# Dual motor-direct drive system



## frodus (Apr 12, 2008)

It won't work with AC, unless they were mechanically coupled, but there may be give in drivelines and it wouldn't work well, if at all. For AC and PMAC (BLDC), one controller per motor. There may be ways to get it to work, but it would require lots of care in aligning the stators and rotors and you'd use one encoder. The motors would have to be end-to-end so that the shaft would lock them together. Even then, one 650A controller for 2 motors wouldn't be any different than 1 motor at 650A.

These motors wouldn't care if you had 2 motors at half amperage or one motor at twice the amperage, they'd give the same combined output torque.


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## Ryan800 (Apr 15, 2010)

I agree with Frodus, but for someone who knows what they're doing, I think the following could be made to work:

1 controller, 2 motors, 2 encoders

The trick would be to send only send one encoder signal to the controller. Also, this would only work with induction motors.

In general, just send the slower of the two signals to the controller. This way if one motor starts spinning faster (it's not getting traction or something) the synchronous frequency would be determined by the slower motor and the motor without traction would not spin faster than the synchronous speed.

If you want to get fancy, for small slip differences (going around a turn), send the faster motor speed to the controller. This way the outside wheel, which presumable has more traction, is being drive optimally while the slower wheel is closer to the synchronous speed and thus produces less torque.

This second idea might not work once the controller begins flux weakening since the controller chooses an electrical frequency closer to the rotor frequency and maybe this would cause the slower wheel to start regen-ing (I don't actually know how flux weakening/vector control works).

Maybe this would allow more motor controller options? If the idea is valid, the Tritium could drive an AC15 or something on all 4 wheels. Well... only if both ends of each winding are accessible.


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## mizlplix (May 1, 2011)

Yes, I stated two motors coupled in tandem. I agree in the one encoder. 

I have seen two motors as described mounted on an ore feeder conveyor. It had one controller. It needed to start under fully loaded conditions. Then one motor cut out when up to speed.

It kinda makes me wish I had payed more attention back then.

Miz


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## mizlplix (May 1, 2011)

So....I take it that no one has tried hooking 2 motors inline with a solid coupler and controlling them with one controller? {DC or AC}

I have seen DC and AC set-ups on stationary equipment doing this. The motors were matched and wired parallel. They were used in applications where they started under load. With no one to ask, I assume they were doing it for start up torque. {as one of them had a provision to cut out 1 motor when it was up to speed.}

So without another AC50 to perform tests, I guess there is no real answer.

TY- Miz


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## major (Apr 4, 2008)

mizlplix said:


> So without another AC50 to perform tests, I guess there is no real answer.


Hi miz,

You don't need a test. I thought you got the answer. What don't you understand? With the AC50 it makes no sense to use 2 motors with one 1238 controller. It might work but you get no more torque or power than you would from a single motor because you're controller limited. You can use 2 AC50 motors hard coupled to the shaft each with its own 1238 controller and get double the performance of a single AC50. You could use a single encoder with that but also an encoder for each. You just need rotor velocity (not position) feedback for induction motors and the rotors would essentially be on the same shaft therefore same RPM.

If you were to gear or belt couple 2 induction motors I would keep an encoder on each due to possible velocity error from backlash. I recall a guy posting on the evAlbum having a pair of AC50's coupled together with a belt. Looked like a reasonable way to get in the 140 hp range 

Regards,

major


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## mizlplix (May 1, 2011)

You are correct in that I did not read this in the two above posts. 

Your explanation is clear though. 

Thx, Miz


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