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Unread 10-11-2011, 17:07
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Re: Brake vs. Coast in the Drive

Quote:
Originally Posted by EricVanWyk View Post
I don't think it is necessarily a very bad thing, but it will cause some extra battery drain. One motor will be converting the other motors mechanical energy back into electrical energy.

Given the same duty cycle, brake mode and coast mode have different response curves. It is almost like you have them mis-geared together, with one having a higher ratio than the other. Or from another point of view, it is as if you are sending different throttle commands to motors that should be driven in unison.

I have to admit that boiling the math into a forum post is a bit beyond me; There are just too many circular dependencies! What it comes down to is that a coasting motor is floating for the part of the cycle that the braking motor is shorted. It is a similar effect as using a victor and a jaguar in parallel. They provides different effective drive voltages, and this results in a fight.
I did not realize that the speed controllers brake during every PWM cycle. I had assumed that they were only shorted when the signal was at/near the "neutral" pulse width.