yazuyang / carnd_t2_p3_pid_submission

CARND Project: PID Control

Introduction

This repository is a submission of CARND Project "PID Control". In this README, I will explain the point of rubric.

Compilation

This repository has CMakeList.txt and source codes under the directory "./src". To complie and run, pleae do below. I confirmed that this repository works well.

• Clone this repo.
• Make a build directory: mkdir build && cd build
• Compile: cmake .. && make
• Run it: ./pid.

Implementation

In PID.cpp, calculate steering angle with standard PID method. It means below.

• A value of cross track error (variable name is cte) is input to the class method PID::UpdateError. It calculate three cte errors below.
  • p_error: A proportional error.
  • i_error: A integral error.
  • d_error: A derivative error.
• The class method PID::UpdateError multiplies three errors by parameters respectively and sums them up to make a steering angle.

Reflection

The effect each of the P, I, D components in this implementation.

"P" is a parameter that if the current cte is bigger, "P" becomes bigeger. So, if K_p is large, the car will oscillate.

"I" is a parameter that reflects long-term effects. In this simulation, I thought that the change of the curve of the road was the scene which clarified the influence of the parameter. I executed a simulation with small K_i parameter. The behavior is unstable when entering the curve.

"D" is a parameter that responds more as the difference from the previous cte increases. I executed a simulation with big K_d parameter. Because cte changed rapidly according to the curve, the parameter of D reacted excessively, and the behavior reacted excessively.

How the final parameters were chosen

First, I decided the initial value and printed the value of each error. From the results, I decided a good initial value, and twiddle ran the simulator many times and got converged parameters.

Simulation

I confirmed that the program in this repository controls the car well by making the track run 5 times in simulation.