CHAPTER 18 ■ ADDING GEARHEAD MOTORSThe Solarbotics motors aren’t the same shape and size as the Hsiang Neng motors. Therefore, you’ll
need to use your own creativity to attach them to your robot.
The downsides to the GM2 motors are that they consume slightly more power, are moderately louder,
are more electrically noisy, and theoretically would have a shorter lifespan if you ran the robot continuously
every day. For this application, those tradeoffs are worth it for the significant reduction in cost.
Inspecting the Gearhead Motor
Looking inside the Hsiang Neng motor, the pieces are found to be as expected for a low-price motor.
Referring to Figure 18-3, the parts are (left to right): stator with permanent magnet, three-shoe iron-core
rotor, cap with pleasantly thick brushes, spur gearbox, metal gearbox cover, and joining screws.
It’s a shame the gearbox cover isn’t plastic. This motor doesn’t produce a lot of torque, so metal
probably isn’t necessary. Plastic would save a lot of mass and quicken responsiveness. The gearbox is 73%
efficient, which is reasonable.
Although you can open the gearhead portion easily, don’t try disassembling the motor portion. I had
to permanently grind off several metal pieces to open the motor portion for the photograph featured in this
book. Therefore, the brushes obviously aren’t meant to be user-serviceable. When the motor wears out, toss it.
The motor is 3.8 cm long with a diameter of 2.6 cm. That’s nice and small. The output shaft is offset.
That means the shaft doesn’t come out of the cap’s center. An offset shaft is actually beneficial for mounting
wheels closer to the ground, as you can rotate the motor into a position with the shaft nearest the bottom of
the robot. The shaft is 1.5 cm is length, providing lots of room for attaching wheels.
Current Usage of the Gearhead Motor
As part of a motor’s inspection, you should measure motor current. By connecting a multimeter between a
9 V battery and the motor (see Figure 18-4), you can determine the actual current used by the motor without
a load and the amount of current used when stalled. Make sure the multimeter is in the highest current
mode, so that a fuse isn’t blown in the multimeter during peak current usage.
Figure 18-3. Exploded view of a Hsiang Neng gearhead motor