Abstract: An encoder assembly is disclosed which comprises a drum-like rotor having an outer circumference and a central bore with at least one slot, and a plurality of encoder elements arrayed around the outer circumference of the drum-like rotor. The assembly further comprises a shaft having a diameter sized to fit into the central bore, and having a flattened key which is configured to fit into the at least one slot. The rotor and shaft fit into a housing having an inner section sized to receive the drum-like rotor and encoder elements. The inner section has an opening along one side such that the inner section incompletely encloses the circumference of the rotor. There is also at least one spring contact locatable within the housing such that it can make contact with the encoder elements through the opening in the inner section of the housing.