Gearbox for 550-size motors

youmagine

I designed this compact gearbox specifically for use in RC boats where a brushless motor is needed but needs to be slowed down, as my propellers' efficient speeds are much lower than my motors'. The gearbox will work with most small motors that have a 25mm bolt spacing. A set of gears with the same pitch must be purchased, one small for the motor shaft and one large for the propeller shaft. I use 48P because many of my friends prefer this pitch, but almost any other pitch can be used. The basic assembly is straightforward; ensure the output shaft stuffing tube hole fits your chosen stuffing tube or bearing by fettling it to size. Two files are provided, one for a 1/4" (6.4mm) stuffing tube and one for a 5/16" (8mm) one. Gently slide the stuffing tube into the fettled hole, securing it with CA glue or a slurry of ABS scrap and acetone if desired. The stuffing tube end should not protrude more than a couple of mm into the gearbox. Insert the driveshaft into the stuffing tube and add a brass collar followed by your large gear. Mark the shaft for flats before pulling it out to drill them in, as this is crucial for smooth operation under load. Reinsert the shaft and attach the collar and large gear. Attach the small gear to your motor's shaft, adding a flat if necessary, and fit two M3x8mm screws into the motor's mounting holes but do not tighten them yet. If larger screws are used, you may need to adjust the ways slightly. Align the screws with the vertical channels and slide the motor down until the gears almost mesh. Place a piece of printer paper between the gears and move the motor down until good contact is made. Tighten the screws and test the gearbox by spinning the motor by hand; the paper will come out, ensuring proper gear alignment. The point of this step is to prevent excessive wear and noise.