This page contains my notes on the design and construction of an autonomous quadrotor micro air vehicle (MAV) / UAV.
The principle of operation of a quadrotor as described by Wikipedia: Quadrotor#Flight_Control
Main Components
- central processor (for flight control, navigation, power management, and other duties)
- inertial navigation unit
- Global Positioning System (GPS) receiver
- 4x brushless motor
- 4x electronic speed controller (ESC)
- 2x clockwise (CW) and 2x counter-clockwise (CCW) propeller
- power source
- stiff frame
These components comprise three main systems:
Major systems
- Control and sensing
- Propulsion
- Power
Control and Sensing System
Central Processing Unit (CPU)
The central processing unit (really a microcontroller, but a pretty nice one) is an ARM Cortex-M3 processor, the NXP LPC1768.
It does most of the control and processing work, sampling the sensors in the inertial measurement unit, running PID control loops, plotting navigation paths, and driving the electronic speed controllers (ESCs).
I'm currently using the mbed platform to accelerate development by relying on libraries and object-oriented abstractions for things like SPI communication, PWM signal generation, and GPS parsing.
Inertial Measurement Unit
Tri-axis accelerometer and 2x dual-axis MEMS rate gyroscopes. Sensors are analog, interfaced to an MCP3208 12-bit A/D, which is connected to the microcontroller through SPI.
GPS Receiver
USGlobalSat EM-406A SiRF III GPS Receiver. It does operate correctly at 3.3V; I haven't rigorously tested this.
Description from SparkFun:
- Dimensions: 30mm x 30mm x 10.5mm
- Weight: 16g including cable
- Power consumption: 70mA at 4.5-6.5V
- 20-Channel Receiver
- Extremely high sensitivity : -159dBm
- 10m Positional Accuracy / 5m with WAAS
- Hot Start : 1s
- Warm Start : 38s
- Cold Start : 42s
- Outputs NMEA 0183 and SiRF binary protocol
Bluetooth Serial Module
For communications and debugging. It will probably be replaced by something longer range, maybe a Nordic module such as the nRF24L01+ from SparkFun.
Propulsion System
Brushless Motors
18-11 2000kv Micro Brushless Outrunner from HobbyKing.com
Specifications:
- Model: 1811-2000
- Kv: 2000rpm/v
- Weight: 10g (With wires and mount)
- Suggested Prop: 7×5
- Suggested Power: 7.4v
- No Load Current: .4a
- Thrust: 130g / 5000rpm
- 7.4v no-load speed: 15000rpm
- Peak Eff Current: 5.5A
- Shaft: 2mm
- Diameter: 18mm
- Length: 30mm (including mount & shaft)
Electronic Speed Controllers
These electronic speed controllers (ESCs) drive 3-phase brushless DC motors, sensing orientation through the back EMF. Speed is controlled through PWM signals from the microcontroller, and direction is determined by how the motor leads are connected to the ESC. Swapping any two motor leads will reverse the direction of rotation.
Turnigy Plush 10a ESC specifications:
- Cont Current: 10A
- Burst Current: 12A
- BEC Mode: Linear
- BEC : 5v / 2A
- Lipo Cells: 2-4
- NiMH : 5-12
- Weight: 9g
- Size: 27x17x6mm
Propellers
The aircraft uses two pairs of counter-rotating propellers. In total, there are four propellers, two rotating clockwise and two rotating counter-clockwise, but all producing thrust in the same direction. The torques cancel out, so that the aircraft does not rotate under static hover.
Frame
TODO add some more info. Will be two identical pieces that fit together into a cross, with holes drilled out on the end to mount the motors through set screws.
Power System
2S 1000 mAh Lithium-Ion batteries; 20 C maximum sustained discharge rate at 7.4 V = 148 W max.
Supporting hardware
Temperature probes
These monitor the temperature of the ESCs and the battery packs for dangerous or irregular conditions.
Servos
For auto-stabilization of camera and possibly actuation.
