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Originally Posted by lupjohn
I noted in your PPT workup that you mention back EMF. I have tried to get this concept across to several teams that this problem means that one motor is actually reducing the power available to drive the robot since that translates to a "braking" effect on the power train. I have not measured this effect but what does it do to the drivers on the motor controllers. These devices are current sources and not current sinks unless I have my theory wrong. Anyway thanks for the great work up. I just need more time to translate this for my students. LRU
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I don't quite follow what you meant in your original post but I'll try to respond as best I can. I'm not quite sure what you mean by the one motor reducing power available to the power train.
The back EMF generated by a motor is caused by the spinning magnet field of the motor. The back EMF is proporitional to the rotational velocity of the motor. The higher the back EMF, the less current that the motor is drawing.
I think what you're worried about for the speed controllers is driving a current back into them. The speed controllers which are based around an H-bridge basically just use transistor switches. They do not use transistors as current sources. When a current is driven back through them, they will pass it much like they'd pass a current the other direction (particularly since they're based on FETs). This just means that the current is going back to the battery. There's no problem with sourcing current into the speed controllers.
Matt