Thursday, January 05, 2006

The Radio Controller

I just read this very detailed piece on Radio Control. It's kind of an overview of radio control theory, entitled "What Happens When I Wiggle the Sticks." The author, Neil McGrath, is a British radio-frequency electrical engineer whose hobby is radio controlled power boats.

The title was quite the grabber. What does happen when I wiggle the sticks? Below I quote:

1. The transmitter broadcasts a radio signal via the antenna containing the positional information set by the controls.
2. The receiver picks up the radio signal via its antenna and decodes the positional information.
3. The receiver distributes the information to the electronic speed control and the rudder servo
4. The electronic speed control switches the main battery power on and off at high speed to regulate the power output of the motor to the level set by the associated transmitter stick.
5. The servo arm will move to the position set by the transmitter stick.
6. Power for the motor comes from the main battery pack.
7. The power for the receiver comes from an independent battery eliminator circuit. The BEC will provides voltage to the receiver from the main battery pack.
8. The power supply for the servo and the control circuitry in the speed controller come from the receiver

All radio control systems generate a radio carrier wave, at a frequency that is determined by the crystal used in the transmitter. These are thankfully not licensed individually. The FCC handles these devices in bulk by allotting a certain set of frequencies and parameters to the devices. The carrier wave is modulated to carry the digital information set by the transmitter controls. There are two methods of modulation used by R/C systems, AM and FM. As a third variable some use a PCM radio to transmit digital data on the FM carrier wave. This is conceptually not that different from IBOC.

In 1898, Nicola Tesla staged the first demonstration of radio control. His invention (patent No. 613,809), took the form of a radio-controlled boat, a heavy, low-lying, steel craft about four feet long. At that time radio itself had not been officially patented yet! Tesla's own radio patent wasn't granted until March 1900! Initially examiners from the US Patent Office were reluctant to recognize improbable claims made in the application "Method of and Apparatus for Controlling Mechanism of Moving Vessels or Vehicles." Confronted with a working model, however, examiners had to issue approval. ...And today we use it to drop missiles on people. Oh, How far we have come.

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