Programming Your Robot (in C)

Terry Grant,NASA, Ames Research Center

1/23/03

1/30/03

Outline

• 1/23– Robotics Hardware & Software Architecture– Programming in C Introduction

• 1/30– Review: Robot Project Requirements &

Example – Simple Sumo Contest - Simple line follow– Teacher as Coach– Wrap-up

Robot Building & Coding• Completed LEGO robot from MLCAD

– Ref: http://www.lm-software.com/mlcad/

– Art of LEGO Design

– http://handyboard.com/techdocs/artoflego.pdf

• Pictures and Code from the Workshop– http://robotics.nasa.gov/edu/BBworkshop03

• IC4 Environment downloads:– http://www.botball.org/about_botball/ic4.html

• Hands-on Challenges Ref:– http://robotics.nasa.gov/students/challenge.htm

Robotics H/W & S/W Architecture

Interactive C v. 4.10* Editor* Debug Interpreter* LoaderOther Apps

Desktop Operating System

Desktop Hardware

Bot Multi-tasking S/W Components Real-Time Operating System * P-code interpreter * Input/Output Drivers - Clock * Load/Run modes

Handy Board or RCX H/W*Central Processor* Random Access Memory* Special I/O Circuits* Battery & Power Conditioner

Serial Data Interface

Charger (HB only)

Lego Motors& Sensors

LegoMechanical

IR for RCX*

Robot Project Requirements

• Hardware configuration and general environmental constraints

• Operator Requirements

• Controller requirements

All Three Elements are needed and should be written down for a common team understanding

Team Strategy & Plans

• Translating a Challenge into Requirements– Robot physical capabilities– Robot behavior (high level code)– Operator – robot interaction

• Assigning tasks and milestones

• Writing a total schedule (initial and revised)– Plan to test capabilities & behavior– Plan for full robot tests & re-planning– Plan for team coordination meetings

Programming in C - Introduction

• IC4 provides an editing, compiling, and downloading environment for either RCX or Handy Board.

• Follows C syntax (grammar)• Uses functions < xyz() > declared and called• Many functions for Input/Output are preloaded in a

library• Good tutorial examples provided with the application • Multi-tasking capability in O.S.

– allows sampling & holding multiple conditions in parallel:

position, direction, and other sensors

General Syntax

• declaring:

output type Function(inputs e.g. int x, int y) {block of statements}

• calling: Function(x, y);

• types: int x, y, z;float a, b, c;

all variables must have a declared type.– global types are defined at the top, outside of a

function, and usable by all functions.

Simple Example

Make a Robot Go Forward and Return– H/W & Environment:

Build a bot with the RCX, wired to motors such that forward power moves wheels forward, and put on a demonstration table with enough flat surface

– Operator:Write the code, load the RCX, and initiate the execution

(running) of the code

– The controller:Turn on the motors forward, wait 2 seconds, reverse the motors,

wait 2 seconds, then stop.

Simple Code ExampleIC4void main(){ fd(A); fd(C); sleep(2.0); bk(A); bk(C); sleep(2.0); off(A); off(C);}

• Open Interactive C to view the actual environment & write code

More Basics• Three modes: off, standby, run• Use of ‘view’ button function w/o running a program• Use of ‘Interaction’ window in IC4

– battery_volts() to check battery– Test new functions for I/O,

• Check list of library functions, global variables• Download firmware• Upload Arrays for spread-sheet analysis• Edit aids

– Auto-indentation– Parenthesis matching– Syntax checking (on download)

• Use of ‘save as’ to file new, or trial code

Notation of IC 4IC notation is the same for

RCX & HBif ("condition"){ "statements"}else{ "statements"}

while ("condition")

{

"statements"

}

Notation of IC4 -2

Defining a function or task:xxx “name”(){ "statements"}xxx = ‘void’ if no return variables = ‘int’ if integer return variables = ‘float’ if floating point return variables

Notation of IC4 - 3

Starting and ending parallel tasks:

pid = start_process(taskname());

kill_process(pid);

Notation of IC4 - 4

Inputs for RCX

- light(y) for y = 1,2, or 3

- light_passive(y)

- digital(y) or touch(y)

Notation of IC4 - 5

IC OutputsMotor outputs, ports 1 to 3 (or A to C)

To use port 1:

fd(1); forward, positive voltage

bk(1); backward, negative voltage

Motor(1, x); x = -100 to 100

off(1); leave port ‘open’

brake(1); for the RCX only, to brake the motor

Notation of IC4 - 6

To display on Controller LCD e.g.

printf(“Hello\n”);

printf(“X= %d\n”, x); /* x is an integer */

printf(“X= %f\n”, y); /* y is floating point */

printf(“%d -%d\n”, a, b); /* a & b are integers */

In the RCX only five characters total can be displayed,

and “\n” is not needed.

Sumo Example

Sumo Requirements• Robots start facing each other at the edge of a central ring.• Robots must start when a button is pushed or the light

comes on.• Robots must stop after T (5-15) seconds.• The first robot to touch the barrier (or cross line) loses.

Bot 1 Bot 24’ x 4’ barrier

Starting Light

Light Sensor

• Sensor includes a LED source: red & near IR.

• Photodetector responds strongly to near IR as well as red. [lower = more]

• Response changes according to ambient light & Battery voltage.

• Mounting assembly attaches to front bumper facing down as shown in the cover picture.

Simple Sumo Behavior

• Display program title

• Wait for prgm_button push, then beep

• Wait 3 seconds to start

• Go straight forward – while T not exceeded,

• Stop quickly and turn if line is sensed

• Back away & turn if bumped

– When T exceeded brake to a stop

Simple Sumo code// LEGO-based Sumo #6 for widetrack bot tlg 1/20/03

// assumes front bumper on port 3, light sensor on 2, motors on A & C

// start 3 seconds after prgm button push

#define TURN_TIME 0.45

#define THRES 750 /* assumes nominal white is ~ 720 */

void main()

{

long time;

printf("SUMo6");

while(!prgm_button());

beep();

sleep(3.); // wait 3 seconds

time =mseconds();

//beep();

Simple Sumo code – cont’dmotor(A,30); motor(C,30);// start straight ahead while(15000L > (mseconds()-time)){ //run time if(light(2)>THRES){ //wait for edge brake(A);brake(C);sleep(.05); //quick stop motor(C,-45);off(A); //turn sleep(TURN_TIME); motor(A,30); motor(C,30); sleep(.2); } if(digital(3)){//back away and turn if bumped motor(A,-30);motor(C,-30);sleep(.2); brake(A); sleep(TURN_TIME); motor(A,30); motor(C,30); sleep(.2); } } brake(A); brake(C);}

Light Trigger Calibration• Hardware & Environment

– L1 is the remote trigger light.

– L2 is the room lighting.

– Pd photodetector has a wide field of view.

• The Controller display helps the operator measure both the dark and light response.

• The controller [RCX code] sets the “light vs. dark” threshold and waits for the threshold to be exceeded to trigger the action.

Sumo - Sensor Test Project

• To support a robot sumo contest with a light start, design a robust light trigger for a “sumo wrestling” action which runs the motors for 5 seconds after a light is turned on.– Discuss all requirements (total group)– Write a code design for each Bot. – Write and debug the code

• Participate in a Bot Sumo contest• Compare trigger and behavior designs and results

Sumo - Sensor Test Behavior e.g.• Display program title [for a few seconds]• Repeat sequence while program is running• While prgm_button is not pushed,

– Display sensor level and– Prompt for prgm_button push– While view_button is pushed,

display and increment the trigger threshold

• When prgm_button is pushed,– Display sensor level – Wait for sensor level to cross the trigger threshold, then go forward,

etc as original sumo - measuring run time

• When T is exceeded: stop, – display “done” for a few seconds

• Repeat

Line Following Experiments

Line Following Experiments

• Simple, one sensor

• Line turns to the right

• Check sensor responses first

• Use touch sensor to start & stop

Checking sensor firstwhile(digital(1)==0){ // check sensor until switch is hit

printf("%d", light(2)); //move on and off line here

sleep(.3);

}

while(digital(1)==1); // wait here to release switch

Follow line until touch sensor hit// follow line to the rightmotor(A,30); motor(C,30); // start going straight while (digital(1)==0) { // until switch is hit

if (light(2) < THRESHOLD) { // if brighter than line motor(C,-30);off(A); // turn right

while (light(2) < THRESHOLD); // wait until >= motor(A,30); motor(C,30); // go straight

} }

ao(); // turn off motors when done