Archive for October, 2013


On 2.00Gokart; Or, Designing a Design Class to Disrupt Design Classes as We Know It; Or, How to Make MIT Undergraduates Build Silly Go-Karts so You Don’t Have To

Oct 23, 2013 in Electric Vehicle Design, MIT, Bostoncaster, Cambridgeshire

I think I’ve promised a 2.00gokart “total recap post” after every session of it so far. This is a piece that is long overdue on this site, and in all honesty, probably also way past its time to present in a more formal venue. Edit: It’s now on Make Blog! Thanks Make! For the past now 2 years and four sessions, what I consider to be my most long and extensive project has been developing quietly in the halls here at MIT – that is, as quiet as the high-pitched whine of square-wave commutated brushless airplane motors can get you, anyway, interrupted periodically by the interdiction of concrete-backed drywall upon metal; facilities and my space directors will never let me live that down.

I’m two months late and running from when I first said to expect a wrapup of the summer SUTD special session I ran for their visiting students.  What this post will be is a ton of writing. Interspersed with as many photos and references as I can manage, of course, in my usual style of discourse, but most of it will be me waxing poetic – and perhaps polemic at times – regarding my own motivations to start this course, experiences in running it, and ultimately what my end goals are and where I want to see this class end up.

I anticipate this post being extremely long. In fact, so long that I’m going to split it into multiple sections ahead of time. What will be presented from here on is basically a much more concise, casual, and perhaps more profane and offensive version of my original Master’s Thesis, minus most of the the graphs and tables (because every Master’s Thesis in engineering needs graphs and tables, for whatever reason), and with more pictures and videos. The first two parts essentially amounts to me ranting, and the second half is the productive info, followed by more despotic proselytizing.

Here’s the table of contents: First, a summary of my motivation for making the class. Next,

  1. A brief rundown of my own history with engineering projects and how that both aided and hindered my academic performance at MIT
  2. How I took an interest in teaching and why I saw issues with the current system of design classes
  3. A history of my involvement and leadership in the electric vehicle design realm
  4. Recap of the 2012 class “2.00scooter”
  5. The changes made for the 2013 class “2.00gokart”
  6. The 2013 summer special session and the changes made for it
  7. Where the class stands now; content, procedural, and logistics.
  8. What I think the class brings to the world of design classes that is different or novel.
  9. More about the resource base of the class and the cost of running
  10. An SAE Asston (like an ISO/DIN Arsetonne) of lecture notes, resources, and links I have built up so you can run your own silly go-kart class


Loose Ends and Tag Closing for Bits of October: Site Updates, Chibikart and Mini-Jasontrollers, New Expensive Things!

Oct 15, 2013 in D.P.R. Chibikart, Shop Ninja

Now that the season of Dragon*Cons and Maker Faires and everything else has finally settled down, I’ve reached the curious state of having nothing to do with my life, being between large builds in much the same way you’d be between coffees or meth hits. My day to day activities revolve around managing the IDC (excuse the cheesiness) fabrication facilities, of which there will be some updates shortly, and monitoring & mentoring the classes running in the center, including the renowned How to Make a mess out of Almost Anything. I’m not a TA for the class per se, but part of the process of making sure the shop isn’t lit on fire is some times giving extra attention to those who would be most likely to do it.

That isn’t to say that my life is entirely empty and devoid of meaning. I’m tending towards taking the downtime to fix up my eternally problematic go-kart children, starting with Chibikart2. During some hard running at the Powerwheels race, I lost one of the Jasontrollers to Sudden Jasontroller Death Syndrome, a fairly common failure mode for them when they are over-run. The failure is always gate drive destruction since the circuitry is so fragile, and always not worth repairing to myself because it involves replacing so many small shitty transistors. Next up on my list after this is probably to add the electronic solenoid shifting to burnoutChibi and finally get rid of my super-rigged cable linkage. I’ve also been collecting many prospective parts for the “Chibi-Mikuvan” project, so stay tuned for a massive Beyond Unboxing the likes of which have never been seen!

But first, by popular request, I’ve added Pad Thai Doodle Ninja and Colsonbot CAD files to the References page. PTDN’s files are only made of 3D printable frame parts, but Colsonbot is the full bot – you’ll need Autodesk Inventor or a compatible viewer for anything but the STL files. All of the details on these bots are available in their respective build threads.

Onto Chibikart’s controller update. Like the dual controller mount I made for BurnoutChibi, I designed up a two-mini-Jasontroller snap-fit mount which also holds an 80mm fan. Essentially the same idea of BurnoutChibi’s. I was planning to current-hack these controllers to 40A, and for sure they will need supplementary air cooling.


The mount was printed on my Up machine, and this is about the largest object I’ve found it can handle reliably. It came out well, with minimal warping. I sincerely recommend the Up (now on 2 Plus!) to anyone thinking of getting a small hobby-class 3D printer.

Short of popping it in the Dimension, the Up is my go-to for structural parts. The ABS formulation they use is a higher hardness/toughness than the soupy generic stuff you feed to RepRaps and Makerbots. I was concerned about the snap fits being too aggressive and snapping off themselves, but they turned out to be just on the side of the acceptable line.

The mini-Jasons were cleaned up of unnecessary wires, leaving only the motor phases, power, the Hall sensors, throttle, and the ‘regen brake switch’ which may or may not be wired in in the future. The regenerative braking on these things is a fixed low current on-off kind of affair, so it’s not very helpful.

I plucked the 80mm case fan from stock – there’s nothing particularly special about it.

In the past, I’ve current-hacked these things with a blob of solder on the current sense shunt, but it’s such a bad hack and is unreliable – I’ve actually had the blob melt back off before. To remedy this, I began looking for large current shunt resistors packages that fit in between the leads of the existing shunt. This is the result – for a mini-Jason, a “2818″ (.28″ long, or so) package current sense resistor is a nice fit. One that is 8mm (“31xx” – “35xx”) will fit even better and not require much solder bridging would fit better, but I could not find any that were not also square in shape – rectangular, the long way, is preferred.

I actually had this hack vicariously tested by Daniel (YAMEB) a while back. These shunts are 5 milliohms (not 10 – I measured erroneously the first time), so it took a nice sandwich of 10 milliohm resistors to get my 40 amps. The exact part number I used was WSHA-.01CT-ND, and it has a 5 milliohm brother in the form of WSHA-.005CT-ND.

I cleaned up the floorpan of Chibikart after removing the old Jasontroller – it was positively disgusting and filled with 2 years of floor grunge buildup, plus mud and dirt from running at two slightly wet Maker Faires. The new installation drops right into where the old controllers used to sit, after redrilling some mounting holes.

Systems wired back up. The first test drive was without the fan hookup, and without the sensors connected.

To rehash, these controllers “self-calibrate” sensors if you connect them and then run once to full speed. I couldn’t achieve this on the ground since the vehicle never really reaches “full speed” in the space available, so I had to freewheel it, being mindful of the 4700rpm-ish commutation limit. After one power cycle, the controllers had learned the sensor configuration and Chibikart could apply “static pressure” to something again. To get a good transition between sensored and sensorless, the sensors have to be aligned properly first (check out Equals Zero Designs’ page where I have an actually well documented example.) – and that’s all you need to do, not actually try and optimize their timing position.

This was, of course, the important part.

Now, the 12v PC fan could not handle 24 volts, so I just dropped a giant 40 ohm resistor in line so the fan only saw about 15v. This resistor surely dissipates more power than the fan actually removes…

With two motors on 40 amps, instead of on ~25 before, Chibikart2 is way more fun. Not, say, tinykart Black Edition level fun, but it is far more peppy. The small Colson wheels are starting to reach their traction limit.

I hit 1.1kW on indoors testing, and there is much room for improvement yet. Because the controllers are doubtlessly still running constant current before I run out of hallway, the power will only increase with vehicle speed.

Say, I haven’t garaged something properly in a long time (mostly because said garage was under repair construction this past summer). Maybe it’s time to take Chibikart back to its proving grounds.

Next, some of the ongoing facilities improvement projects that I have going on in the space! The place is kind of like I-95 around New England – always looking like someone’s working on it and the construction shifts every once in a while. I swear, though, it’ll be over soon – just like they say in Connecticut (In my six years in this area, I have never once driven through 95 in CT without hitting some kind of construction…)

First up, a full size Shopbot – the full 5 x 10, gifted by the Architecture department. I’ve been itching to have one of these for a while – with an 1/8″ carbide bit, they’re practically mechanical waterjets! Expect some Shopbottables to emerge on my end soon due to the “It’s the closest tool next to me and I don’t have to ask anyone to use it” effect. It will be very handy for producing Chibi-Mikuvan’s body panels since they’re all larger than what can be stuffed into the laser cutter.

Above, Media Lab students operate the machine as part of the MAS.863 “Build something big” week.

Next up, the legendary Form 1. Full disclosure: There’s four Form 1en in the space at the moment – this one is “The Lab’s”, and the rest belong to researchers and classes residing in it. Four. That’s more forms than Formlabs (okay, probably not), but the Form 1 density must be up there.

The Form is a SLA-like machine which can hit much higher resolutions, but the  material isn’t too strong – it’s an acrylic resin, so it has some mechanical strength, but does shatter and snap. Dat rez tho…

These are some of Brian Chan‘s insects. Check him out on Shapeways! I also printed the crab, lobster, and some other doodads from his collection.

Of course, with every 3D printer that makes it in here…

The  model is “Pillared Miku” though I used the version without built-in pillars – the Form software generates its own support lattice.

Now, moving up in the Expensivity scale is our latest acquisition:


An Objet24 (By Stratasys™)! This is just contributing to the slow rounding out of 3D printer technologies in the space. Objets are incredibly high resolution, very nice, and very expensive. This unit was purchased used from a local company for only $7,000, but you’d easily eat up that much per year in materials alone. The Objet Goo comes in 700 gram jugs that each cost $300-350 and up.

And this is the entry level machine.

The Objet technology combines SLA (light cured resin) with inkjet style nozzles so it can control the deposition very finely. No giant bubbling cauldron of goo here. It also has its own Windows XP computer built into it.

Now, I know XP is pretty much the OS that saw the Internet grow up with it, but this machine was built in 2011….

…and even worse, it requires a very specific network setup to talk to. Objet-Stratasys (ObSys? Stratajet?), I’m going to publicly shit on how bad the Objet communication infrastructure and software are. I should not have to configure a point-to-point LAN, disable Windows Updates, and disable firewalls just for it. The whole setup procedure gives me the vibe that they had to ship the machine and had 1 day left to write the drivers, so took whatever the developer’s computer was at the time and just made that the exact requirement. That, or given Objet is an Israeli company, probably just opens your computer up to direct monitoring by the Mossad.

I’m amazed I didn’t have to start Space Pinball and log into Pandora before the printer would communicate.

The slicing software is also slow, prone to crashing, and has an inconsistent UI. For such a beautiful piece of hardware, the software end of it seems so incredibly rigged.

Of course, the first thing to do with every 3D printer that makes it in here…..

Yeah. This was like a $30 Miku given how much of the material I used.

This corner of the room has been reconfigured to become what we now affectionately call “printrgartn”. The Form 1 is immediately off to the right, as is the Replicator 1. I’m trying to commission an Up for the lab (in supplement to my personal machine).

What’s absent, sadly, is a powder printer. I need to do some Powder Print Affirmative Action here.

Maker Faire NYC 2013: The Summary; or, How I’m Declaring Shenanigans on the Power Racing Series

Oct 06, 2013 in Events

It (was) that time of year again! Maker Faire has sort of become the Yearly MITERS Showcase – ever since 2011, we’ve traveled to the New York one as a group with varying amounts (and ratios) of electric vehicles and tesla coils. Last year, I brought just Chibikarts in order to take it easy, and this year I brought… Chibikarts. Again.

These days, I act more in a Team Mom or A Father To His Men for MITERS, less so blitzing a build right before a major event (I pass that off to the current member set). So as more of my stuff tends to keep working, I’ll just return with it and spend more of the Faire wandering around the Faire – one thing that Maker Faire tends to do to you as an exhibitor is make you miss out on what else is happening since you’re so often at your booth just talking to people.  Well, why stay at the table and talk when you can just drive around and talk? I’m not sure why I didn’t hit upon this earlier; or perhaps I did and have just dismissed it until recently when I’ve transitioned to a more mentor-like role for student projects, but I spent at least a few hours this time just slowly ambling around on a Chibikart, scooter, or someone else’s contraption.

Here’s what all went on at the Faire, and after all that, some of my thoughts on future projects. As usual, we begin at ass o’clock Saturday morning with van stuffing. Now, in years past, MITERS has rented cars to ship down to New York, but now we have a new weapon:

I joked that I could literally bolt Chibikarts to my 80/20 roof rack. Well, there you go.

Okay, so it’s not bolted, but everything is all nice and strapped. In the end I decided to only bring Chibikart 2 (DPRC), as BurnoutChibi turned out to have some serious unrepaired brake problems from the summer. To its right is Viictor-kart (since you never properly named it, dude). Realistically I could have put both of these inside, and did so on the return trip, but I was expecting more stuff than ended up being loaded after we had already rigged these two.

Plus, the ‘hack factor’ of trolling everyone who drives behind me for 250 miles was too much to resist.

Weeks of careful Googledocs-based planning resulted in me just showing up with Mikuvan and stuff being heaped into it. This is the scooter and support equipment pile. Underneath the folded seat are ten Onetesla kit boxes, which were all sold out by the end of the event (yay!). I was intending to take 4 people and some stuff, but this was reduced to 3 people because the scooters and other boxes were too long. Fortunately, there were more cars available.

I couldn’t resist this photo op when stopped for a last refuel in Milford, CT. There’s a Tesla Supercharger station next to the rest stop, and..

…hey, I can pretend, right? :(

Wouldn’t it be neat if I could jack into the Supercharger network and freeload off Tesla?

Just to give an idea of how absurd the EV situation has gotten at MITERS, this is the ‘all unloaded’ shot just after setup. Melonscooter2 is on the right – I ended up bringing it because after the Great Mt. Washington Small-Wheeled Scooter Debacle, I wanted something that could tear some ass on the half-grassy Maker Faire venue. The giant balloon wheels (but not as giant as Ben-scooter on the very left, of course) made this easy, but once again I had made a vehicle that was too low to get over the electrical cable raceways…

Anything for dat stance.

Also seen in this picture is Victor-kart, productions from Roberto, Peter, and Candace, and the back half of Dane-ger-scooter. This is my public call-out that none of you update your websites.

Not seen but present in the back somewhere is Johnscooter, bentrike, and the magical Orbit Wheels.

By most metrics, MITERS was immensely popular as a display. The table often accrued crowds large enough to obstruct pedestrian traffic (…and other forms of traffic) behind it since people would back against a display tent across the aisle. Most people stopped in for just a minute to gawk and maybe ask one or two questions, it seems, but we got plenty of “people from the Internet” and even a MITERS alum from the 70s!

And infinite little kids. If I had an actual complaint about Maker Faire, it’s the marauding gangs of unsupervised (or barely-supervised) small children that immediately begin climbing all over your display. Some parents seem genuinely upset if you reject their children’s advances, like everything is there for their test rides. I know it’s one thing to hook them early, but I think Maker Faire promotes itself as a circus attraction a little too hard, and no-touching-without-asking is not very well communicated.

Learning from last year’s Fort MITERS, the MITERS Burrito was set up before everyone left Saturday since rain was forecasted for Saturday night. Ultimately the rain turned the ground there to mud, and it was windy enough to drive some rain under it, but nothing was substantially wet.

I mostly left MITERS to explain itself and wandered the Faire, though not too hard. In my view, the NY Maker Faire has slowly been heading towards a ‘trade show’ kind of atmosphere (along with a family circus). This year, it seems, there were many more startup companies and established companies with booths. The startup companies tended to be pitching and demoing products, and the larger companies had hardware there and spent much time proselytizing on how they help ‘The Maker Movement”. Hell, even Delta, the faucet company was there with a booth, with some neat LED faucets. There were less wacky bikes and sculptures slowly roaming the grounds, and overall, the number of individual booths and hackerspace booths seemed less.

Part of me likes to think this is just everyone being burnt out from the many previous Maker Faires of the year, including the mini local ones, but I also wonder if some people are trying a little too hard to commercialize ‘The Maker Movement”. I’m not outright saying it’s a negative thing, since I like it when individual building and learning is encouraged over The System, but part of the charm of the Faire is seeing what’s going on with other peoples’ projects. Maybe the mini-maker-faires are taking over this role since they tend to be smaller and more intimate, and the Big Shows bring all to the table in the end.

Anyways, it just wouldn’t be a Maker Faire without 3D printers! Here, have some:

The 3D printers this year were basically evenly distributed through the back wall of the faire next to the railroad overpass. I found them to have more variety and creativity than last year, which was full of RepRap and Makerbot clones and knockoffs. I actually think there were even more 3D printers, but this time, I saw a lot of interesting geometry and implementations.

My personal favorite in the 3D printer camp was this table of “leadscrewless Repraps” which explored alternative topologies to avoid needing linear bearings and leadscrews. This meshes with the Reprap ethos very well, since if you can avoid those manufactured metal parts while maintaining accuracy and repeatability, you can create a 3D printer that is more 3D printed.

Check out these “geared deltabots”! This was a very clever implementation of the deltabot I had not seen before called the Simpson. The arms are actuated by stepper motors driving cable capstans, keeping it low cost and backlash-free.

The “Wally” is a “tri-polar” design where all 3 axes are technically polar in nature (pivots about a point). The kinematics for this thing must be wild.

XY movement is effected by the motors moving the pulleys directly, to which the smaller cross arms are attached. The links that emanate from the backboard are just idlers, as far as I can tell, otherwise the design would have no mechanical advantage in the configuration shown (when the 2 middle links are locked in a straight line).

Next up, and moving more towards the red end of the color spectrum, the Morgan is a SCARA type design (it’s kind of a double-SCARA). It does use a leadscrew, but I’m sure this can be remedied later on. I believe this to  be the most straightforward implementation – if I were to build a screwless RepRap, I’d have settled (after many failed attempts, probably) on a SCARA type XY.

Enough gushing on my end – just watch some videos of these things! The organicness of the movement, especially of the geared delta, is quite pleasant to watch. I think the geared deltabot looks like some kind of weird sea anemone.

It’s also fun for me to see people using common hardware in interesting ways. This is a ‘parallel Cartesian’ (’round these parts we call them Moyer Linkages)  gantry made with drawer slides.

I’ve grown a recent interest in pursuing the white unicorn of additive manufacturing that is low-cost structural metal printing.. Yes, DMLS and robot-arm-laser-spray-gun-printing (I think “DMD” is too boring to describe this) are things in use, but I can’t afford one. Then, to me, it makes shit difference whether or not that technology exists.

These guys are showing off a ‘liquid metal jet’ printer design, and they allege that they will be printing in aluminum. The metal is heated to liquid state and blasted out by a small (presumably very high temp) inkjet style nozzle, in an enclosed inert atmosphere. Or so they say – unfortunately, this machine was just a shell – there was no hardware inside the granite head.

But everyone there was wearing matching team shirts and handing out business cards, so this must be a legit operation, right? It kinds of collides with my philosophy of if it’s not working, don’t bother showing yourself too hard off yet.

While I am sure their LMJP process will bear fruit (it makes sense in my head), I’m personally more inclined to pursue another approach:

My favorite 3d printing flavor for a while has been DMLS, in which you sinter powder with a giant laser. I finally got to experience some parts from THE NEXT BIG 3D CLOUD MANUFACTURING COMPANY (like all the others) Kraftwurx, which runs, as far as I could extract from the sales bros, an EOS DMLS machine (like this, maybe not that exact model). I was in fact getting quotes from them a while back when I thought the IDC would actually have money, but its 700+K price tag was a little too much to justify dicking around as an application.

I have a few ideas for approaches along this front, but the expensive part ultimately is the part that makes it work: the giant laser. You don’t laser for like $100. Or even $1000, and barely at $10,000 – the usual carbon dioxide lasers used in most laser cutters will just bounce right off metal, so it needs to be a Nd:YAG laser or a fiber laser or similar.

Where I hung out the most, though, was with the Powerwheels crew. Yes, you can present me with the most advanced additive cloud-based superalloy manufacturing system in the world, and I’ll still go chill with the derpy go-kart racing club.

I’ve watched this series grow from a few privateers doing it at their area hackerspaces, to a huge phenomenon that basically happens at all the big Faires and even some of the mini ones. Last year, we had the dubious privilege of racing with them. I kept saying to myself then that I’d build an actual to-spec entry, but that kept getting punted off until Oh Shit It’s Thursday Before Maker Faire. Because I brought Chibikart anyway, I let quite a few other people take it for a spin, as well as jumped in on a qualifying race (where I came in either 4th or 7th – not sure…)

Like last time, it was hard for MITERS to resist the lure of the open track. With new vehicles all around, no less! I got to pilot Ben’s monster-scooter around the track, and I’ll say that it’s no less precarious than riding a Segway, mounted on the very top of a step ladder, on a waterbed.

Here’s a familiar …face? Frame? This is Jeremy‘s Chi(p)ikart, one of the first Wild Chibi species, made super cost-reduced but with more money where it matters: the motor and controllers. I thought Chibikart2′s tire life might have been a bit lacking, but I think Jeremy goes through a set of Colsons per event. Chipikart has the next size motor up (the “63mm” SK3s) and Kelly controllers, so it can actually haul ass.

The entries this year were bigger, faster, and more powerful than ever. And this is where I started wondering what the hell was going on. The motors I saw were way bigger than last year! I asked the usual “noob questions” like what motors and controller setups people used, and it seems that within the past while, scrapping forklifts and floor scrubbers have become a thing. So nominally everything is “free” or almost free, since used & destroyed machinery of that sort tends to be of very close to scrap metal value.  The motor above is typical of an industrial floor scrubbing machine – it’s about 9″ in diameter and about as long.

The series indicates a nominal budget of $500 for parts including batteries, with some caveats such as brakes and e-stop systems not being counted, etc -typical amateur racing stuff. Yet I can’t help but wonder what would happen to some of the teams if the budget were actually enforced, or if a fair market value had to be assigned to everything that was found. I’m usually very supportive of people being resourceful with projects – if you actually did find a destroyed golf kart to take the motor and controller from, for $0, then by all means spend $500 on glitzy lighting.

I think my reservation about this being allowed without bounds is that you can “find” almost arbitrarily nice things, where “find” I define as “you yourself didn’t spend money on it originally”. For instance, I can go and “find” a few left over (a few!) Ampflow A28-400s. We have them in my old Media Lab research group, bought when they were still called Magmotors, and never used in the final application. I suppose the “buyout rule” will prevent anyone from being too egregious about it, but I also think nobody’s going to be assholish enough in the series to try and buy someone out. After all, that would be taking it too seriously.

Coming from the perspective of instructing 2.00gokart and building Chibikart to be easily replicable, I’m supportive of ‘everything on the vehicle has to have a nominal fair market value’ – it’s good practice, in my opinion, and it’s how I personally head off student ‘creativity’ at the mountain pass. It would also more accurately reflect the true value of the vehicle, that is, what you’d need to spend to replicate it once. While I’m sure most of these teams don’t have that as their first agenda, I usually try to make sure my projects are replicable by others, whether by documentation or accessibility of parts. In my opinion, it makes the series that much more accessible if, to be competitive, you don’t have to say to someone “Well, you call some junkyards and try to get a scrap forklift, then you take the motor and controller out of it…” and can give them a rundown of parts and sources.

But remember, my perspective is tainted with teaching an engineering design class first and foremost. I think BOM-smudging isn’t even my peeve with seeing these new builds. I ain’t even mad – I like “run what you wrought” competitions and think too many technical rules is silly – hence why I go back to Battlebots over and over. I instead contend that with these ‘heavy metal’ industrial parts, everyone’s optimizing in the wrong direction.

Here’s an example of what I call “optimizing in the wrong direction”. That’s a 8″ series wound DC motor connected to a moped rear end which provides the right angle drive. Most of these ‘big metal’ karts weighed north of 250 pounds, I think, when empty.

What I think you get into is a recurring cycle of putting bigger motors on something, then it needing more batteries or a stiffer chassis because of it, then the increased vehicle weight necessitating a bigger motor… you see where that’s ending up. The vast majority of everyone, besides, say, Chi(p,b)ikart, was really chunky. Chibikart, completely unmodified, held its own against most of the field, and I think if I’d put some more easily swappable batteries on it, could have done well (besides the whole non-spec cost issue). And even with these extra batteries (say 6 or 8 more A123 bricks, which would shoot the cost waaaaay up!) it would still weigh under 60 pounds.

Hey, now that’s more my preferred flavor of design. The “Lame-borghini” sports an Epic Hobbyking Inrunner driving one rear wheel through a roughly 16:1 reduction. Unfortunately, they used a generic HTD 5M timing belt drive on the output, and it was incapable of taking any of the power, – it kept shredding belts. I suspect misalignment also contributed to belt death.

It also had a small brick of Hobbyking lipoly packs – which I thought were banned from the series? I’d be completely okay with small lipoly bricks if they were all mounted inside a hard shell, actually. Energy density!

A better shot of their power system. I’d also be hard pressed to believe that controller can handle the full power of that motor. Someone didn’t read my scooteructable! Or perhaps, read it but not believed it.

I suppose it did handle the motor well, for their operating regime, which was ultimately belt shredding limited.

Early Saturday afternoon, the first race of 15 laps was held. The whole event was extremely popular audience-wise – people lined up against the entire length of the fencing and overflowed the single set of bleachers set up at the end.

Check the cameo by Johnscooter. I didn’t race it in the series (duh), but it was one of my float-around-the-Faire vehicles. Chi(p)ikart can be seen also to the right, preparing for the start.

My personal observations of the event: Reliability still won out in the end, no matter how big of a motor pen0r (that’s a technical term) you had. In fact, the same team from last year won yet again, with basically the same car. The “big motored” karts were fast, but the track kept everyone together and negated any speed advantage you might have had. Big also meant hard to wrestle around the tighter turns.

For poor Johnscooter – or more like Kitmotter2, this was its last event. As Sunday drew to a close, I started letting other people ride it around, and after a while, it seems like the puny #2-56 hardware began coming apart, and Kitmotter ripped at the seams. I think a real side plate material (read: not MDF) would have allowed the bolts to retain tension, but I’m amazed it lasted as long as it has.

the official response

Since the last year’s event, I’d been in on-and-off contact with the event organizers and Jeremy, a central participant, mostly sending them troll ideas. I really do want to put together an entry since the series is so well aligned with the intentions of 2.00gokart. Perhaps this coming year’s instructor vehicle could also be an entry and a ‘technology demonstrator’ for the series. And if some of the students want to, I’d probably let them keep their vehicle after the semester and enter one of the races.

If I were to enter the series seriously, the shoddy contraption I’d construct would adhere to the following set of constraints:

  • Everything on the BOM would be a ‘gettable’ item – no salvaging from some manufactured item unless it’s an easily available part or common item; this is in the vein of how I put together the Chibikart2 design.
  • It wouldn’t be a DC-motor-and-lead-bricks design. My school of thought dictates brushless power, light weight, and small size. Brushless is easy, but batteries are a major cost item if I actually want to count them in the BOM. Either NiMh or some kind of super low-brow LiFePO4 system will be needed, since lithium polymer is not allowed in the series.
  • It would need to be innovative or different in some other way, or do something most people say can’t be done. For instance, quad-kitmotters was an early (and still viable) idea. This I think would actually make for quite a punchy and very efficient vehicle. Since the motor would only count as its component parts (labor, manufacturing processes, and materials beyond cost of obtaining aren’t counted), it would fit easily in the budget.
  • It would need to look like Mikuvan. Cuz hell, if I can’t have a real electric car, I’m gonna make a small version of it!

Now, I’m entire aware of the fact that nobody in history made a Mitsubishi Delica ride-on toy (if someone did, tell me right now). But that didn’t stop me from putting together a proposal for the organizers. So I hereby present…

Now, this design was actually made many weeks before Maker Faire, and I had half a mind to blitz the basic working platform beforehand, but due to my summer EV design class requirements (I still owe everyone a report on that, and will say so every time I mention it until I finish it!), then Dragon*Con, it got punted off.

The concept is to use a brushless airplane motor and the same airplane (or boat – “hobby R/C” is the key word) ESCs that I often deride. The key implementation details from the sketch, though, are:

  • Avoiding ever using the motor at low RPMs, where the airplane ESCs tend to not do anything (or explode) the most, by having a DC ‘pony motor’ bring everything up to speed first. This speed can be very low, – all it needs to do is start the brushless motor spinning. The DC motor would just be on a relay or contactor, be the first to cut in, then cut out very shortly afterwards. The DC motor ‘s input would be one-way clutched such that the brushless can take it over at any time. After not looking at my own troll drawing for a few weeks, and speaking to Jeremy at the event, I’ve pretty much decided that the “pony motor” is not necessary.

    Instead, I think the BurnoutChibi solution is more warranted here – use a much faster motor on a higher voltage and gear it down more such that the motor can overpower the vehicle inertia on the R/C ESCs’ starting pulsing alone. I’m now looking at the same Hobbyking boat inrunner that Lame-borghini used. It has just enough brushless pen0r (that’s a technical term) to fulfill that design goal. The matching controller would be something like the 1/5 scale in terms of ability to actually handle this motor under significant loading.
  • Scrap a worn out hybrid battery from a Toyota Prius or similar. This is the part of the plan which I have been researching the heaviest. NiMh cells actually are competitively power dense, and the first and second generation hybrid cars are well on their way to maturation and are bound to be in auto yards in droves by now. The plan would be to reconfigure the high voltage battery into a 28.8v, 40+ Ah low voltage pack. My research so far, which has involved dredging eBay and also calling area wrecking yards (I’ve explored as far as mid-Connecticut and New Hampshire), has shown me that most of these batteries get plucked away early by “rebuilders” which sell the cell modules for a markup. Typical pack costs are $1000-1500 after one of them gets their hands on it, and in my short calling sprees, have gotten as-pulled prices as low as $600 from yards.

    This is still too much. I’m hoping a bit more calling and schmoozing the ‘college student project’ angle, even though I’m sooooooooooo past being able to morally use that angle, can get the price down to closer to $250-300, which, at the 50% rate of battery cost accounting, would end up being around $125-150. I’m also trying “other” hybrids, such as Honda Insights, Ford Fusions, and Mercury Milans, which are lesser known and could fetch lower prices as a result of less turnover. I’m not even seeking an “A”-grade pack – the car could have had 250K miles on it and just stopped working finally, with several dead modules, and the plan would still work.

    This is the lynch pin of the build – if I land a big hybrid pack for a reasonable price, then it’s going forward. On top of that, the more people build with hybrid packs, the less of them end up in the hands of shady-ass “rebuilders”. If it turns out that Prius batteries aren’t economical, then I’m going to look at Chinese “bargain basement” LiFePO4 systems such as Headway cells – they won’t be the most stellar of performers at the single and two-parallel cell level, I think, but they’ll give me the energy needed for running longer than 15 or 20 minutes like the Chibis do.

So there you have it. I have no definite timeline for this project yet, but it’s been occupying my spare neural cycles in terms of lining up the best possible arrangement of parts for the given budget. I’ve ordered some things to play with, and some of these plans might change outright (Hell, I might switch to a V8 made of CIM motors). A more complete engineering post is forthcoming. I’m serious:

 What you see there is me discovering that, with 8″ Harbor Freight tires (which are actually 8.5″), the vehicle is a near perfect pi:1 scale replica. (Note: Drawing measurements in millimeters, my dimensions in inches)

This was meant to be.