Mixing Jaguars and Victors

[Jared Russell]

Originally Posted by Ether

If you use 2 Jags with CAN, you can balance the load by balancing the current. You could close the loop on speed for motor#1 and close the loop on current for motor#2 (to make motor#2 match motor#1 current). With some filters and careful tuning I'm guessing this could be made to work well.



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You have to be careful with an arrangement like this. If motor #2 is a little bit less efficient than motor #1 (and no two brushed DC motors are exactly the same), you can get into a positive feedback situation. Motor #2 could draw an equal amount of current to motor #1 but at a lower speed, which drags on motor #1, which forces #1 to draw more current to maintain its speed, which causes motor #2 to draw more current, etc. That said, there are some things you could do to help limit this behavior.

Ideally, you would match the speeds of the motors and let the loads balance themselves according to output torque at that operating point on both motors' curves. However, that is easier said than done (due to difficulties in measuring each motors' free speed at a given voltage, for example).

If permitted, one way to do nifty load balancing is to put both motors in a series circuit - when one motor gets overloaded, its back EMF decreases and more electrical power becomes available to the other motor (an electronic differential).