Build Your Own Combat Robot

Chapter 8: Remotely Controlling Your Robot 163
not recommended. The antenna on the radio transmitter must have an attached
flag indicating the frequency with which they are transmitting. The flag colors for
channels 1 through 6 are brown, red, orange, yellow, green, and blue, respectively.
50-MHz Radio Frequency Band
This channel band is licensed for use by air or surface models, although it is usually
used for R/C airplanes and helicopters. The 50-MHz band is divided into 10 frequency
channels starting from 50.800 MHz and spaced every .020 MHz. Although
several high-quality radios are available for this band, use of them requires
a ham radio amateur license from the FCC. Although this band is rarely used for
competition, the individual lucky enough to use this channel will be virtually assured
of a clear channel, with no other robot builders using the same frequency.
Two flags must be flying on a 50-MHz radio transmitter antenna: a flag with a
number between 00 and 09 to identify the frequency number, along with a black
streamer to identify the 50-MHz radio frequency band.
72-MHz Radio Frequency Band
The 72-MHz radio band is reserved by the FCC for aircraft use only. In other
words, ground vehicles, including combat robots, are not allowed to use this frequency
band. A total of 50 different channels are available in the 72-MHz radio
band with frequencies ranging from 72.010 MHz to 72.990 MHz, and with each
channel number spaced every 0.020 MHz. The channel numbers range from 11 to
60. The channel identification flags include one with the channel number and a
white streamer, attached to the transmitter’s antenna.
For all modern 72-MHz radios, changing the frequency requires changing the
frequency crystals. The transmitter uses a crystal marked with “TX” and the receiver’s
crystal is marked with “RX.” When changing the crystals, they must both
have the same radio frequency. (More on crystals in the upcoming section “Radio
Frequency Crystals.”
75-MHz Radio Frequency Band
The 75-MHz radio band is reserved by the FCC for ground use only. Thirty different
channels are available in the 75-MHz radio band with frequencies ranging
from 75.410 MHz to 75.990 MHz, and with each channel number spaced every
0.020 MHz. The channel numbers range from 61 to 90. The channel identification
flags are the ones with the channel number and a red streamer.
Changing the channel frequency or channel number within the 75-MHz frequency
band also requires changing the frequency crystals, as with the 72-MHz
radios. However, you cannot change a 72-MHz band radio into a 75-MHz band
radio by swapping frequency crystals. Although the crystals look identical in size