Some design details were carried over from a steam-powered prototype made by the Hildebrand brothers in 1889, including the water tank shaped to form the rear mudguard and the connecting rods of the engine driving the rear wheel directly. The water tank was repurposed to supply water to the cooling jackets surrounding the cylinders. The steam-powered prototype had a double-acting cylinder, applying power to the piston in both directions. With no double action available in the petrol engine, and no flywheel effect apart from the movement of the rear wheel, the return impulse for the piston was provided by heavy rubber bands.