High RPM rc motor for Ebike

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jimseko@yahoo.com
Posts: 2
Joined: 22 Sep 2017, 04:51

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

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
Posts: 940
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

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
Posts: 296
Joined: 28 Mar 2016, 14:37
Location: FR Valence

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

Re: High RPM rc motor for Ebike

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

pf26 wrote: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.


Thank you for this info which prevented me from making a huge mistake!! Apparently, if I want a high high RPM motor it needs to have fewer poles. I'm now thinking of using this 4 pole (2 pole pair) motor http://www.ebay.com/itm/LEOPARD-RC-Mode ... SwQplZe1LG

...but through further research I learned that the VESC doesn't like low inductance motors. I'm going to go with the Turnigy 6374 192 kV motor actually used on one of Benjamin Vedder's boards and adjust the gearing.

User avatar
Ecyclist
Posts: 30
Joined: 24 Jun 2017, 01:26
Location: San Diego, CA

Re: High RPM rc motor for Ebike

Postby Ecyclist » 21 Dec 2017, 00:22

jimseko@yahoo.com wrote:
pf26 wrote: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.


Thank you for this info which prevented me from making a huge mistake!! Apparently, if I want a high high RPM motor it needs to have fewer poles. I'm now thinking of using this 4 pole (2 pole pair) motor http://www.ebay.com/itm/LEOPARD-RC-Mode ... SwQplZe1LG

...but through further research I learned that the VESC doesn't like low inductance motors. I'm going to go with the Turnigy 6374 192 kV motor actually used on one of Benjamin Vedder's boards and adjust the gearing.

I'm using 6374 125 Kv outrunner in my build. You will get about 30 mph out of it.
You can read about my build here:
https://endless-sphere.com/forums/viewt ... =3&t=90432


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