relation with respective intermediate gears 56 and 58 a handle 66 is mounted on the outer end of manually operable input shaft 42 shown at 68 and 70 are stops for adjusting the angle of swing or the inclination of lever member 48 which in turn adjusts the depth or extent of engagement between planetary gears 50 52 and intermediate gears 56 58 respectively fig5 shows part of an electric circuit incorporated in the device described above electromagnetic clutches 26 and 34 are each connected in series with respective diodes and microswitches ms1 and ms2 across a dc power source 76 diodes 72 and 74 are connected on the positive sides thereof to the positive sides of electromagnetic clutches 26 and 34 respectively and connected on the negative sides thereof to one terminal of a resistor r1 the other terminal of which is connected through a resistor r2 to the negative ground the junction of resistors r1 and r2 is connected to the base of a transistor tr whose emitter is grounded and collected connected to the positive by a resistor reference mark p designates a known operating means for rendering motor 2 inoperative when the collector potential of transistor tr is lowered and is coupled to the transistor collector in operation when the handle 66 is turned to manually rotate input shaft 42 in the direction.