[BrianG]

At slow rpms, the ESC has a hard time reading the rotor position so it turns off and on giving you the cogging effect. Some ESCs are better at reducing this issue than others though.

You can try with the Captain suggested (good idea!), but don't set your Tx to accelerate too high or you'll damage the drivetrain or just spin the wheels from the instant torque. You just need to adjust it to the point where it doesn't cog at minimum throttle.

Gearing down a little might help too, although you'll lose a little high end speed.