Remote Control

Remote control technology involves the fields of control, computer and radio engineering.

Remote control systems consist of the input, computer for transfer into electrical signal, transmission, receiver and computer for translating signals.  Remote control can be done by sending signals through either infrared light (like a TV remote), visible light, radio waves, wires, fiber optics, or by soundwaves. 

The typical television remote uses infrared and just like visible light and laser signaling it requires a line-of-sight connection. Some radio waves like microwaves also require a line-of-sight however longer waves are more versatile with topography. Besides the well known uses of remote control in toys and the television set the term 'remote control' applies to an innumerable amount of uses from space exploration to industrial manufacturing tools.

Wireless Remote Control:

Radio-controlled vehicles have been around for a long time and there are a myriad of types which use different frequencies and schemes. Here we will discuss consumer radio controlled devices.

The shorter the radio waves, the more 'straight' the line of travel. So many new consumer radio control circuits operate at 2.4 GHz, which means you must be in line of sight with the vehicle you are controlling. The new 2.4 GHz band allotted to R/C use by the FCC is wide and allows for more flexibility in modern systems. Older traditional radio controlled devices used 27, 35, 36, 40, 41 or 72 MHz bands. These were very narrow bands and this created problems when more than one user was on one of these bands.

Two common methods of radio control. In both methods a 'digital' signal is sent to the RC receiver. The signal uses a square wave with the 'up' part of the wave being '1' and the flat part being '0'.

Pulse Width modulation (PWM)
The length of the square pulse determines a left or right, up or down command. Typically if a pulse lasts 1 and 2 milliseconds the ESC or servo will detect the length of the pulse and translate that into a command. For example if a pulse width lasts 1 millisecond it may tell the device to move all the way left, and 2 milliseconds duration would result in full right movement. These pulses are packaged into a 'frame'. The frame will last about 20 milliseconds. PWM signals are the basis of many devices in the automatic control field.

Pulse Position Modulation (PPM)
In PPM we can pack in many PWM pulses into the same frame. This allows us to send more information within the 20 ms frame. An 8 channel transmitter/receiver is typically used in radio control devices and stabilization systems.

Many users, limited bands
Use of 2.4 GHz radio controlled devices now allow for methods to have many users occupy the same bands thanks to computer assistance. The most common type of method is DSSS (Direct sequence Spread Spectrum) where the system stays within a fixed channel of the 2.4 GHz spectrum. In DSSS the signal is transmitted over relatively wide area in many thin parts which constantly shift to the adjacent frequencies within the wider fixed channel. This shifting and use of narrow bands allows other users to occupy the same area of the spectrum with minimal interference. The other method used in the 2.4 GHz band is FHSS (Frequency Hopping Spread Spectrum) in which the signal constantly changes frequencies, but unlike DSSS they can change to a completely different band (not just the adjacent bands in a fixed channel).

See our video below as to how typical pulse width RC works in a drone:

Engineers are always trying to find ways to overcome current technological limitations. Some of the limitations facing radio controlled devices include propagation loss (the decay of power over distance). We can measure the the amount of power lost by looking at the decibels of received power versus the transmitter. There are equations for understanding radio wave behavior at Circuit Design, Inc's site.

Learn More:

You can get hands-on knowledge of remote control technology quite easily by using programmable modular kits. Arduino is one very popular kit system which can get you started.

Learn about this cool microcontroller using this video below from Make:

Related Pages:

Gas Turbines

Semiconductor Electronics

Rocket Guidance

Control and Systems Engineering


More Stuff

Interview with James Jensen. Edison Tech Center. 2013
Interview with Gene Wright. Edison Tech Center. 2013
Vasile Burluc - Control Engineer
Learnabout-Electronics, Oscillators
Endurance R/C

For use of Edison Tech Center images and videos see our licensing agreement.