Programming Your Robot (in C) Terry Grant, NASA, Ames Research Center 1/23/03 1/30/03 1

Outline 1/23 1/30 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 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 Interactive C v. 4.10 * Editor * Debug Interpreter * Loader Other Apps Desktop Operating System Desktop Hardware IR for RCX* Lego Mechanical Lego Motors & Sensors Serial Data Interface Charger (HB only)

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 2

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 Example IC4 void main() { fd(A); fd(C); sleep(2.0); bk(A); bk(C); 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 4 IC notation is the same for RCX & HB if ("condition") { "statements" } else 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 Outputs Motor 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. Starting Light 4’ x 4’ barrier Bot 1 Bot 2

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’d motor(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); 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 first while(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 right motor(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