Save the Gearbox, Save the Game

[Matt Krass]

Originally Posted by Abwehr

We put a low-pass filter on the motor speed command almost every year. A more compact way to accomplish this follows. Note that you can (and I always do) use integers for the fractional part, but it's quicker to show you what's going on with floats:

// Put this at the top of "user_routines.c"
#define K_LP .2

// Put these at the top of Default_Routine()
static unsigned char pwm01_old = 127;

// Put these in your drive code
pwm01 = (your drive code here)
pwm01 = (unsigned char)(K_LP*pwm01) + (unsigned char)((1.0-K_LP)*pwm01_old);
pwm01_old = pwm01;

Adjust the "K_LP" parameter to change the response of the filter. Higher numbers make the system more responsive, but with more noise. Lower numbers make the system smoother, but with more lag.

Actually, that's going to make the motors go full reverse, since you're handling everything as an 8-bit integer value calculation, anything between 1 and 0 as a decimal defaults to zero, and you're multiplying both sides of the plus by 0, so you'd end with 0 + 0 = 0.

The concept is right but might I suggest a better execution?

// Put this at the top of "user_routines.c"
#define K_LP 2
unsigned int temp_pwm01;

// Put these in your drive code
pwm01 = (your drive code here)
temp_pwm01 = (unsigned int)((K_LP*pwm01)/10) + (unsigned int)(((10-K_LP)*pwm01_old)/10);
if(temp_pwm01 > 255)
{
   temp_pwm01 = 255;
}
pwm01_old = pwm01 = (unsigned char)temp_pwm01;

This scales everything up for the calculations to avoid floating point (MUCH FASTER, and the extra int we used is still less memory than a float), then divides it back down to minimize rounding errors, then checks to make sure its not too large for a char and sets pwm01 to it.