Quadcopter Remote Control Circuit without MCU

Although a quadcopter remote control circuits can be very easily procured from the market or from any online store, an avid electronic hobbyist is never allowed to learn how actually these function and whether or not these can be built at home?

In this article I have explained how to build a simple quadcopter remote control circuit using discrete components and using RF remote control modules, and without involving the complex MCU based circuits.

The step by step guide will actually make the interested hobbyists understand how simply a quadcopter can be controlled using a PWM concept.

We have already learned the quadcopter basics, now let's investigate a the remote control section which will ultimately help to fly the unit remotely.

Basic Modules Required

The main ingredients that may be required for the project are given as under:

We will fundamentally require the following 3 circuit stages:

1) 4 way RF remote control Tx, Rx modules - 1set

2) IC 555 based PWM generator circuits - 4nos

3) BLDC motor controller circuits - 4nos

Since it's a homemade version, we can expect some inefficiencies with the proposed design, such as the absence of joysticks for the controls, which are replaced with pots or potentiometers, nevertheless the working capability of the system can be expected to be on par with the professional units.

The handheld PWM transmitter unit will basically consist the Tx remote module integrated with 4 discrete PWM control circuits, while the quadcopter will need to be enclosed with 1 Rx circuit integrated with 4 discrete BLDC driver circuits.

Let's begin with the quadcopter motor circuits, and see how the BLDC motor controller needs to be configured and attached with the Rx circuit.

Quadcopter PWM Receiver Circuit

In one of the previous posts I have explained how a versatile BLDC motor controller could be built using single chip, however this design is not designed to operate relatively heavier motors of a quadcopter, therefore it may not be suitable for the present application.

A "big brother" option for the above circuit is fortunately available and becomes perfectly suitable for driving quadcopter motors. Thanks to TEXAS INSTRUMENTS, for providing us with such wonderful single chip application specified circuit modules.

To learn more about this high current BLDC driver IC, you may refer to the following pdf datasheet of the same

The set up below shows the complete circuit schematic of the quadcopter motor driver controller using the DRV11873 IC which is a self contained low current BLDC motor circuit consisting of all the required protection features such overload protection, thermal protection etc. This module basically forms the ESC for our present quadcopter unit.

For more info on this design and PCB details, you can refer to the original document below:

http://www.ti.com/lit/ds/symlink/drv11873.pdf

How it Works

The FS and FG pinouts of the IC are for enhancing the IC with added controls through external circuits, since we are not using these features in our design, these pins may be kept unused and terminated to the positive line through a 100K resistor.

The RD pinout of the IC decides the rotational direction of the motor. Connecting this pin to Vcc via a 100K resistor allows an anticlockwise rotation on the motor while leaving it unconnected does the opposite and allows the motor to spin in the clockwise direction.

Pin#16 is the PWM input is used for injecting a PWM input from an external source, varying the duty cycle of the PWM alters the speed of the motor correspondingly.

The FR, CS pinouts are also irrelevant to out need and can be therefore left unused as shown in the diagram, and terminated to the positive line through a 100K resistor.

The U, V, W pinouts are the motor outputs which needs to be connected with the respective quadcopter BLDC 3 phase motor.

The COM pinout is for connecting the common wire of the 3 phase motor, if your motor does not have a common wire, you can simply simulate it by connecting 3 nos of 2k2 resistors to the U, W, W pins and then join their common ends with the COM pin of the IC.

The schematic also shows an IC 555 configured in the PWM astable circuit mode. This becomes a part of the circuit module and the PWM output from its pin#7 can be seen connected with the PWM input of the DRV IC circuit in order to initiate the 4 motors with a constant base speed and to enable the motor a constant hovering speed at a given spot.

This concludes the main ELC circuit or the BLDC driver circuit for out quadcopter design.

We will need four such modules for the four motor in our quadcopter design.

Meaning, 4 such DRV IC along with the IC 555 PWM stage will need to be associated with each of the 4 motors of the quadcopter.

These modules will ensure that normally all the 4 motors are set at a predetermined speed by applying a fixed and identical PWM signal to each of the relevant DRV controller ICs.

Now let’s learn how the PWM may be altered through a remote control in order to alter the speeds of the individual motor using an ordinary 4 channel remote control handset.

The RF Receiver Module (PWM Decoder)

The above circuit shows the receiver remote RF circuit which is supposed to be accommodated inside the quadcopter for receiving an external wireless PWM data from the user’s remote transmitter handset and then process the signals appropriately in order to feed the accompanying DRV controller modules as explained in the previous section.

The 4 outputs named as PWM#1….PWM#4 needs to be connected with the PWM pin#15 of the DRV IC as indicated in the previous diagram.

These PWM pinouts from the RF receiver unit becomes activated whenever the corresponding button is pressed by the user in its transmitter handset.

How the RF Transmitter needs to be Wired (PWM Encoder)

In the above section I have explained the Rx or the remote receiver circuit and how its 4 outputs needs to be connected with the quadcopter motor ESC driver modules.

Here we see how the simple RF transmitter needs to be created and wired with PWM circuits for transmitting the PWM data wirelessly to the quadcopter receiver unit so that the speeds of the individual motor is controlled simply with a press of a button, which ultimately cause the quadcopter to change direction or its speed, as per the users preferences.

The circuit shown above exhibits the wiring details of the transmitter module. The idea looks pretty simple, the main transmitter circuit is formed by the TSW434 chip which transmits the encoded PWM signals into the atmosphere, and the HT12E which becomes responsible for feeding the encoded signals to the TSW chip.

The PWM signals are generated by 4 separate IC 555 circuit stages which may be identical to the one which was earlier discussed in the DRV controller module.

The PWM contents of the 4 ICs can be seen terminated to the respective pinouts of the encoder IC HT12E through 4 discrete push buttons indicated as SW1----SW4.

Each of these buttons correspond and toggle the identical pinout of the receiver module which I have explained earlier and indicated as PWM#1, PWM#2…..PWM#4.

Meaning pressing SW1 may cause the PWM#1 output of the receiver unit active and this will pinout will start feeding the received decoded PWM signals from the transmitter to the associated DRV module and in turn cause the relevant motor to change its speed accordingly.

Similarly, pressing SW2,3,4 can be used for influencing the speeds of the other 3 quadcopter motors as per the users wish.

IC 555 PWM Circuit

The 4 PWM circuits shown in the above RF transmitter handset can be built by referring to th following diagram, which is exactly similar to the one which was seen our DRV controller ESC circuit.

Please remember that the 5K pot could be in the form of a usual pot and this pot could be used additionally with the buttons for selecting different speeds on the corresponding motors.

Meaning by keeping a selected button pressed and simultaneously moving the corresponding 5KPWMpot one can cause the quadcopter to increase or decrease its speed in the intended direction.

Alternatively the PWM could be initially set at some higher or lower level and then the corresponding button pressed to enable the corresponding quadcopter motor to attain the preferred speed, as per the PWM setting.

Quadcopter Motor Specification

The above explained Qiadcopter remote control circuit is intended to be used for display purpose only, and cannot be used for lifting loads or a camera. This implies that the motors used in the design should be preferably a low current type.

The DRV11873 IC is designed to opeate motors rated at 15V, 1.5 amps or around 20 watt motor...so any 3 phase BLDC motor rated at 15 to 30 watts can be used for the purpose.

The battery for this quadcopter design can be any 12v Lipo pr Li-ion battery capable of supplying 15V peak at 1.5 amps continuous current.

Specification Details

1306N Brushless Outrunner Miniature DC Motor

Type: Micro Motor

Construction: Permanent Magnet

Commutation: Brushless

Speed(RPM): 2200rpm/v

Continuous Current(A): 1.5~2.6A

Voltage(V): 7.4~11.1V

miniature dc motor: AX-1306N

weight: 8g

diameter of shaft: 1.5mm

Battery LI-PO: 2-3s

operating current: 1.5~2.6A

max efficiency: 67%