# Question about 2 motor 1 controler voltage



## Bowser330 (Jun 15, 2008)

Jason Lattimer said:


> I found some hub motors for a small scooterish car I want to build, 2 13" hub motors at 6kw each. They are rated to reach 130kmh at 72 volts. If I use Two of these, do I still use a 72 volt controller and split the current or a 144 volt controller and split the voltage?


those sound like similar motors that the poulsen hybrid system is using...7kW pancake style...


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## Tesseract (Sep 27, 2008)

It's not impossible to synchronize two motors - it's done all the time industrially - but I am not aware of any off-the-shelf controllers for EV use that have this capability. Keep in mind that even a tiny difference in RPM between the two motors, or of the inflation pressure of the tires, or drag from the brake rotors, etc..., will result in the car pulling to one side - maybe to such an extent that it is not controllable.

Industrially this is done most often with conveyor belts (constant speed) and calendar rolls (constant torque). One motor controller is setup as the master and the rest are slaved to it. Frequently, the slaves will use the opposite control scheme as the master, so in a conveyor belt system the master motor will be set for a constant RPM to move the belt at a specific speed, while the slaves will be set for constant torque mode to, in essence, boost the torque capability of the master motor.

In a dual wheel drive setup in an EV you would probably want to use a master-slave setup as well, but I'm not sure what control scheme would be best. I do know that it is not smart to rigidly couple two separately controlled constant-speed motors together - it's the mechanical equivalent to connecting to separate constant voltage power supplies in parallel (sparks fly; hilarity and magic smoke ensues). You'd probably want the master to have its primary feedback loop be constant torque and its secondary loop be constant speed. The slave controller could then be setup similarly, but with a much looser RPM control (to allow better tracking of the master when the vehicle turns).

Make no mistake, though, this is a complicated problem to solve, practically speaking.


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## MalcolmB (Jun 10, 2008)

Jason
Are the hub motors brushless or brushed?
If they're brushed then it's relatively simple and you can use a single controller, as described here: http://www.4qd.co.uk/faq/bmnc2.html#diff
The cheapest approach with brushed motors would be to wire the motors in parallel so that they can be run from a 72V controller rated for twice the current limit of each motor.

If the motors are brushless then it's more complicated, and I'll leave that to someone more experienced with these motors


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## Jason Lattimer (Dec 27, 2008)

The hub motors in question are on the Kelly Controller website. I sent them an email for more information but it does not state one way or the other. I will update as soon as info becomes available.


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## MalcolmB (Jun 10, 2008)

Looking at the photos on the Kelly site, they look like brushless motors, with three phase wires plus hall sensor wires...


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## Jason Lattimer (Dec 27, 2008)

Just heard back from Kelly. The 13" 6kw hub motors are brushless. They are 260mm mounting, 300amps max and 120 continuous. The tires they can use is 130/60 13.

I am hoping it can move a trike along pretty good at 1000 loaded.


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