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272    MOUNTING MOTORS AND WHEELS



           G       If you don’t need or want to permanently attach the servos, use less  hot- melt glue or use a dab
                   of ordinary white household glue. The bond is weaker, allowing you to more easily pry the
                   servo off and reuse it for something else.

                   Mounting Drivetrain Components to Shafts


                   Drivetrain components are things like wheels, gears, sprockets, and other stuff that attach to
                   your robot’s motors. Unless the parts are specifically designed for one another, connecting the
                   shaft of the motor to drivetrain components is one of the more difficult tasks in building a
                   robot.
                     Still, it’s not impossible, and robotics  wouldn’t be as much fun without the occasional chal-
                   lenge. What follows are the most common methods used to connect a motor shaft to a wheel,
                   gear, or other drivetrain component.

                   PRESSFITTING

                   For smaller drivechains, it’s not uncommon to use pressfit parts, where the shaft fits very
                   tightly into the wheel or other component. Usually these are manufactured to fit this way, and
                   the parts are assembled with  heavy- duty hydraulic presses. You probably don’t have such a
                   press in your garage; you’ll need to instead use a small hammer, a bit of spit for lubrication,
                   and a few  well- chosen curse words to knock the shaft into position.


                   SETSCREWS
                   A setscrew physically clamps the wheel or other part directly to the shaft. Setscrews are con-
                   venient and elegant, but they’re not common in amateur robotics because drivetrain parts that
                   use them tend to be more expensive. You’re more likely to encounter setscrews when using
                   small metal R/C parts like gears or locking collars (see the section that follows, on making
                   your own shaft couplers).
                     Setscrews usually have hex socket heads, so you need a hex wrench in order to remove or
                   tighten the screw. When purchasing R/C parts that use setscrews, the wrench is usually
                   included.


                   PROPRIETARY INTERLOCK
                   Some motors and wheels (and other drivechain components) are made to go together. Good
                   examples are the various DC gearbox motors and wheels from Tamiya. Many of the motors
                   and wheels are designed for interchangeability. The wheels fit onto the motor shaft using nuts,
                   pins, or other means.


                      SERVO HORNS
                      The output shaft of R/C servo motors has about two dozen tiny splined teeth carved
                      around its circumference. These splines, and a metal screw that’s inserted into the bore
                      of the shaft, are made to secure various styles and sizes of servo horns. Most servos come
                      with at least one of these  horns— typically a round or small,  X- shaped jobbie.
                        Servo horns are made of plastic or metal (when of metal, it’s usually aluminum). You








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