High RPM rc motor for Ebike

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jimseko@yahoo.com
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Joined: 22 Sep 2017, 04:51
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High RPM rc motor for Ebike

Postby jimseko@yahoo.com » 08 Oct 2017, 05:13

I'd like to share a little about myself before getting into this topic. I have hip pain and can't peddle a bicycle. I have not ridden a bicycle for six years until I put a 750 Watt mid drive Bafang motor on my son's mountain bike. I had so much fun riding my son's ebike, I wanted one for myself. I'm building a custom trike using carbon fiber/foam composite for the frame and 20" rear wheels. This bike will have no crank set because I have no use for pedals.

I plan to use this motor https://hobbyking.com/en_us/assault-700 ... tore=en_us

It's a 530 kV, 4500 Watt motor. The two stage gear reduction will include a HTD3m belt with 20:120 tooth pulleys followed by #219 chain with 12:90 tooth sprockets for an overall gear reduction of 45 to 1. Speed at 80% of max RPM will be about 27 MPH which is fast enough for me. I'm more interested in hill climbing ability and acceleration than top speed. I plan to use the open source VESC controller and take advantage of regenerative braking.

I'm a retired electrical engineer but I've never tackled a project like this. I'd love to have some input and suggestions before I purchase a motor and controller. Right now I'm spending my time building the carbon fiber frame and wheels.

ThierryGTLTS
Posts: 86
Joined: 09 Aug 2017, 11:10
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Re: High RPM rc motor for Ebike

Postby ThierryGTLTS » 08 Oct 2017, 06:57

Hi,

That will make a lot of noise, because of several things: chain reducer, high speed motor, and carbon frame resonance.

Compared to this, the Bafang is very silent :!: :!:

But if noise is not an issue for you, it's possible.

You can have a look at several project on Endless Sphere.

Have a Nice Day.

Thierry

rew
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Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.
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Re: High RPM rc motor for Ebike

Postby rew » 08 Oct 2017, 08:13

In theory that motor has a torque constant of 0.018 Nm/A. At 100A that would be 1.8Nm. Multiply that by 45 and you get 81Nm at the wheels. A 20" wheel has .25m radius, so that would provide you with 320N of "thrust" at the wheels. Not unreasonable.

pf26
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Re: High RPM rc motor for Ebike

Postby pf26 » 08 Oct 2017, 17:07

With 530KV and 12s at 100% duty cycle, you get something like 25000RPM and 250kERPM with 10 pole (assuming pole pairs). If I rekon well.
I think this is about 4 times as many as the VESC can handle without issue in FOC mode. Maybe it is a bit better in BLDC mode.
Anyway, this would limit you to 1/4 of your calculated top speed.
This is just a warning, I haven't used such motor myself - it would be nice if it worked though - nearly 10kW/kg is huge.

jimseko@yahoo.com
Posts: 2
Joined: 22 Sep 2017, 04:51
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Re: High RPM rc motor for Ebike

Postby jimseko@yahoo.com » 08 Oct 2017, 21:52


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Ecyclist
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Re: High RPM rc motor for Ebike

Postby Ecyclist » 21 Dec 2017, 00:22



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