Build Your Own Combat Robot

174 Build Your Own Combat Robot
though, and you should never “point” the transmitter’s antenna directly at your
robot. The antenna on your robot and your hand-held transmitter should always
point straight up for optimum signal transmission and receiving.
tip You should develop a habit of holding the transmitter vertically in tests and trial runs so
the strain of a hot battle won’t have you accidentally pointing the transmitter at your machine
or, worse yet, shorting out the antenna on the metal rail or supports of the arena.
Antenna Placement
You may have seen some combat robots zipping about the floor in competition
with what appears to be an antenna protruding out the top. It probably was an antenna—perhaps
with a little flag attached so the operator can see the orientation
of his machine for control purposes. This certainly is the ideal placement electrically,
but it’s a pretty bad thing when a flailing robot severs the antenna with a
weapon. Sometimes you cannot find an adequate vertical location for the antenna,
especially in a small, flat machine, so you are forced to place the antenna in
a horizontal position. Fret not, though, because most model airplanes also have to
place the antenna in this orientation. If this is the case with your machine, you
should mount a nonconductive (nonmetal) strip of material on the robot’s shell,
under which you can place the antenna. Do not attempt to cut the antenna wire a
bit (or add more wire) to make it fit in an area or try to improve the signal; the wire
is cut at the factory to accommodate the appropriate frequency.
A rookie bot builder might simply pile the antenna wire loose inside the robot,
or cut it short and tape part of it to the outside of the robot’s shell. While the radio
reception will be far from ideal, at a typical combat range of less than 50 feet you
might get away with it. A better setup, though, is to have a flag or post extending
out the top of the robot, and run the antenna up it to get it away from the main
body of the robot and get better exposure to the radio signals. Even this is not an
ideal antenna setup, but it will work for most bots.
The ideal antenna setup for a combat robot is to use a base-loaded antenna.
Base-loaded antennas get away with having a short length of actual antenna by embedding
a tuned resonance circuit in the base of the antenna module. Base-loaded
antennas have to be purchased for a specific frequency band, but they save a lot of
room over standard antennas: a base-loaded, 72- or 75-MHz band antenna can be
as short as 6.5 inches. In some cases, the base-loaded antenna can be mounted inside
the robot’s body next to the radio, although this is not recommended. As mentioned,
the antenna should be mounted vertically on the top of the robot. The base
of the antenna should be at least 1 inch away from any metal parts on the robot’s
frame, and the wire from the antenna to the radio should be as short as possible and
not run near any motor power lines. W.S. Deans sells a base-loaded antenna that is
popular with veteran robot builders and can be obtained at most hobby stores.