As far as it's my understanding, cogging in a BL motor happens when the ESC loses track of the rotor. When there's no load on the motor, as each pair of armature stacks in the can fires the rotor follows and life's good. But if enough of a load is placed on the rotor (i.e., hard acceleration under the weight of the car) that it slows down, there's a chance that the stack's firing can get far enough ahead of the rotor that the easiest path for the rotor to take is backwards. Of course, this happens so fast all you get is this strange buzz and the motor tripping flat on its face instead of running.
That's the big advantage to sensored systems, the sensor tells the ESC where the rotor is so if it starts to fall behind, the ESC can automatically slow down the firing sequence & let the rotor catch up. Sensorless systems, the ESC just keeps sending power 'round and 'round the can regardless of the rotor's position.
Faster Than Factory
On The EDGE Racing, est. 2001 - Home of the 524, the Silverado Slammer E-MAX6X6, and the Sand Dollar prerunner
Mike Budzien | facebook.com/OTE.TheMissile | RIVCO Products | The RC Corral | iRacing.com