Silly Go-Kart Design: The 2014 Summer Season

chorl

Hello and welcome to another episode of Silly Go-Kart Design! I’m your host, Charles.

I knew that immediately after coming back from the Detroit race, I’d totally drop off the radar for two weeks as the MIT-SUTD Global Leadership Program drew to a close and everyone rushed to finish their creations. What does global leadership have to do with silly go-karts? Hell if I know, but they asked me to run it last year and it sure as hell worked out! I don’t try to read too deeply into things with “leadership” in their titles.

This year, the program was expanded to 36 students. Oh, dear.

Thirty were shipped from Singapore, while there were six MIT students who were accepted into the program after a local call for sign-ups.

Luckily, the crew for this summer was made up of some pros. First, long time compatriot in robot arms Jamison, then there was Banks (who was also an undergrad TA for the spring 2.00gokart session), and joining new this summer was Paige, who was actually a student in this year’s 2.00gokart and decided to help TA this summer session. Without highly experienced TAs, this summer would have been actually impossible.

Before I dive into the action, here are the deltas from the spring 2.00gokart. There’s some important changes that we made to scale the class to the biggest it’s ever been, now with multiple instructors. Much of the documentation was moved to The Cloud™ through Dropbox or Google Docs.

The Secret Ingredient

This past spring, I decided to spice up the design space by giving all teams the opportunity to use a troll free part: a pair of pink Harbor Freight wheels, which has since been decided was the best idea ever. As I mentioned in the spring 2.00gokart recap, I wanted to use Vex Omniwheels as the troll free part, because why the hell not. I’d checked out Vex omniwheels in person before and they seemed to be well-constructed enough to handle vehicle loads.

I’m proud to say that the troll design sweetener totally worked. Multiple teams went for the omniwheel solution, and none of it ended in little rollers being scattered across the parking lot.

Parts Buffering

In the three or so weeks preceding the program, I ordered a load of parts that, from past experience, students tended to gravitate towards the most.


My body is ready.

In past classes, everyone’s mostly gone for the classic Kelly Controller and Turnigy SK3-63xx combination, a wheel or two from Monster Scooter Parts, chain drives, pedal throttles and thumb throttles alike, the weird little black brake calipers, a Hella switch, and so on. Then there’s always the odd DC motor team, so I got stuff to cater to them too, with the most common DC motor used previously (the 24V “500W” size scooter motor). This cabinet was pretty empty by the end of the class.

I try not to ‘kit the class’, but with time so crunched during the summer session, this was one way of making sure people could finish time. Teams that ordered a part I just happen to have received their parts generally after a day or two’s delay so they could get working quickly, but not right away to preserve an element of fairness. My benchmark for fast shipping is McMaster and Amazon Prime, so most teams got most of their shipped parts in the same timeframe anyway. Surplus Center folks, however, were out of luck.

It’s important to note that the contents were not made known to the teams beforehand. By the end, everyone pretty much figured out what kind of throttles and stuff I had anyway, but the work towards the beginning was reasonably independent.

Bill of Materials

One of the cornerstone elements of my ‘class’ is that all teams order their own parts (beyond the small material pile I provide them). In all past terms and semesters, this was accomplished by one team member sending me, via e-mail, a list of stuff to order. This worked well enough, especially since I am the only person with a procurement credit card.

What this system didn’t have is a way for any other instructor to verify/advise on perhaps badly informed or thought out purchases. Nor could students see ahead of time what their teammates ordered – near the end, everyone starts sharing parts and excess materials. We wanted there to be a bit more networking available to them, as well as to have the ability for each instructor to oversee the activities of a handful of teams.

For this BOM, we set up a Google Doc spreadsheet that was editable by invited students. Each team designated one member to be the go-to for finances. Through this spreadsheet, they were able to not only specify parts to be ordered, but also have a real time check of their remaining budget.

Students had made their own BOM Excel spreadsheets in past classes, but this made everything uniform and accessible.

The ordering protocol was that every purchasing day (Monday and Thursday of the 3rd through 7th weeks) I’d sweep through the BOM and then highlight green any items that were ordered. I’d highlight in red any items that were NOT ordered – the reason usually being that the specification was incomplete or the item was out of stock. Students were warned repeatedly ahead of time in both Milestone documents and the “Resources and Parts” lecture that this was going to be enforced strictly. We had very little issue with this overall.

This is an example of a fully filled out team BOM from the end of the class:

As can be seen from the image, I indicated when the order was fulfilled – for “class stock” parts, I changed the line to green when I made the “delivery”.

This BOM system worked out great, and I highly recommend it for anyone else trying this. Around the middle of the summer, one team made a “Stuff to share” tab with a similar format and quite a few teams listed their excess screws and materials.

Waterjetting and 3D Print Queueing

In semesters past, I was also the concentration point for all teams’ waterjetting files. Since 2.00gokart and last year’s GLP program only hosted 10 teams, it was still reasonable to keep track of. With competent instructors and more teams this time, we chose Dropbox as the venue for team parts submissions. I set up an instructor’s Dropbox account using our instructor email list as the account holder. The students were asked to either form a new Dropbox account or purpose an existing one (such as a personal account) for the class, and we sent invites to the e-mail addresses they gave us.

This way, any one of us could see in real-time what they uploaded. This caught a handful of potential “waterjet derps” before they were accidentally manufactured. I also recommend using this method, or an equivalent service, to sync fabrication files with instructors.

Within each team folder, students were asked to create folders with the date of submission (e.g. “Waterjet 23 July”) so we could keep track of what was submitted when. I put example folders in each group, such as “Waterjet 1 January” – this backfired at least once when one team absentmindedly put all of their waterjet files into that folder instead of one with the submission date on it, so we didn’t find it for days! Confusing examples are to be avoided in the future, but I gotta wonder some times, you guys….

So these back-end improvements are basically what differentiates this summer session from past sessions. I’m pleased with how they turned out – overall, there was minimal instructor confusion.

the build season

Now it’s time for the war stories! By all measures, this was the smoothest show we’ve pulled off yet – there were only a handful of issues that I’ll address soon. We begin with the first day:

One perk of having multiple instructors is someone can always be taking pictures. So here’s a photo of me giving the introductory lecture. In this one, details were given about the class, schedules, TA/Instructor/shop hours, design rules, and so on. Videos were shown of past semesters. That was more or less the calmest this whole summer was going to get.

Right afterwards, all hell breaks loose:

The demo parts were busted out and people began getting a sense of dread for exactly what they’ve gotten themselves into.

…and test drives were handed out. Not of Chibi-Mikuvan, mind you – that’s how people die. I put it out for display as a slight contrast against most of the aluminum extrusion framed, outrunner-powered karts present as examples (including the Chibi Twins).

It’s interesting to note that the majority of Singaporeans do not drive or own a car. The Singaporean government has purposefully made it very expensive and time-consuming to own a private vehicle on the island, due to traffic congestion and land concerns, so instead they spent massive money on a very well developed transit network. Seriously, I can get clean across the whole country in an hour on the trains, and buses will take me to the nooks and crannies. That’s how Shane and I explored so many resources when we were in Singapore. What buses don’t do, taxis will. So really, most of these students have never touched a motor vehicle in their lives.

And boy, did it show. The test drives comprised a whole lot of “100% throttle, 100% brake, 100% throttle AND brake at the same time”.

I once calculated that it would have cost about $85,000 to put mikuvan on the road in Singapore, not that they’d even let it in the country in the first place for being such a disaster. In the U.S., it cost me about $950: $800 to buy the thing, $50 for a PA temporary plate, $75 for a MA registration, and $30 for a MA state inspection sticker – ignoring the transit costs of renting a truck and trailer, of course. In singapore, the “Certificate of Entitlement” saying you may even own a car in the first place would have been around $80,000 (converted to US).

These kids will never understand the joy that is being under your vehicle, covered in burnt motor oil grunge, while contorting to European gymnastics levels to reach an impossibly tightened nut which you quickly discover you used the wrong socket driver size for. Maybe this is for the better.

In the first and second weeks, students generate ideas for their designs and perform analysis of  their desired drivetrain/performance parameters to select the core components – generally system voltage, which motor, which controller, and what size wheels.

One major aspect that differed from last year was that most of these students (something like 66%) were not engineers, electrical or mechanical: they were Architecture or Design students. Many of them had never touched hardware or tools in their lives. I was not informed of this beforehand, else I would have tailored the curriculum with more introductory material. It became painfully apparently during Week 2 when the heavy drivetrain and motor math was introduced – the amount of blank stares and glazed-over looks I received was disconcerting. As a result, we had to hold more hands during “office hour” tutorial sessions. Eventually, most everyone got their heads together and understood why I was making them perform these analyses. Other “crash course” subjects that were a direct result of the students being majority not MechE (unlike last year!) were Solidworks and machine design/mechanical parts knowledge areas.

Pursuant to the lack of experience in this field, many of the karts were somewhat derivative technology-wise. Seen above are students measuring and appraising Paige’s 2.00Gokart project. Many measurements of Chibikart were also made. In the end, though, I’d say the majority of vehicles were not copy-and-paste: the students took the modular concepts of what worked from our examples and reused the modules in their own designs. For example, the Chibikart style of motor mount/corner structure was popular, but in a kart which otherwise had nothing to do with Chibikart. This is totally fine by my books.

Hey! That looks familiar!

Now we’re moving onto week 3-4. Prototyping and getting your full-size mockup together was key, here. I bought something like 300 pounds of 1/4′ and 1/8″ MDF from a local wood supplier , just like during spring 2.00gokart, to let the students prototype to their heart’s content.

Again, the difference between the ‘prototyping’ they’ve been taught and my style became apparent. During this period, some students were frustrated that they were lacking material to make the traditional “prototype” seem in college design and build courses: foamcore, cardboard, wooden dowels, and the like. A few were not sure where to start because of this.

We explained as best as possible that the idea was to go directly from detailed CAD to full-size mockup. And again, this would have been totally fine for a crew of Mechanical Engineers, but time was lacking to accommodate the desires of the Architects and Product Designers. After some frowny faces, people dealt, and the mockup frames sprouted quickly.

The MDF ran down low towards the end of the class (week 6 and on) because many teams used very generous amounts to create bodywork, custom seats, and the like; necessitating me reordering the MDF shipment. My apologies to everyone in the Cambridge-Somerville-Medford area who might have been trying to obtain 1/8″ and 1/4″ MDF materials in the past few weeks.

Hardcore fabrication begins around week 5 as peoples’ parts come in and they realize that “steel rods” don’t make “steel axles” necessarily, among other intriguing facets of mechanical engineering. Also, you don’t tap threads with Loctite as a cutting lubricant.

Above, Tinymill is seen with its groupies. We ran machine training sessions as-needed for team fabricators.

Here, a student is seen nesting in a pile of go-kart parts.

We began taking waterjet cutting submissions during week 4 (basically early July), and one Milestone requirement was to submit several different waterjet parts. Unfortunately, not having a grade or something of coercive force behind it, few teams adhered to the requirement. Submissions really began hardcore around Week 6, which resulted in plenty of waterjet spawncamping by all the instructors.

One aggravating factor was that we originally intended to split the duty between two machine shops which had waterjet machines, but one of them ended up having machine and water supply problems in the middle of the summer, causing us to have to ditch entirely to one shop. That shop was one where only I and Jamison had authority to run the machines, so we ended up having to babysit the waterjet for 2x longer than intended.

It’s important to have a reliable service supplier, and possibly even a backup supplier, if you run a class similar to this. We could not have foreseen the first shop’s issues (and frankly, neither did they), so if I did not negotiate the second shop’s permissions earlier, we’d been b0ned (that’s a technical term).

During the last weeks, the design students’ creativity really began showing through.

I actually like having this summer crew of mixed backgrounds and majors. Why? Because nobody really build a normal go-kart. Even though there were challenges, it’s refreshing to see some experimental, kind of out-there designs, instead of 4 wheels and a steering column. There were rear-steers, there were hand controls, there was an attempt at torque vectoring, and so on. The lineup looked like something out of Wacky Racers.

Nobody’s under grading pressure to “do it right”, so they do it how they want – once again, aligned with my goals for the class.

Just take a look at “Trollkart” here. This was one of the normal ones. They found out that they didn’t really have a good ergonomic location for the throttle pedal. Solution? Make it a hand throttle pedal.

Also, they used the 1 Harbor Freight pink wheel that I gave them for free as a seat cushion. As it turns out, the hub really does not project upward enough to… uhhh, cause damage. They assured me of this fact, which I later confirmed.

…and yes, we had an “Omnikart” team! It took them a ton of effort to squeeze four motors and controllers under the statutory $500 budget, but they did it . Sadly, they spent too much time getting the mechanics running and dropped from the running for the race – instead, spending the whole period during the race trying to get it to drive. Maybe this was a little too ambitious, but the team was super into it the whole time. It was simply too much work for relative novices in an 8-week build period.

I hope to see Omnikart slowly hovering around SUTD in the future.

As week 7 draws to a close, chaos breaks loose in the IDC. Lines for the cold saw are backed up out the door, and people are starting to work on vehicles wherever they can find space!

the contest

We set up the track the same way as last year and this past spring’s 2.00gokart. This procedure is now well established enough with the safety office and parking office that I think I can throw a full event with 2 weeks’ notice, which is pretty awesome. The students were all eager to finally test their vehicles – remember that for many, this was the first complete functional project they’ve worked on.

It was a hard decision for us, but at the end of the build weeks, we decided to scrap the Time/Energy contest we’ve run in years past. The reasoning was that so many teams were just out to drive around novel designs that it made little sense to try and meter their energy usage. So really it became a race of time-only, and a few teams were clearly out to just drive their creations regardless of lap time! I believe that learning is most effective when you’re not under duress, so in the spirit of the program I went along with the instructors’ opinion to scrap metering the energy usage of the teams. It removed a significant bottleneck in queueing karts up for the individual runs.

As I was busy running the event itself, these (awesome) photos are mostly courtesy of Banks and his übercamera.

A great motion anti-blur of one of the omniwheel teams. They were clearly just having fun spinning around everywhere with omniwheels in the back. I took this thing for a spin after the formal event was done, and it’s borderline impossible to control after you get up to speed!

This is what happens when you don’t listen to me about fastening your wheels on properly, guys. One of the teams had an unfortunate, chronic disease of shedding wheels.

Field repairs! I strictly enforced a no-bringing-your-own-tools rule this time, so teams had to make do with a “pit kit” we assembled of the most common hand and power tools. During 2.00gokart in the spring, there were some problems with teams sneaking tools out of the IDC because they needed a special size of long-reach ball-ended hex key to reach their wheel mounting screws or whatever. Well, this time, I had a whole lecture devoted to design-for-maintenance, so y’all have no excuses!

One of the ‘off the wall” karts: a rear-steer, tiller-controlled trike. This is basically a normal go-kart turned completely around. Their complex rear steering linkage ended up biting them, but otherwise it was highly entertaining to watch snake around the course’s cones.

One of the “normal” karts, from a team of self-proclaimed newbies. For being said newbies, they did quite well; ultimately, they shredded their two rear tires!

An issue crops up with Team Newbie Kart.

We called this one “Overconstrained-kart” because they had a single middle rear wheel with drive wheels on the sides. They insisted that the center wheel was needed to support the driver’s weight. Pretty much everyone insisted back that they’d get much better performance if they removed it, which did happen during the middle of the event.

It did perform better.

One way to be fiercely stylish is to match your custom go-kart’s seat.

Don’t worry, Omnikart did get up and running during the event, but they burnt out two of their motor controllers. If I had known that the “40A” robot controller they picked for their design were about as well-built and rated as most robot controllers on the market, I would have offered them a free pair of RageBridges.

After the individual team runs were done, we moved onto “Anarchy Hour” where everyone who wanted to run head-to-head could do so.

At this point, MITERS invaded with Chibi Atomic Jeep! Sadly, I couldn’t get Chibi-Mikuvan back up and running in time due to the necessity of running the whole show.

The Electric Vehicle Team also showed up with its motley crew of rideables. And… wait, is that LOLrioKart?! Why, yes it is – under the command of a new captain. LOLrioKart sat abandoned in MITERS for almost 3 years before it was revived this year. This is the first time it’s been on a track of any kind.

Yeah, it’s as precarious and top-heavy as I rememebered it. Even more so, with it lacking 150 pounds of nickel batteries at the very bottom!

The photo of entirety for this year. Check us out in the background acting all goofy!

the future of 2.00gokart

There were plenty of improvements on the class structure that will make future sessions that much more streamlined, including the use of Dropbox and Google Docs to coordinate instructor effort. I think the class procedures and content is very much at a plateau of stability such that the class can be redistributed easily to anyone who thinks they can run a version of it. Already, I’m seeing derivative and inspired seminars/classes pop up – from a group at UC Berkeley to the Artisan’s Asylum to individual makerspaces.

Unfortunately, I think I’m no longer in a position where I can run 2.00gokart (or the summer session) again. I’m first and foremost responsible for the daily operation of the IDC fabrication shop. It used to be that the IDC was very small and easily managed alongside teaching, but nowadays it’s grown to house dozens of researchers and students. I can no longer justify the time put off running the shop spent towards teaching the class. Each time the class runs, the shop falls into disrepair because I literally only have time to fix what’s broken just enough to keep the students working.

This summer saw my spare time stretched to nearly its limit, and at times, it was frustrating to try and keep up with researcher’s needs while answering go-kart questions. It sucks, since I want to see this happen consistently and would vountarily do so if relieved of the need to run the shop it’s housed in. I’ve let the higher-ups at SUTD know about this issue, and I’m making plans for the continuity of 2.00gokart for next spring and years to come, but for now, I see myself fully entering the role of facilitator and stepping aside on my teaching duties.

(read: IT’S YOUR DAMN PROBLEM NOW! MUAHAHAHAHAHA…)

As for the class itself, I’m once again making the materials I generated freely available online. There are two forms:

  • First, a ZIP file containing only my lecture notes, “milestone” weekly report documents, and other files which I have sole copyright over: MIT-SUTD EV Design 2014 Reference Files. Not only does this have the 8-week program for the GLP, but it also contains this past spring’s 2.00gokart class Milestones, which is a 12-week program with more discrete weekly goals. This past spring, 2.007 itself implemented a “physical homework” system, which is also included in the Milestones but are not tied to or required to use the course materials.
  • Second, I’ve made the MIT Stellar Course Management System page for this summer session publicly accessible (Global Leadership Program 2014). I’ll investigate maybe having this ported to OpenCourseWare for more permanence, but for now, Stellar is stable enough.

That pretty much wraps it up for this year. The smoothest and most enjoyable season of “silly go-kart design” might very well be its last, but we’ll have to see what the future holds there. The students have once again packed up their vehicles and parts for the trip home, so at the very least, we have sprinkled Singapore with even more seeds of mischeviousness!

As for myself, it’s going to be a week of cleaning up the tornado disaster that is the shop, as well as shifting my focus onto ROBOT SEASON! BECAUSE DRAGON*CON IS SOMEHOW 2 WEEKS AWAY! Stay tuned for updates on that front.

Chibi-Mikuvan: Detroit Recap and The Conclusion

chorl2 Comments

I have the worst go-kart hangover ever.

In the end, the reversing module, spare parts, and electrical system refactor didn’t happen, so I basically went down to the race with Chibi-Mikuvan in its late Wednesday condition. However, all the sciencing and preparation did pay off: Chibi-Mikuvan won 1st place in its 30-lap sprint race. The Endurance race the next day, however, saw my very much still beta-version non-refactored electrical system catch a case of the loose wires from the very bumpy track, an issue which couldn’t be diagnosed in time for the end of the race. The final ranking for Chibi-Mikuvan for the weekend was #6 out of a field of 19.

Also, this picture happened:

We actually didn’t travel down with Chibi-Mikuvan in the open, to avoid things like rocks and bird droppings. Instead, it was tarped over, but the tarp came loose at times and required readjustment, and ultimately had a few large holes torn in it – heavy duty it was certainly not. It was easy to see when the tarp was loose: the intrigued and possibly disgusted stares of passing motorists (and when you’re me, carrying four people and hundreds of pounds of pit equipment, everyone passes you) was the clue that we needed to check the tie-downs.

I’m also fairly sure that if we DID travel with it in the open, we would have caused at least one accident.

But wait! There’s MORE!

In the roughly 1.2 weeks before leaving, the MITERS folks who helped me test became inspired enough to cobble together their own independent entry using literally whatever was standing around in MITERS and upstairs in my shop at the time. I’m sure you’ll hear more of this from the likes of Benkatz and Dane.

Here’s the load-out shot from above as I was scanning the shop for things which I forgot to bring, showing the tarp bubble. The choice of route was straight west on I-90, and then a right turn. I wanted to go through Canada, but figured the 1.5 hours saved was not worth the potentially more than 1.5 hours being hassled by border crossings. Plus, not everyone who came had passports. Sadness – maybe a future vans-on-vans trip into Canada is warranted if they ever hold a race at the future Toronto Maker Faire or whatever. Google Maps said the trip would take 12 and a half hours, but for me it was more like 14 each way.

The Detroit track was made in the parking lot of the Henry Ford Museum using tire barriers. It’s easily the largest PRS track I’ve seen (and I think the series has set up) – it’s easily twice as large as the New York Maker Faire one. For the most part, it was smooth with the exception of three very large bumps that ran perpendicular to the track. I think these bumps were ultimately the cause of the failures I experienced during the Endurance race due to the wiring not being secured well.

One half of pit row. Pit space was tight, and we had to intermingle tools and parts with surrounding teams. This was a shot from the morning, before everyone’s pit became earthquake disaster zones.

We’re contemplating something here… Probably our newly acquired safety bracelets.

An hour or two of open practice was available, so I took the time to get a feel for the track and try out the racing line.

The reason PRS appeals to me as much as it does is how varied the level of technology in the entrants is. It reminds me very much of my other favorite sport of fighting robots – you have personal garage builds, schools, and basically professional shop spaces playing at the same level, and the professionals don’t always win. The rules are purposefully open-ended instead of heavily codified like most motorsports. It’s purposefully and unironically derpy. As I’m sure I’ve made abundantly clear, I’m a huge fanatic about learning via building derpy shit taking initiative and having fun.

Here I am running a qualifier lap. I got the 2nd and 1st best times for qualification, but the 1st place one was negated due to me not stopping in time (it has an integrated brake test). It was no fault of the brakes – my first run, I braked so hard the front discs locked up and one of the Harbor Freight tires got a huge divot eaten into it. So I took it easy – a bit too easy the second time around.

The video of that run is here:

After the qualifying round was a short break before the “Moxie round”, which is a freestyle showoff kind of affair. A few teams acted out skits, one made a simple presentation, and there were some drifting and speedruns. Then there was me:

When I go, I go hard.

In the picture of the qualifying run, notice the small antennae-like structures glued onto the helmet. They’re mounting points (such technical words) for the Miku pigtails seen above. I cut them to 2ft instead of the stock 4 feet to avoid becoming a hazard to everything.

However, all things considered, this was probably the wrong audience for such a display and most people were seemingly more confused than amused – coupled with the fact that I went last (with helping Hack Pittsburgh with their Back to the Future skit, and MITERS with their small goofy vehicle parade), means I didn’t score many moxie points.

During the intermission period, there were, of course, shenanigans. Along for the ride were eNanoHerpyBike (which later gave up a throttle to Chibi-Mikuvan), this contraption the One-Day Kart, and Bentrike.

Here’s MITERS relaxing, right before the heat races began in the afternoon. The field was split into odd and even qualifier positions, so the MITERS entry was in the first race starting near the middle of the field.

Some kind of strategy discussion or trash talking before the 2nd heat race that I was in pole position for. That, or we’re just talking about who to spin out and who to run into the tire walls.

The 30-lap sprint confirmed to me a weakness of Chibi-Mikuvan that I had predicted – that anyone with a DC motor is going to get the jump on me. The Trackstar takes a sweet second to ramp through its starting routine, during which Hack Pittsburgh (in a superbly built custom-bodied DeLorean with Back to the Future theme and everything) was able to get around me. We’re also fairly matched for speed, so it was difficult for me to catch back up unless there was traffic ahead. In the end, it dropped from the race due to a loose wire – letting me take first place. The same fate was to befall Chibi-Mikuvan in the endurace race.

The ‘press shot’ for the weekend, during the 30-lap heat.

Here’s one video of the race, shot from the finish line truss.

A fancy new hubcap!

I discovered during this race that heavy is not necessarily a bad thing. In fact, it keeps you on the ground a whole lot better. I had to slow down more for the turns than some teams to avoid rolling over – I got on two wheels two or three times. This prevented me from effectively using the turns to pass. I may have to reconsider that full-size battery pack for Chibi-Mikuvan in the future.

Both MIT vehicles in one shot during the endurance race.

The endurance race for the first 15 minutes or so was a faceoff between Chibi-Mikuvan and NIMBY‘s Ferrari. There was “some” contact made. Nearing the end, the battery began running down and I started seriously feeling the power dip, so I pulled into the pits, allow them to regain the first position for laps. I neglected to remember that the Hyperion 1420i charger has a charge capacity limit of 9.9Ah – it always stops at 9.9Ah, and I have to manually restart it. I left the battery charging on Saturday, but forgot to restart the charge on Sunday, and so with the sprint race taking out (most likely, due to our science’d data collection) more than 10Ah, it wasn’t running on a full charge.

The starting lineup for the endurance race.

 

 Chibi-Mikuvan caught in a bit of a traffic jam next to NIMBY. We traded spots a few times.

Around 20 minutes into the race, after the battery change, was when things start going wrong. At first it manifested itself as an intermittency in the throttle – it would work after one bump, but not after the next. It quickly progressed into Chibi-Mikuvan having to be carried off the track and into the pits. I did some short voltmeter investigation and discovered that the 5V throttle wire broke off at the terminal strip.

After re-stripping and pouring hot glue into the area to restrain the rest of the cables better, the next thing that happened was the throttle straight up dying on the second driver 0.9 volts all the time, no response. I harvested the throttle quickly from eNanoHerpyBike and Chibi-Mikuvan got in the running for a couple more laps, but very quickly had to return to the pits because I smelled something funny.

Thinking it was the Trackstar ESC, I shouted for a replacement ESC to be made ready, but it wasn’t that simple – the Trackstar was working great right until the end. I’m not sure what exactly happened but the Arduino Carrier board’s thick ground trace was blown apart, and 14 volts was present on all the 5V rails. The Arduino itself was nonresponsive, probably due to said 14 volts.

In a moment of either desperation or insanity, Dane chopped apart a Harbor Freight 4.5v flashlight, I rigged its battery into a servo tester knob, and then I cruised very slowly like that for a few more laps before something just completely gave out. And that was it for the Endurance race!

The picture above is of the servo tester and flashlight hack. It was taped to the seat back, so I had to drive with 1 hand behind me to gently twiddle the knob. I got used to this style and actually began to try and run the race again until the final, as of yet known failure occurred.

Chibi-Atomic-Jeep (among other names), the MITERS one-week entry, actually did finish the endurance race, but not before busting off a few Harbor Freight tires. I’ll let the others tell that story.

Chibi-Mikuvan didn’t escape the tangles with NIMBY unscathed. I clearly also scrubbed someone’s tire, and that knocked off the catface, which was never recovered. Otherwise, the front body mounts were broken off in a run-in with the tire wall, and I drilled through the body (cringe) and used large zip ties to secure it for the rest of the time. The rear body mounts were redone shortly after completion using E6000 rubber construction adhesive and never had problems again, whereas the fronts stayed epoxied on. The epoxy seems like it was just too inflexible for the task.

Obviously body repair will need to happen, but all things considered it’s in great shape. I had expected far worse. This is all stuff that can be taken care of with some Bondo. I probably won’t be able to get it back running again before Dragon*Con (there is not a race there anyway, just a short exhibition), but I and MITERS alike are making serious plans for Maker Faire New York…

conclusion and next steps

So now that the race is over, how well do I think Chibi-Mikuvan performed overall? Time for helpful infographics in my usual style. As I have said since the start, Chibi-Mikuvan is intended to push several technological and resource boundaries at once, in the interest of anyone else wanting to get into the sport of silly rideable things. Some of it went great, others not so much.

The biggest risk was probably pressing into real heavy duty racing service a R/C car controller, the Trackstar 200A. Granted, it’s for “1/5th scale” R/C cars, which I swear Chibikart is already a 1/5 scale… Ariel Atom with growth stunting problems or something. Chibi-Mikuvan is a 1/3.14 scale R/C car… that’s close enough, right? Checking out the internal construction of this thing along with watching the current draw with the digital dashboard, I’m satisfied that this controller can output its continuous rating at full throttle. In the context of PRS, you’d probably never run 200A at full throttle unless something really interesting is happening.

During testing, I did manage to kill two – one by letting the signal board shake loose (so attach it firmly!) and the other by regenerating into a disconnected battery – instant voltage-induced death. However, it did not miss a beat during the competition, in 90F+ weather, in conjunction with the current limiting algorithm. Too bad everything else did!

One of the things which continually gets me “interesting” reactions from curious builders and onlookers is the gear ratio I’m running on Chibi-Mikuvan – a healthy 20.5:1, compared with the 5:1 to 10:1 of average small vehicles. In part, that was to take advantage of this fist-sized motor in a ground vehicle application. I’ve had 1 person so far ask me if the blue thing was a supercapacitor, thinking the motor itself was under my electronics deck somewhere. Because power is composed of both speed and torque, you get “free power” to a degree by running a faster motor. That’s why R/C outrunners are able to advertise such ridiculous power ratings – in their designed application (aircraft), the motors run very close to their no-load speed so they can indeed be very “powerful”. Chibi-Mikuvan proved that you can indeed run a very small, high speed motor in conjunction with sensorless control if you gear it highly enough.

Sensorless, though, isn’t without its trappings as I mentioned previously in the face-off with Hack Pittsburgh. The sensorless starting routine can still bite you and let someone else get a jump on you.

To use this motor above 1500W or so for an extended time, a water cooling circuit is necessary.

The way I was able to design a 20.5:1 reduction in the rear left corner of the vehicle was by passing the Aquastar motor through angle grinder gearbox. The 9″ generic Chinese angle grinders seem to come with 4.1:1 right-angle spiral bevel gear drives. Now, I can’t vouch for the gear quality, but they seem to be holding up great in this application.

There’s several types – one of which Harbor Freight uses and has a smooth input shaft, and another style which has a Woodruff-keyed input shaft. I modified the Harbor Freight input shaft and the bore of the pinion into a machine taper to get better torque transmission properties, and it worked for the most part, but I had troubles with the pinion gear getting pulled off its taper by the action of the spiral bevel gears: on negative torque (regenerative braking, for instance), the thrust force tends to pull the pinion off the taper.

I ordered two “Truepower” branded ones from Amazon, and they come with Woodruff keyed input shafts. I upgraded the key one size to a 1/8″ thick, 0.5″-circle Woodruff key, and that’s the one that was used during the race with absolutely zero problems. The gearcases were packed full of grease to minimize wear – I wanted to do an oil fill with some differential gear oil, but the gearbox has no gaskets and it would have gone everywhere. I’d recommend the woodruff key version just because it is conceptually easier to interface to. You could cut off the angle grinder motor’s shaft and use the leftover 12mm stub shaft with a coupler, or machine a custom one like I did.

The Ford Fusion batteries came through with absolutely no problems! Dumping 100+ amps is probably not good for the life of the battery, but if Ford’s actually advertising 20-30kW hybrid systems in those things, they then have to be able to push that much current. I gave an in-depth dissection of a 2009-2011 (generation 1) Ford Fusion hybrid battery in its own post (BE CAREFUL! is the theme here), as well as how I packaged them for use.  You can get 28.8v and 16Ah in about 22 pounds the way I assembled them.

A recent (a few minutes ago…) scan of New England yard listings shows most of these batteries starting around $500, which at the rate I used them, is still borderline economical given how many independent packs you can get out of one.

What can I say – the Mac G5 pump and radiator (and my reservoir made of an olive jar that I ate on the spot to get) worked great! The only issue was that the Aquastar motor wasn’t well sealed for most definitions – it leaked consistenly, and by the end of the 30 lap sprint race, the cooling system had leaked dry. A coat of silicone will probably solve that problem, so that’s on deck for New York. The system was silent and effective.

My favorite part, the Hysterical Current Limiter, worked to great effect during both the race and testing. It’s best explained in its own two posts. During the race, I did blow one fuse, possibly the result of running too hard when the weather was hot (the temperatures were nearing 90 degrees Fahrenheit in Detroit that day) – quite metaphorically flying too close to the sun. But I and anyone else could slam the throttle to full without, you know, dying or something. Without the HCL, it takes a trained throttle finger to drive Chibi-Mikuvan, which is why I basically didn’t let anyone else drive it until this was completed. Functioning code for the HCL is provided on those posts/pages.

Ah, the Harbor Freight pink tire. Full disclosure: We cleaned out the nearest three Harbor Freights to MIT of these things, as well as the closest Harbor Freight to the Detroit Maker Faire. I still think they’re a good choice for low powered vehicles. They are grippy, but the rubber is sadly too thin to last long. They’re well cost-optimized for the 0.5mph handtruck or pushcart. The tread is at most 4mm thick, with the tire carcass (plies) barely below that.

The stock hub also has well known durability issues – they crack apart at the weld under sideways pressure (from turning). I made my own hubs and designed these to be swappable, so that was not the issue. In fact, they turned out better than expected on the DMF parking lot – for some reason, their asphalt is less abrasive than ours.

Sadly, I don’t think I’m returning to these – something that I made up my mind about before the race after seeing the results of the “science”. They work, but they simply don’t last long enough. I’d like to get through a race without having to change tires, and that involves moving up to something designed for mobile vehicles. Popular at the PRS race in Detroit were riding lawn mower tires and real honest-to-Go-Kart-Jesus scooter tires, both designed to move under power.

The thing that bit me in the end was my ad-hoc wiring job. Breadboards, multiple cables running into each other, and poorly strain relieved terminal strips don’t make for a high-durability, robust mobile electrical system. The parking lot ruts finished off what the science testing surely started – fatigued wires and unknown shorts and lost connections. With this system dead, I have no choice but to refactor and rebuild it from the ground up. I’m envisioning a single PCB with all the features I need on it – or at the least, prototyping board with actual solder joints!

So what’s in store for the future? Well, nothing for the time being, since Dragon*Con and other projects (not to mention, umm, my shopmaster job) are higher priority. Strictly speaking, the vehicle can run again in its current state with just an electrical system rebuild. Cosmetically it’s beat up, but nothing some Bondo and paint will fix (as well as rebonding the front body mounts properly). Perhaps the highest priority would be repairing that electrical system.  I have a few ideas for drivetrain upgrades, but they’re a long ways off – maybe for next PRS season.

This concludes the Chibi-Mikuvan action for a while. Look out soon for details on how the summer EV Design class has been going, as well as updates on the robots for Dragon*Con!

For reference convenience, I’ve copied over the “cheat sheet” from the introductory post I wrote when I got it running back in May.

Cheat Sheet

Motivation

I started this project as a museful distraction in October of last year after returning from the New York Maker Faire and mingling with the Power Racing Series folks for the third year. Having seen the league grow immensely, I decided to finally enter something while exploring new and unusual components for hobby builders (my usual MO) while also wanting to see a change away from the “model year bloat” I saw in many teams, who started using heavy forklift motors and other salvaged industrial components. Hence, the focus on R/C electronics and non-lead chemistry batteries.

Work on the project began more in earnest with this season of “2.00gokart“, since I figured I needed to have an instructor vehicle to troll my own students with.

The project was my first jump into making a composite bodied anything, motivated in part by the bodywork repair I’ve had to perform to real-Mikuvan.

Build History

In chronological order up to the previous post, here’s the process of Chibi-Mikuvan creation from conception to implementation:

Naming

The project is named Chibi-Mikuvan after its principal design predecessor, the Chibikart twins which were the “prototypes” for the design class I teach today, and my 1989 Mitsubishi Delica known familiarly as Mikuvan.

It has little to do with Chibi-Miku-san though a few large decorative decals would not look out of place on the shell. I’m an avid follower of the crowdsourced synthetic Japanese future girl-pop that you’ve never heard of world of Hatsune Miku and Vocaloid. That’s literally the most concise way to fully describe it, as I have learned over many difficult discussions about what the inglorious shit is it that’s playing all the time in my shop.

Components

Specification

  • Top Speed: 25mph (as-geared, Y-termination)
  • Acceleration: to 25mph in < 3 seconds
  • Braking distance: < 30ft from top speed
  • Skidpad: Uhhh, gimme a sec.
  • Clearance: Still not enough for the Maker Faire cable protectors
  • Drivetrain: RR layout, 1 speed, spool axle (no differential)
  • Dimensions: 50″ L, 28″ W, 24″ H
  • Weight: 113lb with battery
  • Seats: 1, though if Chibikart was any indication to go by, up to 7.

Bill of Materials

Here’s the latest iteration of the BOM (5/1/2014 version), which contains at least 95% of everything on the thing, short of the trivial like zip ties. I went into much more detail than the average PRS list; the quality is a little more closer to what I expect out of my students when it comes to found parts and used parts. Everything, to the degree possible, is given a Fair Market Value which sort of artificially inflates the cost a little. While technically over the PRS $500 statutory budget, I believe this is a more realistic representation of the cost needed to replicate this once.

The BOM has 3 cost categories. First is the actual money I spent. I had a fair amount of parts already on hand, but did have to buy things full-price like the Ford Fusion battery pack and the motor & controller. Next is the PRS rules based accounting, exempting some things like brake parts. Finally, what this vehicle would cost under my 2.007 EV Design class rules, where some raw materials are provided to the students so they only need to count materials if they need to be purchased additionally.