THE ELECTRONICS OF AN RC AIRPLANE

This instructable will briefly cover all the basic concepts regarding the electronics of an electric RC airplane.

We will try our best to provide clear instructions and tips regarding the same.

Lithium-ion Polymer, AKA LiPo cells have higher specific energy (electrical energy per unit mass) when compared with other Lithium-based cells. This feature enables it to be the perfect candidate as the main power source in RC projects as it helps in keeping the overall weight quiet low without compromising on power.

We will now take a closer look at a commercial LiPo battery pack and understand the basic terminology.

1) "xS yV": Stands for "x CELL COUNT with corresponding y VOLTAGE"

A 1S LiPo consists of a single LiPo cell, and a corresponding nominal voltage of 3.7 volts.

A 6S LiPo consists of six LiPo cells connected in series to bring up the nominal voltage to (3.7 X 6) = 22.2 volts.

A fully charged LiPo cell is almost always 4.20 volts, and a fully discharged cell is 3.00 volts.

It is never advised to fully discharge a LiPo cell as it brings dangerous consequences with it, and that's why a LiPo voltage indicator cum low voltage alarm is highly recommended.

2) "xmAh" : Stands for "x milliampere hour"

This term indicates the CAPACITY of the battery pack.

A 1000mAh battery pack can power a load that consumes 1 Ampere for 1 hour, theoretically speaking.

A 2200mAh battery pack can power a load that consumes 1 Ampere for 2 hours and 12 minutes, theoretically.

3) "xC/yC": Stands for "X DISCHARGE COEFFICIENT or C-RATING or DISCHARGE RATING and y BURST DISCHARGE RATING"

This term indicates the MAXIMUM SAFE CONTINUOUS LOADING on the battery.

The value can be determined by multiplying the CAPACITY in Ah with the DISCHARGE RATING (Dimensionless number)

M.S.C.L in Amperes = (CAPACITY in Ah X C RATING)

A 1000mAh (1Ah) cell with a C RATING of 10 can safely discharge 10 Amperes to a load connected to it.

RUN TIME in minutes = { (CAPACITY in Ah / LOAD in Amperes) X 60 }

For example, a load consuming 10 amperes can run off a 1000mAh 10C cell for { 1(Ah) / 10 (Amps) } X (60) = 6 minutes.

The burst discharge rating indicates the current that can be drawn from the battery pack for an instant.

For example, a 1000mAh 30C/60C battery pack can provide a burst discharge of 60 AMPERES.

A very detailed post explaining the majority of sizes and styles of power connectors for various applications can be found here.

We will most widely be using 3.5mm bullet, XT60, and dean-style T connectors for our projects as they possess the sufficient current-carrying capacity for our power plants.

AKA ESC is a very crucial component for RC projects as it enables us to take control of the brushless DC motor we will be connecting to it.

Most of the ESCs today come with a built-in UBEC (Universal Battery Eliminator Circuit).

It converts the high voltage from, say, an 11.1 V LiPo battery into a steady, lower value which behaves as an auxiliary power source for other electronic components on our airplane like the receiver, servo motors, and miscellaneous gear.

The UBEC rating "xV yA" stands for "x Volts y Amperes", and indicates the continuous DC voltage and maximum current supplied by the BEC. Most of the components we use consume only 5 volts at some x milliamperes.

An ESC has 3 output leads that directly plug into the BLDC motor. Swapping any two leads of a bidirectional BLDC motor with the ESC will change the motor's direction of rotation. It also has a power cable and a signal cable.

An ESC has a nominal current rating and a peak current rating. The nominal current rating indicates the maximum safe load on the ESC in Amperes and the peak rating indicates the maximum load on the ESC in Amperes along with the specified duration of time.

For example, a 30A ESC with a peak rating of 40A for 10 Seconds can drive a BLDC motor consuming 30 Amperes safely for however long the battery pack lasts while it can drive a BLDC motor consuming 40 Amperes safely for only 10 Seconds. Pushing the limits will end up in the ESC going up in marvelous flames!

A BLDC motor packs a lot of punch for its size.

It operates on AC ( Alternating Current ) so an ESC is required to convert the DC ( Direct Current ) from a LiPo battery pack to AC.

Its high efficiency, speed, torque, and lightweight make it a perfect candidate for use in RC airplanes.

We will now understand the basics of a BLDC motor.

1) " xKV ": Stands for " x RPM per Volt " at no load.

A 1000KV BLDC motor running off of a 10-volt power supply will spin at ( 1000 X 10 ) = 10,000 RPM ( Revolutions per Minute ), theoretically.

After considering the efficiency of the motor which is usually 80%, the motor running off of the same power supply will spin at ( 1000 X 10 ) X ( 80 / 100 ) = 8000 RPM.

2) "xS-yS": Stands for " x CELL COUNT to y CELL COUNT "

Indicates the range of accepted battery packs

A 2S-3S BLDC motor requires a minimum of 7.1 volts and can handle a maximum of 12.4 volts.

A 2S-4S BLDC motor requires a minimum of 7.1 volts and can handle a maximum of 16.8 volts.

A servo motor works on a closed-loop system which enables it to produce precise positioning.

A standard hobby servo motor works on 3.0 - 7.2 volts and can produce some serious torque for its size.

We will widely use these motors to position our control surfaces like the elevator, rudder, and ailerons.

Unmodified RC servo motors have a rotational range of 0 - 180 degrees. Modified servo motors can provide continuous rotation.

Servo motors come in many sizes and shapes and gearing options.

We will most widely be using the 9 grams plastic gear servos.

The servos on our RC plane will directly plug into the receiver. They will attain their power from the UBEC which gets its power from the ESC which gets its power from the battery. So, it is advised to consider the current draw of the servos too when calculating the average flight time of our models.

A radio transmitter and receiver will work as our primary communication system between the ground operator and the aircraft.

They work in harmony on the 2.4GHz frequency band and enable channel hopping, which basically ensures the smooth operation of your aircraft.

A transmitter configured as MODE 2 :

1) Channel 1: Right stick, Horizontal ( Rudder )

2) Channel 2: Right stick, Vertical ( Elevator )

3) Channel 3: Left stick, Vertical ( Throttle )

4) Channel 4: Left stick, Horizontal ( Ailerons )

5) Channel 5: Right potentiometer ( Misc )

6) Channel 6: Left potentiometer ( Misc )

NEVER COUPLE A PROPELLER WITH YOUR MOTOR WHILE INITIAL TESTINGS

A2212 1000KV BLDC outrunner motor

SimonK 30A with built-in BEC ESC

Orange 3S 1000mAh 30C/40C LiPo battery pack

TowerPro SG90 mini 9 gram servo motor

TowerPro MG995 metal gear servo motor

FlySky CT6B Transmitter and R6B Receiver

1) Connect the three leads of your BLDC motor to the three leads coming out of the ESC with the help of bullet connectors. Ensure that the connectors can't cause a short.

2) Connect the ESC's signal cable to the 3rd channel on your receiver.

3) Connect your servo motors to the 1st and 2nd channel on your receiver.

4) Power up the transmitter and connect it to your PC.

5) Upload the default settings.

6) Move the throttle stick all the way up.

7) Connect the battery pack to the ESC using appropriate connectors and wait for the BLDC motor to make the beeping sounds.

8) Move the throttle stick all the way down and wait for the motor to make the beeping sounds again. The long beep at the end will indicate that the motor is now armed.

9) Test your BLDC motor and servo motors.

10) DISCONNECT THE POWER TO THE ESC AND THEN TURN OFF THE TRANSMITTER

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