CarND-Controls-PID

Self-Driving Car Engineer Nanodegree Program

Explanation of the PID controller

PID stands for "Proportional-Integral-Derivative", and is a control loop feedback mechanism used for continous modulation of control systems. The P (Proportional), I (Integral) and D (Derivative) controllers are combined to produce a control signal. In our case, we use the PID controller to steer our car as close as possible to our desired trajectory setpoints . The deviation from the trajectory is given by the cross track error (CTE).

P (Proportional) Controller

The P controller gives an output that is proportional to the CTE by multiplying the CTE with proportional constant. This helps to steer the car towards the set points, and the speed of response is proportional to the proportional constant.

D (Derivative) Controller

The P Controller by itself, while useful, results oscillations as we constantly offshoot the setpoints due to the delay between measurement and response. The D controller helps to offset this behavior by introducing a dampening effect. This is done by giving an output that is proportional to the rate of change of the CTE; the higher the rate of change, the higher the counter steer effect will be, proportional to the derivative constant.

I (Integral) Controller

The I controller introduces an output that is proportional to the cumulative CTEs of the car. This helps to offset the effect of any systematic error that will lead the car away from the trajectory setpoints.

Tuning the parameters

I tuned the parameters manually. I increased Kp in order to increase the car's sensitivity towards responding to curves, and then tuned Kd in order to decrease the oscillations. I only used a very low value for Ki as the car seemed to be very sensitive to Ki, and does not seem to have any noticeable systematic error that might cause it to drift away from the middle of the lane.

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.

There's an experimental patch for windows in this PR

Basic Build Instructions

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

Tips for setting up your environment can be found here

Editor Settings

We've purposefully kept editor configuration files out of this repo in order to keep it as simple and environment agnostic as possible. However, we recommend using the following settings:

indent using spaces
set tab width to 2 spaces (keeps the matrices in source code aligned)

Code Style

Please (do your best to) stick to Google's C++ style guide.

Project Instructions and Rubric

Note: regardless of the changes you make, your project must be buildable using cmake and make!

More information is only accessible by people who are already enrolled in Term 2 of CarND. If you are enrolled, see the project page for instructions and the project rubric.

Hints!

You don't have to follow this directory structure, but if you do, your work will span all of the .cpp files here. Keep an eye out for TODOs.

Call for IDE Profiles Pull Requests

Help your fellow students!

We decided to create Makefiles with cmake to keep this project as platform agnostic as possible. Similarly, we omitted IDE profiles in order to we ensure that students don't feel pressured to use one IDE or another.

However! I'd love to help people get up and running with their IDEs of choice. If you've created a profile for an IDE that you think other students would appreciate, we'd love to have you add the requisite profile files and instructions to ide_profiles/. For example if you wanted to add a VS Code profile, you'd add:

/ide_profiles/vscode/.vscode
/ide_profiles/vscode/README.md

The README should explain what the profile does, how to take advantage of it, and how to install it.

Frankly, I've never been involved in a project with multiple IDE profiles before. I believe the best way to handle this would be to keep them out of the repo root to avoid clutter. My expectation is that most profiles will include instructions to copy files to a new location to get picked up by the IDE, but that's just a guess.

One last note here: regardless of the IDE used, every submitted project must still be compilable with cmake and make./

How to write a README

A well written README file can enhance your project and portfolio. Develop your abilities to create professional README files by completing this free course.

shunjilin/UdacityCarNDPIDControlProject