Page 131 - Build Your Own Combat Robot

Build Your Own Combat Robot
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Location of the Locomotion Components
Most combat robots are fairly simple, internally. They consist of a power source, a
set of batteries; motors for the wheels; a radio-controlled (R/C) system receiver;
controllers to take an R/C signal from the receiver and send power to the motors;
and a weapon system’s actuators, if they’re required in your design. Other compo-
nents appear in various robot designs, such as microcontrollers to process incom-
ing data to pulse width modulation signals, DC to DC converters, fans to cool
controllers, and so on, but these are generally smaller and can be placed in
tight-fitting places.
The location of the main drive motors is the most critical concern in the placement
of large robot subsystems. Usually, these motors are quite large. The other large
subsystems, such as batteries and controllers, can be located “wherever possible.”
Motors have to be close to the wheels, and their position and orientation is critical.
Quite often they are mounted in the lowest part of the robot. The motors must be
positioned accurately, especially if a series of gears are used to transmit the power
to the wheels, and the chains or gears need to be aligned in the same plane as the
wheel system.

Mounting the Motors
Mounting of the motors in any application is important, but combat robots pres-
ent another magnitude of problems for their motors. The motors are trying to
wrench themselves out of their mounts from extreme torque conditions. At the
same time, their mounts are being shaken so intensely that the mounting screws
can be sheared in half. So you must design your robot to handle such extremes.
Quite often, a DC motor you might find in a surplus catalog has several threaded
holes in the front face where the output shaft is located. Using these mounting holes
for screwing the motor to a plate is okay for the types of applications for which the
motor was originally designed, but using these holes may not suit an extreme situa-
tion in combat robots. To determine whether these holes are suitable, you may need
to subject the motor / mounting brackets to a shock test. The large inertial mass of
the motor may just shear off the screws as you slam the assembly into your garage
floor. Unfortunately, you might have to use an “easy-out” to remove the remaining
portion of the screws. Use your judgment here.
You’re in a far better situation if your motors have a flange mount around the
front face of the motor. If you need more strength, you can drill out the threaded
holes and make larger holes for through-hole, high-strength bolts. A flanged base
mount can be found on some older motors. Flange-based motors offer a higher
strength method of mounting compared with the threaded face hole method.
Another method to use for mounting motors is to secure the face with the exist-
ing mounting holes to a motor bracket you’ve fabricated, and then secure the back
part of the motor with several high-strength clamps and a machined block in
which to rest the motor. Use high-strength hose clamps that have a machined
screw—not the “pot metal” types found in some hose clamps. This back clamping
will prevent the heavy motor from moving. See Figure 6-4.