Introduction
This Article gives a brief summary on The Quadcopter System Architecture and the modules to create a quadcopter.
Quadcopter Controls and flying Mechanics :
A Quadcopter is controlled by 4 commands as mentioned below :
Throttle : The throttle controls are generally present on the left joystick of the remote control and can be increased or decreased by moving the stick up or down respectively.
The Throttle control moves the drone up and down.
Roll : The Roll controls are generally present on the right joystick of the remote control and can be controlled by moving the joystick left or right.
The Roll control moves the drone right and left.
Pitch : The Pitch controls are generally present on the right joystick of the remote control and can be controlled by moving the joystick up or down.
The Pitch control moves the drone forward and backward.
Yaw : The Yaw controls are generally present on the left joystick of the remote control and can be controlled by moving the joystick left or right.
The Yaw control rotates the drone on its own axis towards left and right.
Quadcopter motor controls and flying direction
A Quadcopter has 4 propellers which are connected to the Motors.
The movement of the drone in a particular direction can be controlled by controlling the speed of these 4 motors as shown in the below diagrams :
Hover : The drone Hovering can be controlled by driving all the 4 Motors at same speed.
This is controlled by throttle balance.
Descend : The drone can be descended or landed by reducing the speed of all the 4 motors simultaneously. This is controlled by remote throttle down.
Ascend : The drone can be ascended or take off by increasing the speed for all the 4 motors simultaneously. This is controlled by remote throttle up.
Forward : The drone can be moved forward by increasing the speed of motors 3 and 4 and decreasing the speed of motors 1 and 2 simultaneously. This is controlled by Remote Pitch Control up.
Backward : The drone can be moved backward by increasing the speed of motors 1 and 2 and decreasing the speed of motors 3 and 4 simultaneously. This is controlled by Remote Pitch Control down.
Turn Left : The drone can be turned in the left direction by reducing the speed of motors 1 and 4 and increasing the speed of motors 2 and 3 simultaneously. This is controlled by Remote Roll Control left.
Turn Right : The drone can be turned in the right direction by increasing the speed of motors 1 and 4 and decreasing the speed of motors 2 and 3 simultaneously. This is controlled by Remote Roll Control Right.
Rotate Right : The drone can be rotated in the right direction by increasing the speed of motors 1 and 3 and decreasing the speed of the motors 2 and 4 simultaneously. This is controlled by Remote Yaw Control Right.
Rotate Left : The drone can be rotated in the left by increasing the speed motors 2 and 4 and decreasing the speed of the motors 1 and 3 simultaneously. This is controlled by Remote Yaw Control Left.
Quadcopter Hardware Modules
A Quadcopter or a Drone has the following basic Hardware Modules :
- Radio Transmitter Module
- Radio Receiver Module
- Flight Controller Module
- Electronic Speed Controller Module
Quadcopter Receiver System :
The below diagram represents a basic Quadcopter Receiver System, It comprises of Radio Receiver, Flight Controller and Electronic Speed controllers and Motors with propellers connected to them.
The Radio Receiver receives the Input commands from the Remote Transmitter, it then sends these commands to the Flight controller which then converts these commands to the corresponding PPM signals which are sent to the Electronic speed controller.
The Electronic speed controller converts these PPM signals to the PWM signals and sends them to the corresponding Motors thereby controlling their speeds.
Flight Controller Module
The Function of the Flight controller is stabilizing the quadcopter and executing user control. The below diagram represents the Chipsets used in a typical Drone Flight Controller Module.
Radio Chipset :
Function : The Function of the Radio Chipset is to transmit and receive wireless signals in the form of channels.
Inputs : The Inputs to the Radio Receiver is basically the RF signal using 2FSK modulation and ISM band frequency of 2.4Ghz.
Outputs : The Output from the Radio Receiver is the digital SPI interface connected to the MCU.
IMU Chipset :
Function : The function of the IMU-Inertial Measurement Unit fusion chipset is to estimate the quadcopter’s orientation, It is a sensor fusion of 3 parameters : 3 axis accelaration,3-axis gyroscope and 3-axis magnetometer.
Inputs : The Inputs to the IMU are the acceleration, gravity ,vibration and earth’s magnetic field.
Outputs : The Output from the IMU chipset are the digital SPI/I2C interface connected to the MCU.
MCU Chipset :
Function : The function of the MCU is to perform the computations for drone stabilization and Inputs and convert these inputs to the digital signals to control the Motors through ESC.
The MCU basically processes the code for the PID(proportional integral derivative) control Loop.
Inputs : 2 x SPI connections, 1 x USB
Outputs : 4 x PWM connections
Programming : 1 x ISP connection
Core : 32 bit, 120 MHz ARM Cortex-M4
Flash : 512 KB
RAM : 128 KB
ADC/DAC : 2 x 16 bit ADC converter, 2 x 12 bit DAC converter
Timers : 2 x 8 channel PWM Timers
Operating Voltage : 3.3V
Function : Low dropout Voltage regulator is used to regulate the output voltage to the desired value, A portion of the LDO output voltage is fed back to the internal error amplifier and compared with the precision internal band gap reference.
Input : Voltage range 2.5V to 13V.
Output : Regulated Voltage of 3.3V.
Electronic Speed Controller Module
The Electronic speed Controller Module consists of Microcontroller (MCU), gate drivers and high power FET’s for driving brushless motors.
MCU Chipset :
The function of the MCU is to take the inputs from the Motors and the Flight controller module and process these inputs to drive the 3 phase brushless motors through the gate drivers and the FET’s.
The MCU basically processes the code for the zero crossing back EMF(BEMF) and filter to suppress the PWM Noise.
Inputs : 1 x I2C connection, 1 x USB
Outputs : 3 x PWM connections
Programming : 1 x ISP connection
Core : 32 bit, 48 MHz ARM Cortex-M0
Flash : 128 KB
RAM : 16 KB
ADC/DAC : 7 channels ADC converter
Timers : 6 Timers
Operating Voltage : 3.3V
Gate Driver Chipset :
Function :Dual MOSFET Power Driver to drive the gates of High side and Low side Power MOSFET’s.
Inputs : 1 x PWM signal
Outputs : 2 x MOSFET’s ports
Gate Chipset :
Function : MOSFET gate
Input : 1 gate port
Output : 2 x ports.
Drone Remote Controller Module
MCU Chipsets :
The function of the MCU is to take the inputs from the joysticks and process these inputs to connect the SPI interface of the Radio Chipset.
Inputs : 2 x Analog Inputs, push button inputs, 1 x USB
Outputs : 1 x SPI connection
Programming : 1 x ISP connection
Core : 8 bit,16 bit, 32 Bit
Flash : 128 KB
RAM : 16 KB
ADC/DAC : 1 ADC converter, 1 DAC converter
Radio Chipset :
Function : The Function of the Radio Chipset is to transmit and receive wireless signals in the form of channels.
Inputs : The Inputs to the Radio Receiver is the digital SPI interface connected to the MCU.
Outputs : The Output from the Radio Receiver is the RF signal using 2FSK modulation and ISM band frequency of 2.4Ghz.
Charger Chipset :
Function : LiPo charge controller
Inputs : 1 x Charge enable, 1 x VDD
Outputs : 1 x VBAT
Embedded Firmware Modules
The key firmware modules to be used for this design are:
- Analogue to Digital Conversion Firmware Module
- RF Transmitter Firmware Module
- RF Receiver Firmware Module
- Flight Controller Firmware Module
- PWM Controller Firmware Module
