Programming Your Robot in C Terry Grant NASA

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/BBworkshop 03 • IC 4 Environment downloads: – http: //www. botball. org/about_botball/ic 4. 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 Interactive C v. 4. 10 * Editor * Debug Interpreter * Loader Other Apps Handy Board or RCX H/W *Central Processor * Random Access Memory * Special I/O Circuits * Battery & Power Conditioner Desktop Operating System Lego Mechanical Lego Motors & Sensors Desktop Hardware IR for RCX* 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 • IC 4 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 Example IC 4 void 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 IC 4 – 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") while ("condition") { { "statements" } } else { "statements" }

Notation of IC 4 -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 IC 4 - 3 Starting and ending parallel tasks: pid = start_process(taskname()); kill_process(pid);

Notation of IC 4 - 4 Inputs for RCX - light(y) for y = 1, 2, or 3 - light_passive(y) - digital(y) or touch(y)

Notation of IC 4 - 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 IC 4 - 6 To display on Controller LCD e. g. printf(“Hellon”); printf(“X= %dn”, x); /* x is an integer */ printf(“X= %fn”, y); /* y is floating point */ printf(“%d -%dn”, 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 Bot 1 Bot 2 4’ x 4’ barrier

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("SUMo 6"); 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(15000 L > (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 – L 1 is the remote trigger light. – L 2 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