What is "friction drive"

A '''friction drive ''' or friction engine is a type of transmission that, instead of a chain and sprockets, uses 2 wheels in the transmission to transfer power to the driving wheels. This kind of transmission is often used on scooters, mainly go-peds, in place of a chain. The problem with this type of drive system is that they are not very efficient. Since the output wheel (leather covered wheel) has width, the area of contact is spread across various radii on the primary disc. Because the tangential velocity varies as radius varies, the system must overcome velocity differentials across the surface. The compromise is slippage of the leather to metal contact area which creates friction, which in turn converts much of the energy transfer of this system into heat. Heat generation also requires a cooling system to keep the transmission working effectively.