Need Direction on a Compact Project

[Ratchet81]

Hey, all,

I'm completely new to the world of go kart building, and I have a project that I decided to take in that direction. I'm currently leaning toward going electric, but I know very little about how to properly go about building an electric go kart.

First, a little bit of background to illustrate my constraints. It originally started when I decided to build my daughter a custom power wheels car. So I started making a body out of fiberglass that was pretty much a unitized construction (tub and fenders all one piece). As I've been working on the body, I got to thinking that it would make more sense to build it with the strength and power of a go kart---so that she can ride it for as long as she still finds it fun, instead of until she gets too heavy for the little power wheels gear boxes to push her around. The car is bigger than a power wheels car, but not by too much. At one point I was going to put a gas engine in it, but the back end of the body is too small to fit anything bigger than a 3HP engine, and I'm leery of the idea of a gas engine being surrounded tightly by fiberglass with my kid sitting inches away from it.

So what I'm looking at doing is fabricating a frame to fit the fiberglass body (should be easy), fit it with the right 24V motor and gearing, and figure out what speed controller and floor-mounted throttle I'll need (as well as anything else I'm not currently aware of). I've looked at some different threads, and see that golf cart parts are recommended...but those parts are well out of the budget for me. I was thinking of using electric scooter parts, if that would work. I'm planning on fitting a live axle with a disc brake.

I'm looking at trying to find wheels for it that are between 10" and 11" in overall diameter, and would like to try for 15+ mph top speed capability when done. I don't know how much the car/kart will weigh when I'm done, but my guess would be around 80-100 lbs without the batteries. I'm not sure how to figure out what gearing to use.

Based on the above, do you think I can successfully achieve what I'm looking for with scooter parts? I know to stay away from anything meant for a Razor product.

Thank you!

 

[itsid]

let's go step by step...

First: why 24V .. that's a rather low voltage and in turn that means you're going to deal with very serious Amps even for lower power motors.

Also it'd be hard to find a decent powered motor in that voltage (truck starters aside)
and even if you do.. the amount of amps required will push the controller prices up really fast.

personally, As always, I think a my1020 will push your daughter around quite nicely, especially considering it's really cheap to get both, the motor and the controller (set less than 150 bucks)

If I would have to make a guess I think a 650 Watt motor will fit your bill;
BUT it's about weight speed and all that, so please do some math
here's how

Okay, let's just say you'll choose a my1020 (whatever size you calculated it to be)
The ones that do not have a reduction gearbox installed (i.e. any above 350W)
will turn at around 3000 rpms max (but check on the exact model to get the correct number)

so in order to get the torque and speed you want, you can use that to calculate the speed.

Since an electric motor doesn't need a clutch, nor a torque converter or anything;
you can just do some simple math..
for a 10" wheelsize that conveniently turns out to be a 6:1 ratio to go 15mph..
(isn't it beautiful )

And no.. razor products are fine.. the smaller ones are just meant for kids and cannot provide enough power to move adults..
AFAIK razor also uses UNITE motors (manufacturer of the my1020 series)
just lower powered most of the time...

'sid

PS please take the battery weight into account, they can be extremely heavy and thus have a big impact on the performance.

 

[Ratchet81]

Thanks for that information! I was wondering about the amperage; I'm going to consider higher voltage as you suggested.

I was thinking 24v because that's what I'd seen talked about with power wheels "upgrades" that people had done, and I'm not sure how much room I have for batteries on this platform (assuming I use individual 12v batteries).

The math link is exactly what I need--great thread!

I definitely need to research the batteries to figure out weight and dimensions. would you recommend any particular specifications?

 

[8t6bronco]

I'd do some research here:

http://forum.modifiedpowerwheels.com/index.php

There are some incredible builds on that site that are closer to what you're after

This build has similar sized tires and top speed

http://forum.modifiedpowerwheels.com/viewtopic.php?f=18&t=16077

 

[itsid]

I definitely need to research the batteries to figure out weight and dimensions. would you recommend any particular specifications?

Not really..
gel cells are great since they won't leak if the kart rolls..
but they're expensive compared to ordinary wet cells.

If costs are not an issue, maybe LiPo cells are viable too.. they're even more expensive, but if you can get a eBike battery sealed and prefabbed with the capacity and voltage you'd need it's still worth considering.

just one thing, sometimes it can be better to drain amperage from two smaller batteries in parallel than to draw the same amps from a single bigger cell.

And whatever you do, make perfectly sure that your kid cannot accidentally touch any terminal
(hot or not, battery or controller... doesn't matter!)
as well as make sure that she couldn't get entangled by any rotating parts or moving chain..

'sid