US Patent 8136514 Device for propelling a projectile

An archery or similar projectile launching device having a spring assembly to energize the device and a release mechanism to transmit energy stored within a torsion or alternative spring to the bowstring, so as to accelerate an arrow nocked to the bowstring once the trigger is released. In one embodiment, conjoined cranks wind a torsion spring within a spring motor affixed along the riser of the bow while the bowstring and arrow are concurrently brought into the discharge position. A mechanical advantage may be achieved with the cranking mechanism to reduce the effort exerted by the archer and thereby increase accuracy, velocity and ease of use.