Society of Robots - Robot Forum

Electronics => Electronics => Topic started by: robotcoder on July 13, 2009, 12:13:06 AM

Title: Servo rotates in one direction
Post by: robotcoder on July 13, 2009, 12:13:06 AM: I just modified 2 servos (HS-311) to rotate in 360 and I can get one of them to move clockwise and counter clockwise, but the other servo only moves in one direction. Any ideas on what I can do to correct this?
Title: Re: Servo rotates in one direction
Post by: SmAsH on July 13, 2009, 12:21:57 AM: does the servo stop if you send a 1.5ms pulse (center)?
Title: Re: Servo rotates in one direction
Post by: sonictj on July 13, 2009, 12:23:23 AM: you probably did not properly center the servo(s). The potentiometer inside the servo has to be fixed at its neutral position to fool the servo.

http://www.societyofrobots.com/actuators_modifyservo.shtml (http://www.societyofrobots.com/actuators_modifyservo.shtml)

step 5
Title: Re: Servo rotates in one direction
Post by: robotcoder on July 13, 2009, 12:28:41 AM: I am new to all of this, so I am not sure exactly how to send 1.5ms. I am using the sample code for the $50 robot, so to move the servo's I am using, for example C7(500); If you have a code example of how to send 1.5ms to the servo that would help. Thanks for the reply.
Title: Re: Servo rotates in one direction
Post by: SmAsH on July 13, 2009, 12:31:25 AM: set the pin high, wait 1500us, set the pin low.
if i can find the code anywhere ill upload it for you.

EDIT: here it is http://www.societyofrobots.com/downloads/hold_servo.hex (http://www.societyofrobots.com/downloads/hold_servo.hex)
Title: Re: Servo rotates in one direction
Post by: Joker94 on July 13, 2009, 12:37:04 AM: one time the cord that connects to the mcu board had a break in one of the lines there for only span one way

it is most likely not that, mabey .0000000000005 % chance

the reason it happened to me is i had a box or carbon fibre sheets fell onto my servo box which pearced the servo cable, if that ever happens hold you shipper accountable.

good luck finding the problem
Title: Re: Servo rotates in one direction
Post by: sonictj on July 13, 2009, 12:40:07 AM: a servo works by listening for a 50Hz pulse. The length of he pulse is ~ from 1 to 2 ms. 1500us or 1.5ms is the pulse length to make the servo go t the center position.
So essentially

set pin HIGH
_delay_us(time)
set pin LOW
_delay_us(20000-time)

time equates to the pulse time of 1 to 2 ms that is the general idea.
Title: Re: Servo rotates in one direction
Post by: robotcoder on July 13, 2009, 12:42:43 AM: I just found this example code, I will try this and see what the servo does.

int main()
{
   int i;
   DDRB = 0xff;
   PORTB = 0xff;
   while(1)
   {
      //Hold the motor in neutral for 2 seconds (Each signal is 20ms, so repeating that 100 times = 2000 sec

      for(i=0;i<101;i++)
      {
         PORTB = 0xff;
         _delay_ms(1.5);
         PORTB = 0x00;
         _delay_ms(18.5);
      }
      //Turn 90deg clockwise for 2 sec
      for(i=0;i<101;i++)
      {
         PORTB = 0xff;
         _delay_ms(2);
         PORTB = 0x00;
         _delay_ms(18);
      }
      //Turn to -90deg ccw, while passing the neutral state for 2 sec
      for(i=0;i<101;i++)
      {
         PORTB = 0xff;
         _delay_ms(1);
         PORTB = 0x00;
         _delay_ms(19);
      }
   }
return 1;
}
Title: Re: Servo rotates in one direction
Post by: sonictj on July 13, 2009, 12:45:54 AM: what pin do you have the servo connected to? Do you have anything else connected to PORTB?