Overview

Project Introduction

Implements a PID controller in C++ to maneuver the vehicle around the track. The simulator provides the cross track error (CTE) and the velocity (mph) in order to compute the appropriate steering angle.

Results

Sped up example of final parameter run (no dangerous manuevers)

PID Algorithm

A PID controller uses three parameters to adjust steering; P ("proportional"), I ("integral"), D ("differential"). Together, these parameters can be adjusted to better steer the vehicle based on the associated errors measured in real-time.

The P parameter causes the vehicle to steer in proportion to the vehicles's distance from the lane center (CTE). If the vehicle is too far in a direction, it will more drastically correct its steering. If the vehicle is only slightly too far in a direction, it will only slightly correct its steering.

The I parameter corrects the bias in the CTE (such as steering drift). Without this term, the controller can have a difficult time reaching its ideal position.

The D parameter counters the controller to overshoot the desired position due to the P parameter. This parameter allows the vehicle to more smoothly the desired position.

Choosing PID Parameter Coefficients

Coefficients were determined with trial and error methods until the vehicle could reasonably move around the track safely.

The final values were P=-0.10, I=-0.0001, and D=-1.50(with a throttle of 0.3).

• P: Many runs saw a too slight of an overcorrection. This meant the parameter needed to be increased in magnitude.
• I: This parameter didn't needto be very large since it appears there was little bias in the system.
• D: This parameter was a very important one to counteract the P parameter. In initial tests, the D parameter was accidentally set to 0 and the vechicle would frequently overshoot its desired position (center of the lane). After adjusting and re-adjusting the parameter, the vehicle does a better job in more smoothly correcting the steering.

Set Up: Basic Build Instructions

1. Clone this repo.
2. Make a build directory: mkdir build && cd build
3. Compile: cmake .. && make
4. Run it: ./pid.

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Dependencies

• cmake >= 3.5
• All OSes: click here for installation instructions
• make >= 4.1(mac, linux), 3.81(Windows)
  • Linux: make is installed by default on most Linux distros
  • Mac: install Xcode command line tools to get make
  • Windows: Click here for installation instructions
• gcc/g++ >= 5.4
  • Linux: gcc / g++ is installed by default on most Linux distros
  • Mac: same deal as make - [install Xcode command line tools]((https://developer.apple.com/xcode/features/)
  • Windows: recommend using MinGW
• uWebSockets
  • Run either ./install-mac.sh or ./install-ubuntu.sh.
  • If you install from source, checkout to commit e94b6e1, i.e.

    git clone https://github.com/uWebSockets/uWebSockets 
    cd uWebSockets
    git checkout e94b6e1
    

    Some function signatures have changed in v0.14.x. See this PR for more details.
• Simulator. You can download these from the project intro page in the classroom.