8051 Pid

[ahmedragia21]

Hi, im trying to do a PD for a robot to let it move in straight line , im just experimenting with just one motor connected to an encoder , well , when i get some samples from the enocders and when its not pointed to the motor encoder's strips , the motor change its speed as a function of the samples from the encoder is that correct ? also when i point the encoder sensor to the motor , the motor oscillates , dunno why ? and the desired_speed constant doesnt affect the speed of the motor ....

im using that code

#define left_velocity 10 
#define K_PRO 3		/* proportional constant */
#define K_DRV 3		/* derivative constant */

int Lvel, Rvel;		/* requested input velocities, ticks per 1/20 sec */
int leftacc, rightacc;	/* accumulators for motor output values */
int leftlast, rightlast; /* history values for calculating derivative */

void speedcontrol()	/* PID controller*/
{
	int lf, rt;

	lf = (Lvel - left_velocity)*256; 
	leftacc +=  ((lf/K_PRO) + ((lf - leftlast)/K_DRV));
	leftlast = lf; 
	
	pwmL(leftacc/256); 
}

for getting the Lvel , im just using an external interrupt .. and made a global variable unsigned char Lvel =0;