Build Your Own Combat Robot

284 Build Your Own Combat Robot
FIGURE 13-5
Cutting off the
feedback shaft
inside an
R/C server.
Building a Mini Sumo
The main components of a mini sumo are a body frame, motors, wheels,
microcontroller, sensors, and batteries. For this project, we’ll use two modified
R/C servos for the motors for the mini sumo, as we just described. Figure 13-6
shows a drawing of a set of wheels, a body base, and a front scoop. Only use the
servos that are listed in the table within Figure 13-6. Other servos will be too large.
These parts can be made out of pretty much any material. Expanded foam PVC is
an excellent material for bots. One of the common trade names for this material is
Sintra. It is strong and very light. It can be easily cut with a coping saw and carved
with a shape knife. This material can even be tapped with #4-40 threads. When using
screws with this material, use only nylon screws, and only finger tighten them.
You can also glue it with most superglues (cyanoacrylate glues). It is best to use
thin aluminum for the front scoop.
The sumo wheels should be made out of a harder material such as plexiglass or
aluminum. The hole spacing on the wheel should be selected based on the type of
servo that you use, and it should align with existing holes in the servo horn. The
existing holes should be redrilled to allow for either tapping a #4-40 thread or a
0.11in diameter clearance hole for a #4-40 screw.
Mini Sumo Body Assembly
Glue the two servo mounts to the base plate, as shown in Figure 13-7. Make sure
that the mount with the 0.50-inch diameter hole is facing the rear (the hole is for
routing the servo control wires). Feed the servo wires through the hole and screw
the servos to the servo mounts as shown. It will be a tight fit when you’re inserting