The Turbulent Rise of Chibi-Mikuvan

Friday, May 2nd, 2014 @ 5:12 | Chibi-mikuvan

After much engineering ado, it’s time for tiny van shenanigans!

This test was the first done with the NiMh modules from the Ford Fusion battery whose construction was detailed previously. I’d say subjectively the pickup is as strong or even stronger because of the added traction of doing it outdoors, coupled with the much larger wires (no more 12 gauge and Deans connector bottleneck) of the LiPo test pack. However, since I don’t have (yet) a Wattmeter-to-150A-Anderson-Powerpole adapter, I haven’t metered it proper. I do know that indoors, I’m traction limited at 3600 watts (as in no matter how hard I gun it, the rear wheels will just slip, leaving a thick trail of itself on the waxed linoleum hallway floor and making the reesarch center administration murderous).

One of the potential plans is to get a Cycle Analyst digital dashboard system or similar. Or, since I already have processing power in the back, and the salvaged current sensors from the Fusion pack, to just make my own.

The terrible sound at 0:47 was the pinion of the angle grinder gearbox slipping its taper seat, unscrewing itself, and then falling off. It continued to jiggle and tumble in the gearbox as I pushed everything back upstairs. It’s now repaired – I didn’t torque the locking screw properly the first time because it’s in a hard-to-access spot where a regular hex wrench couldn’t get to.  After this experience, I cut down a standard L-shaped hex wrench until the short leg did fit.

To complete this round of build details, here’s the last bit work on the battery pack before the outdoor test.

After adding the tie rods to hold the endcaps together, I decided that an intelligent thing to do would be to make an easy way to lift the battery with one hand. I used the left over black 1″ wide cargo strapping which was part of the ratchet strap holding the electronics deck down, along with some rivets and washers, to make a handle. This worked out great, and I have enough of the strap to make 2 more batteries at least.

This is how the battery mounts in the frame, with the two knobs on the sides. Since this is a less than half sized battery from the original design, and the two knobs up front are directly opposite one another on the same axis, the pack can pivot forward and backward right now if the knobs aren’t super tight. Clearly not optimal. I’ll probably just resolve this by adding two bars to the front and rear of the battery pack, such that once dropped into place, they can no longer pivot.

Once I confirm that design, I have enough modules from the Fusion battery to make three more spare packs. The knobs allow the battery to be dropped out quickly, so having a ton of spares on charge during a PRS race makes sense.

And a “press shot” outside in the parking lot.

What’s missing at this point is the water cooling system for the Trackstar motor.  After the numerous high-power takeoffs during the test, the motor was hot but not unhappy hot – I could still hold onto it. But, it’s clear to me that if I want to run above 1000 watts for a long time, it’s going to need the water cooling loop. This will come after the 2.00gokart race when things quiet down a little bit.

It also doesn’t have the wye-delta switching contactor assembly I wanted to incorporate, but I’m of the opinion that the speeds attainable by the Delta termination is utterly unnecessary for an event like PRS. The project top speed under this condition is north of 40mph, which is a domain already well optimized by, like, real Mikuvan.

Here’s the final details…

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.

Future Work

I plan to finish building the water cooling rig in the coming weeks, as well as play with the nice automotive-grade Hall Effect current sensor salvaged from the Fusion pack. For the telemetry/dashboard, all I’m really interested in is instanteous volts, amps, watts, and cumulative watt-hours spent, and all of that info can be gleaned from a voltage sense (easy) and current sense (also easy with the sensor). I do need to build more battery packs, and create or buy a dedicated Giant NiMH Battery charging solution. I have a Hyperion 1420i charger that can blitz into this pack well, but having more chargers would be essential in a race scenario.

Also, make more silly magnetic stick-on anime faces.

And as usual, some fun times in our proving grounds, the spirally garage:

 

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    3 Responses to “The Turbulent Rise of Chibi-Mikuvan”

    1. Phunk Says:

      Just…. so damn cute!

    2. Doug Gallardo Jr Says:

      Dude, you need a horn on that thing!

    3. Chris Says:

      http://www.powerracingseries.org/rules

      LOL @ ” 2.2.1 | The Charles Guan Clause ”

      Unfortunatly, after the lol i then saw they have instituted a peak power limit ( 1440 W, like wtf? ) and became sad inside.

      Either way though, congratulations on being further and officially immortalized in the world of silly-things-with-motors