Abstract: A traction wheel motion sensor for endless conveyors which is self-cleaning of foreign matter that may enter the traction wheel housing and is spring biased toward the associated conveyor. A traction wheel housing located adjacent a moving conveyor engages the conveyor for sensing the rate of linear displacement thereof, and the wheel drives motion sensing apparatus through a belt. The housing includes a bottom surface which is obliquely oriented to the horizontal wherein foreign matter entering the housing is automatically discharged therefrom and further, the traction wheel is mounted upon apparatus biased toward the conveyor by spring means wherein the traction wheel maintains an operative driven relationship with the conveyor during conveyor operation.