Open and closed loop refers to whether a feedback mechanism is included in the controller-motor assembly for the controller to verify that the motor is actually moving as expected by the command. In open loop, there is no feedback, so a command will vary the controller's output to the motors, but the actual speed will depend on the friction, slope, load and the presence of obstacles. In speed closed loop, the controller will measure the actual motor speed and adjust the command accordingly. In position closed loop, the controller will measure the angular position of the motor's axle and move the motor until the desired position is reached. The AX2550 supports all three modes described here.