my mom’s garage in Atlanta. The most common models of these in the U.S. are the Toyota “Van” and the Mitsubishi “Van” and the Nissan “Van” (in that order). Such naming creativity. The Toyotas dominate by sheer numbers, and there is even a fan club dedicated to them.

Three weeks ago, I came upon this listing in the Harrisburg area Craigslist.

Hmm. I’m not even sure what that is, but it looks a little dinged up. The ad specifically said it wasn’t running. It was $1,000, but I figured I could leverage that fact to talk the seller down a bit. This was clearly where all the Equals Zero Designs revenue was gonna go (OH GOD EVERYONE, BUY MORE RAGEBRIDGES PLEASE)

A few back and forths with the seller about what the state the vehicle actually was in, and I became more confident that it could be a worthwhile effort.  A history report on the vehicle checked out clean, and further pictures from the seller showed that the body and interior were in good condition, save for some rust spots on the outer body panels typical of a 20+ year old northern car. I trusted the seller when he said there was basically no frame rust, and that it has just stopped running about a month ago. At the time, it sounded like an easy fix.

Fast forward until Saturday morning, Harrisburg, Pennsylvania.

Team Mikuvan comprised myself, Dane (of Transistor-Man), Adam (of Flux Wonderland), and Cynthia (of Cynaesthetics). The plan was simple: Rent a local U-haul truck and trailer, and drop the thing at the nearest auto parts outlet and try to get it running in the parking lot, then (very carefully) driving it back to Boston. I would mention the best laid plans of mice and men, but these plans, best laid they were not.

This was actually my first time driving a trailer, especially a trailer I couldn’t see. I had to get used to getting into the next lane over to make a turn, and my simulated trucker skills were tested to the max on occasions.

On location and checking out the goods. I basically declare it “Item As Described”. Indeed, there were two rust holes in the bodywork – near the front wheelwell where it intersects with the boarding step by the front door, which seems like water could just have puddled in that area. Other than that, very minor patches on the body, and virtually none on the frame and underbody. For the price, I’m not going to be extremely picky.

Here’s what it looks like from the front.

Dat 5mph bumper.

And a rear quarter shot. The blacked out OEM paint in the front makes the greenhouse look bigger than it is, and it really imparts an 80s LEGO set spaceship kind of appearance. I approve.

Here’s a look inside. These types of vans have the engine compartment directly over the front axle, in a camel hump. The passenger essentially sits over the engine, and the driver over the battery and coolant bucket. To do most mechanical work, you have to drop the engine or get it on a lift. I kind of see why these things never took off. Plus, the later models tended to catch fire because the Japanese had to design bigger engines into them than was thermally prudent in order to keep up with American demands.

The engine did turn over, but did not fire. It burped once or twice to no avail, which was at least a good sign that it wasn’t seized or something. There was basically no coolant, and very little oil.

Scoping out the rest of the interior and checking out the electrical dongles. The seller let us temporarily install one of his batteries in the bay to make sure the lights, sounds, and spinning hubcaps all worked.

With the deal completed, it was time to attach it to the trailer. Because the engine wouldn’t generate horsepower, we resorted to manpower. I sat in the cab and steered (and pulled the e-brake).

We backed it up about 50 feet from the trailer and gave me a running start…

I was legitimately afraid of becoming a Youtube sensation, but it all worked out in the end. I stopped early the first time, since I forgot that this thing doesn’t have front wheels, it just has middle wheels.

Glory. After the physical loading, the seller and I went to a local tag office to transfer the title and for me to pick up a temporary plate (seeing as how at this point we were still sure that we could get it running in a few hours)

If I thought driving a trailer was fun, then driving a trailer with 3000 more pounds on it was even more fun.

We landed in south Harrisburg near a strip of road where there were a dozen garages and car parts places within 2 miles. During this trip, I learned that there were really only 2 ways to drive a trailer – either you are slow and gently moving, turn signals flashing all the time such that people are eyeing you and staying away…. or FUCK YOU, I’M BIGGER. Both seem to be legitimate.

I’m proud to say I only hopped one curb. Here’s the initial stating and plotting of the attack plan. We were going to just follow the “Engine won’t start” debugging chain in the shop manual I bought on eBay the week before.

Starting the intial teardown of the cab. We wanted to expose as much of the engine as possible, just in case the Thingiemadoobob needed to be removed to access the Widgetizing Sensor.

 

Trying to locate and figure out where various pipes, hoses, and wires go.

Mike, another friend skilled in automotive misadventures, lent me a timing light for the weekend, and we also had a compression checker. The first thing to check was spark and compression, just to verify the fact that yes, in fact the engine is still engine-like. Despite having the timing light, I don’t think we used it correctly, and ended up checking the sparks manually (taking one out at a time), which may not actually have told us anything about how it worked in-place. All 4 cylinders of the engine were verified good for compression.

I bought a new starting battery from Advance Auto Parts. The battery tray was full of random bits of styrofoam for some reason. Another interesting thing to note is that the coolant tank was missing. The seller claimed it worked fine and that he just needed to periodically top off from the radiator.

…Okay?!

I also bought all new spark plugs. This is a picture of an old one – it’s pretty gross. The seller mentioned the engine did burn oil, and it looks like it has been doing so for a long time.

The afternoon is slowly turning into evening. We’ve moved onto checking the fuel system now – fuel pump, fuel filter, the injector rail, and finally the injectors themselves.

The trailer itself acted as a makeshift auto lift. The van is hollow enough underneath that we could sit up and work instead of lying on our backs. The first order of business was checking the fuel pump for functionality. We jumped 12 volts directly to it and heard it run (and felt it pressurize the fuel line), then verified that the plug going back to the rest of the vehicle was also giving it 12 volts when trying to start.

Two’s company. One person held the alligator clips and the other checked the fuel line pressure.

We did find a pen in the engine, but sadly it was not the cause of the problems.

The rest of the day before it got dark was spent failing to get at the injectors (it would have required significant disassembly of the throttle body, as far as I could tell), and using carb cleaner directly in the rail to try and clean the input side out. We didn’t try replacing the fuel filter or bypassing it. After it got too dark to work, we called it a day and checked into a local hotel.

Here I am quintuple-parking in the lot. I had Dane box me in using the rental car to ensure that nobody else does – I’ve seen someone else get boxed in by other cars, so that’s why I thought of it. It’s now Sunday morning.

With the U-Haul already late a day, we made the decision to get back to Boston before sundown. I rented local, so for the one-way trip back, we had to swap trailers. This involved some amusing e-brake offloading from the trailer, then subsequently reloading onto a new one. The U-Haul guys were grumpy at first that we were demanding a one-way rental at the end of the month on a walk-in reservation, but they came back out with towing chains and ratchet straps shortly thereafter and helped with loading up.

The same “Come At Me, Bro” run-up technique was used to load the van for the return trip.

All loaded up and ready. We broke convoy since there were two of us who were van bums and two with real jobs they needed to get back in town soon for. The drive back was like any, except slower and with a lot more staring at lane changes.

And tolls. My god, the tolls. I’m fairly certain they were counting axles on the van, too. The Tappan Zee bridge (my usual northeast gateway) suddenly became $25, from $5 for a single car.

Adam rode in the van all the way back.

No, not really, though we did want to troll drive-through fast food places by placing 2 orders from the same vehicle train.

The unloading procedure was only slightly shady. Basically, the entrance to the garage is on a long down-sloped road. The trailer was parked upstream, and I rolled down, whipped a quick turn to point into the garage, then was pushed over the curb cut and coasted most of the way to the spot. A final shove exploited the van’s 25-ish foot turn circle and I nosed into my spot.

Now, getting this thing back out is going to be incredibly adventurous.

My time in the next few days will be spent preparing for the Second Great Go-Kart Race, the finale of 2.00gokart. I want to get in a good debugging day on this thing in the coming week, at least to pinpoint what’s wrong. I really do want to get it running, but because of the overlying goal of going full electrons, I’m not going to spend a great deal of effort trying to get the gas engine going again. If the fix requires an engine drop, it’s staying dropped and going on eBay or Craigslist, and I am going all-in.

The current state of the engine:

  • Fuel pump: Functional
  • Fuel filter: Unknown, but feels fine
  • Fuel injectors: Unknown
  • Spark: All 4 plugs verified independently, not in-place
  • Compression: Yes
  • Timing: Unverified
  • Vacuum: Why the hell do cars have vacuum systems?
  • Crank sensor: Unverified
  • Fuel pressure sensor: Unverified

Most of the people I’ve talked to who know a thing or two seem to point to the injectors, but I’m really wondering if all 4 of them can clog or break at once. It seems like a small, single point of failure which is not mechanical is stopping the engine from working.

I’ve considered patching together a quick slow drive system that bolts into the rear bumper or underframe which will at least help with garage extraction and act as a push-assist. Nothing major, just big wheelchair motors or a spare ETEK motor or two and welded steel. The trip from garage to auto lift is basically 1 mile, but on city streets. I suspect much night-hoofing will be done and orange glowy triangles and emergency blinkers will be involved. I don’t anticipate starting the conversion until summer at the earliest, and am basically anticipating it being a multi-year project much like LOLrioKart, except much bigger and more complicated! Shenanigans shall commence.

So, why is  it called MIKUVAN?

No particular reason.

Just one of my usual random project nicknames.

I’ll probably end up naming it Derpyvan or something. However, this is definitely one form of decoration I would unironically drive.

A Preview of 2.00Gokart and Finishing BurnoutChibi

Apr 26, 2013 in Chibikart, Electric Vehicle Design, MIT, Bostoncaster, Cambridgeshire

With the semester winding down (or, perhaps, finally ramping up!), many of the 2.00gokarts are in the process of being wired up and tested. The final product is due next week, and our competition (last year’s video)  is on May 5th!

Some of the students have been industrious and scheduled their checkoffs and inspections early. Here’s a preview of the action that will unfold in a much larger space next week:

Because conventional controls and riding postures are for wussies, apparently. I’m both amused and somewhat terrified at the prospect of there being three (out of eight) karts in which you ride head first. As it was my stated mission to not interfere much with the design and construction of the karts to let students experience as much of the design process, I might have to start padding BurnoutChibi and run interception for wayward karts.

Speaking of which…

Here’s a picture of the aftermath of BurnoutChibi’s motor detonation. As I would later find out, the sparks seen in the video were not the magnets grinding on the can, but rather them cutting up the phase wires.

Here’s a better picture of the ownage. The red wire, in particular, was cut almost all the way through. The annoying thing about this is that the wires were so close to the stator. If they were further out, patching would be a simpler job. I’d have to loosen the epoxy holding the wire stubs in place and also trim the heat shrink selectively.

While I await better motors, i decided to try and repair these. First step was to pop them open. There is a front retaining ring that comes out, then 2 set screws loosen up to free the shaft from the rotor. Then it’s a matter of pushing the shaft out to the right in the picture – this step was done on an arbor press.

Ouch. In total, five magnets broke loose. I figure this must have been a chain reaction where one magnet ditched first, and the resultant imbalance caused can deformations which broke the rest loose.

This is why I recommend motors that have “rotor bearings” or “skirt bearings” to everyone who asks me about them for vehicle apps. Even though it adds a little drag, the distal end of the can is properly supported on its own bearing. The only exception is if the motor is very short, like a more “pancake” style design.

I mixed up a generous dose of long-cure epoxy with glass microsphere (microballoon) filler, to slightly under nutella-like consistency. The offending magnets were pried out, the mating surfaces cleaned, then this epoxy smeared into the new joint. I replaced the magnets and used as much of the remaining epoxy as possible to completely fill in the gaps between them.

Evidently, I didn’t add enough microballoons, as the mixture did sag a little. To keep the cure symmetric, I actually chucked this thing into Tinylathe and ran it on a very low speed for several hours.

After the mixture was firm (but not cured), I set it on a radiator to cure with heat. Luckily for me, the radiators in the building were still on; they were switched off successively as recently as 2 days ago!

I didn’t get a good picture of the wiring repair before, but it basically involved exactly what I described before – carefully scraping away the heat shrink tubing to expose as much wire as possible. The wire was actually all magnet wire, so it would have been difficult to solder. To combat this, I “frayed” each lead as much as possible to expose the maximum amount of magnet wire surface area. Then I cranked the 80W soldering iron up all the way to 850 fahrenheit and literally burned away the enamel by embedding the frayed ends in a big ball of solder for heat transfer.

I think I managed to get back 75% of the red lead. The rest were patched similarly, but did not need as drastic soldering measures.

After the real epoxy fully cured, I reassembled the motor and crammed it back into the left side transmission.

I have yet to ditch a single magnet. Though I figure it’s only a matter of time before the right side lets go…

And with that, BurnoutChibi is ready to lasso its rogue… brethren? Bastard children? Offspring conceived via assistive reproduction technologies? Something. The only thing it does not do very well, sadly, is burnouts! Because the rider weight is basically square in the frame, and is up so high, it really just like to drag the front wheels along even if I’m holding the brakes. The same reason contributes to its severe power understeer (and associated lift-off oversteer!) behavior. Oh well…

Finishing BurnoutChibi: Transmission & Drivetrain, Controller Mounts, and Wiring

Apr 19, 2013 in Chibikart, Project Build Reports

In the previous week of work on BurnoutChibi, I’ve fully completed the vehicle but have yet to get it out to really test. This thing really is too damned fast for our indoor.. uhh, test track. A motor quality issue also prevented me from blasting it around in our usual outdoor venue (for very long, anyway). These issues have since been addressed, so it’s almost time for more test video!

As previously discussed, BurnoutChibi is a refit of the derelict Chibikart1 frame into something a little more hair-raising, as if Chibikart 1 wasn’t bad enough already. Since the last update where I had just finished reconnecting the steering, I’ve finished mounting the braking system, the transmission shifter cables and linkages, and also completed electrical hookup. At the behest of some of my students, I completed it in time for CPW last weekend, though the aforementioned motor problem meant it was not out scaring parents and wide-eyed potential freshmen.

Here’s the story in the pictorial form.

I began with a little aside in order to solve the problem of how to mount the two “Sand Castle” controllers. They have no mounting flanges and both sides are made of heat sinks, so just gluing it to a plate would make for some pretty poor thermal design. I decided to come up with a “cradle” that held the two controllers right under a fan for some forced convection  cooling. The fan I selected was out of my plentiful stock of 80mm LED case fans.

This design was an exercise in designing a snap fit for 3d printing. While I could have made the base a little wider and added some through-holes to hold the two halves together, I decided to get creative and dovetail each corner post together. The angle is extremely steep – about 85 degrees – so the whole assembly could be pulled out with force, but otherwise snaps into place cleanly.

…and it’s printed out of PLA.

Yeah, so what if it’s going to melt at about 60 celsius? It’ll just smell like delicious waffles while the ESCs burn.

I decided to try the “translucent light blue” PLA which is sold commonly, and I must say it’s my favorite PLA color so far. It’s not the vaguely jaundiced-rainwater color of natural PLA, and I also don’t like solid color PLA. A tinge of blue helps, but is not overwhelming and makes me think it’s some real plastic.

Putting together some of the electrical deck and testing the fit of the ESCs. Result: pretty perfect!

I set aside the e-deck for a while to return to the transmission and drivetrain.

First order of business is to attach the sprockets to the wheels. This basically entailed making four standoffs which acted as the lug nuts (M6 thread) on one side, and regular 1/4″-20 on the other side. The standoffs hold the sprockets a set distance from the wheel so the chain clears the tires, and also holds them concentric.

Or so I hoped.

There is practically nothing concentric or wobble-free about these shitty caster wheels. I had picked them up since they’re $10 each, but I swear not even Harbor Freight wheels are this bad. While the sprocket seemed to have minimal runout (radial misalignment), the wobble from the poorly stamped wheel rims was incredible.

I literally had to take a dial indicator to the sprocket and hammer on the wheel rims to bend them around. I got most of the axial wobble out of the sprocket this way, but this meant it all ended up in the wheels themselves, which now are a bit “googly-eyed” as a result. It will look hilarious when running.

With all wheels mounted, the frame could finally support weight. It’s definitely lost the Chibikart look a little since it’s so far off the ground (in comparison…). I have an incredible 2.5″ of ground clearance now.

The brake pedal hookup was the exact same as for DPRC. This pedal design doesn’t have a spring return on the pedal side since it is handled by the built-in spring elements in the brakes themselves.

Which, as it turned out, weren’t quite strong enough, so the pedal felt quite mushy and also did not return all the way. I added a long compression spring on each side between the cable stops and the brake lever, and this made the pedal feel much more positive. The brake cables sit in barrel adjusters so the balance could be finely tuned.

Shifting to the back again, I’ve appended the Vex sprockets to the Vex transmission’s VHex output shafts. The Vex sprockets didn’t come with any set screws or other means of axial retention, so for a quick fix, I drilled and threaded three #10-32 screws 120 degrees apart. The three set screws will offer way more retaining power than just one. I decided to forego any other spacers and shaft end-tap screws for now.

 

Here’s a view of the shifter linkage. The mechanism is a spring-balanced cable setup where I provide the pull to shift into 2nd gear, and the spring pushes the shifter back into first.

This was simple enough, but I chose springs which were way too strong initially. I figured “10 pounds of force” at max deflection was enough, but that translated through the cable into the shift lever, times two, meant it was just too hard to throw!

I went to a hardware store and bought several sizes of springs in roughly the same length that were much ‘softer’. The replacement spring is about half the spring rate, and was also too long in that it could not compress enough. The solution to that was to really quickly dremel a few loops off the spring, just  like a good ricer. The shifter now has a positive click as the ball detents lock into place.

Once that affair was taken care of, I routed the chain and moved the gearbox up to tension it (the “goalposts” having slotted mounting holes for this reason). To lock the gearbox in place, I simply tightened the…

… Oh, I can’t reach those bottom socket screws.

Must have bought those hex headed screws for a reason! I was wondering briefly where they were supposed to go on this thing. With the hex heads accessible with a regular wrench, now I could actually tighten the drive up.

With both transmissions hooked up, I spent some time getting pushed around synchronizing the cables. I put another set of barrel adjusters on the shifter cables so they could be adjusted as needed.

What I (not surprisingly) discovered during this push testing is that the brake shimmy is pretty severe. This is caused by combination of factors, two of which include my “kinematically suboptimal” rotor retention method (two screws across a diameter) as well as the complete non-concentricity of the wheels. To reduce the severity of the effect, I had to dial the cables to different tensions. The braking is still effective, but it definitely feels like it’s trying to jerk all over the place.

Ultimately, I’m likely to ditch these drums and go to a disk brake setup with its own guide bearing on the front spindles to maintain concentricity. But for now…

…back to the electronics deck. Here’s the wiring mostly in place with batteries mounted. The batteries are my old 5Ah, 10S sticks. Two of them.

The batteries are secured by Velcro ties and sandwiched between two rigid plastic panels (the baseplate on one side, a 1/4″ thick polycarbonate strip on the other). A 1/8″ silicone rubber pad sits below each battery for shock absorption and more impact protection. Combined, this ought to ensure the batteries don’t move anywhere.

The ESC power leads directly into a 150A fuse junction, and ground has its own big brass distribution block also. Overall, this is the beefiest power system I’ve built since probably LOLrioKart.

At the point, the frame was flipped over for installation of the power electronics deck. The rest of the wiring, including connections to the motors and to the main switch, happened in-place after the installation.

The long run to the power switch is doubled-up 12 gauge wire in each direction.

The only other power side wiring was to make one motor extension cable. With main power wiring completed, I quickly hooked up a HV BEC to provide 5V and a servo tester to convert the foot pedal’s analog 1 to 4 volt output to servo pulses. These two components were heat shrunk and sealed, then attached with Velcro to the top of one of the battery pack plates. The signal electronics for this thing are extremely basic – no fancy signal processing is occurring.  One thing that could happen with this system in the future is converting to electronic shifting, such as with solenoids, upon which I think a system which cuts throttle before the shift and slowly brings it back in would be helpful.

After confirming the functionality of the ESCs and calibrating the controllers, the whole rig is put together.

Here is BurnoutChibi posed next to DPRC! The wheelbases for both vehicles are the same, but BC has a slightly wider track because of the pneumatic wheels. Otherwise, they handle alike and are mututally just as difficult to sit in.

testing

The first few test runs of BurnoutChibi were done indoors, in our Conveniently Circular Building hallway. Due to the extreme acceleration ability of the vehicle, I couldn’t really test it any faster than DPRC or original Chibikart, so we decided to not take video. More testing commenced in an underground garage, then our usual spiral parking garage haunting ground. Unfortunately, I really only got a minute or two of hard driving in before the left motor threw several magnets.

The high speed of the motor caused some serious sparking as the loose magnets scraped the stator and also cut up the motor leads. Unfortunately, the only video that was taken was not focused properly…

The accomplice vehicle is the (still unnamed) tricycle.

Since that test, I’ve reglued the magnets and repaired the wiring, and BC is currently operational. I am currently waiting for a day in Boston / Cambridge when all hell is not breaking loose (in fact, as I write this) to test in the garage again. These pictures and videos will be uploaded when they are taken.

What’s Happening in 2.00gokart?

Apr 11, 2013 in Electric Vehicle Design, MIT, Bostoncaster, Cambridgeshire

It’s been a month or so since my last post about my personal undergraduate victory garden, “2.00gokart”. At that point, nobody’s really assembled anything or completed their designs yet. That’s all changed. Here’s what’s going on now, and what will happen in the next few weeks!

Chaos and half-assembled karts is the law of the land as the “Milestone 7″ checkoff and inspection draws near. This is a full “rolling frame” demonstration – brakes must work and steering must be hooked up and functional. The vehicle mechanicals do not have to be final, but to get to this point, it’s sort of implied. Hacking systems together to pass the inspection was discouraged, and nobody really tried to push anything sketchy. After MS7, the only tasks remaining should be to finish up electrical assembly.

At this point, things were being raised onto wheels and the true creativity of the students began to show.

This thing, for instance, had a custom wooden coachwork/centerpiece which was partially CNC router machined and also featured living hinges laser-cut into thin plywood.  On top of all that, the steering isn’t a normal wheel or handle, but it’s tilt based. The builders, Nelson and Carolyn, both have blogs and I swear they add content more often than I do. This creation has been officially named Zoran, which I briefly confused with Zorak.

Some of these things are conventional, others just a little off the wall, and still others… well, they have interesting operating postures. I’m kind of glad to see that nobody is really building a normal 4 wheel kart – there’s really only one. But hey, that’s not bad either – last year, the most normal and innocuous vehicle was done on time, on budget, exactly as described, and performed reliably.

Other vehicles are defined by a central feature, such as Dat Wheel.  That’s a 18″ lawn tractor tire that the team specified off Surplus Center. You’d  basically be sitting directly over it.

So that’s a sampler of the oddball creations coming out of this crew of MechE sophomores. What’s next for everyone is putting electrical systems together. I’ve been giving short “mini lectures” about places to get electrical parts such as switches and contactors, and also good wiring practices and other safety-related device (such as in the background of that picture – no male-side connectors allowed on batteries!)

In about 3.5 weeks time, everyone will once again (hopefully) fly down the service road and up the garage. This year is going to be tremendous.

On my end of things, I’ve been recently tasked with creating a relevant homework assignment for the EV students. One of the homework assignments for 2.007 proper relies significantly on you having built a competition robot. Since none of the alternate lab section students have, everyone was a little distressed. I therefore had to invent an alternative.

My alternative is a miniature (1-3 amps) current mode controller for a DC motor. That’s right, your homework is to torque control. I created the hardware hookup most of the way, requiring students to read a datasheet or two to discern what else needs to be hooked up, and also how to read the DC current sensor. The half bridge is standard fare for me – an IRS21844 gate driver hammering on some obsolete but sufficient IRF2807 N-channel FETs. The whole rig is synchronous rectified by nature. Really, this can be scaled up 100 times and be fully legitimate plus or minus some power supply changes.

Once the students finish said homework, I’ll release the working code & “class solution”, which is the most documented and commented thing I’ve ever written, as a general resource.

Here’s a picture of testing the whole setup, with a DC motor plant, ammeter to verify output, and a battery which can take regeneration current. Power supplies may be safer to hand off to a fuzzy duckling, but they cannot handle regeneration current, so a 10 amp fuse in the test battery will have to prevent things from going too awry. The controller is based off a simple integral-only (i.e. ramping) loop, which is more than suitable for driving highly inertial, dynamic loads like a vehicle.

So that’s explanation for the video last week! What really happened there was that I was pushing 15 amps (at 20 volts or so) into the field winding of the large blue motor (it’s a “separately excited” DC motor, so the mini half bridge board could crank 5 amps (briefly – I raised the limit just for the video) into it and have it just barely spin up. No, it is not creating perpetual energy. Without the torque control loop, it would have grenaded instantly.

From here out, I’m only bumping the students in the right direction to finish, and also making sure the appropriate paperwork and signoffs are in order for the final contest. In other words, “Wait, you want to do what with the garage?” “Yeah, we did it last year.”

 

BurnoutChibi’s Steering and Braking

Apr 06, 2013 in Chibikart, Project Build Reports

In the past week, I’ve been managing to intersperse bits of BurnoutChibi work between hosting extra hours for the 2.00gokart students as they edge ever more towards completion. On Wednesday, the “Milestone 7″ mechanical inspection occurred, where everyone had to demonstrate their rolling frames with steering and braking. The next steps for the students from here are focused entirely on assembling their electrical system. In fact, two teams have already blitzed their vehicles to completion, and more are surely to follow (parading them around during CPW is a huge motivator). I’m going to make a separate post about the progress of the class later – all I can say for right now is that this year’s competition is going to be awesome.

The first thing I had to do to build a new Chibikart is to disassemble the old Chibikart. Here’s the scene of the crime:

This work left me with a pile of redundant electricals – namely 4 more Jasontrollers and the massive A123 B456 battery. Needless to say, these will probably find their way into some other silly rideable thing.

The plan for BurnoutChibi’s electrical system is actually to use my left over 10S 5Ah lithium polymer packs, instead of making a custom pack or keeping the A123 pack. I decided to this mostly for the power and energy density of the lithium polymer packs (Chibikart 1 weighed 53 pounds because the big A123 bus battery module weighs almost 20!)  as well as the simple fact that said lipo packs have been sitting for almost 2 years, and I really don’t want to see them go to waste. The lipos themselves are from the erstwhile Deathcopter, so BurnoutChibi will surely be the health and well being hazard I envisioned it to be.

The first appendage to the old frame is the new style brake pedal. At this point, I haven’t even removed the old steering linkage yet, but I wanted to see if it would interfere with the new position of said linkage.

I started from the rear with fitting the Vex Ball-shitter transmissions onto the “goalpost” mounts. This whole ‘rebuild’ is essentially replacing Chibikart 1 frame plates with specially crafted DPRC ones. The only difference between this rear corner and DPRC’s is the goalposts!

I focused on getting the motors mounted and the rear end together. Here, I’ve mounted the NTM motors to my NTM-to-CIM converter plates. Eliminating units, the result of this evaluation is something which is basically like a CIM, but 4 times more power dense.

There’s only one problem. The NTM shafts need to have a 2mm keyway cut into them so I can easily used the keyed bore supplied with most FIRST OEM parts such as the Vex transmissions (The fact that I can say “FIRST OEM” is unsettling).

As it turned out, these shafts are casehardened. Wow, Hobbyking, you’re classy now – what this meant was I could not use my single HSS 2mm endmill to machine the slot. Instead, I went on eBay a few weeks ago and bought some 2mm solid carbide endmills. I recommend keeping a set of carbide cutters around for dealing with troublesome materials; the downside, of course, is that they are more brittle and need a stiffer machine setup.

I faced the slight issue of the endmill being too short and the Bridgeport spindle being too fat to reach the nether regions of the  motor. So I did what any self-professed machinist wouldn’t do, and chucked it up in a drill chuck. In my defense, I bought this integral-shank keyless chuck just to do dumb things like this.

I cut the keyway just a little short of actual dimensions because the NTM shafts were not long enough to use the included retaining ring with the gears. So I had to press the key in,and will need some creative gear pulling if I ever wanted to remove these gears.

And here they are mounted. I found the sheer number of hexagonal sockets on the gearcases a bit confusing at first, but now appreciate how versatile they can be.  Chain tension is adjustable using the slightly slotted mounting holes. I inserted locknuts (nylocks) into the opposite side hex sockets, so torque retention will be positive.

Notice how the seat mounts have been turned around. This was necessary because of how big the gearcases were. The seat mounting centers, and overall position, will remain unchanged.

Crawling up the side of the vehicle, I reached this build’s star attraction: The gear shifter. This came together amazingly well, and the feel of the ball detent plungers is extremely satisfying.

Heading up front, I popped out these new steering knuckles. In keeping with the tradition of doing the least possible work, these were specifically designed as drilling operations in a 1″ aluminum square barstock. The four flange holes will be where the drum brake mounts.

Continuing work on the front end, the drum brake mount has been attached and the new narrower steering…ears? are mounted. I’m not sure what to call them on Chibikart. They’re too short to be A-arms or wishbones.

Recall the new steering linkage arrangement – the crank arms are basically socket wrenches that fit over the hex head bolts. Motion is transmitted via giant set screw in the steering knuckle. To ensure positive engagement, I machined a deep flat into the hex head bolt shanks and picked flat-bottom set screws to maximize the contact area. To retain the crank arms, I center drilled a hole and threaded it for a retainment bolt. Otherwise, the crank arm is thinner than the bolt head and will be free to float about 1/16″ or so.

I moved on to chopping up the 90mm drum brake to fit up front. The mounting method I ended up devising would have been fine with keeping the giant torque arm, but the design would be cleaner without.

To maintain the cleanest possible lines, I brutally slashed the housing with a Dremel cutting wheel.

To attach the drum brake itself to its mount, I first had to machine the little round spacer which adapted the 14mm bore of the brake housing to my 1/2″ bolt wheel spindles. I sandwiched the brake housing between the mounting bracket and the spacer so it was reasonably centered. Next, it was a quick drill press job using the mounting bracket holes as a drill template. The steel housing on these brakes is just thick enough to hold a few threads of #10-32, so a socket cap screw was screwed directly into it through a standoff.

The mounting bracket itself involve one sheet metal bend to create a spot which will eventually anchor the brake cable. Well, I managed to bend it the wrong way the first time. Heating up the aluminum with a torch and carefully bending it back the other way worked, but the metal still cracked on one side. I had a buddy on MIT FSAE lay a quick TIG bead across it (see the irregular texture where the sheet metal arm bends left).

The brake drum mounting itself is what I’d call “kinematically suboptimal” very nicely. Basically I squished the slightly tapered stamping flat on a hydraulic press to get a flush mounting face on the bottom side. Then, two standoffs which each have a small shoulder that is precisely fitted to a mounting hole keep the drum attached to the wheel. On the top side, the standoffs have a 1/4″20 thread so I can use already available button head screws to retain the rotor. On the other side, the standoff is tapped M6 X 1 to interface with the original wheel lugs bolts.

The concentricity, needless to say, is less than stellar, but turned out way better than I had anticipated. I’m likely to replace this whole rig with a custom machined aluminum dish that has M6 x 1 holes tapped into it so I can just dismount the whole tire without causing loss of alignment. The brake does scrub, but only slightly and intermittently, and works very well otherwise. I have no doubt that this thing can lock up and skid.

And the front end is basically together.

Work now will move to the rear again with assembling the drive wheels and sprockets. I have an order of brake cables and associated parts coming, so I hope hooking up the whole drivetrain and shifter this week is a possibility.