A motor unit comprises a housing for containing a motor, a motor shaft for receiving a motor provided driving force, a torque sensor mechanism for detecting torque, and a controller for controlling power to the motor in response to a detected amount of torque. An actuator couples the torque sensor to a sensor of the controller. The actuator is configured to move relative to the controller sensor thereby causing the sensor to produce a signal indicative of the detected level of torque. The controller is contained within the housing of the motor. The motor unit may also have an auxiliary shaft for receiving an externally provided driving force with a first torque transmission path for transferring the externally provided driving force to a drive mechanism and a second torque transmission path for transferring the motor provided driving force to said drive mechanism. A first one way drive means is provided in the first torque transmission path between the auxiliary shaft and the drive mechanism such that when the drive mechanism is being driven by the motor provided driving force through the second torque transmission path, the auxiliary shaft is able to freewheel. The motor unit can drive any apparatus, but may be used in a pedal driven apparatus such as a bicycle where an externally provided driving force is provided by manually operable pedals of said apparatus which are fixed for rotation with the auxiliary shaft. In this case, the auxiliary shaft comprises a pedal spindle of the bicycle and the drive mechanism comprises a sprocket or belt drive.