Monday, 31 August 2015

Electronics and Propulsion System in RC Flying Part 1 - Electronics - Radio Control.

Electronics involved in RC Modelling.
  1. Radio Control.
  2. Servo.
  3. Electronic Speed Controller (ESC).
  4. Battery.
  5. Flight Controllers.
  6. FPV (First Person View) Equipment. 
  7. Misc Items.
  1. IC Engine.
  2. Electric Motor.
1. Radio Control - Transmitter & Receiver(Tx-Rx).
  • A transmitter is a handheld device that transmits a signal according to the input given by pilot/operator that is picked up by a receiver and then given to different devices fitted to control a RC-Aircraft .
  • Most RC transmitters nowadays work on the 2.4 Ghz frequency.
  • RC transmitters can be classified according to how many channels they have.
  • Channels are the number of things you can control.
  • For a typical RC plane it has a rudder, elevator, ailerons, and a motor: so a 4 channel transmitter is required.
  • Modern transmitters are having 6 or more channels. Four channels are used for rudder,elevator, ailerons, motor, and  AUX channels can be used for controlling various things, such as bomb drops or air brakes, under carriage , flight control, etc.
  • Transmitter can either be computer programmable, in-radio programming, or non-programmable. Computer programmable transmitters has to be connected to a computer via a USB cable to change/modify program/settings of the transmitter.
  • In-radio programmable transmitters have a a small LCD screen on the front with several buttons for programming.
  • Non programmable basic Tx may have servo reversal, V-tail and Delta wing selection with the help of switches. 
  • Programming a radio allows us to change most settings, such as reversing the direction of a servo ,changing the functions of the AUX switches, dual rates for servos, timers, throttle hold, hovering control , setting end points for the servo, etc.
  • A typical RC Transmitter has about 4 to 6 channels with at least 4 of them being proportional, which means the controlled surfaces or devices will move proportionally to the movements of the control sticks.
The example below shows a five channel RC Transmitter with two joysticks (left/right and up/down movement) enabling four proportional channels, while the fifth channel is of switch type (on/off).

The example shows the mode 2 configuration (most common) having the elevator control on the right joystick and the motor throttle on the left one. 
The right joystick self centers in the both axis, whereas the left joystick only self centers in left/right axis. The mode one configuration has the elevator control on the left joystick and the throttle on the right one.  
  • The modern RC Transmitters have "dual-rate" facility, which means the pilot may change the max throw angle of the control surfaces during the flight, e.g. the max throw may be reduced when flying fast and increased when flying slow.
  • Many Transmitters have a servo-reversing feature, which facilitates the changing the direction of servo movement.
  • Other feature such as channel mixing enables V-tail configuration and flaperons.
  • Some Transmitters include a microprocessor and memory, enabling the user  to save different model configurations and settings.
  • Another facility is the so-called buddy box, which allows two compatible transmitters being connected by a cable.
  • This is used for training purposes where a transmitter is held by the instructor and the other by the student.
  • The student may control the model as long as the instructor holds down a push- button on his/her own transmitter.
  • When the student get in trouble, the instructor releases the push-button, and quickly takes over the control.
  • The RC Transmitter sends data to the RC Receiver by generating a modulated radio frequency carrier, while the Receiver is tuned to detect the Transmitter's carrier frequency.
  • The accuracy of sending and receiving frequencies are usually achieved by the use of crystals.
  • The Receiver detects data from the modulated carrier, decodes and deliver it to the respective Servo, Electronic Speed Controller, control boards and any other electronic devices used on board.
  • Current technology in the R/C hobby is called "Spread Spectrum". This is a radio system that can be used without having to worry about what frequency you're on.
  • The 2.4GHz system comes with a unique, permanent ID code that is preset at the factory.
  • Pushing the bind button locks the receiver to the transmitter using that code.
  • It's the only code that it will recognize - and since it has over 134 million possible codes, there's no chance of a signal conflict.
There are several data encoding/decoding systems on the market today.
  • PPM (Pulse Position Modulation).
  • PCM System-PCM stands for Pulse Code Modulation.
  • IPD System -IPD stands for Intelligent Pulse Decoding, and the receiver incorporates a processor, which analyses the incoming signal for validity. 
  • DSR System-DSR stands for Digital Signature Recognition.(The DSR receivers block the interference by memorising the actual transmitter's unique signal frame and rejecting all the others, even if they are in the same frequency.)
How to select your Tx-Rx.
  • If you are a beginner  you can start learning flying with a basic 4 channel Tx-Rx.
  • A basic 6 channel computer Tx-Rx with memory and limited programming functions will be a better choice if you are going to make this as a serious hobby.
  • The difference in price of a 4 ch and 6 ch Tx-Rx is very less and more over a 6 ch with programming function will allow you to add additional functions and controls to your models.
  • Basic programmable 6 ch Tx-Rx will be a good selection, with this you can start learning flying and additional 2 channels avialiable can be used for flight controller application in multi rotors and airplanes.
  • As you improve upon your skills and finally when you becomes an expert you can opt for high end Tx-Rx models.
  • Before selecting a Tx-Rx you should go through the manufactures data and check the functions avialiable and make sure that it suits your requirement and budget.
  • You should check with different manufactures and suppliers before finalising your order.
  • Same specification products price vary with suppliers and manufactures, proper comparison and survey will save you a lot of money.
  • The RC receiver (Rx) picks up the control signal sent from the transmitter and converts the signal into PWM signals (pulse width modulation) for servos , ESCs (electronic speed controller) and other devices connected to AUX Channel .
  • The transmitter and receiver are wirelessly bound together using a process called,  binding. 
  • Once the binding is done for a Tx-Rx combination, the receiver will not work with other Transmitters.
  • The receiver get power from the ESC, which converts the battery volts down to 5v for the receiver and servos.
  • Range of the TX/RX system depends on the transmission power of the Tx and field conditions.
Given below is an example for manufactures data.
Turnigy 6XS FHSS -  2.4ghz Computer Transmitter w/6 Model Memory Inc 7 Ch Receiver
(Mode 2)
Features: Dual Rate/Trims/Gear/Flap/Gyro Gain Adjust/Flight Mode/Throttle Hold/Hover Pitch Switches / Trainer Port /Charging Port / LCD Screen/ Easy to use Programming & Navigation Buttons/ Supports Heli/Standard Wing/Elevon/V-Tail/ 6 Model Memory/ Model Name/ 4 Stick Mode Selectable/ Trainer Mode
Basic Programme Functions:
Dual Rates/ Sub Trim/ Travel Adjust/ Channel Reverse/ Swash Mix/ Gyro Sensitivity/ Throttle Curve/ Monitor/ Pitch Curve/ Throttle Hold/ Model Name/ Timer
Turnigy 6XS Transmitter Specs:
Frequency: 2.4ghz ISM Frequency Range/  Modulation: GFSK
Spread Spectrum Mode: FHSS
Number of Frequency Channels: 20
Output Power: <=20dbm
Working Current: <=100mA
Working Voltage: 1.2v x 4 (AA/Nimh)
Dimensions: 200mm x 185mm x 105mm 
Turnigy XR700 Receiver Specs:
Channel: 7 (inc RX Battery Input)
Frequency: 2.4g ISM Frequency Range
Power: 4.5v ~ 9.6v/<30ma
Net Weight: 11.5g
Dimensions: 41mm x 28mm x 14mm 
Requires:4 x AA Type Battery For Operation
  • Highlighted things are the features you should look for and compare.
  • Mode 1 - Throttle control on your right hand.
  • Mode 2 - Throttle control on your left hand.
  • Mode selection is one of the main feature you should carefully select.
  • Some manufactures offers user changeable mode selection in their transmitters.
Binding of Tx-Rx.

  • Binding procedure for the Tx-Rx will be given by the manufacturer.
  • Most of the Tx-Rx come with factory bidden receiver.
  • But some times binding is required to be done by the user, especially when you use a second receiver of same make to your collection.
  • I will briefly explain the common binding procedure.
  • Switch on your Tx. (select it to binding mode if instructed by manufacturer or leave it simply in ON condition).
  • Press down and hold the binding button on your Rx and power ON your Rx with 5v supply or by using BEC of ESC as specified by manufacturer.
  • LED indicator on your Rx will be blinking for some time and then turns to solid ON. (normally RED blinking followed by solid GREEN or RED blinking and then solid RED).
  • Power Off your Rx first and then Tx.
  • Switch ON your Tx first and power on your Rx. The LED indicator on your Rx should remain solid RED/GREEN.
  • Connect a servo to on of the Rx channel and check the operation by moving that corresponding channel lever/switch in your Tx.
  • If the servo is moving as per your input then the binding is complete, if not repeat the above procedure till solid binding takes place.
  • Binding is required to be done only once, then the Tx data will remain stored in Rx.
Various Brands Tx-Rx
Basic 3ch Tx.
 Fly Sky Basic 4 channel Tx  with channel reversing function
Hobby King Basic 4 channel Tx. with channel reversing ,
V-tail and Delta Wing mixing function.
JR-Propo advanced fully programmable Transmitter(Tx) - DSX7, 7 channel.
Various brand 6 channel Receivers (RX)
Avionic 6 channel programmable Tx.- Entry level and cheap. Good performance and advised for a beginner.
 JR-Propo 7 Channel RX
 DX6i Computer Tx.
 Fly Sky fully programmable Tx.

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