programming lego minsdstormes nxt with nxc -...
TRANSCRIPT
Programming Lego Minsdstormes
NXT with NXC
Theoretic & Practical Work
Lego Mindstorms RCX The first retail version
of Lego Mindstorms was released in 1998 and marketed commercially as the Robotics Invention System (RIS).
http://en.wikipedia.org
Lego Mindstorms NXT In August 2006, LEGO released a new
Mindstorms kit called the NXT http://en.wikipedia.org
Lego Mindstorms
NXT
RCX
Curiosity
In 2006, nearly 8,846 teams and 90,000 children participated in the event, with the topic Nano Quest
In 2007, approximately 106,000 children and 10,600 teams participated worldwide
Programming languages
NXT-G Retail
NXT-G Educational
RoboLab 2.9
NBC NXC
Graphic Graphic Graphic Assembly C-like
RobotC NI LabVIEW Toolkit
leJOS NXJ
pbLua LEJOS OSEK
C Graphic Java Lua ANSI C
Building a robot
Not eXactly C (NXC)
NXC - Variable Declaration
int x; // declare x bool y, z; // declare y and z long a = 1, b; // declare a and b, initialize a to 1
x = 2; // set x to 2 y = 7; // set y to 7 x += y; // x is 9
NXC - Arrays
Declare a array
To initialize local arrays or arrays with multiple dimensions it is necessary to use the ArrayInit function
int my_array []; // declare an array with 0 elements bool my_array [][]; // declare a 2-dimensional array
int myArray [][]; int myVector []; ArrayInit (myVector, 0, 10); // 10 zeros in myVector ArrayInit (myArray, myVector, 10); // 10 vectors myArray
NXC - Arrays
Return the length of the specified array
Copy a subset of the source array starting at the specified index and containing the specified number of elements into the destination array
x = ArrayLen (myArray); //return the length of the array
ArraySubset (myArray, srcArray, 2, 5); //copy 5 elements, // beginning in 2
NXC - Structs
struct person { string name; int age; car vehicle; };
person myPerson; myPerson.age = 40;
Like C
NXC - Control Structures
The goto statement forces a program to jump to the specified location (I do not recommend is a bad idea)
until will continue looping until the condition becomes true
my_loop: x++; // something // …
goto my_loop;
until (SENSOR_1 == 1 ); // Wait for touch sensor pressed Off (OUT_AC); // and stop motors.
NXC - Control Structures if (x==1){ y = 1; z = 2; } ------------------||-------------||--------- while(x < 10){ x = x+1; y = y*2; } ------------------||-------------||--------- do{ // body }while (condition); ------------------||-------------||--------- for(stmt1 ; condition ; stmt2){ // body }
repeat (expression){ // body } ------------------||-------------||---------
switch(x){ case 1: // do something when X is 1 break; case 2: // do something else when x is 2 break; default: // do this when x is not 1 or 2 break; }
NXC - Functions
This allows the callee to modify the value and have those changes visible in the caller
It is also passed by reference, but with the restriction that the callee is not allowed to modify the value
ᗛ In general this is the most efficient way to pass arguments in NXC
void foo (int &x){ x = 2; }
void foo (int bar, const int baz){ // do something here... }
NXC - Tasks
A function call is a statement of the form
Tasks may be started or stopped with the following statements
You can adjust the priority of a task using the priority statement
name (arguments);
start task_name; stop task_name;
priority task_name, new_priority;
NXC - Tasks
The NXT supports multi-threading A task in NXC directly corresponds to an NXT thread Tasks are defined using the task keyword using the
following syntax
A program must always have at least one task - named “main”
The maximum number of tasks is 256
task name() { // the task's code is placed here }
NXC - API
The NXC API defines a set of constants, functions, values, and macros that provide access to various capabilities of the NXT such as: sensors outputs communication
Typically it takes some action or configures some parameter
NXC – API (Timing Functions)
Wait (1000); // Make a task sleep for specified amount of time // wait 1 second
Wait (Random(1000)); // wait random time up to 1 second
x = FirstTick(); // the time that the program began running
SleepNow(); // turn off the NXT immediately
x = CurrentTick(); // the current system timing value // (called a "tick") in milliseconds
NXC – API (Program Control Functions)
Stop (x == 24); // stop the running program if ( x==24 ) is true
StartTask (sound); // start the specified task (sound task in this case)
StopTask (sound); // stop the sound task
ExitTo (nextTask); // immediately exit the current task and start // executing the specified task
StopAllTasks(); // stop the program
NXC – API (Program Control Functions)
Follows (main);
Precedes (moving, drawing, playing); // the tasks will all execute // simultaneously unless other dependencies // prevent them from doing so
Schedule the specified tasks for execution once the current task has completed executing
Schedule this task to follow the specified tasks so that it will execute once any of the specified tasks has completed executing
NXC – API (Program Control Functions)
Acquire (motorMutex); // make sure we have exclusive access // to the motors
Release (motorMutex); // release mutex for other tasks
This function is used to ensure that the current task has exclusive access to a shared resource, such as the display or a motor. After the current task has finished using the shared resource the program should call Release to allow other tasks to acquire the mutex
Release should always be called after a matching call to Acquire and as soon as possible after a shared resource is no longer needed
These mutex-type variables are called semaphores
NXC – Input Module (Sensors)
SetSensorLight (port); //for exemple IN_3 SetSensorSound (port); //for exemple IN_2 SetSensorTouch (port); //for exemple IN_1 SetSensorLowspeed(port); //for exemple IN_4
Light sensor → can measure the amount of reflected light or ambient light in a particular direction
Sound sensor→ detects sounds and play sounds Touch sensor → indicates that this is a touch sensor Ultrasonic sensor → works as a sonar, it sends a burst
of ultrasonic waves and measures the time needed for the waves to be reflected back by the object in sight
NXC – Sensor Information
SetSensor (S1, SENSOR_TOUCH); x = Sensor(S1); // read sensor 1
/*for the ultrasonic sensor:*/ SetSensorLowspeed (S4); x = SensorUS (S4); // read sensor 4
x = SensorRaw (S1); //Return the raw value of a sensor on port n x = SensorNormalized (S1); //Return the normalized value of a sensor on port n x = SensorScaled (S1); //Return the scaled value of a sensor on port n
NXC – Convenience Calls
OnFwd(OUT_A, 75);
Off(OUT_A); // turn off output A
Coast(OUT_A); // coast output A Float(OUT_A); // float output A
Turn the specified outputs off
Turn off the specified outputs, making them coast to a stop
Set outputs to forward direction and turn them on
Set outputs to reverse direction and turn them on OnRev(OUT_A, 75);
NXC – Convenience Calls
RotateMotor(OUT_A, 75, 45); // forward 45 degrees RotateMotor(OUT_A, -75, 45); // reverse 45 degrees
OnFwdSync(OUT_AB, 75, -100); // spin right
OnRevSync(OUT_AB, 75, -100); // spin left
Run the specified outputs forward with regulated synchronization using the specified turn ratio ( between [-100; 0[ → left, between ]0, 100] → right )
The same for the output reverse
Run the specified outputs forward for the specified number of degrees
NXT / NXC - advices
The NXC filenames, should be maximum 15 characters Example: follow_line_HARD_final.nxc appears in NXT screen: follow_line_HAR
Before starting plan the main program, you should do tests with the engine speed and time to determine the angle Example: (using ruler and square determine the angle)
OnRev(OUT_A, 30); Wait(300); Off(OUT_AC); OnFwd(OUT_C, 30); Wait (50);
NXC – Example 1
#define TURN_TIME 360 // waiting time int move_time; // define a variable task main() { move_time = 200; // set the initial value repeat(5) // repeat five times { OnFwd(OUT_AC, 75); Wait(move_time); // use the variable for sleeping OnRev(OUT_C, 75); Wait(TURN_TIME); move_time += 200; // increase the variable } Off(OUT_AC); }
Driving in a spiral
NXC – Example 2
#define THRESHOLD 40 #define MIC SENSOR_2 task main() { SetSensorSound(IN_2); while(true){ until(MIC > THRESHOLD); OnFwd(OUT_AC, 75); Wait(300); until(MIC > THRESHOLD); Off(OUT_AC); Wait(300); } }
Waits for a loud sound, and drives the robot until another sound is detected
NXC – Example 3
task main(){ SetSensorLight(IN_3); while(true){ if (Sensor(IN_3) <= 40) { OnFwd(OUT_AC, 30); Wait(2000); } else Off(OUT_AC); } }//end Task main
task main(){ SetSensorLight(IN_3); while(true){ if (Sensor(IN_3) <= 40) { OnFwdSync(OUT_AC, 30, 0); Wait(2000); } else Off(OUT_AC); } }//end Task main
Where is the difference?
NXC – Example 4
#define NEAR 25 //cm mutex block;
task verify_obstacle(){ while(true){ OnFwd(OUT_AC,20); while(SensorUS(IN_4)>NEAR); Off(OUT_AC); OnRev(OUT_AC,20); Wait(400); OnFwd(OUT_A,20); Wait(400); } }//end Task verify_obstacle
task verify_touch(){ while (true) if (SENSOR_1 == 1) OnFwd(OUT_AC, 55); Wait(100); }//end Task verify_touch
task main(){ Precedes(verify_touch, verify_obstacle ); SetSensorLowspeed(IN_4); SetSensorTouch(IN_1); }//end Task main
React to any obstacle in front or behind
NXC – Example 5
Follow a Line
#define THRESHOLD 50 // < 50 é preto #define NEAR 15 // cm mutex block; int conta=0;
sub turn_R(){ Acquire(block); do{ OnRev(OUT_A, 30); Wait(300); Off(OUT_AC); OnFwd(OUT_C, 30); Wait (50); conta=0; }while(Sensor(IN_3) > THRESHOLD); Release(block); }//end Sub turn_R
sub turn_L(){ Acquire(block); OnFwd(OUT_A, 30); OnRev(OUT_C, 15); Wait(400); Off(OUT_AC);
if (Sensor(IN_3) > THRESHOLD){ Wait (1000); conta++; }
if (conta==5){ Wait(3000); turn_R(); } Release(block); }//end Sub turn_L
task move_forward(){ while(true){ while (Sensor(IN_3) <= THRESHOLD) { Acquire(block); OnFwdSync(OUT_AC, 30, 0); //specify the 'turnpct' steering percentual (from -100 to 100) pagina 32 || [0 ; 100] desloca-se para a direita [-100, 0]eskerda Wait(5); Off(OUT_AC); conta=0; Release(block); if (Sensor(IN_3) > THRESHOLD) break; } //while
turn_L(); //corrige a tragectoria }// end while }//end Task move_forward
task main(){ Precedes(move_forward); SetSensorLight(IN_3); SetSensorLowspeed(IN_2); }//end Task main
http://en.wikipedia.org/wiki/Lego_Mindstorms_NXT#Programming
http://www.teamhassenplug.org/NXT/NXTSoftware.html http://bricxcc.sourceforge.net/nbc/ http://www.botmag.com/articles/10-31-07_NXT.shtml http://forums.nxtasy.org/index.php?
&&CODE=autologin&fromreg=1
Bibliography
