Mixing Jaguars and Victors

[Ether]

Originally Posted by Jared341

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.

It doesn't work that way, Jared. The motors are connected to the same toughbox so they are always at the same speed. Motor2's control loop adjusts Motor2's PWM so that Motor2 has the same current as Motor1. If Motor2 is less efficient than Motor1, that simply means that Motor2 is providing slightly less torque than Motor1 (at the same speed and current). It does not mean that Motor2 "drags on" Motor1; it is in fact assisting Motor1. With proper tuning and filtering the loops can be made stable. If you have access to Simulink/Matlab or some other dynamic modeling software, try it and see for yourself.

Originally Posted by Jared341

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).

The two motors in question are connected to the same toughbox, so they are always at the same speed. If connected in series, they will both have the same current. So the scenario "one motor gets overloaded and its back EMF decreases and more electrical power becomes available to the other motor" does not occur.

Connecting two 12-volt motors in series, and then powering them with a 12 volt supply reduces the efficiency of the motors.


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