# Dividing power evenly between dual motors?



## powerhouse (Apr 1, 2011)

I have always wondered this, and I am sure a couple of you guys know the answer.

When running a dual motor setup with a single controller, similar to John Wayland's setup (except not siamese), or John Metric's setup (except 1 zilla), how does one ensure that both motors are receiving equal partitions of the controllers power? 

To clarify - How do you make sure each motor is running at the same power? 

For example, if one motor were receiving less power (or even receiving same power, but not converting it as efficiently) than its 2nd motor counterpart, wouldn't the weaker motor be negligible in the setup as the 2nd, stronger motor, would be doing all the work?

In an AC setup, I suppose the weaker motor would assume the position as a generator as the stronger motor overpowers it. But in a DC system, is this extra energy practically wasted?

Most people will think of a warp coupled to a transwarp when they envision a dual motor setup. In my case, I am running a warp 9 and transwarp 9, coupled together at the shafts. 
I feel as though this stronger motor / weaker motor scenario is further exaggerated since the warp 9 and transwarp 9 have different dimensions, and would thus have different internals, meaning they wouldn't suck the same amount of power.

I'm sure there is some really easy solution to this dilemma, and I would appreciate if someone would enlighten me!


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## major (Apr 4, 2008)

powerhouse said:


> To clarify - How do you make sure each motor is running at the same power?


Hi power,

It doesn't matter if the power is different in the 2 motors. The power from each adds to the total to the wheels. 

If running for extended periods at heavy load you may find one motor heating more than the other. But if you keep each within limits, I see no problem.

The MC teams running dual Agni PM motors had a rough time of it though. Here they were pushing the thermal limits with fragile motors, IMO. They were shaft coupled, left and right side of the bike, so rotating CW and CCW. The engineer would spend hours trying to set the brushes to equalize current draw. Parallel PM motor operation is an unstable system. However parallel series wound motors do very well. The characteristics make for a stable system.

Regards,

major


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## Bowser330 (Jun 15, 2008)

In the performance section John Metric started a thread detailing his build with dual Warp9's and 2 Zilla2KEHV's.

http://www.diyelectriccar.com/forums/showthread.php/dc-plasma-build-thread-10sec-fiero-69476.html

He included a graph of the Zilla outputs below...."Comparison of one zilla across two motors in series...."

Check out the duty cycle lines and the motor voltage lines, it looks like one of the motors duty cycle ramped up much quick than the others...I wonder why? Could it have anything to do with one motor being a Warp9 and the other being a Transwarp9?

Very interesting graph nonetheless. Thanks John!


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## jwalin (May 7, 2008)

What about running the motors in series vs. parallel? I would love to build an all wheel drive setup with a high pack voltage, one controller, and one motor at each end of the car, with the motors in series. Say, 240 pack voltage so each motor should see approximately half that.

Is this rational? I have never seen a setup like this....


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## major (Apr 4, 2008)

jwalin said:


> What about running the motors in series vs. parallel? I would love to build an all wheel drive setup with a high pack voltage, one controller, and one motor at each end of the car, with the motors in series. Say, 240 pack voltage so each motor should see approximately half that.
> 
> Is this rational? I have never seen a setup like this....


You can run DC motors in series with each other. You get an electric differential. Current is the same in both, so each produces the same torque, and that torque is the lesser of the two's load. Voltage divides according to the RPM of each. So should one lose load (wheel off the ground or on ice), it sees little load so the other motor stalls and the loose motor gets twice voltage resulting in excess RPM. Other than that, it works well, especially if they are hard coupled shafts.


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## jwalin (May 7, 2008)

major said:


> You can run DC motors in series with each other. You get an electric differential. Current is the same in both, so each produces the same torque, and that torque is the lesser of the two's load. Voltage divides according to the RPM of each. So should one lose load (wheel off the ground or on ice), it sees little load so the other motor stalls and the loose motor gets twice voltage resulting in excess RPM. Other than that, it works well, especially if they are hard coupled shafts.


 
So if I use two independent motors and one controller, one motor through one open differential driving front wheels and one driving the rear wheels, and I hit ice or hydroplane one wheel, all other wheels lose torque, and the 'loose wheel' increases in rpm's?

if this is the case, it seems running LSD's at each end would help greatly, though not eliminate the problem completely in the case of loss of traction on one end of the car.

just thinkin'


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## somanywelps (Jan 25, 2012)

jwalin said:


> So if I use two independent motors and one controller, one motor through one open differential driving front wheels and one driving the rear wheels, and I hit ice or hydroplane one wheel, all other wheels lose torque, and the 'loose wheel' increases in rpm's?
> 
> if this is the case, it seems running LSD's at each end would help greatly, though not eliminate the problem completely in the case of loss of traction on one end of the car.
> 
> just thinkin'


It would be better to convert a BMW 325xi/330xi and let the computer do the individual wheel torque control.


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## PhantomPholly (Aug 20, 2008)

jwalin said:


> So if I use two independent motors and one controller, one motor through one open differential driving front wheels and one driving the rear wheels, and I hit ice or hydroplane one wheel, all other wheels lose torque, and the 'loose wheel' increases in rpm's?
> 
> if this is the case, it seems running LSD's at each end would help greatly, though not eliminate the problem completely in the case of loss of traction on one end of the car.
> 
> just thinkin'


Sounds like that scenario is just about exactly the opposite of "Posi-traction." Someone will probably make a smart 2-moter controller one day that senses the current changes and shifts current to the slower turning wheel(s).


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## jwalin (May 7, 2008)

somanywelps said:


> It would be better to convert a BMW 325xi/330xi and let the computer do the individual wheel torque control.


Regarding the BMW: Is the computer separate from and independent of the engine control computer? also, does the traction control work by applying braking forces to the spinning wheel?


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## somanywelps (Jan 25, 2012)

jwalin said:


> Regarding the BMW: Is the computer separate from and independent of the engine control computer? also, does the traction control work by applying braking forces to the spinning wheel?


1) I'm pretty sure it's independent from the ECU, it might be the same part that controls ABS.

2) Yes it's double open Diff so it just brakes the spinning wheel(s) and forces the power elsewhere.

Valerun would know more though.


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