Radio control
Radio control (often abbreviated to RC) is the use of control signals transmitted by radio to remotely operate a device. Examples of simple radio control systems are garage door openers and keyless entry systems for vehicles, in which a small handheld radio transmitter unlocks or opens doors. Radio control is also used for control of model vehicles from a hand-held radio transmitter. Industrial, military, and scientific research organizations make use of radio-controlled vehicles as well. A rapidly growing application is control of unmanned aerial vehicles (UAVs or drones) for both civilian and military uses, although these have more sophisticated control systems than traditional applications.
Second World War[edit]
Radio control was further developed during World War II, primarily by the Germans who used it in a number of missile projects. Their main effort was the development of radio-controlled missiles and glide bombs for use against shipping, a target otherwise both difficult and dangerous to attack. However, by the end of the war, the Luftwaffe was having similar problems attacking Allied bombers and developed a number of radio command guided surface-to-air anti-aircraft missiles, none of which saw service.
The effectiveness of the Luftwaffe's systems, primarily comprising the series of Telefunken Funk-Gerät (or FuG) 203 Kehl twin-axis, single joystick-equipped transmitters mounted in the deploying aircraft, and Telefunken's companion FuG 230 Straßburg receiver placed in the ordnance to be controlled during deployment and used by both the Fritz X unpowered, armored anti-ship bomb and the powered Henschel Hs 293 guided bomb, was greatly reduced by British efforts to jam their radio signals, eventually with American assistance. After initial successes, the British launched a number of commando raids to collect the missile radio sets. Jammers were then installed on British ships, and the weapons basically "stopped working". The German development teams then turned to wire-guided missiles once they realized what was going on, but the systems were not ready for deployment until the war had already moved to France.
The German Kriegsmarine operated FL-Boote (ferngelenkte Sprengboote) which were radio controlled motor boats filled with explosives to attack enemy shipping from 1944.
Both the British and US also developed radio control systems for similar tasks, to avoid the huge anti-aircraft batteries set up around German targets. However, no system proved usable in practice, and the one major US effort, Operation Aphrodite, proved to be far more dangerous to its users than to the target. The American Azon guided free-fall ordnance, however, proved useful in both the European and CBI Theaters of World War II.
Radio control systems of this era were generally electromechanical in nature, using small metal "fingers" or "reeds" with different resonant frequencies each of which would operate one of a number of different relays when a particular frequency was received. The relays would in turn then activate various actuators acting on the control surfaces of the missile. The controller's radio transmitter would transmit the different frequencies in response to the movements of a control stick; these were typically on/off signals. The radio gear used to control the rudder function on the American-developed Azon guided ordnance, however, was a fully proportional control, with the "ailerons", solely under the control of an on-board gyroscope, serving merely to keep the ordnance from rolling.
These systems were widely used until the 1960s, when the increasing use of solid state systems greatly simplified radio control. The electromechanical systems using reed relays were replaced by similar electronic ones, and the continued miniaturization of electronics allowed more signals, referred to as control channels, to be packed into the same package. While early control systems might have two or three channels using amplitude modulation, modern systems include twenty or more using frequency modulation.
Industrial radio remote control[edit]
Today radio control is used in industry for such devices as overhead cranes and switchyard locomotives. Radio-controlled teleoperators are used for such purposes as inspections, and special vehicles for disarming of bombs. Some remotely controlled devices are loosely called robots, but are more properly categorized as teleoperators since they do not operate autonomously, but only under control of a human operator.
An industrial radio remote control can either be operated by a person, or by a computer control system in a machine to machine (M2M) mode. For example, an automated warehouse may use a radio-controlled crane that is operated by a computer to retrieve a particular item. Industrial radio controls for some applications, such as lifting machinery, are required to be of a fail-safe design in many jurisdictions.[20]
Industrial remote controls work differently from most consumer products. When the receiver receives the radio signal which the transmitter sent, it checks it so that it is the correct frequency and that any security codes match. Once the verification is complete, the receiver sends an instruction to a relay which is activated. The relay activates a function in the application corresponding to the transmitters button. This could be to engage an electrical directional motor in an overhead crane.
In a receiver there are usually several relays, and in something as complex as an overhead crane, perhaps up to twelve or more relays are required to control all directions. In a receiver which opens a gate, two relays are often sufficient.[21]
Industrial remote controls are getting more and higher safety requirements. For example: a remote control may not lose the safety functionality in case of malfunction.[22] This can be avoided by using redundant relays with forced contacts.