Build Your Own Combat Robot

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H E control system you use for your robot must fulfill several requirements.
It should be reliable and reasonably immune to interference. It should have
at least enough range to communicate to your robot in the far corner of the
arena—and preferably much more to be safe. The receiving system should be
small and able to withstand a lot of vibration and shock. It should be able to command
multiple systems on your robot simultaneously. It should be capable of varied
degrees of control so that your robot does not have to drive at full speed all the
time. And, finally, it should be available as a reasonably inexpensive off-the-shelf,
solution so that you do not have to spend more time engineering the radio control
(R/C) gear than the rest of the robot.
In the early days of robotic competition, robot builders attempted to use everything
from garage-door–opener radios modified for multiple command channels
to radio gear sending commands encoded in audio tones, infrared remote controls,
tether-line controls, and networked computers running over wireless modem
links. The most effective technology turned out to be hobby radio control (R/C)
gear, the relatively low cost, off-the-shelf R/Cs intended for use in model cars and
planes. Today, nearly every robot in major competitions uses some form of commercial
hobby R/C, and competitions have based their R/C rules around this standard
control system.
Traditional R/C Controls
All R/C systems, whether AM or FM radio systems or high-end computerized transmitter
and receiver sets (which are all discussed later in this chapter), use essentially
the same electrical signals to transmit control information from the radio receiver to
the various remotely controlled servos and electronic motor controllers. See Figure
8-1. A three-wire cable runs from the radio receiver to each speed controller and
servo in the robot. One wire provides about 5 volts of power to run the servos. A
second wire is a ground reference and power return line. The third line carries the
encoded 1- to 2-millisecond pulse train signal that commands the motion.
Movement commands are encoded with a pulse position modulation system
(some people call this “pulse-width modulation”; Chapter 7 explains the difference