Introduction to Rc airplane electronics

             

     

                                                                          

     In this post about Rc airplane electronics. I will be talking about the main electronics of an rc airplane.

   The main electronics are:

1. Transmitter
2. Receiver
3. Battery
4. Motor
5. Electronic Speed Controller(ESC)
6. Servo


Transmitter

   The transmitter is what you hold to control your airplane. This is usually the most expensive component that you will buy.
 Most modern transmitters use a 2.4ghz frequency. These new ones have shorter antennas and are easier to work with than the older FM radio.
 Transmitters have channels. Some have 2, 3, 4, 6 and 12 channels. For a beginner you won't need a 12 channel transmitter, 6 channel is everything you need to get started.
 Channels are the number of things you can control. A 4 channel transmitter means you can only control four things; Motor, elevator, rudder and aileron.
 So if you have a 6 channel transmitter, you can have throttle, rudder, elevator, aileron, aux 1 and aux 2.
 You can add a bomb drop, lights or retracts in the aux channel. The auxiliaries are usually controlled extra switches or knob on the transmitter.


Receiver

 The receiver is what goes into your airplane and control the servos and motor(s). The BAT slot is not considered a channel.
 The receiver and transmitter communicates on a 2.4ghz frequency. The receiver runs off 5v, andsend signals to the servos to turn them. It also sends signals to the ESC to tell it how fast the motor should run. The receiver get its power from the ESC(BEC). We will take about that later.
 The antennas on the receivers like to break, so I suggest covering the part where the antenna and the receiver meets with a bit of hot glue.

Note: Each receiver will only work with specific brand and type of transmitter.



Battery

 Batteries have different chemistries. The most commonly used ones for RC are Lipp(lithium polymer) batteries.
 The first thing to talk about is the battery's voltage. Lipo batteries are made of cells. Each cell is 3•7 volts. The battery shown above is a 2s battery which is 2×3.7=7•4 volts. These cells fully discharged should NOT go below 3•3v and the cells fully charged should not go above 4•1 v.
 The next thing is the Amp capacity. The battery shown above is a 2200Mah battery. This means the battery can supply 2200miliamps over 1 hour period.

Discharge rate
 This battery has a 25c discharge rate. This is how much current the battery is able to supply. The higher the discharge, the more power you will get. In order to find out how much current the battery can deliver, multiply the C rating by the battery capacity in Amps. Example, the battery above is a 2•2amps(2200mah) battery with a C rating of 25c. So 25×2•2=55. So the battery can constantly supply 55amps of current.
 These batteries tend to catch fire or explode when short or not charged properly. It's is advised to use the specific charger and to charge in a fire proof bag.


Motor

 The most popular motor used in Rc airplanes are brushless motors. These motors are faster and more powerful than traditional brushed motors. They deliver huge amount of speed. These motors runs off AC current, that's when the ESC comes. Brushless motors have Kv ratings. KV means for every volt applied, the motor will spin to the number of the KV. To find out the motor's rpm, multiply the KV by the voltage applied to it. Example, if you have a 2400Kv motor and a 2s (7•4v) battery. 2400×7•4=17,760rpm. The motor will spin at 17,760 revolutions per minute. Lower KV motors have less speed but more torgue. The motor will drive a bigger propeller without the need of a gearbox.

Power rating
 In order to find the wattage of the motor, multiply the max current of the motor by the voltage applied to it. Example if a motor pulls 15amps and uses a 2s battery 15×7•4= 1110 watts.


ESC( Electronic Speed Controller )

 An electronic speed controller does several things. First, it's converts your battery voltage down to 5v which your receiver runs off it. Not all Esc do this, when buying make sure your Esc says BEC or UBEC on it. This stands for [(Universal) Battery Elimination Circuit]. The ESC receives signal from the receiver to tell how fast the motor should spin.
 The second thing the ESC does is it converts the DC power from your batter to AC current which your motor runs off.
 When choosing an ESC, leave at least 25% headroom of the motor's amp rating. If I have a 15amp motor, I would not buy an ESC with 15amps rather 20amps.
 ESCs are also programmable, usually through a programming card or through the transmitter and receiver. This may vary depending on the ESC but usually they have programmable braking, starting, and battery voltage cutoff settings.
 Battery voltage cutoff settings means, the ESC can be programmed to cutoff power to the motor while still powering the receiver and servos for some time to safely glide the plane down to above over discharging the battery.


Servos

 Servos are geared motors connected to potentiometers that moves the control surfaces of an airplane. They receive signals from the receiver and rotate to a set position.