A piston drive assembly, including: a housing enclosing each of: a plurality of cylinders, each cylinder having an axis substantially parallel to the axis of the other cylinders; a plurality of pistons, one piston in each cylinder; a wobble plate connected to each of the plurality of pistons; a swashplate rotatably fixed to a drive shaft such that the drive shaft can rotate the swash plate or the swash plate can rotate the drive shaft, wherein the drive shaft extends through the entire length of the housing.