Available at: – Program Optical Quad Encoders in Autonomous Mode Program optical quad encoders in autonomous mode

Available at: – Program Optical Quad Encoders in Autonomous Mode Program optical quad encoders in autonomous mode  Performance Objective: Given the components of a VEX robotics design system program optical quad encoders in autonomous mode to have the robot travel in a two foot square.  Enabling Objectives:  explain the purpose of an optical quad encoder  explain how an optical quad encoder operates  draw a flow chart for using an optical quad encoder  program an optical quad encoder

Available at: – Program Optical Quad Encoders in Autonomous Mode Optical Quad Encoder  An encoder is a digital sensor whose signals can be used to measure and define rotational movement  A quad encoder has two outputs, typically called the A Channel and B Channel.  These outputs are out of phase with one another and are used to determine direction of rotation (CW or CCW)

Available at: – Program Optical Quad Encoders in Autonomous Mode How does it work?  The encoder works by shining light onto the edge of a disk outfitted with evenly spaced slots around the circumference  As the disk spins, light passes through the slots and is blocked by the opaque spaces between the slots  As the disk rotates, the encoder detects and counts the number of slots light has passed through (pulses) determining distance traveled and direction of rotation

Available at: – Program Optical Quad Encoders in Autonomous Mode Optical Quad Encoder  The encoder counts pulses and keeps track of the number in the variable name that you set for the encoder  1 full revolution of the encoder is 90 pulses  If you program a motor to turn for 90 pulses of an encoder, it will turn one revolution

Available at: – Program Optical Quad Encoders in Autonomous Mode Encoder Resolution  The number of pulses per revolution of the encoder is its resolution  If the encoder is turning faster than the motor, the resolution will be increased, if the encoder revolves twice (180 pulses) for one wheel revolution, you can be more accurate with the encoder  The resolution can be increased by putting the encoder on a shaft that is spinning faster than the shaft on the motor (gearing up)  The optical VEX quad encoder can detect up to 1,700 pulses per second, which corresponds to 18.9 revolutions per second

Available at: – Program Optical Quad Encoders in Autonomous Mode Optical Quad Encoder  When you drag an Optical Quad Encoder block into the Programming Window, the Optical Quad Encoder dialog box appears, allowing you to choose one of four commands for the encoder function to process:

Available at: – Program Optical Quad Encoders in Autonomous Mode Programming a Quad Encoder  The Start option tells the encoders to start counting encoder pulses  The Preset option allows you to set the encoder to a fixed value or to the value of a variable  The Get option allows you to store the feedback from the encoder into a variable  The Stop option tells the encoders to stop counting encoder pulses.  It is important to stop your encoders when they are not in use to keep from overloading your system

Available at: – Program Optical Quad Encoders in Autonomous Mode Programming a Quad Encoder  Select the Interrupt Port number for the A channel that corresponds with the port on the Vex controller  Select the Input Port number for the B Channel that corresponds to the port on the Vex controller  Use Invert Direction to reverse the positive direction of rotation

Available at: – Program Optical Quad Encoders in Autonomous Mode Flow Chart a Quad Encoder  Draw a flow chart for a program that will turn two encoders on, set preset value to 1, and begin to count the pulses  If the encoders are less than a certain value, then turn the motors on, once the encoders reach that value, the motors should shut off

Available at: – Program Optical Quad Encoders in Autonomous Mode Flow Chart for Quad Encoder Start Encoders End Drive Forward Stop Motors Yes No If encoders < X

Available at: – Program Optical Quad Encoders in Autonomous Mode Program the robot using the quad encoders  Using the prepared robot, plug the two quad encoders into appropriate ports on the microcontroller  Begin a new competition project in easyC  Configure the project microcontroller accordingly  Define two global variables for the two quad encoders  Program the robot in a driving mode of your choice in the Operator Control tab  Go to the Autonomous tab to being programming the quad encoders

Available at: – Program Optical Quad Encoders in Autonomous Mode Program the robot using the quad encoders  Insert a start block for each of the encoders  Insert a preset block for each encoder, presetting each encoder to 1

Available at: – Program Optical Quad Encoders in Autonomous Mode Program the robot using the quad encoders  Insert a while loop for 1==1  Inside the while loop insert a block to get the value for each variable defined for the quad encoders

Available at: – Program Optical Quad Encoders in Autonomous Mode Program the robot using the quad encoders  Insert an If statement  The If statement should read “encoder1 && encoder2 <= 90”  “Encoder1 and encoder2” are the variable name for each encoder  “&&” means “and”, both variables must be less or equal to 90  Insert two motor modules to make the move forward

Available at: – Program Optical Quad Encoders in Autonomous Mode Program the robot using the quad encoders  Insert an Else statement that stops the motors once the value in the if statement has been reached

Available at: – Program Optical Quad Encoders in Autonomous Mode Download the code  Build and download the code to the microcontroller  Use the Competition Switch Simulator to test the program  The robot should turn the motors/wheels one revolution and then stop  If your code works show your instructor before proceeding to the next slide  If your code does not work, go back through the lesson and see if you can determine the cause

Available at: – Program Optical Quad Encoders in Autonomous Mode Move the robot 5 feet  With the quad encoders you can program the robot to move a predetermined distance  This can be done by adjusting the number of pulses the motors move  How many pulses will make the robot move 5 feet?

Available at: – Program Optical Quad Encoders in Autonomous Mode Travel Distance  Recall the 90 pulses equals one revolution  We can determine how far the robot moves with one revolution of the wheels  The wheel moves the distance of its circumference for each revolution  What is the circumference of the wheels?

Available at: – Program Optical Quad Encoders in Autonomous Mode Calculating Circumference  Circumference(C) equals the diameter(d) of the wheel times(x) pi(3.14)  C = d x 3.14  Measure the diameter of the a wheel on the robot  Multiply that measurement by 3.14  You now have the circumference of the wheel

Available at: – Program Optical Quad Encoders in Autonomous Mode  If a wheel is 5 inches in diameter, its circumference is 15.7 inches  If I wanted to move forward 15 feet (180 inches) I would divide 180 inches by 15.7 inches (the circumference) to calculate the number of revolutions required, ” / 15.7” = rev  Then multiply times 90 (number of pulses in one revolution) to calculate the number of pulses, rev X 90 pulses = pulses How many pulses?

Available at: – Program Optical Quad Encoders in Autonomous Mode You Calculate  If you wanted the robot with the encoders to travel 5 feet, how many pulses should it go?  Modify your program code to have you robot move forward 5 feet

Available at: – Program Optical Quad Encoders in Autonomous Mode Finished!  If your robot moves forward 5 feet and then stopped, your done!  Show your instructor your success  For more technical data on the optical quad encoder, visit:

Available at: – Program Optical Quad Encoders in Autonomous Mode Challenge  Now that you know how to program the optical quad encoders...  Draw a flow chart that utilizes optical quad encoders to have the robot travel in a two foot square  Program the robot to travel in a two foot square  When you have completed this challenge, have your instructor check this activity off on the performance evaluation