The 4 Quadrant Dynamometer Motor is a permanent magnet DC motor that can be coupled to the 4 Quadrant Power Supply and Dynamometer Controller. As an add-on to the 4 Quadrant Power Supply and Dynamometer Controller, it provides access to all mechanical features of this device. The 4 Quadrant Dynamometer Motor can be coupled face to face or side by side with a motor/generator. A guard protects the user from unintended start of the motor, without the guard the motor does not start.