Hello
I am trying to control my bot using a sharp IR sensor mounted on hitec servo with arduino mega. The pseudocode i have so far is as follows:
1. Set servo at 90deg and read IR sensor value
2. If val > 200, then stop the bot for a second
a. Turn servo 0 deg completely and read ir val
b. if val < 200 then turn bot left
c. else turn servo 180 deg and read ir val
d. if val < 200 then turn bot right
e. else if cant turn right or left, reverse a bit and then turn the bot 180 degree and go straight.
3. repeat
What happens now is that the bot goes forward, if the IR reading comes within 200, the bot turns 180 and goes in that new direction. It doesnt pan the servo left or right. On two occasions it did turn the servo, but that was only to the left (0 deg).
Have i missed something here? Im just learning how to program, so perhaps someone could suggest a far better method?
I know this code is extremely crappy, but what i was hoping, if it works, was to modify it so that the servo pans say in intervals of 30 degrees, takes a reading and stores it. It then calulates based on the readings the best route(ie with least obstacle distance) and moves the bot in that direction. Im not very sure how to implement this either.
Any help would be appreciated. Thank you
Code:
#include <MegaServo.h>
#define IR_pin 0
int IR_val = 0;
MegaServo servo1;
void setup() {
Serial.begin(9600);
pinMode(50,OUTPUT);
servo1.attach(50);
servo1.write(90); //center servo intially
}
void loop() {
IR_val = analogRead(IR_pin);
if (IR_val > 200) // obstacle detected
{
motor_stop(); // Stop both motors...
delay(1000); // ...and pause for a second
servo1.write(0); // Turn servo left completely and scan
IR_val = analogRead(IR_pin);
if (IR_val < 200) // if left seems to be clear
{
turn_bot_left();
delay(535); // Turn till bot has turned 90 deg left
servo1.write(90); // center the servo
}
else
{
servo1.write(180); // Turn servo completely right and scan
IR_val = analogRead(IR_pin);
if (IR_val < 200) // if right seems to be clear
{
turn_bot_right();
delay(540); // Turn till bot has turned 90 deg right
servo1.write(90); // center the servo
}
}
servo1.write(90); // position servo back at center
go_reverse();
delay(500); // wait for sometime till it reverses
turn_bot_180();
delay(1030);
} // end of routine that checks if IR_val > 200
else
go_straight();
Serial.println(IR_val);
}
/* Motor movements...removed to save space!! Btw..all these functions work fine. I've tested them.
void motor_stop()
void go_straight()
void go_reverse()
void turn_bot_right()
void turn_bot_left()
void turn_bot_180()
*/
Try removiong the
Try removing the
pinMode(50,OUTPUT);
line, as I don’t see it used in other servo examples. Think pinmode is for digital IO, not PWM.
**Ive never used that library**<br>Ive never used that library but I dont think the servo position routines are blocking. Try putting some delays after assigning the servos a new position, perhaps they simply dont have time to move and it`s affecting the readings.
Yes, pinmode is for digital
Yes, pinmode is for digital output/input. Actually, that line isnt needed there at all! If im not mistaken, servos use PPM?
@ezekiel181 & Gareth > The
@ezekiel181 & Gareth > The introdcution of a delay before the analogRead is exactly what it needed. Thank you very much.
I tried modifying the code based on this table below:
Left Center Right Action
<200 <200 <200 move forward
<200 >200 <200 turn left
<200 >200 >200 turn left
>200 >200 <200 turn right
>200 >200 >200 turn bot 180 and go straight
Its all gone completely haywire now…all it does is that it bangs straight into a wall, then starts turning 360 degrees.
Im gonna check and see if it can work with a very simple case of stopping when it encounters an obstacle. I might actually upload a vid before i do that…its hilarious!! 
mmm…crazy code below…
void loop() {
go_straight();
scan();
if (left_val < 200 && center_val < 200 && right_val < 200) // Left, center and right paths clear??
{
go_straight();
}
else if (left_val < 200 && center_val > 200 && right_val < 200) // If center is blocked, then turn left or right
{
turn_bot_left();
servo1.write(90); // turn servo back to center
delay(500);
}
else if (left_val < 200 && center_val > 200 && right_val > 200) // If center and right are blocked, turn left
{
turn_bot_left();
servo1.write(90);
delay(500);
}
else if (left_val > 200 && center_val > 200 && right_val < 200) // If center and left are blocked, turn right
{
turn_bot_right();
servo1.write(90);
delay(500);
}
else if (left_val > 200 && center_val > 200 && right_val > 200) // All paths blocked…turn bot 180, center servo…
{
motor_stop();
delay(1000);
turn_bot_180();
servo1.write(90);
delay(500);
}
}
void scan()
{
servo1.write(0);
delay(650);
left_val = analogRead(IR_pin);
servo1.write(90);
delay(600);
center_val = analogRead(IR_pin);
servo1.write(180);
delay(600);
right_val = analogRead(IR_pin);
if(left_val < center_val && left_val < right_val) // Routine to find out smallest sensor reading and store it in a variable. Perhaps the bot can then be programmed to turn in that direction…
{
min_val = left_val;
}
else if(center_val < left_val && center_val < right_val)
{
min_val = center_val;
}
else
{
min_val = right_val;
}
}
}
PPM refers to a radio
PPM refers to a radio control radio formating of the signal, compared to PCM. Servos operate off a PWM signal, changing postion based on the width of the incoming pulse.
radio control as in radio
radio control as in radio transmitters/receivers?
Ok…i’ve changed the code to
Ok…i’ve changed the code to test for basic movement/detection
If the bot comes within a reading of 100, it stops, turns 180, scans and goes straight…
the code…
void loop() {
scan(); // scan left, center and right
while (center_val < 100)
{
go_straight(); // keep going straight until value of reading at center postion > 100
scan();
}
motor_stop(); // if reading taken > 100, then stop motors for a second
delay(1000);
turn_bot_180(); // turn bot 180 degrees…
delay(400); // wait until it completes turn…
motor_stop(); // stop for a second…and loop…
delay(1000);
}
This is what it does…
http://www.youtube.com/watch?v=FO-h6mz1X7M
I tried lowering the value of the center reading…( while center_val < 50 condition); it kinda stops before it bangs into the wall. I am going to try and put in other conditions, ie to turn based on most feasible path.
Is there anyway i can speed up entire scanning process? What i really want it to do is to read values in increments of 20 or 30 degrees, and then turn into the most suitable path. I think ive figured out how to do the reading part, but im not so sure about how to make it actually turn into that specific angle. Any suggestions on how to go about doing this?
Thanks very much.
Your bot moves too fast for
Your bot moves too fast for the scanning to keep up with. If its inside the loop and moving forward when it starts scanning by the time the scan is finished its too late.
Your robot doesnt need to check its left and right ALL the time unless its looking for something specific. If you just want it to avoid obstacles, have it go forward until it detects an obstacle ahead, make it stop and scan left/right and then it can decide where to go.
Alternatively you could have the robot continuously scanning a much smaller arc, say 20 degrees either side of center. Then you can get him to scoot around obstacles without slowing down.
Yes, as in model airplanes
Yes, as in model airplanes and cars/trucks. The receiver gets the PPM or PCM signal from the transmitter and converts it to several PWM signals for the servos.
Ok, that seems to be exactly
Ok, that seems to be exactly what the problem is. Thanks for the suggestion. Im going to give it another go.
Obviously, i was mistaken.
Obviously, i was mistaken. Thanks for the info.
Oki…i got it work, and im
Oki…i got it work, and im guessing it cant go wrong this time… the code so far…
void loop() {
scan_center();
while (center_val < 45) //keep scanning center and going forward until obstacle is detected…
{
go_straight();
scan_center();
}
// if center > 45 , then above loop exits, and the bot does the following:
motor_stop(); // stop for a bit
delay(200);
scan_around(); //scan left and right and record both values
servo1.write(90);
if (left_val < 50 && left_val < right_val) //if there is a better chance for turning left, do so
{
turn_bot_left();
delay(250);
motor_stop();
delay(200);
}
else if (right_val < 50 && right_val < left_val) // if right seems better, turn right
{
turn_bot_right();
delay(250);
motor_stop();
delay(200);
}
else //if both left, right and center paths are blocked, go reverse and turn 180
{
go_reverse();
delay(600);
motor_stop();
turn_bot_180();
delay(600);
motor_stop();
delay(20);
}
} // end of main routine…repeat
// Position servo at the center (90 degrees) read IR values
void scan_center()
{
servo1.write(90);
delay(500);
center_val = analogRead(IR_pin);
}
// Turn servo left (160 degrees) and right (20 degrees), and read & store IR values. The servo is mounted upside down, hence the range is from 160 - 20 (or 180 - 0)
void scan_around()
{
servo1.write(160);
delay(750);
left_val = analogRead(IR_pin);
servo1.write(20);
delay(800);
right_val = analogRead(IR_pin);
}
Video here > http://www.youtube.com/watch?v=KtxbcUZFjpk
Thanks for all the suggestions
