FRC Robot Framework

1
FRC Robot Framework

• Add and Use a Sensor
• Autonomous
• For FIRST Robotics

2
Sensors Adding Intelligence and Enabling
Automation

• Types of sensors
• Limit Switches on/off
• Gyro - provides Robot rotation angle position
• Potentiometer like a volume control can be
  used to control arm rotation
• Encoder - measures shaft rotation robot
  distance, lift height
• Light sensors detect object breaking beam
• Infrared - detect presence of object nearby
• Ultrasonic - detects distance to object such as
  wall
• Camera (Vision) - Direct feed to dashboard,
  Targeting with vision processing
• Kinect (Camera Infrared) For Driver Station
  or on board robot?
• not used .. yet

3
Session Objectives

• Discuss principles and applications for Gyro
  sensor.
• Bicycle wheel demo
• Incorporate Gyro into Autonomous code
  Control Robot to drive in straight line
• Open Gyro in Begin.vi
• Get Gyro Angle Tele-op.vi display on Front Panel
• Next use Gyro reading as Feedback to tell if
  robot is driving straight (at angle specified)
• PID control

4
FRC Project

• Browse to find your last code
• (or open new)
• Navigate to the Robot Main block diagram
• Then select Begin
• Go to Block Diagram

5
Begin .vi Updated for adding Gyro

• Edit vi Add an accessory motor
• Open function palette and select WPI Robotics
  Library / Sensors / Gyro
• Add Open Gyro .vi
• Identify where plugged in
• Add Refnum Set.vi
• Give it a name

6
Open the Autonomous VI

• Remove diagram disable
• Put cursor on edge of disabled structure, right
  click and select Remove Diagram Disable
  Structure
• Delete the last 2 while loops
• After noting what the default code is intended to
  do
• A method of sequencing operations in autonomous
  that we may return to

7
Set up a While Loop in Autonomous

• In remaining While Loop
• Enlarge, create space to add Gyro and PID
  functions
• Change length of time to 5 seconds
• Each loop is 50 ms, 100 loops 5 secs.
• Change motor inputs to 0
• For now

8
Modify Autonomous.VI to Read Gyro

• From WPI Robotics Library/ Sensors/ Gyro palette
• Bring the Refnum Get and provide name it was
  given in the Begin.vi
• Bring Gyro Get Output vi and connect them
• Put cursor on angle output, right click,
  select, create indicator
• Indicator shows up on Front Panel
• Digital indicator is default but can be replaced
  with a Dial or Linear Indicator

9
Modify Front Panel Indicatorfor Gyro reading

• Put Cursor on indicator, right click and select
  Replace, then Gauge
• Enlarge gauge by dragging diagonally
• Click on the 10 and change to 180
• Click on the 0 and make it -180
• Hover on the 180 until you see the rotation
  arrows then drag the 180 around to the -180.

10
Test the CodeSee if in Autonomous the Gyro is
being read

• Next Lets use it for an Autonomous code
• With Feed-back control

11
Feed-Back Control

• Open Loop
• Examples
• In an (older) car turn heater knob to high
• Heater turns on and stays on until the driver
  gets too hot and manually turns it down
• Robot Harvester(2012) Operator holds button to
  turn harvester motor, watches until sees ball
  move up and then releases which stops motor

Controller
Robot
12
Feed-Back Control

• Closed Loop
• Examples
• In a (newer) car turn heater knob to 70oF
• Heater goes on until the thermostat (sensor)
  reads that it is 70oF , then automatically turns
  it off until it gets too cool, then back on, etc.
• Robot Harvester Operator presses button to
  start harvester motor
• Motor goes until on board light sensor sees
  ball sends signal back to cRio
• Labview program then directs motor to stop

Controller
Robot
Sensor
Generally using it to see if a process is
complete, then stabilize
13
PID Control

• PID stands for Proportional-Integral-Derivative
• A method of closed loop feedback control
• A way of using what you know from your sensors to
  compute an intelligent motor output.
• Proportional P looks at difference between
  desired position and actual and sets motor speed
  to close gap proportional to that gap
• Incorporates the idea that you need to slow down
  as you get close so you dont overshoot the
  target.

14
The PID Function Block

• Set-point
• Desired value to get to
• Process variable
• Actual value as measured by a sensor
• Output determined by magnitude of difference
  (error) between setpoint and process variable
• PID Gains adjust sensitivity

15
Add Read Gyro And PID Control Of Steering
Correction

• Get Gyro Refnum, Get Gyro Angle
• Add PID function block
• Setpoint set to 0 to drive straight forward
• Connect Gyro output as Process variable input to
  PID
• Limit output range
• Set PID gains
• Connect output to X input to arcade drive
  (Steering)

16
Suggested method for determining PID gains

• Method for Setting Values
• ? Start with CP small and CI, CD both zero.
• ? Raise CP until the robot is oscillating
• consistently around the target.
• ? Once this is accomplished, start increasing
• CD until the robot stops oscillating.
• ? Then add CI until the robot stops within a
• desired range of the target.

Often we have only used the P, or PD
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Next we will see if our code works!
18
Homework Challenge Slides

• Learn how to modify the Dashboard
• Make an autonomous Drive Sequence
• Drive a square pattern
• Learn to use the examples and be able to code a
  variety of sensors including encoder

19
Modifying the Dashboard Gyro Indicator

• Open Dashboard Project, Modify to display Gyro
  angle on a gage
• (follow Labview tutorial number 7)
• Modify Robot code Tele-op to send data to
  dashboard (also part of Labview tutorial)

DashboardMain.vi
Front Panel
20
Incorporating Sensors Gyro

• Open Dashboard Project, Modify to display Gyro
  angle on a gage (follow Labview tutorial)
• Modify Robot code Tele-op to send data to
  dashboard (also part of Labview tutorial)

• Follow Tutorials 4-7
• Adds Gyro
• Opens Dashboard Project

21
Homework / Challenge 2

• Update the Autonomous code
• Add 3 sequential While loops (like in default
  disabled structure)
• Have robot go straight, turn 90 degrees,
• Repeat 3 times to drive in a square.

22
Homework / Challenge 3

• Add variety of sensors to Begin and Tele-op
• Use Examples as source to copy correct formats

23
Begin.VI - Open and name sensors
24
Tele-op.VI - Get values and display