Irish company Nordigo has developed a unique propulsion system that can be fitted to manual wheelchairs. According to Nordigo, their patented "lever propulsion system" allows the user a 30% increase in speed and a 30% reduction in energy use when compared to a traditional pushing motion. The system allows traditional self propulsion to be done so that use of their system is only done when the user wishes to use it... all without having to disengage anything. The system works by a simple rowing motion which provides a nice cardiovascular workout for the user while also keeping the user's hand clear from the dirty wheels. Steering and braking are done by the disc brakes that are fitted to each quick-release wheel. Pretty clever for a system that appears to be lighter than traditional powered-assist motors! Check out their site for more details!