Description
1 Introduction
In this project, we introduce the modeling of quadrotors used in the Drone Lab at UMD
in the Department of Computer Science under Prof. Yiannis Aloimonos. These drones are
used in the lab for research purposes. The modeling, control and integrating off-the-shelf
components approach to build quadrotors is based on the research work being done in the
Drone Lab at UMD and Mellinger’s thesis [1].
2 Quadrotor Platform
The quadrotor platform constructed for the course is based on the very popular 250 racing
quad frame. The frame is in the X configuration, making it ideal for the control equations
you have learned in the course. The size of the quadrotor 250, means the diagonal distance
between the motors is 250mm. The total weight of the platform is around 500 grams. The
power train of the quadrotor consists of 4 × 2400KV motors driving 5 inches propellers
which provides a combined thrust of about 4kgs. The quadrotor has a multitude of sensors
which includes cameras, range finders and an IMU. The hardware consists of 3 layers:
• A Betaflight flight controller which controls the power train of the quadrotor. Under
the ‘level flight’ mode, an control input is translated into desired roll, pitch, and yaw
angles.
• A microcontroller which handles the low level communication, input and output to
and from the peripherals.
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Figure 1: Quadrotor 250: DroneLab @UMD
• A single board computer running Ubuntu 16.04 is the brain of the platform. It uses
Robot Operating System (ROS) as the middleware to communicate and manage various
software modules in the quadrotor.
3 Background Literature
Please refer to the lecture slides/videos and D. Mellinger’s thesis [1] for this phase of the
project as listed below:
• Lecture Videos
– Quadrotor Dynamics Video
– Quadrotor Controls Video
• Lecture Slides
– Quadrotor Dynamics Slides
– Quadrotor Controls Slides
• Trajectory Generation and Control for Quadrotors, D. Mellinger, Chapters 2.1 and 2.2
[1]
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4 Tasks
You will simulate the quadrotor dynamics and control using the matlab simulator provided
as part of this project [1]. The simulator relies on the numerical solver ode45, details about
this solver can be easily found online. Your tasks include:
4.1 Trajectory Generator
You will first implement two trajectory generators that generate a circle and a diamond
trajectories. In order to specify the trajectory in the simulator, you will need to change the
variable trajhandle. trajhandle is the name of a function that takes in current time t
and current quadrotor number qn and returns a struct of desired state as a function of time.
The struct desired state has 5 fields, which are pos, vel, acc, yaw and yawdot. For a
proper trajectory, you need to specify pos, vel and acc, whereas yaw and yawdot can be
left as 0. This is because we are assuming that we don’t change our yaw angle.
• circle.m
A helix in the xy plane of radius 5m centered about the point (0;0;0) starting at the
point (5;0;0). The z-coordinate should start at 0 and end at 2:5. The helix should
go counter-clockwise.
• diamond.m
A Quadrilateral of a given size with corners at for example (0;0;0), (0; p2; p2),
(0; 0; 2p2), and (0; -p2; p2) when projected into the yz plane, and an x coordinate starting at 0 and ending at 1, where p2 could be some arbitrary integer value, for
example, you can assume p2 is 1. The quadrotor should start at (0;0;0) and end at
(1;0;0).
4.2 Controller
You will then implement a controller in file controller.m that makes sure that your quadrotor follows the desired trajectory. This controller will be used again in the following phases.
The controller takes in a cell struct qd, current time t, current quadrotor number qn and
quadrotor parameters params and outputs thrust F, moments M, desired thrust, roll, pitch
and yaw trpy and derivatives of desired roll, pitch and yaw drpy.
qd is a cell array contains structs for each quadrotor. This means qdfqng contains all
the information (position, velocity, euler angles and etc.) about quadrotor number qn.
Pose information can be accessed via qdfqng.pos for example. The reason for using qd
here is to be compatible with Drone flight control software that you will use in the final
phase of this project to fly the quadrotor.
4.3 Simulation
Lastly, you need to fill in the appropriate variables for trajhandle and controlhandle in
the script runsim.m for simulating your result.
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5 Simulator
The quadrotor simulator comes with the student code. Before implementing your own functions, you should first try running runsim.m in your matlab. If you see a quadrotor falling
from position (0;0;0) then the simulator works on your computer and you may continue
with other tasks. This is because the outputs of controller.m are all zeros, thus no thrust
generated.
When you have the basic version of your trajectory generator and controller done, you
will be able to see the quadrotor flying in the space with proper roll, pitch, and yaw, leaving
trails of desired and actual position behind. The desired position is color-coded blue and the
actual position is red. After the simulation finishes, two plots of position and velocity will
be generated to give you an overview of how well your trajectory generator and controller
are doing. Note that you will not be graded on these plots but by the autograder.
5.1 Submission
When you are finished, submit your code using the CMSC 828T website.
Your submission should contain:
• A README.txt file that includes a short summary of what you did, lessons learned, any
key hurdles you faced and how you overcame them. Please also include text detailing
anything extra we should be aware of about your submission.
• A LateDays.txt file with the number of late days you wish to use, from whatever is
remaining. The file should contain only a single digit number less than 4 as that is the
maximum number of late days you will receive.
• Files drone250x.m, controller.m, diamond.m, circle.m, as well as any other Matlab
files you need to run your code.
Zip everything into code.zip and use the Submit Page on the website to make your
submissions. Based on the load on the server, the report might be immediate or might
take up to 24 hours. You have limited submissions so please do not use the submit server
as a debugging tool. It is to validate your final submissions and to make any additional
modifications and optimizations.
You will be graded on successful completion of the code and how quickly and accurately
your quadrotor follows the circle and diamond paths and one other trajectory which will not
be released to you and will be our secret evaluation tests. There is no hard time cutoff on
this phase of the project. However, as mentioned earlier, your score will also be a function
of how quickly and accurately it follows the desired paths.
6 Acknowledgements
The project has been adapted from the University of Pennsylvania MEAM 620 course.
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7 Collaboration Policy
You can discuss with any number of people. But the solution you turn in MUST be your
own. Plagiarism is strictly prohibited. Plagiarism checker will be used to check your submission. Please make sure to cite any references from papers, websites, or any other student’s
work you might have referred.
References
[1] Daniel Mellinger. Trajectory generation and control for quadrotors. University of Pennsylvania, 2012.
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