Build Your Own Combat Robot

Chapter 8: Remotely Controlling Your Robot 179
every microcontroller can receive and transmit serial communications data. Because
of this, operator interfaces and robot controllers can be designed to transmit
and receive serial communications, and the radio modems can be used to transmit the
data between them.
A simple operator interface can be a microcontroller, such as the Basic Stamp or
the Motorola 68HC11, to read in analog data from a joystick and digital data from a
weapons switch, and to convert that data into serial communications data that
can be transmitted. The robot controller can also use the same type of
microcontrollers to convert incoming serial data to output digital signals for turning
on and off solid-state relays for weapons and generate the 1- to 2-millisecond
pulse modulation that motor controllers use to drive the robot’s motors. The details
of how to create the specific subsystems is outside the scope of this book, but
in Appendix B you’ll find several references to books that will explain how to
build the various components that can be used in your own custom combat robot
R/C system.
It is recommended that beginning robot builders use either a traditional R/C
system or the IFI Robotics Isaac system. If you try to build your own R/C system,
you will eventually end up with something that is functionally similar to the Isaac
system, and you might end up spending most of your time building the remote
control system.
For those of you who really want to build you own custom remote-control systems,
research FCC rules on radio communications, seriously consider using radio
modems, and remember safety is the number-one consideration that must be
built into controllers. You must have failsafe and interference-handling features
built into the control system, or you will not pass safety inspections. In addition,
some competitions require noncommercial custom radio systems be separately
pre-approved, far in advance of the actual event.
Failsafe Compliance
Whichever radio setup you use, most competitions have strict rules on failsafe
compliance that must be met for your robot to pass safety inspection. Your robot
must stop moving and deactivate all its weapons when it loses radio contact. This
shutdown must occur even if the robot was in motion or had its weapon running
at the time it lost radio contact.
Radio systems respond differently when a loss-of-signal condition occurs. AM
and low-cost FM receivers simply stop transmitting servo pulses when they stop receiving
a valid radio signal. Most electronic speed controllers shut down when they
stop receiving a valid servo pulse, and R/C servos will simply freeze in place. The
ESCs that shut off when a loss-of-signal condition occurs will fulfill the failsafe requirement
with nearly any non-PCM radio. Mechanical speed controllers that use a
servo to trigger relays to run motors will not pass a failsafe requirement test, as the
servo will remain in its last commanded position when the radio shuts down.