Programming and Controls for FIRST – The Basics

Tom Barch, Scott VanBrocklin and Kayla Peltier

February 5th, 2008

Agenda System Overview

How the systems works – Controls Block Diagram Robot Controller Operator Interface

Controls Overview of the controls used and how they work

Programming How to get started with the EasyC Program Software Default Code Reference Guide – How and why to use MPLAB and IFE Loader – How to install and use Default Code – An overview Downloading the Code to the Robot Controller

Pneumatic Controls Overview of the pneumatics system – Block Diagram Controlling the pneumatics – Understanding the controls

Robot Controller or RC

Robot ControllerSystem Block Diagram

Operator Interface or OI

Operator InterfaceSystem Block Diagram

Tether Communications

Radio vs. Tether communication

If the controllers ‘see’ a tether cable connection, then they will communicate via the tether port.

If no tether connection exists, then they will attempt to use the radio signal.

Note: Connecting via radio at the competition other than during a match is not allowed and can be dangerous if another teams operator interface controls your robot.

Controls Understanding the controls will help to understand the

software variables and how the software is modifying and outputting them to get the Robot to move.

The joystick is read by the Operator Interface and is transmitted to the Robot Controller. It usually drives a pwm output which controls a Victor 883 or 884 speed controller. The speed controller maybe wired to a drill motor.

By pressing the joystick, we hope to control the speed and direction of the motor to get the Robot to move.

Lets start with the Joystick.

Joystick The joystick consists of two potentiometers mounted

to a stick that vary as the stick is moved along its axis.

One potentiometer is mounted in the x axis or left – right direction and the other is mounted in the y axis or forward – backward direction.

As the potentiometer moves from one extreme to the other, the operator interface reads the voltage from 0 to 5 volts.

This voltage is broken into an 8 byte variable that ranges from 0 (0 volts) to 254 (5 volts).

Joystick - continued Full forward in the y

axis will result in p1_y = 254.

When the joystick is in the center, it reads 127.

Full backward would read 0

Victor Speed Controller The input to the speed controller is a pwm signal that

varies from software value of 0 to 254. Battery and ground is supplied to two input terminals

and the two output terminals can be wired to an electrical load like a drill motor.

At an input of 127, the two outputs which we will call m+ and m- are at 0 volt difference

As the pwm increases from 127 toward 254, the voltage varies from a positive difference of 0 to 12 volts.

As the pwm decreases from 127 towards 0, the voltage varies from a negative difference of 0 to 12 volts.

Victor 884 speed controller

Joystick to Motor The joystick variable read by the Operator Interface is

the same as the variable outputted to the pwm output to drive the motors forward and reverse.

In the default software, port one y axis is output directly to pwm01 port:

pwm01 = p1_y; In the default software, port two y axis is output

directly to pwm02 port:pwm02 = p2_y;

The two of these make up the tank drive (two joystick).

The software also outputs joystick one x and y axis to pwm ports 13 and 15 to get one joystick drive.

Joystick Switches Located on the joysticks are four switches that are read

by the computer as 0 or a 1. When the switch is closed, then the variable is read as a one.

These switch inputs are mapped to the relay outputs.relay1_fwd = p1_sw_trig;relay1_rev = p1_sw_top;relay_5_fwd = p1_sw_aux1;relay_5_rev = p1_sw_aux2;

Spike Controller The spike controller is a relay or electronic switch that will

drive two outputs based on the inputs. The reason for two input and two outputs are to enable the

output to be driven positively or negatively to drive a small motor forward or reverse.

When the inputs to the relay are driven both as 0, then the outputs are both at 0 volts. One input is called Fwd and one is called Rev. One output is m+ the other is m-.

If the Fwd input is a 1 and the Rev input is a zero, then the m+ output will be 12volts and the m- output will be 0 volts.

The spike can be used to drive small motors, lights, air compressor, or any other 12 volt electrical load. The concern is the current draw which is much lower then the speed controllers.

Spike Blue Controller

Spike Truth Table The truth table for the input to output is as

follows:

Spike alternative circuit The spike can also be used to drive two

different outputs in a on/off sequence. An example would be two solenoid valves.

Programming the Robot Controller

Using EasyC

“EasyC” is very useful for people who do not have much experience with programming.

It’s a much simpler version of the “C” language

Teams may choose to program with either “EasyC” or the standard “C” with MPLAB

Getting Started With EasyC

Begin by setting up your robot controller by selecting “Robot Controller Setup” in the Options toolbar.

Select the “FRC Robot Controller” and the “FRC 2006-2008 (PIC18F8722)” device…and click “ok”.

Loader Setup Go to the “Build and Download”

toolbar and click “Loader Setup” Make sure the settings are as

follows…

Downloading Default Code Using EasyC

You can either: Write your own default code or Use the one provided by the EasyC

Software.

To download the default code provided by EasyC go to the “Build and Download” toolbar and click “Download Default Code”

It will ask you if you’re sure you want to download the program…click “yes”

The computer will then erase the memory on the robot controller and download the default code.

Robot Controller Code MPLAB IDE v6.30 is the C programming editor

and complier from PC Microchips used to edit and compile the code.

IFE Loader is a program that will download the complied code into the robot.

None of this is necessary if the default code is used.

If modifications are necessary (custom functions are needed/variables need to change slightly), the code will only need modifications instead of a complete re-write.

Default Code Reference Guide Available from Innovation First website

http://www.ifirobotics.com/(in the Robot Controller section at the bottom)

Shows OI wiring/variables to RC variables/output for the default code functions.

Contains the variable listing for modification of default code.

FRC 2004 RC Default Code Reference Guide.pdf

Table of Contents

Joystick Function

Joystick plugged into port 1

Y-Axis is forward – backwards (tank drive)

P1_y is the variable used in the software to read this function

RC PWM1 is the port that the left side victor should be plugged into to make port 1 the left joystick for tank style drive

Single Joystick Drive Missing from default guide – It is on the

front cover but hard to read.

Connect the right drive motors to PWM13 and/or PWM14 on the RC.

Connect the left drive motors to PWM15 and/or PWM16 on the RC.

MPLAB Install Adobe PDF

document exists on CD

Has the defaults and instructions for installing MPLAB as well as the IFE loader.

C-BOT_Install_1-29-2004.pdf

MPLAB and Default code After downloading the default code, place

the unzipped files in a directory, preferable in c:\code\frccode.

MPLAB and First recommends a simple directory. My Documents is a complex directory in Windows 2000 and Windows XP.

Saving an old revision and creating a new one is done by copying the folder and pasting to new director (i.e. copy c:\code\frccode into a new directory c:\code\frccode1 and so on).

Opening the default workspace Do not use the file open command. Use the

open workspace command.

User_routine.c Most of the code changes will be made in

the user_routine.c file Custom code should be placed in

Process_Data_From_Master_uP function at /* Add your own code here */.

The specific functions for most of the inputs/outputs are in the Default_Routine which is at the bottom of User_routine.c The variables can be modified in the default

routine, but make sure to use new revision directories here so that changes can be reversed.

Modifying a variable Lets say that the right side joystick is backwards.

When the joystick is pressed forward the robot moves backward.

There would be two options. Change the M+ and M- terminals on the Victor (this is actually the recommended fix)

The software could also be changed to reverse the direction on the motor.

Locate the default statement for the right controller pwm02 = p2_y;

The code could be modified as follows: pwm02 = 254 – p2_y;

Modifying a variable (continued)

P2_y Formula pwm02

0 254 – 0 = 254 254

254 254 – 254 = 0 0

127 254 – 127 = 127 127

42 254 – 42 = 212 212

212 254 – 212 = 42 42

86 254 – 86 = 168 168

168 254 – 168 = 86 86

Compiling the code In MPLAB, select the Project menu and

select the Build All command. The Output window will have the comments

on if the build was successful or if there are errors.

If there are errors, locate the error and fix. Be careful with where the error occurs. The

actual error can be many lines of code before the syntax error. An example would be a begin comment marker without an end marker. All the code will be commented out until the next end marker.

Loading the code into the RC IFE Loader is the program used to download the compiled code. Make sure that the RC program port is plugged into a serial

com port on the computer. Set the IFE loader to the com port plugged into. Press the program button on the RC and then press the

download button. The terminal window can be used in conjunction with the printf

command to display variables on the terminal window. Remember that the printf statement will output every time the

command executes. If the printf is in the slow loop it will print every 26.2ms or even faster in the fast loop. This may be hard to read with the data scrolling off the screen.

The buffer is a circular buffer so it won’t fill up. The old data won’t be there either, so you may need some type of logic to keep the data on the screen.

Pneumatic Controls Block Diagram

Pneumatic Controls The air compressor is wired through a relay controlled by the

pressure switch. When the pressure switch drops below the set switch point, the

relay is energized turning on the air compressor. When the pressure exceeds the set switch point, the relay is de-

energized turning off the air compressor.

Controlling the pneumatic cylinders is then accomplished through a single or double solenoid valve. “Single-acting” or single solenoid valve will extend the air cylinder

while the solenoid is energized. When the solenoid is de-energized, the air cylinder will close.

“Double-acting” or double solenoid valve will extend or open a air cylinder when one of the solenoids is activated and will close when the other solenoid is activated. After either solenoid is deactivated, the air cylinder will remain open or closed.

These solenoid valves are controlled via a spike.

Spike Truth TableSingle Solenoid Valve (two valves wired to M+ & M-)

INPUTS OUTPUTS    

Fwd Rev M+ M- Indicator Solenoid Function

0 0 GND GND Orange Off / Brake Condition (Default)

1 0 +12V GND Green Solenoid1 Activates (M+)

0 1 GND +12V Red Solenoid2 Activates (M-)

1 1 +12V +12V Off Solenoid 1 & 2 Activates

Double Solenoid Valve (both positives wired to M+ & M- with grounds to ground block)

INPUTS OUTPUTS    

Fwd Rev M+ M- Indicator Solenoid Function

0 0 GND GND Orange Off / Brake Condition (Default)

1 0 +12V GND Green Solenoid Activates Direction A

0 1 GND +12V Red Solenoid Activates Direction B

1 1 +12V +12V Off Solenoid Activation is unknown

Summary

There are other websites for resources.

The www.usfirst.org has many presentations on the subjects presented here.

Hopefully this has been informative and will help in the coming weeks.