/CarND-PID-Control-Project

Implementation of a PID Controller that is able to drive a vehicle around a simulated race track.

Primary LanguageC++MIT LicenseMIT

CarND-Controls-PID

Self-Driving Car Engineer Nanodegree Program

CarND-Controls-PID

The goal of the project is to implement a PID Controller that will be able to drive a vehicle around the track which is part of the Udacity Simulator. To do so two PID controllers are introduced. The first one controls the steering angle based on the deviation of the center of the car relative to the center of the road. The second one controls the throttle value based on the steering angle. The idea is to throttle the car when the steering angle is high.

Influence of constants on the vehicle behaviour

A PID controller is based on following differential equation, where e(t) is the error over time:

PID mathematical formula

  • Kp - the proportional term

    • Deals with how far the vehicle is from its target(the center of the road) and how hard does it need to steer back in order to reach that target
    • Setting a large value makes the car oscilate a lot on the road
    • It needs to be counter-balanced by the Kd term

  • Ki - the integral term

    • Deals with the fact that the vehicle might pull to the left of to the right, due to wheels not being pefectly aligned
    • This constant has been set to 0.0 while using the simulator

  • Kd - the derivative term

    • Deals with reducing oscilation around the center
    • It aims at flattening the error trajectory into a horizontal line

Steps of implementation

  1. Initialize the PID contoller with values for the constants Kp, Ki and Kd that allow the vehicle to drive around the track safely

    • Functioning values for the constants have been selected through trial and error method
    • Below are some of the tested values, in ascending order from worst to best (comments on each set of settings are made with respect to previous line of settings):
    Kp Ki Kd Result
    1.00 0.00 0.00 a lot of oversteering, car eventually leaves the track
    1.00 0.00 1.00 less oversteering, car moves from side to side, car eventually leaves the track
    0.50 0.00 0.50 less oversteering, car moves from side to side, eventually leaves the track
    0.50 0.00 1.00 oversteering, car moves from side to side, car stays on track
    0.50 0.00 1.50 oversteering, car moves from side to side, car stays on track
    0.25 0.00 1.50 car is a lot more centered on the track, less movement from left to right, car stays on track
    0.15 0.00 1.50 car is a lot more centered on the track, less movement from left to right, car stays on track
    0.10 0.00 1.50 car is centered on the track most of the time, car is stable and stays on track

  2. Calculate the error value which is needed to calculate the discrete form of the above mentioned differential equation:

double pre_cte = p_error;

p_error  = cte;
i_error += cte;
d_error  = cte - pre_cte;
  
double value = -Kp*p_error - Ki*i_error - Kd*d_error;

Final tunning values and results

  • The selected tunning values for the steering angle controller are the following:
Kp Ki Kd
0.10 0.00 1.50
  • The selected tunning values for the throttle controller are the following:
Kp Ki Kd
0.45 0.00 0.5
  • The result of the simulation using these parameters can be found in testdrive_pid.mp4. Screenshot Test Drive

Dependencies

Fellow students have put together a guide to Windows set-up for the project here if the environment you have set up for the Sensor Fusion projects does not work for this project. There's also an experimental patch for windows in this PR.

Basic Build Instructions

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

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