Quote:
Originally Posted by Ether
Is that because the back EMF of the motor is trying to push current in the same direction as the FETs ?
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Yup. Your back EMF field doesn't disappear just because you want to change directions. When you reverse, it's suddenly pushing those electrons in the same direction as your applied voltage. If you're actually driving at full speed, you might be (very) briefly driving the motor at effectively more than 12V. The massive current draw is obviously going to drop your battery voltage massively, which will reduce the current draw until you hit some sort of equilibrium.
Even 1/8 a second ramp is going to make the whole process much, much nicer on the motors and battery. You'll start developing significant braking torque on your way down to 0V, which will drop your back EMF enough that you're not TOO likely to reset your entire robot on your way up to -12V.