The crankshaft is a shaft that has u-shaped cranks that take the reciprocal motion (opposite motion) of the pistons, and converts it to rotary motion that turns the wheels. The crankshaft is a part of the engine that takes the energy of the pistons, and sends it to the drive system.
The Unmuffled Auto News 
I could use a crankshaft in my house in the mornings. Cynthia