Chibi-Mikuvan

Vans on vans

No matter what kind of cutting-edge precision cloud-hosted universal replicating machine you have me work on, I always seem to find a way back to hang out with the silly go-kart building crowd.

Having shadowed the Power Racing Series since 2012 at the New York Maker Faire, and having gotten to know the organizers well, I pledged that I would enter a to-spec entry in 2013 instead of just trolling the race with Chibikarts. Sadly, the 2013 New York Maker Faire came and went, but from my observations of the 2013 race, I thought the sport needed an injection of varied parts and technologies. There were too just many floor scrubber motors and forklift motor controllers for my liking.

Part of my continued interest in the makersphere, at a stage where I am often a mentor or resource for people just starting out or building more advanced projects of their own, is expanding the resource horizon and teaching people to see potential parts and resources in everything. That’s the cornerstone of the 2.00gokart and SUTDkarts lab classes I’ve taught, and is the foundation for things like Beyond Unboxing.

Thus began Chibi-Mikuvan. On the surface, it’s ridiculously cute composed of seemingly unrelated industrial and commercial parts: R/C boat and R/C car parts, an angle grinder, pieces of a hybrid car battery, an ammo can, trashy wheelbarrow tires, and the harvested water cooling circuit of a PowerMac G5. And an Arduino. Combined all together, though, it’s one of the cutest most fun and terrifying rideable devices I’ve ever built, as testified by quite a few who have experienced it… and I’ve built a lot of rideable things.

Chibi-Mikuvan is also the first thing I’ve built which had a secondary mission of looking like something. For my own edification, I dug up a copy of Moldless Composite Sandwich Aircraft Construction by Burt Rutan and learned how to carve and shape foam (both by CNC and by hand) and lay up fiberglass. Using what skills I had picked up doing real van bodywork, I smoothed and painted the shell, then commissioned my buddy Brian of Much Steadier Hands and Artistic Wizardry to match the exterior body lines and seams with paint markers and masking tape. And then the flood of eBay vinyl stickers began.

Chibi-Mikuvan is dedicated to the queen of crowdsourced synthetic Japanese future girl-pop that you’ve never heard of, Hatsune Miku. Just saying that sentence alone gives you hipster, Kickstarter, and open source activist cred at the same time.

Build History

In my usual style, essentially every detail on this build has been logged and written about. In chronological order, here’s the process of Chibi-Mikuvan creation from conception to implementation:

Bill of Materials

Here’s the latest working 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.


Specifications

Vehicle Electric go-kart
Drivetrain RWD solid axle, rear motor
20.5:1 ratio
Mechanical 1″ x 0.06″ wall steel tubing and 0.100″ steel plate frame
Fiberglass-foam composite sandwich shell
Motor Turnigy Aquastar T20 with water cooling
PowerMac G5 water cooling circuit
Controller Turnigy Trackstar 200A
Arduino Nano-based vehicle control module with current sensing
Battery 28.8v 16Ah NiMH hybrid car traction battery modules
Top Speed 25 mph
Range TBD
Curb Weight 110 pounds

Some videos of Chibi-Mikuvan testing and running in races:


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