WIRELESS REMOTE CONTROL

INTRODUCTION


Probably Man's age old dream: wireless remote control of objects. This was realized only in the 20th century after the vacuum tube was developed ( which was discovered after Edison invented the lightbulb). Well, Samuel Morse conceptualized and developed the Morse Code, perhaps unknowingly, stumbling into digital concept, a two state mode communication, dot and dash. Today, dot and dash is reresented by 1 and 0 which can be manipulated mathematically. It was Marconi who made it wireless. Instead of voice over the Atlantic, Marconi sent dots and dashes, using Morse's code. There were only two sounds to recognize. Of course voice followed but it is interesting to note that today, we are back to using only two distinct symbols to send voice great distances, the farthest is to the moon when austronauts were there. In reality, 0 and 1 are sent but the way it is electrically sent is on or off. On for 1 and off for 0. Voice is converted to 0 and 1's (binary) sent, then reconstructed in the RX.

The modellers were at the forefront of RC. Actually, before the vacuum tube era, a spark gap was used to transmit a wideband electrical noise. The receiver was a coherer tube, a glass tube with iron fillings. When electromagnetic energy was detected, the iron fillings lined up inside the tube in an orderly North-South arrangement, thus making the iron fillings conduct. The first public display was somehow controlling a balloon inside a building, probably looking like a dirigible. Rapid progress was made in the 30's when vacuum tubes was used to oscillate at a frequency kept steady by a crystal. A fixed frequency on a narrow bandwith was transmitted.(this was broadband by today's standard). A broadband receiver with very little selectivity picked up the propagation which at the beginning was nothing but the carrier wave of the TX. Modellers put a button on a TX and a relay in the RX. The world was "quiet" in those days (transmission wise). Later, it was found out an audio tone modulated on the CW (AM) was better. To move the control surface of a model aircraft, an escapement was developed which multiplied the force of the relay. The escapement was mechanical where rubber band was wound to generate torque on a spindle. The spindle had an dual arms caught on a latch to hold it from turning. The relay released the latch and engage it in the next arm, thus changing the positon of a horn attached to the spindle. Thus rudder was controllable to be at center, left or right by pressing the TX button. This was called "single channel" in those days and was probably like owning a I-pod today! If only we could control the elevator as well was the main wish. There were various attempts and the one that became widely acceptable was to use tones to send different commands on the same frequency. The sound discriminator in the RX was mechanical: reeds. Reeds resonant to the tone were placed on top of an electromagnet. The corresponding reed vibrating given a tone. Soon, there were 8 channels, eight reeds on top of an electromagnet. These reeds touched a contact when vibrating which turns on a relay which activates escapements. This went on for a time. In 1949, the Americans discovered semi conductors called transistors, much much smaller than a vacuum tube and did not need heaters. By the fifties, transistors were appearing everywhere. Still, tones and escapements were used. Eventually, small dc motors replaced the rubber band and the escapement itself. High speed motors were geared down to have torque to turn the control surfaces(Rudder and elevator, ailerons and throttle). These were called "servos". In the forefront of servo development was Howard Bonner(American). Bonner servos reached moddellers across the globe. But this servos were not proportional, meaning they did not move linearly with stick movement in the TX. In the beginning, they only had end switches to stop at extreme ends. In fact, a transition was a servo that was swinging back and forth to a position based on an ON/Off switcher in the TX. The rudder appeared like a dorsal fin of a fish on flight. It became known as the galloping ghost.

The first attempt at proportional control was called analog in nature. The TX transmitted a signal which can increase/decrease a voltage level. A transistor is turn on but a variable resistor connected to the output shaft of the servo changes the sensitivity of the transistor thus bringing it back to an OFF state and shuts the motor. By then the horn connected to the control surface has changed position. The problem was delayed reaction, proportionality,and overshoot. By then, two young Americans electronics buffs were working on a concept. They were Mathers and Spreng(Dough).