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

2. 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

3. Robot Building & Coding
Completed LEGO robot from MLCAD
Ref:
Art of LEGO Design
Pictures and Code from the Workshop
IC4 Environment downloads:
Hands-on Challenges Ref:

4. 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)

5. 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

6. 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

7. 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

8. 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.

9. 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.

10. 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

11. 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

12. Notation of IC 4 IC notation is the same for RCX & HB if ("condition"){
"statements" }
else
while ("condition") {
"statements" }

13. 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

14. Notation of IC4 - 3 Starting and ending parallel tasks:
pid = start_process(taskname());
kill_process(pid);

15. Notation of IC4 - 4 Inputs for RCX - light(y) for y = 1,2, or 3
- light_passive(y)
- digital(y) or touch(y)

16. 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

17. 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.

18. Sumo Example

19. 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

20. 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.

21. 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

22. 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
#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();

23. 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);

24. 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.

25. 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

26. 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

27. Line Following Experiments

28. Line Following Experiments
Simple, one sensor
Line turns to the right
Check sensor responses first
Use touch sensor to start & stop

29. 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

30. 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