FRC Robot Framework

Add and Use a Sensor& Autonomous

For FIRST Robotics

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…

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

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

• 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

Begin .vi Updated for adding Gyro

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

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 0For now

Modify Autonomous.VI to Read GyroFrom 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

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.

Test the CodeSee if in Autonomous the Gyro is being

read

Next: Lets use it for an Autonomous code

With “Feed-back” control

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

Feed-Back ControlClosed 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

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 don’t overshoot the target.

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

Add: Read Gyro And PID Control Of Steering Correction

Get Gyro Refnum, Get Gyro Angle

Add PID function block

1.Setpoint – set to 0 to drive straight forward

2.Connect Gyro output as Process variable input to PID

3.Limit output range 4.Set PID gains5.Connect output to X

input to arcade drive (Steering)

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

Next we will see if our code works!

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

Modifying the Dashboard – Gyro Indicator

a) Open Dashboard Project, Modify to display Gyro angle on a gage • (follow Labview tutorial number 7)

b) Modify Robot code Tele-op to send data to dashboard (also part of Labview tutorial)

DashboardMain.vi

Front Panel:

Incorporating Sensors – Gyro::a) Open Dashboard Project, Modify to display Gyro angle on a gage (follow Labview

tutorial)

b) Modify Robot code Tele-op to send data to dashboard (also part of Labview tutorial)

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

Project

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.

Homework / Challenge # 3Add variety of sensors to Begin and Tele-op

Use “Examples” as source to copy correct formats

Begin.VI - Open and name sensors

Tele-op.VI - Get values and display