Abstract: A primary scotch yoke and a secondary scotch yoke are coupled in opposing arrangement and rigidly attached to a linearly reciprocating element. Each scotch yoke includes a rotary actuator with a cam follower and a yoke attached to the reciprocating element. Each yoke has a cam with an open gap through which the follower may be disengaged from the cam and stopped to an idle position. The follower of the secondary scotch yoke is kept idle in a position similarly disengaged from its cam. A controller detects a failure in the primary scotch yoke, disengages the cam follower of the primary yoke from its cam, and energizes the secondary scotch yoke, thereby causing its cam follower to engage its yoke and continue to provide uninterrupted motion to the reciprocating element, in particular the portable pneumatic pump driving an artificial heart.