A problem in tune the PID

ArduRover ArduBoat
1

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  1. When I tune the PID, I found that there always a error in the desired and achieved PID, but it can reach same in the end, I think P is low, then I increase it. but even l increase P to 2 the error can’t eliminate.
  2. then I decrease the accelerate , but the error is still there, can someone help me.
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Post a log. What is your ATC_STR_RAT_FF?

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I think in tune the steering PID just increase the FF is not enough, at the beginning I follow the wiki’s guidance, but during tune the steering: IF FF is high to1.6 and PI low to 0.2 is always an error, THEN low decrease the FF to 0.6 and increase PI to 1.6-1.8 , the error is eliminated.