1. F.I.R.S.T Robotics Sensors 101
January 5th 2008 Montgomery High School Skillman, NJ
Michael Reffler
Mentor FRC Team 1089
Hightstown, NJ

2. Agenda Sensors 101 General Points CMUCam-2 Yaw Rate/Gyro Accelerometer
Gear Tooth
Encoders
Potentiometers
Sonic Range Finder
Other Sensors
Sensor Navigation
Information Resources
Vendors and Suppliers
Questions ?

3. General Points Sensors 101
Balance your drivetrain mechanically
Programming Techniques
State Machines
Function Driven
Multiple fallback implementations for when sensors or appendages break
Pay close attention to LIMITS when designing for sensors
Use RF shielded cabling/wiring
Physical protection/project boxes

4. CMUCam2 Sensors 101 What can you do with the camera?
Track colors, e.g., illuminated target
Locate the scoring goal
Orient the robot or a turret to the goal
Heading & angle or distance
Drive to the goal

5. CMUCam2 Sensors 101 CMUCam2 Camera Labview / Focusing and Calibrating
CMUCam2 GUI / Focusing and Calibrating
RC default camera code-Kevin Watson

6. CMUCam2 Labview Interface
Camera Focus
Load Sample Configuration
Track Colors / View Results

7. CMUCam2 Kevin Watson Camera Code
Just does the camera tracking
Load initial calibration data
Tracking.h Settings
PAN/TILT servo pwm assignment
Reversing servo direction
Camera/tracking menus through Hyperterminal
Camera settings stored permanently on the RC
Use Get_Tracking_State()
Use Pan/Tilt angles for direction and distance

8. CMUCam2 Finding Range to the Light
range = Height_of_Light – Height_of_Camera / tan(tilt_angle_radians)

9. Yaw Rate Gyro Sensors 101 Yaw Rate Gyro (ADXRS150)
Measures angular rate (150o/sec) along the Z axis.
Supply voltage 5V.
Output – analog.
Alternative Yaw Rate Gyro (ADXRS300)
Measures angular rate (300o/sec) along the Z axis

10. Yaw Rate Gyro Sensors 101 What can you do with the gyro sensor ?
Application: Stability control, guidance.
Rotate robot left or right while the gyro reading is less than Xo.
If robot rotates too fast (the rate of change of the gyro sensor) then reduce motor speed (good in any mode).

11. Dual Axis Accelerometer Sensors 101
Dual Axis Accelerometer (ADXL 311)
Measures dynamic and static acceleration on both X and Y axis.
Supply voltage 5 V.
Output – analog. Bandwidth 3KHZ.
Sampling frequency > 6 KHZ.

12. Dual Axis Accelerometer Sensors 101
What can you do with the accelerometer?
Application: tilt or motion sensor.
Am I standing straight?
Measure pitch and roll in degrees.
Pitch = asin(Ax/1g); Roll asin(Ay/1g).
Orient an arm.
Collision detection.

13. Gear Tooth Sensors 101 Gear Tooth Sensors (2)
AT642LSH Peak Detecting Gear Tooth Sensor.
Generates a pulse when a gear tooth is detected.
Speed of the gear: pulse rate.
Cannot easily determine direction of the gear
Digital Output.
Supply voltage: 12 V.

14. Gear Tooth Sensors 101 What can you do with the gear tooth sensors?
Control the speed of the wheel.
Adjust for relative speed difference between wheels.
AUTONOMOUS MODE:
Move d feet distance.
Circumference of the wheel.
2 * PI * R / Gear Teeth = Inches per Pulse.

15. Quadrature Encoders Sensors 101
Encoders are commonly used as feedback devices for motor controllers.
An encoder is a sensor that uses light to sense the speed and direction of a rotary shaft.
Encoders produce quadrature outputs which indicate the speed and direction of the shaft.
Inherently free from contact wear and the digital outputs are bounce less.
Provide greater accuracy and precision.
Digital Output (2) (A & B).
Supply Voltage 5 V.

16. Quadrature Encoders Sensors 101
What can you do with encoders?
Everything you can do with a gear tooth sensor.
PLUS :
Direction indication (you can now tell which direction your going even if you are being pushed in an opposite direction).
Greater Precision/Accuracy
Higher Speeds
AUTONOMOUS MODE:
Move d feet distance.
Circumference of the wheel.
2 * PI * R / CountsPer = Inches per Pulse.

17. Potentiometers Sensors 101
Measures the rotation angle in terms of electrical degrees.
0o to 300o-340o depending on the pot.
Use Linear Taper NOT Audio Taper.
Wire Wound, Conductive Plastic.
Limited number of revolutions.
Unlimited versions are available, but rare.
Sliders are available instead of rotational.
100K ohm for the OI.
10K, 5K, 1K ohm for the RC.
Analog Output.
Supply Voltage 5V.

18. Potentiometers Sensors 101
What can you do with potentiometers?
Measure the angle of an elbow on an arm
Move the arm up or down until Xo is reached
Measure the turn of a turret
Turn left or right until Xo is reached
Raise or lower a telescoping arm
Move up or down until Xo is reached

19. Sonar/Sonic Rangers Sensors 101
Emit a sound and measure the time of flight  distance.
Ranges: 6 inches – 20 feet, with a field of view of approximately 30o.
Other versions available with smaller/narrower beam widths.
Analog Output ~9.8mv inch
Supply Voltage V

20. Sonar/Sonic Rangers Sensors 101
What can I do with a sonic range finder?
Measure the distance to an object.
Listen for approaching objects.
Another robot is approaching so move away.

21. Touch/Bumper Sensors Sensors 101
If pressure is applied to it, an electrical signal is generated.
What can you do with it?
I already bumped into something. I better get back, stop, or move around it.

22. Infrared Sensors Sensors 101
Emit modulated infrared (IR) energy and measure amount of (IR) returned.
Range: inches to several feet.
Led IR sensors have ranges of 3-5 inches.
Problems: Most venues use halogen/tungsten lighting. 90% of the energy emitted is infrared radiation.

23. Light Sensors Sensors 101
Red LED emits light and a phototransistor measures the incoming light.
What can you do with a light sensor?
Recognize objects of certain colors.
Follow a line.
Problems: Ambient light and battery level affect sensor readings.

24. Autonomous Navigation Sensors 101
Find the light.
CMUCam2 Get_Tracking_State().
Get direction left or right degrees (pan angle).
Get distance to the light (tilt angle and a lookup table).
Turn towards the light.
Use the gyro to turn to the matching pan angle.
Drive towards the light.
Encoders / Gear tooth (Counts per inch).
Gyro keep driving straight (+/- a few degrees).
Fine tune.
Sonic Ranger creep in until inches away.
Raise the arm.
Potentiometer measure the upward angle.

25. Information Resources Sensors 101
ChiefDelphi – White Papers
Working the Angles
Sample Gyro code
Quadrature Encoders
Sample Encoder code
Kevin Watson FAQ’s and Sample Code

26. Vendors and Suppliers Sensors 101
Digi-Key Electronics
Newark in One
Mouser Electronics
Jameco Electronics
Sparkfun
USDigital

27. Questions ? Answers? Sensors 101
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