Page 191 - Build Your Own Combat Robot

Build Your Own Combat Robot
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Of course, minimizing the transmission of noise from one system to another
does no good if your radio control and power circuits are not electrically isolated.
No common ground or shared power source should exist between your radio and
your drive motor power. Electronic speed controllers (ESCs) that make a direct
electrical connection between the servo signal line and the motor battery, or those
that tap power off the drive batteries to feed to the radio (known as a battery
eliminator circuit,or BEC), should not be used. Electrical isolation through
opto-isolators or relays should be mandatory. A separate battery should be used
to power the radio. If a power converter is used to provide power to the radio from
the motor batteries, it should be a type with full electrical isolation, such as the
Team Delta’s R/CE85-24.

note If speed controllers with BEC must be used, the power pin connecting the ESC to the
receiver can be removed from the connector and insulated to prevent an electrical connection.
A separate battery should then be used to power the receiver.

Gasoline engines can be a huge source of electrical noise—particularly the small,
high-RPM, two-stroke motors used in chainsaws and lawn trimmers. The high-
voltage pulses generated by the ignition system can play massive havoc with a
nearby R/C system. To prevent noise from the engine from getting into the radio
circuitry, place the radio control system in a metal box, test the servo leads for in-
terference, and keep the distance between the radio receiver and the engine’s elec-
trical system as far as possible in the robot. The electrical noise that is radiated
from the motor can be minimized by using resistor-type spark plugs and replacing
the ignition wire with a shielded line. Resisting this sort of electrical noise is where
PCM radios really prove themselves to be worth the extra money. The error-
checked digital transmission system is much better at rejecting extraneous noise
than simpler non-PCM setups.

Radio to Radio Interference
Radio interference commonly occurs when two radios transmit on the same fre-
quency. In such a case, your robot will have a difficult time distinguishing between
the two signals. The robot can stop responding, or it might respond to whichever
radio has the strongest output power, or it might do some combination of the two.
This can be a dangerous situation, because the robot can suddenly start to move or
trigger weapons when it shouldn’t. You should always carry various frequency
crystals with you, and make sure that you are the only robot driver transmitting at
a particular frequency. As noted, this is ensured at some events by the transmitter
impound.
Some people build their own R/C systems that transmit under the 300-MHz,
900-MHz, 1.2-GHz, and 2.4-GHz frequency bands. Many companies sell products
designed to transmit data or control signals that can be used to control a robot.