Cogging
 

just wondering what is cogging and why does it happen at low speeds?

It's simply a stutter that happends when the ESC can't tell where the rotor is. Thats why, with sensored, there isn't cogging. Obviously because of the sensor...

so sensored systems arent as fast as not sensored?

Yes, sensored systems are typically alot slower than sensorless.

It should be noted that some non-sensored ESCs are better than others when it comes to cogging. The only time cogging is an issue is if the motor is stalled or close to it. Really, this only happens is at very low speed, like about 1mph, or if you are trying to take off VERY slowly.

To clarify. sensored esc's need to "find" the location of the motor. A sensored esc remembers where the motor stops at sort of speak so it senses where it is and does not have to "find" it.