Abstract: A drive mechanism for transmitting bidirectional drive to two or more rotary actuator spindles, having a disc driven by an input shaft. Each spindle carries a spur gear which engages alternately with inner and outer tooth sections formed at different positions around a respective track in the disc. To accommodate several gears, tracks are provided at two different radii and three tracks of different width are nested together. The spur gears and tooth sections can be replaced by cams and tracks or shaped levers and pegs. The disc can be moulded and enables standard valves to be used in a complex operational sequence.