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FIRSTFare 2010Sensors for FRC Robots

Dennis C. Erickson ~ Senior Mentor for Teams 1510 and 2898

Daniel Bramblett ~ Team 1510Amy Wiegand ~ Team 2915

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Introduction

A Wide Variety of Sensors can be Used to enhance the operation of the Robot

Primarily used in the Offensive Mode but are also used in Defensive Operations as

an Environment Monitor (e.g., Something’s Coming)

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The FRC Topology

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Sensors

Input devices used to aid in driving the robot and to make

autonomous decisions

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Common Sensors•Photoelectric Sensor•Shaft Encoder Sensor•Yaw Rate Gyro Sensor•3-Axis Accelerometer Sensor•Ultrasonic Detector Sensor•Gear Tooth Sensor•Misc Pneumatic Sensors Also joysticks and video cameras could be considered sensors

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Ultrasonic SensorUse to determine distance to friend or foe. Good from about 8 inches to 20 feetSuggest using a software filter to smooth the data

Operates at 42kHz with readings every 50ms

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Ultrasonic Sensor

The Block Diagram and the Front Panel Used in the Main Robot Application

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Gyroscope SensorYaw Rate GyroSenses angular changes about the top surface axis of thedevice and provides an output voltage proportional to the instantaneous angular rate change. The output is useful for guidance, stability, rate of closure and control of the robot platform. Inertial guidance

Especially useful in designing “smart” Autonomous software

Best to mount flat near the robot’s center of rotation

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Gyroscope Sensor

Front Panel and Diagram

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Accelerometer SensorUse to determine rate of closure, vibration, dynamic or static motion

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Accelerometer SensorSample code used to read the sensor and apply bounds to the data for alarming

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Gyroscope and Accelerometer Sensors

Knowing the instantaneous robot angle and distance traveled at that angle, the position on the field can be determined.

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Differential Peak-Detecting Gear Tooth Sensor

Hall Effect sensor usedfor detecting and counting magnetic fields from ferrous gear teeth related to a robot’s drive operations. For example, it can count teeth on a gear to measure and, through the RC, control robot speed. Use

counter VIs for analysis.

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Encoder SensorUse to determine rate of closure, count events (wheel rotations), monitor chain healthUsed in conjunction with the counter VIsMostly located on a gear box or a motor

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Encoder Sensor

Diagram and Front Panel Example

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Photoelectric SensorsTwo types:•Reflective – A light beam is reflected off an object and that reflection detected by a photo sensitive device•Transmissive (Beam Break) – A light beam is interrupted by an object

Use to determine the presence or absence of objects (balls, etc)

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The JoystickEssentially a sensor that provides for a User interface to the control systemTwo types of data:•Robot direction control (Forward, reverse, turning)•Up to 12 User defined switches (Program modifications, belt controls, etc.)Uses USB connections and can have up to 4 joysticks:•In Tank mode, 2 joysticks are needed•In Arcade mode, one joystick is needed•If switches are required, a joystick is a simple way to control belts and other robot motors, relays, solenoids, etc.

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The Joystick

Front Panel and Diagram

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The Joystick – Using the Buttons as Input Controls

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The Joystick – Using the Buttons as Input Controls

Front Panel and Diagram

Questions?

Dennis C. Erickson - dcerickson1@comcast.net