Moderating Acceleration / Deceleration

[oddjob]

A simple filter is one line of code. Here is a version that works with integer math:

  out = (((n-1)*out)+in)/n;

in = the input to the filter e.g. PWM value as commanded by the joystick code.
out = the filtered quantity e.g. PWM value to the wheel.
n sets the filter bandwidth. Higher values, lower bandwidth. Experiment!

Preserve the value of 'out' (make it global or static). Use separate variables for each wheel. That should get you started.