quadcopters. history also known as quadrotors first flying quadrotor: – 11 november 1922 –...
TRANSCRIPT
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Quadcopters
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History
• Also known as quadrotors• First flying quadrotor:– 11 November 1922 – Etienne Oehmichen
Image: blogger.com
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History
• Quadrotors overtaken by helicopters due to workload of the pilot.
• Some experimental aircraft in the 1950’s
Image: San Diego Air & Space Museum Archives Image: Wikimedia
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Now
• Increasingly more popular– Unmanned and small– Very maneuverable– Mechanically simple– Electronic stabilization
• Used for many applications– Photography, inspections, military … toys.
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Definitions
• Roll, pitch and yaw• Lift, drag, trust and weight
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How does a quadcopter work?
• 2 pairs of counter rotating motors• Roll, pitch and yaw control:– By varying motor speed
1 2
3 4
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How does a quadcopter work?
• Roll and pitch• Differential thrust
• Image: pitch forward
LLLLL 4321
LLLLL 4321
LLLLL 4321
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How does a quadcopter work?
• Yaw• Differential torque
• Image: rotate clockwise
04321
4321
TTTT
LLLLL
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How does a quadcopter work?
• Requires control of the motors• Requires (electronic) stabilization:– Due to aerodynamic effects (vortices) – Differences between motors– Weight distribution
• To do this:– Requires speed controllers– Requires sensors and MCU– Understanding of the forces
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How does a quadcopter work?
• System overview:
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How does a quadcopter work?
• Main components:– Frame– 4 motors and their propellers– 4 speed controllers– Electronic stabilization– Battery– Receiver / other control
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Pitch and roll
• Lift is always perpendicular to the flow direction, in our case the rotor plane.
• The gravity is always perpendicular to the ground.
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Pitch and roll
• Lift and gravity with pitch and roll.– More lift required – Horizontal lift component provides thrust– When thrust overcomes drag the quadcopter
moves.
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Pitch and roll
• Gyro can sense the rotation around the pitch or roll axis.– Unit is rotation in degrees per second.– Integrating this yields pitch or roll angle.
• Accelerometer can measure gravitational components.– Pitch and roll angle can be calculated with three axes, two
per angle (x,z) and (y,z).
• But….
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Pitch and roll
• Why will this not work well in practice?• Gyro’s (especially MEMS and Piezo):– Have a noisy signal– Have an offset (temperature, other effects)– This results in accumulating error in the integration.– Gyro’s can be used for short corrections
• Accelerometers:– The forces described previously are only in uniform linear
motion.– In turns there are more forces due to horizontal lift
component.
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Pitch and roll
• When a plane/quadcopter turns it has to roll.• This results in a horizontal and vertical lift component.• The horizontal lift component gives a centripetal force.• The weight and centrifugal force result in cancel out the
lift (plane does not climb)• This is more commonly known
as g-force or load factor.• This can be estimated by:
For example 30 degree turn is 1.15g• The accelerometer will measure this in the Z-axis, the other
axes are 0.
)cos(1
g
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Pitch and roll
• A quadcopter not only has this for roll but also for pitch in sideways movements.
• How to solve this:– Combine both the gyro and accelerometer
information using sensor fusion.– This also makes measurements less sensitive to
noise (for example due to vibration).
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Yaw
• Turning around the top-axis.• Usually compensated with gyros (short term
compensation). Again: drift.• For absolute yaw control: use a magnetometer– Basically an electronic compass.
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Altitude
• Can be determined with distance sensors (e.g. ultrasone, laser or infrared)
• Can be determined with barometric sensors
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Lateral drift
• Two movements you cannot really detect– Optical flow
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Local control
• Keeps the quadcopter stable.• Requires sensor fusion– (Extended) Kalman filter– Direct Cosine Matrix– Linear complementary filter
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Local control
• Various control schemes are used by open source projects:
Image: IEEE: Build your own quadrotor
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Navigation
– GPS– Visual servoing (markers)– SLAM– Lidar
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TU/e designed quadcopter
• Optional to use, you can design your own quadcopter.
• 17 minutes flying time• Max. 1 kilogram of payload• Component list available• Open source software
(MultiWII)
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TU/e designed quadcopter
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TU/e designed quadcopter
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TU/e designed quadcopter
• MultiWII pro flightcontroller• Flightcontroller communicates via bluetooth• Can be flown manually with RC controller• Sensors:– 3-axis gyro (ITG3205)– 3-axis accelerometer (BMA180) – 3-axis magnetometer (HMC5883L)– Barometer (BMP085)– GPS receiver (MTK3329)
• Motor RPM counter
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TU/e designed quadcopter
• Cost quadcopter including shipping– Approximately 500 dollar (385 euro)
• Frame• 2 Batteries• RC transmitter and receiver• 4 Speed controllers• 5 Motors (1 spare)• Propellers (12 pieces)• Flight controller• Battery charger + power supply for charger• GPS• Bluetooth• Laser module
• Beware of taxes and customs fees!
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TU/e designed quadcopter
• Computer vision:– Cubieboard 3 (2-core CPU, 2GB DDR3, 8GB Flash)– Logitech webcam C270 (1280 x 720)– VGA webcam with wide-angle lens
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TU/e designed quadcopter
• Cost vision boards 155 dollar (115 euro)– Cubieboard 3 – Logitech webcam C270– VGA webcam• Wide angle lens
• Beware of taxes and customs fees!
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Lessons learned from last year
• Try to have your quadcopter built and flying stable as soon as possible.
• Ultrasound distance sensing is problematic on large quadcopters indoors.
• Build quality greatly influences stability, sensor noise, etc.
• Don’t discharge your batteries too much.• … no, a raspberry Pi is not fast enough …
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Assignments
1. Build your quadcopter and get it flying.2. Adjust the PID settings and try to find the
most stable result.3. Implement a downward facing camera to
compensate for sideways drift and use the laser for altitude control.
4. Task of your choice: marker following, face detection, SLAM, etc.
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Questions?
• Thanks for your attention