An electropneumatic hammer is often called a rotary hammer, because it has an electric motor, which rotates a crank. The hammer has two pistons – a drive piston and a free flight piston. The crank moves the drive piston back and forth in the same cylinder as the flight piston. The drive piston never touches the flight piston. Instead the drive piston compresses air in the cylinder, which then propels the flight piston against a striker, which contacts the drill bit.