My alternative to the SHR

By kingkong95
@ November 28, 2011

• Actuators / output devices: two continuous servos
• CPU: Arduino
• Power source: One 9V battery, 7.2v 4700mAh RC battery
• Programming language: Arduino C/C++
• Sensors / input devices: two IR led's, one IR receiver.
• Target environment: Smooooth floors

To begin with I started with my collection of parts, so I already had all the electronic components I needed :D That is: two continuous servo's, two IR LED's, my arduino duemilanove, a 38khz IR receiver and a tamiya RC battery - all ready to use!

Then I needed a chassis for the robot, and I already wanted an excuse to test out a laser cutting service I had found, so I sent off some very (very) basic plans I drew up in Inkscape. I actually made the chassis a while ago, I just never got round to using it until now :P The service was actually quite good, it takes a couple of weeks for them to process your order and there isn't a great deal of materials to choose from, but it allowed me to use my own design at the fairly reasonable cost of around £10. :)

The circuit is quite simple, it's just two IR LED's in series connected to PWM pin 11, an IR receiver connected to pin 5, two servo's in Pins 10 and 11, and a notification LED in 13. Thanks to Ro-Bot-X for his tutorial on that, although I actually used some other code I found on here somewhere for oscillating the LED at 38khz and merged the two together :)

Here is the code:

#define IR_CLOCK_RATE    38000L
#define pwmPin 11
#define IRsensorPin 5
#define D13ledPin 13 
#include <Servo.h>

Servo left;
Servo right;

void setup()  {
  
  right.attach(10);
  left.attach(9);

  TCCR2A = _BV(WGM21) | _BV(COM2A0);
  TCCR2B = _BV(CS20);
  OCR2A = (F_CPU/(IR_CLOCK_RATE*2L)-1);
  pinMode(pwmPin, OUTPUT);
  
  pinMode(D13ledPin, OUTPUT);
  digitalWrite(D13ledPin, LOW);
  
}

void loop() 
{
  
  if (digitalRead(IRsensorPin)==LOW){
    
    digitalWrite(D13ledPin, HIGH);
    Backwards();
    delay(1000);
    Left();
    delay(1000);
    
  } else {
    
    digitalWrite(D13ledPin, LOW);
    Forwards();
    
  }
  delay(100);
}

void Forwards ()
{
  left.write(10);
  right.write(170);
}

void Backwards ()
{
  left.write(170);
  right.write(10);
}

void Left ()
{
  left.write(80);
  right.write(170);
}

void Right ()
{
  left.write(10);
  right.write(100);
}

void Stop ()
{
  left.write(90);
  right.write(90);
}

Lessons learnt from this project:

1. Use a ball caster with a radius greater than the thickness of the carpet and one that doesn't hook onto everything
2. Use sensors nearer to ground level - there's a blind spot almost as long as their detection threshold
3. RC batteries are great! I don't know how much current these servo's draw, but even if it's 500 mah each that's around 4.5 hours of running time for 4.5 hours of charging :D

Anyway, now onto my next project.. I'm thinking I'll add some autonmous controls to my rc buggy (heavily inspired by some of frits' stuff). The tank in the back of the photo there can be fixed another day :)