pabloelizalde / carnd-mpc-project

Self-Driving Car ND @ Udacity - Term 2 Project 5 - MPC

CarND-Controls-MPC

Self-Driving Car Engineer Nanodegree Program

---

Intro

This repository contains the solution to the MPC Project. The projects consits in the implementation of a controller that allows to navigate through the track of the simulator. The controller will communicates to the car the steering and the acceleration at every moment.

The project basically consists in calculating a trajectory as an optimization problem. We need to figure out the trajectory that causes the minimal cost. We will update our actuators to follow that minimal cost. We have to keep updating our optimal trajectory, since we are calculating aproximations, and it is not going to match the real world. That is why we need to reevaluate and find the optimal actuators.

Implementation

There are two tools that helped a lot for the realization of the project:

• IPOPT: help us to find mathematical solutions to optimizations problems.
• CppAD: a library we use for automatic differenciation.

Our first step will be to find a polynomial that fits with the future waypoints that are given by the simulator. Before anything we will change these waypoints from map coordinates to car coordinates. To do that we first substract the car position from the waypoints, and also rotate them for simplification. This way our state vector will have px, py and psi equal to 0, simplyfing further calculations. Once we have that we can use the polyfit function that is given in main.cpp to get the coefficients of our polynomial. It is a third order polynomial since they can fit most roads.

To do the setup of our MPC we start defining the timestep lenght and duration. We started with initial value of N = 10, and dt = 0.5, as in the quiz. After some try and error of our solution, we got the best behaviour when we decreased the dt = 0.1. The change of any of the values had a mayor impact in the behaviour of the car. When the duration was too long, the simulation was slower. And with bigger values for the timested, the car was driving side to side till was out of the road.

The setup is as follows:

• First we pass the currect state to the MPC

  

• We define the vehicle model. As well as contraints, like limitations in the actuators (steering between -25 and 25, and acceleration between -1 and 1).

  

• We pass this data to the optimization solver to return a vector of control inputs that minimize the cost function. These are the values that will pass to our car in the simulator. Once the first pair of values are passed, we will do the same process again in a loop.

Delay

One of the challenges in the project, was including a delay that will mimic the delay that could happen from the actuators to actually perform the action. The solution consists in using the kinematic equations to predict the state of the car after the dealy (100ms). Once we have the new state we pass it to the MPC to get the correct values for the actuators.

Dependencies

• cmake >= 3.5
• All OSes: click here for installation instructions
• make >= 4.1
  • 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.
• Fortran Compiler
  • Mac: brew install gcc (might not be required)
  • Linux: sudo apt-get install gfortran. Additionall you have also have to install gcc and g++, sudo apt-get install gcc g++. Look in this Dockerfile for more info.
• Ipopt
  • Mac: brew install ipopt
    • Some Mac users have experienced the following error:

    Listening to port 4567
    Connected!!!
    mpc(4561,0x7ffff1eed3c0) malloc: *** error for object 0x7f911e007600: incorrect checksum for freed object
    - object was probably modified after being freed.
    *** set a breakpoint in malloc_error_break to debug
    

    This error has been resolved by updrading ipopt with brew upgrade ipopt --with-openblas per this forum post.
  • 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 the Ipopt releases page.
    • Then call install_ipopt.sh with the source directory as the first argument, ex: sudo 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.
• Not a dependency but read the DATA.md for a description of the data sent back from the simulator.

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./

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.