Try out different values for the proportional, integral and derivative gains! The ones I've set seem to work pretty well. In "User" Mode: Use the mouse or the arrow keys to assign a desired direction. Click the "Randomize Direction" button to change modes. When "Reset Integral on Positional Discontinuity" is turned on, the program sets the rolling sum of previous error back to zero upon detecting a large change in the desired position vector.
Here's a video that talks about what PID controllers are: youtube.com/watch?v=UR0hOmjaHp0 I want to work on this more so that the integral gain (K_i) will be changed automatically when the acceleration of the desired direction vector is large.