F'I'R'S'T Robotics Sensors 101

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F.I.R.S.T Robotics Sensors 101
January 5th 2008 Montgomery High School Skillman,
NJ

• Michael Reffler
• Mentor FRC Team 1089
• Hightstown, NJ
• MReffler_at_gmail.com

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AgendaSensors 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 ?

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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

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CMUCam2Sensors 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

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CMUCam2 Sensors 101

• CMUCam2 Camera
• Labview / Focusing and Calibrating
• CMUCam2 GUI / Focusing and Calibrating
• RC default camera code-Kevin Watson

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CMUCam2Labview Interface

• Camera Focus
• Load Sample Configuration
• Track Colors / View Results

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CMUCam2Kevin 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

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CMUCam2Finding Range to the Light

• range Height_of_Light Height_of_Camera /
  tan(tilt_angle_radians)

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Yaw Rate GyroSensors 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

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Yaw Rate GyroSensors 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).

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Dual Axis AccelerometerSensors 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 gt 6 KHZ.

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Dual Axis AccelerometerSensors 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.

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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.

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Gear ToothSensors 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.

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Quadrature EncodersSensors 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.

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Quadrature EncodersSensors 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.

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PotentiometersSensors 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.

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PotentiometersSensors 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

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Sonar/Sonic RangersSensors 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 3.3-5.5V

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Sonar/Sonic RangersSensors 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.

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Touch/Bumper SensorsSensors 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.

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Infrared SensorsSensors 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.

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Light SensorsSensors 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.

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Autonomous NavigationSensors 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.

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Information ResourcesSensors 101

• ChiefDelphi White Papers
• Working the Angles
• http//www.chiefdelphi.com/media/papers/1755
• Sample Gyro code
• Quadrature Encoders
• http//www.chiefdelphi.com/media/papers/1490
• Sample Encoder code
• Kevin Watson FAQs and Sample Code
• http//www.kevin.org/frc/camera/
• http//www.kevin.org/frc/gyro/
• http//www.kevin.org/frc/encoder/

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Vendors and SuppliersSensors 101

• Digi-Key Electronics
• http//www.digikey.com/
• Newark in One
• http//www.newark.com/
• Mouser Electronics
• http//www.mouser.com/
• Jameco Electronics
• http//www.jameco.com/
• Sparkfun
• http//www.sparkfun.com/
• USDigital
• http//www.usdigital.com/

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Questions ? Answers?Sensors 101

• ???