Percussive massage device with selectable stroke length

A battery-powered percussive massage device comprising:

• an enclosure having a cylindrical bore, the cylindrical bore extending along a longitudinal axis;
• a piston located within the cylindrical bore, the piston having a first end and a second end, the piston constrained to move only along the longitudinal axis of the cylindrical bore;
• a motor positioned within the enclosure, the motor having a rotatable shaft, the shaft having a central axis, the central axis of the shaft perpendicular to the longitudinal axis of the cylindrical bore;
• a crank coupled to the shaft, the crank including a pivot, the pivot offset from the central axis of the shaft;
• a gear case coupled to the motor, the gear case comprising:
• a ring gear having at least a first angular position and a second angular position with respect to the central axis of the shaft, the ring gear having internal gear teeth;
• a pinion gear having external gear teeth engaged with the internal gear teeth of the ring gear, the pinion gear having a central bore that receives the pivot of the crank, the pinion gear having a pinion gear pivot offset from the central bore;
• and
• an actuator coupled to the ring gear, the actuator operable to rotate the ring gear from the first angular position to the second angular position;
• a reciprocation linkage having a first end and a second end, the first end of the reciprocation linkage coupled to the pivot of the pinion gear pivot, the second end of the reciprocation linkage coupled to the first end of the piston;
• and
• an applicator head having a first end and a second end, the first end of the applicator head coupled to the second end of the piston, the second end of the applicator head exposed outside the cylindrical bore, the applicator head having a stroke length determined by the angular position of the ring gear.