A gang reel mower comprises a frame that carries a plurality of variable speed, electrically powered reel cutting units. Cutting units having different reel diameters may be installed on the frame. Upon system power up, a mower controller on the frame automatically acquires information identifying the reel size of the cutting units then installed on the frame and uses the acquired reel size information to properly set the speed of the electric motors driving the cutting units to a desired value, such as that needed to maintain a desired clip. Thus, the cutting units can be changed in size with the mower controller automatically recognizing the change in a plug and play manner.