Transcript A Real-Time Linux System For Autonomous Navigation And Flight

A Real-Time Linux System For Autonomous
Navigation And Flight Attitude Control Of An
Uninhabited Aerial Vehicle
Charles E. Hall, Jr.
Mechanical and Aerospace Engineering
North Carolina State University
홍원의
KNU RTLAB
Contents
 LIFT System Hardware
 LIFT System Software
 Implementation of the Flight Controller
 Conclusions
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LIFT System Hardware
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Stingray UAV
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CMH586DX133-64, Real Time Device USA
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800MB Flash drive
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50W power supply
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CMT202(NE2000 compatible) and 10Base-2
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DM6430 Analog I/O data module for transducer
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DM6804 Digital I/O and Timer (PC-104) for radio control and servos
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PC-104 GPS card
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Development system
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Block Diagram of LIFT System
GPS
Receiver
DM6804
Timer Card
Interface Card
DM6430
Analog to Digital
Converter
Transducers
CPU Card
Disk Card
800MB Sandisk
Ethernet Card
Power Supply
PC104 Stack
servos

The interface card multiplexes the radio
control signal and demultiplexes the
servo signal
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Optical isolation of interface card
– prevents inductive spike form the
servo motor getting into the system
– reduce maximum current drain on
the servo power supply
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LIFT System Software

Linux kernel 2.0.36, RTLinux 1.3
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RTLinux tasks are used to implement data acquisition and control laws
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Configuration file in user space is passed to RTLinux task for transducer
with calibration coefficient, control laws configuration and gains
– local certification, flight qualified code

Device drivers for the DM6804 and the DM6430 communicate with RTLinux
tasks
– linking the device driver and RTLinux task in kernel space
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Implementation of the Flight Controller (1/3)

DM6804 hardware Interface : read the pilot commands , generate
commands to servo actuators  no servo pulse chopped
– Too short or long pulse to servos  disastrous for the aircraft

Receiver, R950S(time between servo pulses : 1.8 ~ 3.0ms), reduces the
chance of running together pulse measurement

DM6804 Timer card & two additional timer
– Gear, Aux1, Aux2 and Aux3
– Throttle, Aileron, Elevator and Rudder

Two real time tasks
– Reading pulses from the receiver
• faster executing task, higher priority
– Writing pulses to the servos
• responsible for generation of 50Hz sample rate for the system
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Implementation of the Flight Controller (2/3)
 Read Task
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periodic task with an interval of 0.81ms
priority of 3
can read between 0 and 8 input channels
two arrays that hold input data
can interrupt the Write Task
 Write Task
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periodic task with an interval of 4.0ms
priority of 4
A sequence of 5 Write Tasks generates an interval of 20ms (50Hz)
first four Write Task generate servo pulses
fifth Write Task implements the control laws for the aircraft
• form the output for the next four Write Task execution
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Implementation of the Flight Controller (3/3)
 Fifth Write Task
– inserts a 4 ms delay
– 5 PID control laws and 2 couplers for attitude control and turn
coordination
– 5 PID controller : pitch rate, yaw rate, bank angle, altitude, and velocity
– coupler : calculates commanded pitch rate and yaw rate from bank
angle
• following equations are implemented by the couplers
Φ: bank angle
v : velocity
g : acceleration of gravity
r : pitch rate
q : yaw rate
 User space navigator program read GPS data
– calculate updated commands for altitude, velocity, and bank angle
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Tests
Mean
10.000 ms
Mean
10.5 us
Standard Deviation
4.25 us
Standard Deviation
4.4 us
Maximum
10.042 ms
Maximum
28.0 us
Minimum
9.957 ms
Minimum
3.8 us
RTLinux Jitter Test Result
Read Task Timing
PID Controller
Coupler
(Pitch Rate)
Mean
11.6 us
26.2 us
Std. Dev.
3.15 us
0.25 us
Maximum
15.4 us
28.8 us
Minimum
7.2 us
25.9 us
Controller Timing
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Conclusions
 An onboard avionics package uses the RTLinux to achieve a hard
real time capability for data acquisition and control
 Flight test for attitude controllers will be conducted during the late
summer of 2001
 After these have demonstrated normal operation, the navigator
program will be added to the system
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