A self-propelled sulky for attachment to existing non-self-propelled equipment,thereby enabling the equipment to be converted into a self-propelled equipment with a modular propulsion system. The sulky includes a frame, a motor mounted to the frame, wheels rotatably mounted to the frame, a device for transferring power from the motor to at least one of the wheels, a device for controlling the power transferring device and thereby the ground speed and direction of the sulky, a device for connecting the sulky to a rearward end of the non-self-propelled equipment to enable pushing of the non-self-propelled equipment with the sulky, and a support structure on the frame for supporting an operator in a standing position. The support structure is located and configured on the frame to enable the operator to selectively step onto the support structure to ride the sulky and step off the support structure to walk behind the sulky.