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Stanford APM:Plane Overview

Trent LukaczykApril 7, 2014

AA241X – UAV Design and Build

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The Problem

Fly AutonomouslyAirframe Construction

State EstimationAlgorithm Processing

Control ActuationGround Monitoring

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The Components

• Autopilot Unit• Wireless Telemetry• Remote Control Radio• GPS Radio• Compass Magnetometer• Airspeed Sensor • Battery Monitor• Servos, ESC, Motor

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Autopilot Unit

• Auto Pilot Module (APM) • ArduPilot Mega (APM) 2.6• Based on Arduino • 16MHz Atmega2560 processor• 16 MB dataflash memory

~ 2hours of logging (download often)

• Needs: to point forward to be securely attached accelerometer calibration if relocated

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Wireless Telemetry

• Wireless Telemetry• 915 MHz, 100mW• Shares a “NetID”• “MAVLink Protocol”

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Wireless Telemetry

USB Micro B

USB A

DF13 6-Pin

DF13 5-Pin

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DF13 Connectors

• Pain and a Half to use• Easy to break• But small, reconfigurable• Be careful when

disconnecting!

Can shave these hooks off with a knife

Can add hot glue at the wire-connector joint.

Do not use super glue here.

Lift this lip gently with a screwdriver

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Radio Control Setup

• RC Transmitter, 2.4 GHz• “Binds” with Receiver– Always carry the bind plug

• Four axes + mode switch• Turn on first, before plane

Autopilot Mode Switch

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Radio Control

3pin Servo Wires x5

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Radio Control Setup

Autopilot Mode Switch

The order of these vary with receiver

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Servo Wires

Mixing up signal and ground can fry electronics

Look for markings like this -

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GPS + Compass

• 1.57 GHz GPS radio– 5Hz position update– Needs clear sight of sky

• Magnetometer– Provides heading estimate– Needs to be clear of

high-current electronics– Needs: to point forward calibration if relocated

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DF13 6pinGPS DF13 5pin

DF13 4pinMAG DF13 4pin

Remember to point GPS and APM forward

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Airspeed Sensor

• Pitot tube measures difference in “Static” and “Total” pressure, which is related to airspeed.

• Airspeed is relative to wind – will be higher or lower if you

travel against or with the wind

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Airspeed SensorSilcone Tubing

3pin Servo Wire

A1

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Power Module

• Records current and voltage from battery • Integrate for energy usage, and battery level• Powers APM, Receiver, Radios, and Servos

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Lithium Polymer Batteries

• 3.7 Volts per Cell• Metrics:– N-Cells (2S = 2 Cells = 7.4V)– Capacity (C = 1100 mAh)– Discharge Rate (25C = 27.5A)– Charge Rate (2C = 2.2A)

• Can catch fire or leak during charging– Always be present during charging

• Capacity loss or Bricking if over-discharged – i.e. leaving plugged in over night

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LiPo Discharge• LiPo’s die suddenly around 3.4Volts/Cell• Be ready to land around 3.5Volt/Cell

traxxas.com

Higher Current

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Speed Controller

• Rated by Max Current and Max Voltage• Direct Current Power in,

Three-phase Alternating Current out• “Opto” vs “BEC”– BEC can power RC gear, Opto can’t

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Brushless Outrunner Motor

• “Outrunner” - magnets rotate around stator• Rated by kV = no load rpm/V– High kV = fast rpm, low torque– Low kV = low rpm, high torque

• Too much power melts windings, burns out motor

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Power Electronics Setup

DC Power

DC Power

3 Phase AC

DF13 6-Pin

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Carbon Folding Props

• More rigid, more efficient, more expensive (vs plastic props)

• More dangerous – they are spinning knives• Spinner cap lets them fold on landing,

or if motor braking is on (more efficient glide)

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Servos

• Drive Motor + Rotation Sensor + PID Control board … in 8-grams

• Forcing the control arms by hand wrecks gears

www.twf8.ws

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Servo Setup

Ailerons

Elevator Rudder

Throttle

Servo Wire “Y”

3pin Servo Wires

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The Components

• Autopilot Unit• Wireless Telemetry• Remote Control Radio• GPS Radio• Compass Magnetometer• Airspeed Sensor • Battery Monitor• Servos, ESC, Motor

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The Problem

Fly AutonomouslyAirframe Construction

State EstimationAlgorithm Processing

Control ActuationGround Monitoring

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Stanford_ArduPlane

• An easy embedded flight control software for Aerospace Engineers, based on ArduPlane

• ArduPlane code without the control law

https://github.com/rbunge/Stanford_ArduPlane

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Development Tools

• Download and install the ArduPilot Arduino IDE

• Download Libraries and place in the Arduino sketch folder

• Download Stanford ArduPlane

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Building

• Open \Stanford_ArduPlane\ \Stanford_ArduPlane.ino with Arduino

• Check the board type (Mega 2560) and COM port

• “Verify” = compile• “Upload” = compile and upload to APM

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The Code

• Editable:– AA241X_ControlLaw.ino– AA241X_ControlLaw.h

• Not Editable:– AA241X_Competition.h– AA241X_aux.ino– AA241X_aux.h– Everything Else…

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The Code

• State and Control Variables (AA241X_aux.h)– Roll, pitch, yaw angles and rates– Inertial velocity and accelerations– Heading– Airspeed– GPS X-Y positions– GPS and Barometric Altitudes– Battery Consumption– RC Inputs, Servo + Throttle Outputs

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The Control Loops

• AA241X_ControlLaw.ino– AA241X_AUTO_FastLoop(void){}

Executes @ ~50Hz– AA241X_AUTO_MediumLoop(void){}

Executes @ ~10 Hz– AA241X_AUTO_SlowLoop(void){}

Executes @ ~3.3 Hz• Distribute algorithm to use CPU cycles wisely• Beware of APM Memory limits– 256k Flash Program Memory, 8K SRAM, 4K EEPROM

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The Camera Function

• AA241X_aux.h

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Telemetry Plotting

• Two types of logs – Telemetry log– Dataflash log• store at higher log-rates• Download from APM over USB Cable

• Mission Planner can dump matlab data files

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The Problem

Fly AutonomouslyAirframe Construction

State EstimationAlgorithm Processing

Control ActuationGround Monitoring

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Resources

• FliteTest: youtube channel• DIY Drones: forum• RC groups: forum• GrabCAD: community CAD models• 3DRobotics: Store and Manuals• GitHub: Stanford_ArduPlane Code