Trying to understand controllers and high rpm small wheels...

Lightweight / Folding / Portable EVs - seats optional
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Electric Earth   100 W

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Trying to understand controllers and high rpm small wheels...

Post by Electric Earth » Jun 10 2020 11:03am

I've only built an ebike from a kit before, so I didn't have to work out which controller to use. I was reading something on the Grin website about using a controller with a higher eRPM on a smaller wheel. Now that I'm doing a completely cobbled together project, and with small scooter wheels at higher rpm than a standard ebike controller, I'm struggling. I don't see anything about rpm mentioned on the controller specs.

If I'm running a motor that says the rotating speed is 250-1,000rpm, do I need a controller that will work up to 1,000rpm? If so, how do I find that information? Do I need to calculate it somehow, or is that a spec that I should be able to look up for a controller?

I'm looking at trying a wheel from aliexpress like this one. I'd like to be able to buy a controller that I can use later if I decide to upgrade to a nicer 20" wheel scooter/motor. Is that doable, or is this wheel going to take a completely different controller than a larger wheel?
https://www.aliexpress.com/item/4000562 ... hweb201603_

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DanGT86   10 kW

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Re: Trying to understand controllers and high rpm small wheels...

Post by DanGT86 » Jun 10 2020 12:01pm

The controller only cares about electrical RPM. You need to know the number of magnets in the motor to calculate this.
E-RPM is the number of magnets divided by 2 times the motor RPM.

I have a scooter motor with an 8" tire that has 30 magnets. At 1000 motor rpm that would be be 15x1000=15k eRPM.

Hope that helps.

I don't know what your project is but tech direct club has pretty cheap used scooter motors with cheap or free shipping in the US and usually a few percent off.
https://www.techdirectclub.com/hub-moto ... c-scooter/

Electric Earth   100 W

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Joined: Nov 11 2018 8:02pm

Re: Trying to understand controllers and high rpm small wheels...

Post by Electric Earth » Jun 10 2020 5:23pm

DanGT86 wrote:
Jun 10 2020 12:01pm
The controller only cares about electrical RPM...
I don't know what your project is but tech direct club has pretty cheap used scooter motors with cheap or free shipping in the US and usually a few percent off.
https://www.techdirectclub.com/hub-moto ... c-scooter/
Thanks, for the info and the tip about the website!

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