Build Your Own Combat Robot

Chapter 8: Remotely Controlling Your Robot 169
The other advantage of PCM radios is that they grant you the ability to customize
the control interface. Because the signals are being digitized and encoded, it is easy
for the internal computer to perform custom mixing and scaling operations on the
data before transmitting it. Known as computer radios, these units have a liquid
crystal display (LCD) screen and a miniature keypad that can be used to write custom
programs for the controller interface. Typical settings include custom gain,
and center and end points on individual controls, as well as custom mixing of two
channels to generate left and right motor drive signals from a single joystick for
driving skid-steer robots.
When choosing a radio system, you may want to consider more than just the robot
you are currently using. While the rest of a robot may be scrapped, recycled, or
even completely destroyed in combat, your R/C system can be reused on robot after
robot. If you intend to participate in robotic combat competition year after year, it
makes sense to spend a little more on your R/C system at the start, rather than buying
a low-end radio and then having to pay more on a better radio down the road.
If you buy a PCM radio with at least seven channels, you will probably never have
to buy another radio for as long as you are competing. Most veteran combat robot
builders will recommend that if you use a traditional R/C system, you should use a
PCM radio with your robot. It will save you a lot of headaches when testing and
competing with your robot, since you will know that erratic motion is not due to
radio interference.
Tables 8-1 and 8-2 contain short lists of the available R/C systems. The column
under “Band, MHz” lists the frequency bands these systems can use. If two different
Manufacturer Model Channels Band, MHz PCM Available
Futaba 3PDF 3 27 and 75 No
3PJS 3 27 and 75 Yes
Airtronics CX2P 2 27 and 75 No
M8 3 27 and 75 No
Hitec Lynx 2 2 27 and 75 No
Lynx 3 3 27 and 75 No
TABLE 8-1 Pistol-Grip–Style Radio Control Systems ■