Turning problems in Vex autonomous.

[jamesgecko]

I wrote the following code using easyC for Vex.
It's a function, it's supposed to take the angle I give it and turn in that direction. If I give it a positive angle, it turns to the right. I'm trying to make it turn to the left if I give it a negative angle, but it ain't happening. For some reason it simply turns to the right again. Any ideas?

#include "Main.h"
 
void turn ( int angle )
{ // Turns the robot a set number of degrees
      int done = 0; 
      int abs; 
 
      angle = angle/4 ; //For the optical sensors, one turn is 90 pulses.
      if ( angle < 0 )
      {
            abs = -angle ;
      }
      else
      {
            abs = angle ;
      }
      PresetEncoder ( L_OPTICAL_SENSOR_CHANNEL , Left_Optical_Sensor ) ;
      PresetEncoder ( R_OPTICAL_SENSOR_CHANNEL , Right_Optical_Sensor ) ;
      StartEncoder ( L_OPTICAL_SENSOR_CHANNEL ) ;
      StartEncoder ( R_OPTICAL_SENSOR_CHANNEL ) ;
      while ( done != 2 )
      {
            Left_Optical_Sensor = GetEncoder ( L_OPTICAL_SENSOR_CHANNEL ) ;
            Right_Optical_Sensor = GetEncoder ( R_OPTICAL_SENSOR_CHANNEL ) ;
            if ( Left_Optical_Sensor < abs )
            {
                  if ( angle > 0 & angle <= 90 )
                  {
                        SetMotor ( L_MOTOR , 255 ) ;
                  }
                  if ( angle >= -90 & angle < 0 )
                  {
                        SetMotor ( L_MOTOR , 0 ) ;
                  }
            }
            else
            {
                  SetMotor ( L_MOTOR , 127 ) ;
                  done = done + 1 ;
                  StopEncoder ( L_OPTICAL_SENSOR_CHANNEL ) ;
            }
            if ( Right_Optical_Sensor < abs )
            {
                  if ( angle > 0 & angle <= 90 )
                  {
                        SetMotor ( R_MOTOR , 255 ) ;
                  }
                  if ( angle >= -90 & angle < 0 )
                  {
                        SetMotor ( R_MOTOR , 0 ) ;
                  }
            }
            else
            {
                  SetMotor ( R_MOTOR , 127 ) ;
                  done = done + 1 ;
                  StopEncoder ( R_OPTICAL_SENSOR_CHANNEL ) ;
            }
      }
      return  ;
}

[Keith Watson]

                  if ( angle > 0 & angle <= 90 )

This should be the logical operator &&, not the bit operator &.

Personally, I always write multiple expressions in the following form. It is more readable and forces the precedence I want. I have to type a few more keystrokes but it is worth the correctness and clarity.

                  if ( (angle > 0) && (angle <= 90) )

Otherwise someone who knows the functions you are calling will have to help you.

[koenig3456]

Since the wheels are mounted on opposite sides of the robot, they need to be operated opposite from each other. For example: To drive straight you would use:
SetMotor ( L_MOTOR , 255 ) ;
SetMotor ( R_MOTOR , 0 ) ;

Try swapping the SetMotor ( R_MOTOR , 255 ) ; and SetMotor ( R_MOTOR , 0 ) ; calls.

[jamesgecko]

Thanks, Keith. It works great now.

koenig3456: But I want the robot to turn... ;-)