An auxiliary, removable, modular power drive unit has a pivot point that can be attached to any bicycle or vehicle by way of a quick release clamp system. The power for the drive system may be derived from an internal combustion engine or electric motor. The power developed by the engine or motor is delivered to the rear wheel of a bicycle by a friction drive wheel that presses directly onto the tire of the bicycle. The power unit may utilize a clamp joined to an integrated fuel cell by a pivot point, causing the fuel cell to act as a swing arm and a motor mount. This enables the fuel cell to move up and down to compensate for different tire sizes, variations in road conditions, or movement of a suspension system of the bicycle due to imperfections in terrain.