这是优达学城PID控制器项目实现，这个调试方法是做项目时，mentor给的建议，实践中，效果还蛮不错~~
PID Controller
the project require to create a PID Controller for the vehicle on the high way.
PID effectons
- P Controller is a based controller.
when the car ran with small cte, it had a small oscillation. But when the car truned the curve, the cte became larger and the controller began a big oscillation.
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D Controller create small cte change rate;
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I Controller, It sum a lot of cte;
To tune a PID, I will take some steps below:
step1:create a PID Controller class, and set the parameter of P’s, I’s, D’s to zero;
step2: increase P gain until the response to a disturbance is steady oscillation;
step3: Increase the D gain until the oscillations go away;
step4: Repeat step2 and step 3, until increasing the D gain does not stop the oscillations;
step5: Increase the I gain until it brings you to the setpoint with the number of oscillations desired(normally zero);
