Modellers have always wanted to be able to remotely control their models. Airplanes,boats,tanks,and cars were modeled. Of course, in the beginning strings were used! Even model airplanes were flown with strings, usually 2 strings or more. The model just flew around the flyer in a circle! Wireless remote controller appeared in the forties or even perhaps the thirties. Vacuum tubes were available. England, Germany, and the U.S. led in the development of remote controller. The early controller merely closed a relay in the receiver when a button is pressed in the transmitter! This article will focus on remote controllers for model airplanes.
THE NEED TO CONVERT A RELAY INTO A STRONG MECHANICAL MOVEMENT
Well, conceptually, one was to make the relay bigger. But then weight was a factor. Then a device was developed, sort of a clockwork powered by wound rubber band. The magnetized coil of the relay was then used to release a lever and latch the spindle to a position. The torque came from the rubber band and the relay was more of a key. The most basic was to latch the wound spindle into 3 positions. Imagine a lever called a horn in the hobby which can stop at 3 positions 1,2,3. A push rod is connected to a similar horn in the rudder of a model plane. Since 2 is the midpoint, the rudder is set at center on this position. Position 1 was usually set to be left rudder and Position 3, right rudder. There was no elevator control and no engine control! The way of controlling was called Rudder Only. Early modellers already used glow engines burning methanol with castor oil. To provide for max stability, the model had very low wing loading (huge wings) with lots of dihedral (bent upwards). This way, the model practically float at very slow speed. Left or Right rudder kicked the tail and the turn was slow and shallow. So, here was a typical flight. Wind the rubber band. Position the rudder to center. Start engine. Launch. Up she goes as her elevator is slightly up. But just a tack up. If one flew the model vs headwind, she will just keep climbing. Fortunately, left or right rudder will induce a turn which naturally lessen the lift of the wings and makes the model sink. It therefor countered the climbing. So, here it went. One press of the TX button, the model turns left. Another press, she corrects and goes back to neutral. Another press, she turns right! Another press, she centers again! Neat, isn't it. So, how did the pilot turn the model right without going left? Press the button 3 times! Ingenious! The pilot just waited till the fuel runs out and landed the model. The device was called the ESCAPEMENT.
Next was to control the elevator. Same thing, 3 positions. But how did they get another channel. Maybe they thought of two radios and even two pilots! Actually, it was discovered that sending a TONE was more effective than just sending a clean carrier wave. Naturally, sending two different tones was suddenly a wish. One tone to control the Rudder escapement and another to control an Elevator escapement. It was easy to produce two different tones in the transmitter and send it to the same receiver. The problem was how to discriminate the two tones and activate a corresponding relay. The solution was purely mechanical. Two reeds were placed over the relay coil. One long reed and one short reed. The long reed vibrated to the lower tone and the short reed to the higher tone. On the transmitter were then two buttons. One button was for the rudder and the second button for the elevator. They send different tones via the same carrier frequency. There was no need for a second radio! How did the reed close corresponding relays? Well, contacts were placed above the reeds hardly touching the reed. But when the reed vibrated, they touch establishing electrical contact. There were then 2 escapements.
