looking at your site in detail.
The data in the output grapg the data is the gps heading only.
The data in the input graph is turnSpeed.
In our program is is the error between the aim point on the desired track – the gps heading is generating the turnSpeed and not the gps by itself.
In section select a setp. You have selected what we call the pivot this is when the robot to two 90 degree turns with a short 20 inch straight section to move to the next lane.
We are more interested in the longer straight tracks between the pivots, These trcks are about 60 ft long and we want the robot to not wonder off the straight line in between. Currently we can control the robot to be +-5cm from the desired line. We want to see if we can reduce this cross track error CTE even further. Ie that the robot drives even straighter.
In section 3 I have not clue as to which model to select. I normally use Brett Beauregards PID library and we tune for Kp Ki Kd
I am not sure about the other form of the PID equation that uses a general gain and Time constants approach.