Radio control

Radio control (a.k.a. R/C) is the use of radio signals to remotely control another device. The term is used frequently to refer to the control of model cars, boats, airplanes, and helicopters from a user-held control box (radio). Industrial, military, and scientific research organizations make use of radio-controlled vehicles as well.

History

The possibility of radio remote control was appreciated almost as soon as the first demonstrations of radio itself; the credit for the first to suggest radio control of aircraft may belong to Patrick Young Alexander as early as 1888.

In 1898 at an exhibition at Madison Square Garden Nikola Tesla demonstrated a small boat which could apparently obey commands from the audience but was in fact controlled by Tesla interpreting the verbal requests and sending appropriate frequencies to tuned circuits in the boat. He was granted a US patent on this invention on November 8th, 1898.[1]

In 1904, Bat, a Windermere steam launch, was controlled using experimental radio control by its inventor, Jack Kitchen.

In 1909 the French inventor Gabet demonstrated what he called his "Torpille Radio-Automatique", a radio controlled torpedo.[2]

In 1917, Archibald Low as head of the RFC Experimental Works, was the first person to use radio control successfully on an aircraft.

In the 1920s, various radio-controlled ships were used for naval artillery target practice.

The Soviet Red Army used remotely controlled teletanks during 1930s in the Winter War against Finland and in the early stages of World War II. A teletank is controlled by radio from a control tank at a distance of 500–1,500 meters, the two constituting a telemechanical group. Teletanks were used by the Soviet Red Army in the Winter War and fielded at least two teletank battalions at the beginning of the Great Patriotic War. There were also remotely controlled cutters and experimental remotely controlled planes in the Red Army.

In the 1930s Britain developed the radio controlled Queen Bee gunnery target aircraft, a remotely controlled unmanned Tiger Moth aircraft for a fleet's guns to practice shooting-at. The Queen Bee was superseded by the similarly named Queen Wasp, a later, purpose built, target aircraft of higher performance.

Military applications in the Second World War

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 that is 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-controlled anti-aircraft missiles, none of which saw service.

The effectiveness of the Luftwaffe systems was greatly reduced by British efforts to jam their radio signals. After initial overwhelming 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 guidance once they realized what was going on, but these 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, in order to avoid the huge anti-aircraft batteries set up around German targets. However, none of these systems proved usable in practice, and the one major US effort, Project Aphrodite, proved to be far more dangerous to its users than to the target.

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.

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 20 or more using frequency modulation.

Radio-controlled models

First general use of radio control started in the early 1950s using single-channel self-built, then commercial equipment. Hard valve electronics initially used escapement (often rubber driven) mechanical actuation in the model. Commercial sets often used ground standing transmitters, long whip aerials and single valve receivers. First kits had dual valves for more selectivity. Controlaire introduced a transistor superhet single channel handheld outfit in 1960. By the early 1960s transistors had ousted the valve and electric motors driving control surfaces were more common. Single-channel gave way to multi channel and reed selection; frequency stability used crystals for selectivity and equipment became more readily available. Crucially the equpment weight was constantly diminishing. Soon a competitive market place developed and development was rapid. By the 1970s the trend for full-house proportional radio control was fully established. Typical radio control systems for radio-controlled models employ pulse width modulation (PWM), pulse position modulation (PPM) and more recently spread spectrum technology, and actuate the various control surfaces using servomechanisms. These R/C systems made 'proportional control' possible, where the position of the control surface in the model is proportional to the position of the control stick on the transmitter.

In the type of system most commonly used today PWM is used, where transmitter controls change the width (duration) of the pulse for that channel between 920 µs and 2120 µs, 1520 µs being the center (neutral) position. The pulse is repeated in a frame of between 10 and 30 milliseconds in length. Off-the-shelf servos respond directly to pulse trains of this type using integrated decoder circuits, and in response they actuate a rotating arm or lever on the top of the servo. An electric motor and reduction gearbox is used to drive the output arm and a variable component such as a resistor "potentiometer" or tuning capacitor. The variable capacitor or resistor produces an error signal voltage proportional to the output position which is then compared with the position commanded by the input pulse and the motor is driven until a match is obtained. The pulse trains representing the whole set of channels is easily decoded into separate channels at the receiver using very simple circuits such as a Johnson counter. The relative simplicity of this system allows receivers to be small and light, and has been widely used since the early 1970s.

More recently, high-end hobby systems using "Digital Proportional" features have come on the market that provide a computerized digital bit-stream signal to the receiving device, instead of analog type pulse modulation. Advantages include bit error checking capabilities of the data stream (good for signal integrity checking) and fail-safe options including motor (if the model has a motor) throttle down and similar automatic actions based on signal loss. However, those systems that use pulse code modulation generally induce more lag due to lesser frames sent per second as bandwidth is needed for error checking bits. It should also be noted that PCM devices can only detect errors and thus hold the last verfied position or go into failsafe mode. They can not correct transmission errors.

Modern military and aerospace applications

Remote control military applications are typically not radio control in the direct sense, directly operating flight control surfaces and propulsion power settings, but instead take the form of instructions sent to a completely autonomous, computerized automatic pilot. Instead of a "turn left" signal that is applied until the aircraft is flying in the right direction, the system sends a single instruction that says "fly to this point".

Some of the most outstanding examples of remote radio control of a vehicle are the Mars Exploration Rovers such as Sojourner.

Industrial control

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.

See also

Template:Commons

• Model Fire Boats
• Radio-controlled model
• Radio-controlled car
• Radio-controlled boat
• Radio-controlled airplane
• Radio-controlled helicopter
• Teletank

Wikipedia information about Radio control This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Radio control". It may not have been reviewed by professional editors (see full disclaimer). Help contribute to Americola and edit this article.