Oakland County Competitive Robotics Association

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Oakland County Competitive Robotics Association

• Marc Center, GM Engineer, marc.center_at_gm.com
• OCCRA VEX Mentor
• Mark Taylor, Pontiac Teacher
• Clarkston.metaylor_at_comcast.net
• OCCRA Vex Mentor

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VEX WORKSHOP - Monday September 10, 2007
MEETING AGENDA

• 1 Handout VEX KITS
• BUILD Square Bot by 2nd meeting focus on
  programming Ver 1.1 OCCRA
• Handout VEX Kits Kroll - later
• 3 DEMO LTU ROBOFEST
• 4 OCCRA Rules/Field 430 pm?
• Program Firmware with V5/V7?
• Paul Centers Vex Robots
• Sams (Chief Delphi)Vex Robot
• Manually start autonomous operation

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Workshop Homework This week
Bring Laptops with programming software Easy C
Ver 1.1 (OCCRA)
Version 7 is latest Master Software
Bring Laptops with programming software Ver 1.1
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Lessons shared from existing VEX users
1) Motor module and Servo module look similar
(both green) 2) Shaft collars are required on the
outputs of shafts but are not shown in the
instructions 3) Spacers are missing or use
collars 3) INFO Bolt thread are 8-32 and wrench
size is 11-32 4) TIP- Need to purchase more allen
wrenches (5 ?) 5) TIP-Charge up rechargeable
battery pack, first thing 6) TIP- Try to obtain a
laptop that will be regularly used with the
VEX robot to speed up development process7) 7)
TIP - Use a start switch to activate the
autonomous Program and a separate stop switch
for deactivation
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VEX programming Workshop Oakland Schools
Agenda September 19, 2007

• Get everyone to square one be able to program
  robot
• Answer any outstanding questions
• Are ball casters legal? 2WD versus 4WD
• General Programming Techniques VEX manual
• Line following algorithm development
• Advanced Control Concepts (post High School)
• Hysteresis (switchpoint with gap)
• Transport Delay or Time (hot/cold in shower)
• Programming Loop Time (39x/second?)
• Write Statements for Debugging (10 msec?)
• Calibration Methodology
• Adaptive Algorithms (self-correcting)

7) VEX Computer Programs - Examples
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1) Everyone needs to get to this point before we
move on
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2) Answer any outstanding Questions
10 teams represented at workshop 6 students
from teams represented Most have Basic
programming experience 5 teams had Square-bot
build One team had bad VEX controller that was
replaced
OCCRA needs to upgrade to later VEX Software 2.8
for 2008 500 for 25 versions (Intellitek Easy C
software site license)
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3A) Are Ball Casters (Tamiya?) legal for
OCCRA? Yes, as commercially available parts. One
can also use OMNI-wheels, provided In the VEX
kit, for 90 degree turning.
3B) Can OCCRA playing field black line
be replaced/enhanced with ¾ inch, black,
Standard, electrical tape? Yes. Plans are to
coat the board with Home Depot, BEHR, Semi-gloss
white paint.
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Tamiya Ball Caster (small) suitable for Vex
operation.
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4) General Programming Tips from VEX manual

• Save your program often, in a new file so that
  you have a string
• of files, especially at the end of class,
  session or after having
• completed a milestone. It is a good
  practice to save every
• 15 minutes during heavy activity times.
• Use a file index system (Team1286_VEX_YY1)
• Copy your files to thumb drive for movement to
  new Laptop
• Program one part at a time and debug one part at
  a time
• Try to think like the VEX controller when
  programming and
• debugging (process of making your program
  operate the
• way your think it should design intent)
  your program
• Work with a partner if possible two heads
  better than one
• Pick a smart partner and/or a cute partner,
  your choice
• 80/20 rule 20 percent building / 80 percent
  programming
• After two hours maximum of programming take a
  break
• Dont bother with high-school overnighters

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Line Following Algorithm Development
In mathematics, computing, linguistics, and
related disciplines, an algorithm is a finite
list of well-defined instructions for
accomplishing some task that, given an initial
state, will proceed through a well-defined
series of successive states, possibly eventually
terminating in an end-state
Algorithm definition from Wikepedia
In our case, we are initially concerned with
developing an Algorithm to have the robot follow
a black, straight line for a known distance
(OCCRA VEX play field)
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Line Following Algorithm Development

• Use Start button ,Make robot move forward (2
  motors)
• somewhat straight, then use Stop button to halt.
  When
• completed robot moves forward, somewhat slowly.
• 2) Figure out how to mount the two/three light
  sensors
• near the black line. Mount the two lights
  sensors initially a
• At least one inch on each side of the black
  electrical tape.
• Make sure you know which analog light sensor
  corresponds
• to which input for future programming.
• 3) Good practice to make up a simple one page
  sheet that
• shows where everything is connected (Appendix A)
• 4) Determine what light sensor value corresponds
  to black,
• white for reference (Adaptive programming
  later).

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Line Following Algorithm Development

• Determine what value of motor speed corresponds
  to
• allowing the motor to move the robot in the
  opposite direction
• 6) One possible algorithm, when left light sensor
  indicates
• black line, speed up right motor, when right
  light sensor indicates black line, speed up left
  motor.
• 7) Calibrate (adjust speed) the wheel speed value
  so that it
• slowly navigates the black line without getting
  lost
• Iteratively increase the wheel speed and/or move
  the
• light sensors closer to the black line
  (tape). Experiment.

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Line Following Algorithm Development

• Advanced Control Concepts (post High School)
• Hysteresis (adjustable on/off threshold)
• Transport Delay or Time (wait after executing
  command)
• Programming Loop Time (39x/second?)
• Write Statements for Debugging (10 msec each)
• Calibration Methodology
• Adaptive Algorithms (self-correcting)
• The light sensor should have calibration values
• To be used for setting the black/light value in
  your program.
• When you arrive at a competition, place your
  robot on
• the playing field to determine the black/light
  value.
• Simple way is Dark Calibration value
• Light Calibration value

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7) Mark Taylor/Marc Center Computer Programs -
Examples
The following program was created by Mark Taylor
from Marc/Paul Centers original Line Follower
program for use at the LTU Robofest competition
in 2006. It has not been tested in a robot but
should help guide you in the right direction in
creating your own line following program. Note
that Bumper Switch used to stop the program
and Calibration Values are not used for the motor
speeds or the light threshold values (also not
adaptive).
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7) Mark Taylor/Marc Center Computer Programs -
Examples
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7) Mark Taylor/Marc Center Computer Programs -
Examples
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7) Mark Taylor/Marc Center Computer Programs -
Examples
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Caution Use PrintToScreen statements
sparingly. They consume a lot of programming
time And make your Robot behave differently when
removed
7) Mark Taylor/Marc Center Computer Programs -
Examples
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Programming Gotcha Limit switch Impacts Motors 4
though 7
Solution Use Motors 12 for propulsion 3
Motor/Servo Before using others
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Programming Gotcha Limit switch Impacts Motors 4
though 7
Solution Use Motors 12 for propulsion 3
Motor/Servo Before using others
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• Student can use
• Jumpers to program
• only one program in
• the VEX controller
• and select which
• program to operate
• Straight ahead
• Left Hook (Red Field)
• Blue Hook (Right Field)

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Appendix A
Create one page summary sheet detailing where
your Motors/servos and sensors plug in.
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Appendix A
Create one page summary sheet detailing where
your Motors/servos and sensors plug in.
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Future OCCRA VEX Action Items
OCCRA needs to upgrade to VEX Software 2.8 for
2008 500 for 25 versions (Intelitek Easy C
software site license)