A flexible shaft, sometimes called a bowden cable, transmits rotary motion much like a solid shaft, but it can be routed over, under, and around obstacles that would make using a solid shaft impractical. A “Flexible Shaft Assembly” consists of a rotating shaft (sometimes called a core) with end fittings for attachment to the driving and driven mating parts. A protective outer casing is used when necessary. This casing has its own fittings, called ferrules, which keep it stationary during use.
A flexible shaft is a highly effective means of transmitting rotary motion and is more efficient than universal joints, gears, sprockets and chains, or belts and pulleys. It is typically lower in cost than these other devices and offers the added benefit of compensating for misalignments in a system that can greatly reduce cost and assembly time.
One of the main applications during the twentieth century was as automotive speedometer cables (speedo cables) and as tachometer cables (tacho cables). Today automotive applications centre on seat adjusters for electric powered seating. Aerospace uses include Thrust Reverser synchronisation and drive actuation, flap and slat actuator drives, rudder control and numerous remote control or manual override fail safe systems. Defence applications such as driving optical protective covers and back up systems so that operations can continue in the event of primary system failures. Other uses range from photocopier sorting mechanisms, home cinema projection systems to nuclear submarine valve control, with food preparation equipment and medical in between.