Originally Posted by kapteinkuk
In my opinion I think the reason for the input filter is to avoid large peak current. I previously thought that the filter was to avoid rapid acceleration of the motor causing loss of synchronization.
I still think it's actually for both reasons. There are some motors where the coil demagnetization can take so long (with a large current spike) that it can fool the zero-crossing detection and lose synchronization. I see this with some hard drive motors, the MT-3506, and the 24g hextronik motors, for example. It seems it might be necessary to do something special in these cases, but most motors seem to be fine with jumps from low to high throttle. The problem comes up more often at higher voltages, too.