SPEED-REDUCING TRANSMISSION HAVING A BALL DRIVEN IN AN ORBITAL PATH ABOUT-THE ARMATURE SHAFT OR A DRIVE MOTOR AT A PREDETERMINED SPEED RATIO. THE ORBITING BALL ACTUATES STRAINWAVE-TYPE GEARING THAT FURTHER MULTIPLES THE SPEED RATIO PROVIDED BY THE BALL TO DRIVE AN OUTPUT. THIS TRANSMISSION MAY HAVE ELASTOMERIC PARTS WHICH PROVIDE FOR AUTOMATIC ADJUSTMENT FOR WEAR OF THE TRANSMISSION COMPONENTS AND WHICH REDUCE SLIPPAGE BETWEEN THESE PARTS. A PLURALITY OF THESE TRANSMISSIONS CAN BE READILY COUPLED IN SERIES TO PROVIDE A MULTISTAGE TRANSMISSION FOR PRODUCING LARGE REDUCTION RATIOS.

THERE IS A DIFFERENTIAL REDUCTION DRIVE POSSIBLE BY HAVING STRAIN-WAVE GEARING DRIVE A TRANSMISSION HOUSING RELATIVE TO A SUPPORT IN ONE DIRECTION AT A FIRST SPEED RATIO AND BY HAVING THE OUTPUT SHAFT ROTATABLY DRIVEN BY STRAIN-WAVE GEARING AT A SECOND SPEED RATIO RELATIVE TO THE CASE AND IN AN OPPOSITE DIRECTION TO PRODUCE A DIFFERENTIAL REDUCTION DRIVE. ONE OF THE EMBODIMENTS PROVIDES A MECHANISM FOR UNLOCKING THE DRIVE SO THAT THE OUTPUT MAY FREEWHEEL IN EITHER DIRECTION PERMITTING OVERRIDE MANUAL OPERATION.