Dual Motors Single Controller

[magudaman]

I know this has been discussed before but I could seem to find it. Most places seem to claim that two brushless motors on a single controller is a bad idea but I don't feel it would be that hard to accomplish.

So the idea is to use two RC out runners on a timing belt feeding into a single output shaft. Through a series of adjustments on the plates both motor can be very minutely adjusted in position to essentially lock the rotors into the same position. Utilizing a oscilloscope you can confirm that the winds are in fact locked at the same locations. You end up with 4KW in a 4lbs package with better cooling that a single motor (RC) and a output of a nice comfortable 2800RPM. Lets say at a cost of

Let assume I don't have to worry about the belt slipping, what are all the problems with this scenario?

 

[Thud]

All you need to do is identify the 3 phases on both motors....then run a little power through a phase pr to position the magnet armatur directly on its pole......BAM, your synced.

 

[magudaman]

Yah I figured I would hook up the variable power supply set real low to hold them in place.

 

[SamTexas]

Most places seem to claim that two brushless motors on a single controller is a bad idea but I don't feel it would be that hard to accomplish.

I don't know how difficult/complicate the task is. But China Golden Motor sells one. It's designed for wheelchairs. It has other functions too in addition to phase synchronization. [Edit: I don't know for a fact that synchronization is actually done on this controller. I'm just guessing/assuming that it is.]

All you need to do is identify the 3 phases on both motors....then run a little power through a phase pr to position the magnet armatur directly on its pole......BAM, your synced.

Thud, have you implemented one yet? If so, can you point me to the thread describing your work?

 

[Thud]

Sam,
The answer is no.
Since most of my sensored controlers are already on the ragged edge running a single high rpm motors I havn't taken the time to fail at this yet.

 

[amberwolf]

[I don't know how difficult/complicate the task is. But China Golden Motor sells one. It's designed for wheelchairs. It has other functions too in addition to phase synchronization.

That controller actually would have "two controllers" inside it; or at least two separate power drive sections, even if they are controlled by a single MCU. It is not quite what I think the OP is asking for, because that MCU will drive both sections separately, not in sync with each other, as it doens't need to keep them in phase sync--it jsut ahs to keep them running at about the same speed, and the user will provide feedback via the controls to correct the speed of one side or the other.

I suppose it could be adapted to do full sync, but I'm not sure what would be involved.

 

[SamTexas]

I didn't know that. Are you positive about that, amberwolf? I have never seen one in real life, let alone opening one up for inspection. So you're saying that the MCU continuously adjusts the speed of the motors even when the user is going straight forward or backward? I guess that would work too, but definitely primitive and more complicate than it could have been (at least in my mind.)

[I edited my previous post to add that I was speculating on the phase synchronization.]

 

[Alan B]

In order to be able to turn a wheelchair controller must change the speed of the two motors, so they won't be able to keep them phased.

 

[SamTexas]

I know that. But why can't they be in sync when the wheelchair is NOT turning?

 

[Alan B]

If they are ever out of sync they must have separate drivers.

Even when going straight they won't necessarily be in phase sync, due to differences in surface and tire diameter; also being in sync would only occur in certain directions, turning introduces a phase shift that will be nearly constant when going straight, but won't often be zero.

 

[SamTexas]

So resync when necessary. There's no reason for not being able to do it. I would NOT be totally surprised if such a thing already exists.

 

[magudaman]

Yah that controller won't work for me anyhow I am looking at using my existing kelly controller to drive two sk3 6374 (I think that's what they were) at 50v 50a each. That controller is looks like tank controls and would add a buch of headache

 

[SamTexas]

That controller is looks like tank controls...

It is a tank control as far as steering is concerned. Good luck on your project. I would love to know how it works out.