2012 OregonFIRST LabView Training

FRC LabVIEW INTRODUCTION

Homework exercises for 2012

summer FRC LabVIEW class series

Oregon FIRST Robotics - www.oregonfirst.org Summer 2012 1

Overview

• By completing these exercises the student will become familiar with the mechanics of the LabVIEW programming.

• Each exercise demonstrates the use of digital logic and analog numerical conversion commonly logic and analog numerical conversion commonly used in robotic system design

• A typical FRC robot program will use a combination of many of these examples.

• From “Getting Started” screen. programs start with a New BLANK.vi and can be run on a stand alone PC without a cRIO


General guidelines

• Construct each program inside a “WHILE loop”

• Put a control STOP button in WHILE loop

• Put a 100ms TIME DELAY in each WHILE loop• Put a 100ms TIME DELAY in each WHILE loop

• (Stop button allows us to an easy way to stop the program execution.

• The time delay will keep simple LabVIEWprogram from taking ALL compute bandwidth from your PC.


WHILE LOOP

Control for

WHILE loop

Time Delay

WHILE loop

THIS IS LABVIEW BLOCK DIAGRAM

SCREEN


Use ‘Context Help’

• The best tutor to get more information about

any parts of LabVIEW is ‘Context Help’

• From tool bar (top of Block Diagram screen) ,

click on Help – Show Context Help.click on Help – Show Context Help.

• Then Cusor will display more information on

LabVIEW details.


01 Digital to Analog conversion

• The robot ‘s ball lift mechanism has two motors. Each needs an analog (numeric) signal of .5 to run at the correct speed. WE want the ball lift to turn on when the a Digital (boolean) switch is TRUE. LabVIEW has two convenient methods for D/A conversion : the CASE two convenient methods for D/A conversion : the CASE struct and the ‘Select’ icon on the comparison palette.

• Drive both motors from one button.

• Use numeric meter indicator.

• Change meter properties –scale from 0-1.

• When button – switch is off, motor control should be 0.


Edit

properties

Scale

0 - 1

Control

for

while

loop


Click on

down arrow

to display

FALSE Case

What

value value

goes in

FALSE

Case?


QUESTIONS?

• How would you drive the each motor at

different speeds?

• How would you add a third motor control to

this program?this program?

• We are using NUMERIC CONSTANTS in this

program. If we want to add a BOOLEAN

(digital) constant to control an LED indicator,

how would you add it to your program?


02 Analog signal inversion(convert 0-1 v signal to 12 -0 v signal)

• Use a Control knob to produce analog signal 0 – 1

• Motor (meter indicator) control needs inverted

analog signal 12 volts – 0 .

• When knob is 0 (minimum signal), motor (meter) • When knob is 0 (minimum signal), motor (meter)

should indicate 12 volts

• When knob is 1 (full scale), motor (meter) should

indicate 0 volts.

• Use two stage numeric signal conversion to change

signal


Labview block diagram


Does it run correctly? Click on white arrow

to run LabVIEW vi


QUESTIONS

• If we add a second METER indicator outside

of the WHILE loop, what happens?

• Does it work as you expect?

• Any “output” from a WHILE loop will not be • Any “output” from a WHILE loop will not be

‘active’ until WHILE loop completes

operation!!!


FAQ

• “Jim, why don’t we just change the properties on the knob to give us the signal range that is needed?”

• The knob is a virtual control so we can make it • The knob is a virtual control so we can make it produce any signal we want. In the real world however, the sensors will produce signals as described by the data sheet. We use LabVIEW to convert the signals to match what is needed by the rest of the program.


03 Analog with Gate enable

• The ‘gyro compass’ is a sensor which will tell us which direction robot is facing. We want ball launch to only be allowed when gyro signal is between 100 and 200 degrees.

• Use Knob to simulate analog signal from gyro• Use Knob to simulate analog signal from gyro

• Use LED to simulate digital Ball Launch Signal

• Use Boolean push button to simulate ball launch button on joystick

• Use comparison IN RANGE function and Boolean AND to GATE digital signal to only reach LED when Gyro signal between 60 and 85.


Change ‘property –scale’ to

be 0 - 360


From NUMERIC pallete

From Boolean

pallete


QUESTIONS

• We want to add an LED indicator that shows

when button is pressed.

• Can you add it to the program and make it’s

color properties RED?color properties RED?

• How does the operation of the program

change?

• What happens to the program operation if

you change the time delay constant to 1000??


04 Nested CASE structs

• Robot control panel has three push buttons for drive speed control because operator needs 3 specific speeds for different zones on the field

• Analog motor (meter indicator) is 0 when no button pressed

• Button A pressed motor control = 3• Button A pressed motor control = 3

• Button B pressed motor control = 5.5

• Button C pressed motor control = 7.3

• Use nested CASE structs to generate signal…

• Hint ‘nest’ inside FALSE case

• Hint2 button properties..mechanical action.. “switch until released”


QUESTIONS

• We want an indicator to show which gear we

are in.

• Can you add a Numeric Indicator which shows

a number (0,1,2, 3) for what ‘gear’ we are in?a number (0,1,2, 3) for what ‘gear’ we are in?


05 counters & shift registers

• Increment by one each time the WHILE loop runs will create a counter.

• Set time delay for 700ms

• Starting value is “0” (constant) outside loop• Starting value is “0” (constant) outside loop

• Shift registers carry value from output of the loop around to be input when loop runs next time

• Indicator will show number changing every 700 miliseconds

• See example 5a counter wm shift reg


First set up addition stage to

increment by one each time

while loop runs

Set

long

delay


Right click and ‘replace with shift

register’ put second on left side

where result will be picked up for

next loopWhen you RUN this it should

continue to increment until

you stop it


More counters & timers

• Now we want to use (Quotient-Remainder function) to produce numbers between 0 and 9 , in one second steps

• From the counter loop we started with, add • From the counter loop we started with, add the Quotient-Remainder function and display the Remainder output

• Change time delay to 1000 ms.

• What happens to the read outs?

• See example 5b


Does it work as you

would expect?


QUESTIONS

• Right now the ‘Quotient – Remainder’ is

connected downstream (after) the

increment (+) stage.

• What happens if we change this and connect • What happens if we change this and connect

the ‘Quotient – Remainder’ upstream

(before) the increment stage??


06 Parallel Loops

• WHILE loops can run independently

• LOCAL VARIABLES can be used to carry data outside of WHILE Loop

• Robot has ball launcher mounted on turret.

• A potentiometer rotates to tell which direction turret is pointing and produces analog signal.

• Ball launcher will hit our own robot when potentiometer signal is • Ball launcher will hit our own robot when potentiometer signal is between 4 – 6.

• Put analog sensor and operator button sensor in different WHILE loops, use Local Variables to carry data between loops.

• Put stop control button on one of inner WHILE loops, note you need to change mechanical action of pushbutton to get program to run.


07 timers

• Timers can be used to set activity at specific

times and for specific durations

• We want to put a blinking light on the Robot.

• The Robot Signal Light should go ON for 4 • The Robot Signal Light should go ON for 4

seconds and OFF for 4 seconds.

• Use an LED indicator on front panel as

simulator for RSL

• Use toggle switch for on-off control of light.


questions

• Note the use of local variables

• What happens if we change the inner time

delay to 100 instead of 1000?

• Note… you may have to re-initialize variables • Note… you may have to re-initialize variables

to default values…. From upper tool bar click

on ‘Edit -Reinitialize variables…’


08 Serial loops

• We want the program to perform several actions but only in a specific order

• Several ways to deal with this. Start with FLAT SEQUENCE in ‘Programming Structures’ pallete

• 8a using flat sequence struct with four frames• 8a using flat sequence struct with four frames– Put three sec delay in first and third frame

– Then turn on an LED in second and fourth

– Does it run the way we expect??

– Hint… why does it take so long for Program to STOP after you press the STOP button? (Reinitialize to Run again)


questions

• What happens if we use the constant in the

last frame to stop the while loop???

• We get rid of the delay for the stop • We get rid of the delay for the stop

pushbutton…. Right?


More questions??

• NOTICE that we can use the first Constant True

to control all the of the logic outputs because

the signal is not released until the frame is

executed….?! ? executed….?! ?

• To test this, put another LED to display

INSIDE the frame… what happens?


08b more serial loops

• If we want to turn systems on and off, we need to understand how to turn off the LED in previous example.

• Now we want to control a robot drive motor.

• We want it to turn on for 3 seconds, off for two seconds, back on for 3 seconds, then stop!

• This is a place for Local variables• This is a place for Local variables

• Make the same 4 frame Flat Sequence Struct

• This time put the LED outside and connect it with a local variable. And add a meter for an analog value. See next slide

• Note I have added an indicator to see how many time the While Loop actually runs during this program… is any one else surprised by the number that shows up?


09 Dual motor control

• Most Robot drives have at least two motors

• To maneuver usually requires both motors be controlled.

• The signal coming from the Joystick is an analog signal that varies from -1 (stick pushed all the signal that varies from -1 (stick pushed all the way forward) to +1 (stick pushed all the way back)

• Use a slider numeric control to simulate a joystick.

• Construct a program to simulate the control of two motors (one reversed) with one joystick


10 Simulated tank control

• Construct program with two slider controls (to simulate Joysticks) and two Meters indicators (to simulate Left and right motor signal outputs)

• Assume the right motor is reverse mounted, so signal going to Right Motor needs to be the opposite polarity of the Left motor control

• Change Scale Property on both controls and indicators to be Min = -1 and Max = 1

• EXTRA CREDIT construct logic

• How do the joystick controls need to be set to maneuver and turn the Robot? Remember to move robot forward,

– Left left is greater than right

– Right right is greater than left

– Forward signals less than zero

– Backward signals greater than zero

– Straight both signals are equal

• Set up an indicator and digital logic to show direction of robot movement


11 Dead reckoning

• During Autonomous mode we may want to use Dead Reckoning to move the robot to a specific location on the field.

• Construct a Flat sequence with the following steps:– Robot moves straight forward for 3 seconds (right motor

inverted)inverted)

– Robot turns right (left motor forward, right motor stopped) for 1.5 seconds

– Robot moves straight forward 3 seconds.

– Robot stops and turns on RED LED which will launch the Ball

– Note: remember to set Ball LED off when you start.

– Use Meters to show motor control signals

– Use LED to show Ball launch control signal


12 Weighted D to A this is how MP3 players make music

• Our robot has three loads on the battery that draw different current levels. We want to keep track of total drain to predict how long battery will last.

• Since each load (2 fans and a motor) are controlled by a digital switch, we can assign each switch an analog value and add them up.and add them up.

• Start with three boolean switches.– Drive motors 10 amps

– Top Fan 3 amps

– Bottom Fan 5 amps

• Use ‘Select Function’ to add value to SUMMING Amp

• Use Meter to show analog total current on front panel, change Max value to 20 for total current value


2012 OregonFIRST LabView Training

Technology

Transcript of 2012 OregonFIRST LabView Training