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ME 224 Experimental Engineering: Professor Espinosa 2005
Overview
Goal
Assembly
Programming
Gyroscope Calibration
Feedback Control
Conclusion
ME 224 Experimental Engineering: Professor Espinosa 2005
Assembly• Building and assembly
– Robotic kit
– Additional parts• Handy board
• Metal Wheely Bar
• Bread board– Gyroscope, Operational amplifier,
low pass filter: R, C
• Programming– Several choices in programming
codes
ME 224 Experimental Engineering: Professor Espinosa 2005
Programming
• Choosing the Code– Labview
• Non RealTime
• External connections
– Basic Stamp• Avoid analog to digital converter
• External computations
• Programmed in Basic
ME 224 Experimental Engineering: Professor Espinosa 2005
Programming• Interactive C
– Advantages• Analog input with 8 bit
precision
• No external connections
• Easier to program
• LCD display
– Disadvantages• Causes noise in the
gyroscope rate out
– CODE
ME 224 Experimental Engineering: Professor Espinosa 2005
Self Test
* Verified Chip Function
* Applied the following connections
* Behavior:
- +/-0.66V Change @ rateout
ME 224 Experimental Engineering: Professor Espinosa 2005
ADXRS150 - Angular Rate Sensor
• http://www.sensorsmag.com/articles/0903/53/main.shtml
Fc = -2m(ω x vr)
ME 224 Experimental Engineering: Professor Espinosa 2005
Gyroscope Calibration• First Stage
– Rotate Robot at different angular velocities for different periods of time
– Use Labview to obtain Output Voltage
– Analyze data with Excel, taking an average of the output voltage
– Test Robot
ME 224 Experimental Engineering: Professor Espinosa 2005
Obtained Data
Gyroscope Calibration
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
0 100 200 300 400 500 600 700 800 900 1000
Time (5ms)
Vo
ltag
e d
iffe
ren
ce f
rom
bas
elin
e (V
)
ME 224 Experimental Engineering: Professor Espinosa 2005
Calibration ResultsGyroscope Output Voltage vs. Angular Velocity
y = -0.0022x + 1.9356
R2 = 0.9998
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
50 100 150 200 250 300
Angular Velocity in Deg/Sec
Gyr
osc
op
e O
utp
ut
Vo
ltag
e in
V
ME 224 Experimental Engineering: Professor Espinosa 2005
Gyroscope Calibration
• Angles not followed correctly
• Second Stage Calibration– Reduce noise caused mainly by vibrations and
handy-board by adding a low-pass filter– Supply 5V instead of 4.75 V to gyroscope– Re-Calibrate using different method
ME 224 Experimental Engineering: Professor Espinosa 2005
Re-Calibration
• Write simple program to rotate robot 1080 degrees
• Adjust the “gyro calibration factor” (degrees/second/volt)
• Iterate several times until angle of rotation is accurate enough
• Test Robot by following the path
ME 224 Experimental Engineering: Professor Espinosa 2005
FeedBack Control• Two Sectors of control
– Straight– Turns
• Limitations of servos– Do not change speeds easily– 20 millisecond update limit– Jitter response to noise
ME 224 Experimental Engineering: Professor Espinosa 2005
Is t < desired runtime L
Calibrate gyro center: C(volts)
No YesStop
Servo Pulse: A7=constA5=const
V < C - .03 V > C + .03 V = C ± .03
t = t +.5Gyro output: V(volts)
Correct Left:Servo A7 pulse +1
Correct RightServo A5 pulse + 1
No Correction
Feedback Control Diagram for Strait Linear Motion
User Input: L(seconds)
ME 224 Experimental Engineering: Professor Espinosa 2005
Feedback Control Diagram for Constant Rotation Turns
User Input: D(degrees) Calibrate gyro center: C(volts)
Is Deg < D
No Yes
Servo Pulse: A7=constA5=const
Calibrated gyro conversion factor: S(ω/volt)
Stop
Gyro output: V(volts)
Deg = Deg + ω*.01
ω = (C-V)*S
t = t +.01
ME 224 Experimental Engineering: Professor Espinosa 2005
Special Features
• No extensions / attached harnesses
• LCD read out
• Adjustable trajectory length
• Accuracy