How do I control a small motor, multiple motors?

[newguyintown]

Hi everybody,

I found some high power to weight ratio motors originally intended for use in RC helicopters. Would it be possible to use one as a hub motor for a bicycle? From what I've read a person peddling produces a few hundred watts of power, and I found a motor that can do 2kw continuous. That seems to me as if it would be able to easily sustain the speeds you would do on a bicycle, and possibly get you to a higher speed.

My question is, how would I control such a motor. I assume I need some sort of motor controller or PWM. I don't want to use a resistor as that would just waste energy. It seems like the RC vehicles themselves need some sort of controller. Would it be possible to wire one to a throttle, or are they just using resistors?

My other question is, how would I control more than one motor at the same time? I know people do this when they use 4 hub motors in some EV's but I'm not familiar with how this would work. Would I need one controller for each motor, and even so how would I tell each controller to give the same amount of power? If I can do this, I could in theory put two motors(one on each wheel of a bicycle) to provide more power, right? Also would it be possible to put more than one motor on each wheel? For example could I put two or three motors on the same axle? If I could, then I could theoretically use several of these motors to drive a small car, right?

If the controller isn't too expensive, I might be able to build an electric bicycle for under $100. I'm going to do some more research on what people have done in the past. Please share any experience or knowledge you have.

Thank you

[DawidvC]

If you look at some of the outrunners the rc guys are using, they are more than powerful enough - some of the motors are rated at over 10kw continuous.
Most wheel motors for bike and bicycles are outrunners - the only real difference betweem them and the rc outrunners are details of mounting and outer shell construction - mere mechanical details. All these motors are PM synchronous motors, so they require one controller per motor. For controllers and motors visit rcgroups and related forums - they have plenty of detail on what is required.

[newguyintown]

Thanks DawidvC!

Wow 10kw continuous. Where did you find one that powerful? Could I have the link? I've noticed that the motors used for these helicopters have a very high power to weight ratio, is that true for the 10kw motor you saw? How much does a motor like that cost? The controllers for these motors and the motors themselves seem to cost a lot less than those on an E.V. website.

That's great news on the motor/controller setup. I'm going to read up on how the controller will work for that.

Thanks for the help!

[Ryland]

Alot of these motors are high speed, low torque, so gearing it down somehow it needed without adding alot of weight.
I'm not finding a price list, but one forum I found said that one of the 11kw motors cost $830 just for the motor and weighed over 15 pounds, so amazingly light for a motor of that power, but it's also designed to turn a prop, so the bearings on it are not going to handle a side load very well.

[newguyintown]

Thanks for the input Ryland,

I've been reading, and supposedly the lower the KV value the higher the torque? I read that there are inrunners and outrunners, and the outrunners are supposed to have higher torque and lower rpms.

Regarding the side load, I was thinking it might be possible to mount one motor on each side of the axle. Would that help reduce stress on the motor? Or could I possibly run it through the bike chain?

[hagon]

I bought an outrunner 6 kW PM motor with 6000 rpm from hobbyking.com for about 110 $. It fits in Your hands...

[newguyintown]

That's amazing. I supposed they'd have to be small and light considering it's for an aircraft(or other RC vehicle). What are you using as the controller? I wonder if a programmable ESC would allow me to use the signal from a twist throttle or a pedal. If I can get that figured out I'm going to buy one, build something, and post pictures and things.

[hagon]

I just bought a "normal" suitable controller from the RC-family, that meets the amps requirements (for much less than 100 $). Cooling need some attention. This controller You can control with any potentiometer - a standard one or a throttle poti.

Imagine, putting 4 of these 100$ 6 kW motors on the 4 wheels of a car. If the transmission problem is solved, there would be plenty of space for the batteries replacing the space of the removed ICE and gearbox.

[DawidvC]

Originally Posted by newguyintown

Regarding the side load, I was thinking it might be possible to mount one motor on each side of the axle. Would that help reduce stress on the motor? Or could I possibly run it through the bike chain?

If you can get one of the kits, it should be possible to swap the bearings for a type that can handle the side load better. BTW, with the outrunners, it should be possible to modify the bell ( the outer, rotating part ) to be better adapted to the wheel, including the position and types of bearings.

Regards
Dawid

[newguyintown]

Thanks hagon! That's great news on the controller. Yeah, that's exactly what I was thinking. You could use 4 hub motors and eliminate losses in the transmission, drive shaft, etc. That's still a total power of 24kw, but that should be enough to run a small car. The motors should be light enough to not mess too much with the suspension. They weight so little that even with a fairly heavy battery pack the car should end up lighter. The motors should also be in an area then with plenty of airflow to help cool them down. This could end up being a fairly cheap system to convert a car to electric. You could probably just wire a bunch of the Li polymer batteries that are already intended for the motors into a bigger pack. I found a place on Ebay that if the shipping can be combined for several packs, the cost per kwh would be around $160. If you're interested I'll post the link.

Thanks DawidvC. If it's possible to get that sorted out, they should make pretty good hub motors.