/CarND-MPC-Project

Primary LanguageC++

CarND-Controls-MPC

Self-Driving Car Engineer Nanodegree Program

MPC

For this project we have implemented a global kinematic model which represents the vehicle state model by position, orientation and velocity.

The main goal was to use the mentioned MPC (Model Predictive Controller) to safely drive a car along the track. The key point in this project was to choose the appropiate parameter values that optimize the MPC cost function.

In addition to the variables mentioned before, others parameters were taken into account to define the MPC pipeline.

  • The CTE (cross track error) represents the distance of the vehicle from the trajectory.
  • EPSI (orientation error) which describes the difference between the vehicle orientation and the trajectory orientation.

Two actuators were also used to solve the MPC

  • delta -> the steering angle
  • a -> the acceleration value (can be negative or positive)

Screen

MAIN PIPELINE

The main pipeline receives the next waypoints that the vehicle should drive at. It transforms the coordinates to vehicle-centered ones and fits a third degree polynomial with these values. With the resulting coefficients, it was possible to estimate the CTE and EPSI errors.

Positioning the vehicle in the ideally initial state (0,0,0) and using also the given speed and the calculated CTE and EPSI, it was possible to form the state which was passed to the MPC solve function. It returned the new steering and acceleration values.

In order to achieve the main goal of this project and to drive the vehicle safely and smootly into the track lanes, we needed to tune the cost function factors as follows.

The following values were chosen as hyperparameters.

size_t N = 20;
double dt = 0.20;

int cost_cte_factor = 2000;
int cost_epsi_factor = 2000;
int cost_v_factor = 1;
int cost_current_delta_factor = 100;
int cost_current_a_factor = 10;
int cost_diff_delta_factor = 100;
int cost_diff_a_factor = 10;

double ref_cte = 0;
double ref_epsi = 0;
double ref_v = 70;

To accomplish the 100ms delay requirement, it was set a value of 20 for N and 0.2s for dt in order to have a better and greater predictive estimation. It was also set a max speed value of 70mph to avoid very high speed situations.

Dependencies

  • cmake >= 3.5
  • All OSes: click here for installation instructions
  • make >= 4.1
  • gcc/g++ >= 5.4
  • uWebSockets == 0.14, but the master branch will probably work just fine
    • Follow the instructions in the uWebSockets README to get setup for your platform. You can download the zip of the appropriate version from the releases page. Here's a link to the v0.14 zip.
    • If you have MacOS and have Homebrew installed you can just run the ./install-mac.sh script to install this.
  • Ipopt
    • Mac: brew install ipopt --with-openblas
    • Linux
      • You will need a version of Ipopt 3.12.1 or higher. The version available through apt-get is 3.11.x. If you can get that version to work great but if not there's a script install_ipopt.sh that will install Ipopt. You just need to download the source from here.
      • Then call install_ipopt.sh with the source directory as the first argument, ex: bash install_ipopt.sh Ipopt-3.12.1.
    • Windows: TODO. If you can use the Linux subsystem and follow the Linux instructions.
  • CppAD
    • Mac: brew install cppad
    • Linux sudo apt-get install cppad or equivalent.
    • Windows: TODO. If you can use the Linux subsystem and follow the Linux instructions.
  • Eigen. This is already part of the repo so you shouldn't have to worry about it.
  • Simulator. You can download these from the releases tab.

Basic Build Instructions

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

Tips

  1. It's recommended to test the MPC on basic examples to see if your implementation behaves as desired. One possible example is the vehicle starting offset of a straight line (reference). If the MPC implementation is correct, after some number of timesteps (not too many) it should find and track the reference line.
  2. The lake_track_waypoints.csv file has the waypoints of the lake track. You could use this to fit polynomials and points and see of how well your model tracks curve. NOTE: This file might be not completely in sync with the simulator so your solution should NOT depend on it.
  3. For visualization this C++ matplotlib wrapper could be helpful.

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./