Radio control

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. Carbon black is often used as an additive to rubber to improve its strength, especially in vehicle tires. Radio-controlled teleoperators are used for such purposes as inspections, and special vehicles for disarming of bombs. The successful development of vulcanisation is most closely associated with Charles Goodyear. Today radio control is used in industry for such devices as overhead cranes and switchyard locomotives. Vulcanization greatly improved the durability and utility of rubber from the 1830s on. The most outstanding example of remote radio control of a vehicle are the Mars Exploration Rovers such as Sojourner. Natural rubber is often vulcanized, a process by which the rubber is heated and sulfur is added to improve resilience and elasticity, and to prevent it from perishing.

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". Early experiments in the development of synthetic rubber led to the invention of Silly Putty. 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. Hypoallergenic rubber can be made from Guayule. 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. Over half of the rubber used today is synthetic, but several million tonnes of natural rubber are still produced annually, and is still essential for some industries, including automotive and military. 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. Today Asia is the main source of natural rubber.

The relative simplicity of this system allows receivers to be small and light, and has been widely used since the early 1970s.
. 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. After repeated efforts (see Henry Wickham) rubber was successfully cultivated in Southeast Asia, where it is now widely grown. The latter produces a 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 Congo Free State was forged and ruled as a personal colony by the Belgian King Leopold II where millions of Africans died as a result of lust for rubber and rubber profits. An electric motor and reduction gearbox is used to drive the output arm and a variable resistor or "potentiometer". About 100 years ago, the Congo Free State in Africa was a significant source of natural rubber latex, mostly gathered by forced labor.

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. The para rubber tree initially grew in South America, where it was the main source of what limited amount of latex rubber was consumed during much of the 19th century. The pulse is repeated in a frame of between 14 and 20 milliseconds in length. (American English uses 'eraser' to refer to the rubber block.). 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. Blocks of the material are still used for this purpose, and known as 'rubbers' in British English, causing occasional amusement to speakers of American English, to whom a 'rubber' is a condom (usually made from latex). 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. This was the origin of the material's English name of 'rubber'.

Typical radio control systems for radio-controlled models employ pulse width modulation (PWM) or pulse position modulation (PPM), and actuate the various control surfaces using servomechanisms. When samples of rubber first arrived in England, it was observed that a piece of the material was extremely good for rubbing out pencil marks on paper. While early control systems might have two or three channels using amplitude modulation, modern systems include 20 or more using frequency modulation. A story says that the first European to return to Portugal from Brazil with samples of such water-repellent rubberized cloth so shocked people that he was brought to court on the charge of witchcraft. The mechanical resonant systems using reed relays were replaced by similar electronic ones, and the continual miniaturization of electronics allowed more signals, referred to as control channels, to be packed into the same package. In Brazil the natives understood the use of rubber to make water-resistant cloth. These systems were widely used until the 1960s, when the increasing use of solid state systems greatly simplified radio control. While the ancient Mesoamericans did not have vulcanization, they developed organic methods of processing the rubber with similar results, mixing the raw latex with various saps and juices of other vines, particularly Ipomoea alba, a species of Morning glory.

These were typical on/off signals. Rubber was used in various other contexts, such as strips to hold stone and metal tools to wooden handles, and padding for the tool handles. The controller's radiotransmitter would play the different frequencies in response to the movements of a control stick. The Maya also made a type of temporary rubber shoe by dipping their feet into a latex mixture. The vibration would push on electrical contacts connected to the actuators of the control surfaces of the missile. According to Bernal Díaz del Castillo, the Spanish Conquistadores were so astounded by the vigorous bouncing of the rubber balls of the Aztecs that they wondered if the balls were enchanted by evil spirits. In front of the speaker were a number of small metal "fingers" with different resonant frequencies, each one tuned to vibrate when a particular tone was played in the speaker (a so called reed relay). The Ancient Mesoamericans had a ball game using rubber balls (see: Mesoamerican ballgame), and a few Pre-Columbian rubber balls have been found (always in sites that were flooded under fresh water), the earliest dating to about 1600 BCE.

A small radio receiver was placed in the missile, the signal from the controller (transmitter) was "played" into a small speaker. The Mesoamerican civilizations used rubber mostly from Castilla elastica. Radio control systems of this era were generally mechanical in nature. In its native Central America and South America, rubber has been collected for a long time. 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. . 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. The material properties of rubber make it an elastomer.

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. Rubber is believed to have been named by Joseph Priestley, who discovered in 1770 that dried latex rubbed out pencil marks. Jammers were then installed on British ships, and the weapons basically "stopped working". Synthetic rubber can be made as a polymer of isoprene or various other monomers. After initial overwhelming successes, the British launched a number of commando raids to collect the missile radio sets. Aside from a few natural product impurities, natural rubber is essentially a polymer of isoprene units, a hydrocarbon diene monomer. The effectiveness of the Luftwaffe systems was greatly reduced by British efforts to jam their radio signals. After a few hours, the very wet sheets of rubber are wrung out by putting them through a press before they are sent onto factories where vulcanization and further processing is done.

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 latex from multiple trees are then poured into flat pans and this is mixed with formic acid, which serves as a coagulant. 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. This usually produces latex up to a level of half to three quarters of the shell. Radio control was further developed during World War II, primarily by the Germans who used it in a number of missile projects. The shells are attached to the tree via a short sharp stick and the latex drips down into it overnight. Nikola Tesla patented a radio-control scheme as early as 1899, and various radio-controlled ships were used for naval artillery target practice by the 1920s. In places like Kerala, where coconuts are in abundance, the shell of half a coconut is used as the collection container for the latex.

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. Its density is 920 kg/m³. . These attempts were later supplanted by the development of synthetic rubber. 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 all make use of radio-controlled vehicles as well. Although these have not been major sources of rubber, Germany attempted to use such sources during World War II when it was cut off from rubber supplies. Radio control is the use of radio signals to remotely control another device. Other plants containing latex include figs (Ficus elastica), euphorbias, and the common dandelion.

The seedlings were sent to Colombo, Indonesia and Singapore. Henry Wickham gathered thousands of seeds from Brazil in 1876 and they were germinated in Kew Gardens, England. This is largely because it responds to wounding by producing more latex. The major commercial source of natural latex used to create rubber is the Para rubber tree, Hevea brasiliensis (Euphorbiaceae).

These form part of a broad study covered by Polymer science and Rubber technology. Synthetic rubber comprises the polymerisation of a variety of monomers to produce polymers. Rubber is an elastic hydrocarbon polymer which occurs as a milky emulsion (known as latex) in the sap of a number of plants but can also be produced synthetically.