Power Wheels Racing

[mikegrundvig]

Alright, some of you are familiar with this and some are not:
http://www.powerracingseries.org/

A lot of my friends compete and I'm considering giving it a shot this year. The rules are a little tricky, the total project has to cost less than $500 but that doesnt include the initial power wheels itself or any safety equipment like brakes and helmet. The batteries cost only 1/2 their actual rate. A $100 battery would count only as $50. Multiple battery packs are fine, only what is on the vehicle counts to the price. LifePO and SLA are ok, LiPO are not. Finally, the maximum voltage that can go to the motor is 36v.

Before I go too far into this though, I wanted to run some questions by the experts here. My initial thought is to go with a LifePO pack I make from Headway for $208 ($104 against me) plus another $109 for the BMS. It's very possible the BMS counts as part of the pack as you can buy em that way but let's assume no, that gets me $213 at the worst and $158.50 at the best.
http://headway-headquarters.com/40152s/
http://headway-headquarters.com/xji-12s-36v-50a-100a-bms/

I'm thinking a hub motor on a small 20 wheel will give me the acceleration I'd like. IMO, speed out of the hole is the key in these races as the straights are short and the corners often tight. 3 wheels will have a big advantage in making it smaller and more nimble. My first thought is a MAC motor:
http://em3ev.com/store/index.php?route=product/product&path=36&product_id=54

That full kit is $235. This leaves me about $60 left to finish the project. That's JUST BARELY doable but I think I can do it with scavanged parts. A cheaper BMS would save me 50 bucks (if I used CellMan's for instance) and that would go a long way to getting this done.

So my question is: does this even seem like a viable approach? It did to me, but I'd really love to hear what others think.

Thanks!

-Mike

 

[parajared]

Looks like a pretty good build to me, you can do without the BMS if it counts against you and just use the BMS wires to top balance. I have had nothing but grief with Headway Headquarters, but evassemble and ebikedeal.com sells Headway batteries too.

My Headway Headquarters BMS fried after about a month's worth of use.

Hubs aren't ideal for a racing environments because they heat up more on hard acceleration than the mid-drives. If you do go with the Mac be sure and ask for the temp gauge upgrade. This will help you push the motor as close to a failure heat as possible without breaking down on the track.

You could jackshaft a hobbyking rc airplane motor for a mid-drive for a little cheaper than a Mac, or if you want to stick with a hub, but want to save cash Bafang makes a gear motor that is almost as good as a MAC for $125. It's the BFM or BQM or something like that.

Build the thing as wide as you can and as low to the ground as you can get away with. Three wheelers have a tendency to flip on you if you are not careful.

I built a little e-bike race track in my back yard and I race my recumbent e-bike against myself on it every now and then. This one here:

 

[dogman dan]

No advantage to a geared motor, get a DD so you can heave some amps at it and run it hotter. EM3ev's dd motor can handle 3000w for a short race.

Put money into a big controller, but get it as cheap as possible from ebay. Then maybe solder the shunt for even more amps.

You'll need a fairly fast winding in 20" wheel, since you have a 36v max. Drill big vent holes in the covers.

No point in a bms for a race. just put a low voltage warning on it, or a cheap cheap voltmeter you can see.