Page 198 - Build Your Own Combat Robot
P. 198

Chapter 8:
                                                                                Remotely Controlling Your Robot
                                    every microcontroller can receive and transmit serial communications data. Be-  179
                                    cause 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 turn-
                                    ing 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 de-
                                    tails 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 sys-
                                    tems, 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.

                              F ailsafe 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 re-
                                    ceiving 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 re-
                                    quirement 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.
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