Abstract: A control unit for a chain shifter uses a reversible electric selector motor to position a cam selector within a pawl guide housing so that a traveling pawl will be directed as necessary for chain shifting. The motor rotates a low mass eccentric, the eccentric providing sufficient angular force to actuate a spring-loaded latch key, the key positioning the cam selector. As the eccentric accelerates, it gains sufficient force until it impacts and moves one of a pair of latch arms holding the key in a central position, allowing the latch key to rotate.