Page 150 - Build Your Own Quadcopter_ Power Up Your Designs with the Parallax Elev-8

chapter 6

Radio-Controlled

Systems and Telemetry

Introduction

The remote control by radio waves of devices ranging from battleships to insect-sized flying
machines has been ongoing since Nikola Tesla’s experiment in 1898. I will not repeat the
history here but instead refer you to the interesting Wikipedia entry at http://en.wikipedia
.org/wiki/Radio_control. This chapter focuses on how a modern 2.4-GHz radio-controlled
(R/C) system functions and explores additional features that will make your quadcopter
flying experience more enjoyable, and maybe even a little educational.

Evolution of Model R/C Systems

The R/C systems used to control model aircraft first appeared in the early 1950s. The
practical reason for this was the advent and availability of cheap transistors. Up until that
time period, radio systems were built using vacuum tubes that required bulky components
and batteries, neither of which could be easily placed in small model aircraft. Transistor
circuits changed all of that because they require only a little battery power, run cool, and take
up very little space. Over time, discrete transistors gave way to integrated circuits, which
eventually morphed into the powerful microcontrollers that are in practically all modern
R/C transmitters and receivers. Of course, the servos, which are the mechanical actuators
being controlled by the R/C receiver, also changed from relatively large and heavy units to
very lightweight yet powerful units. I will discuss servos in the next chapter, since there is
plenty of material to cover regarding their use and function.
The best way to understand the modern R/C system is to start with a discussion about
the basics that underpin any radio system. I am not going to make this a tedious tutorial but
will try to hit the high points to provide you with a reasonable idea of what makes the
2.4-GHz system tick.

Carriers and Modulation
All radio communications use a wave known as a carrier. This is the fundamental
electromagnetic wave that is created at the transmitter to carry information or data to a
compatible receiver. Carrier waves normally do not have any information impressed on

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