Control Theory and Sensor Fusion Algorithm

Topics: Control theory, PID controller, Feedback Pages: 10 (4447 words) Published: May 28, 2014


David Malgoza, Engers F Davance Mercedes,
Stephen Smith, and Joshua West

School of Electrical Engineering and Computer
Science, University of Central Florida, Orlando,
Florida, 32816-2450

where flight duration varies directly with its total weight. The frame must be designed strong and rigid enough to
support all the other systems yet, light enough to so as to prolong flight duration to acceptable levels.
The Quad-Copter consists of several subsystems
some of which are more interwoven into the design, such
as the MCU, and some that are more isolated, for example
the video system. The block diagram in figure 1 below
provides an overview of the Quad-Copter's subsystems.


Abstract - This paper is a presentation of the design
methodology and realization of the Quad-Copter, a model
aircraft based on a four-propeller design. The Quad-Copter
can be controlled by radio transmission or operate under the guidance of limited autonomous protocols. Flight stability of the Quad-Copter is achieved using a five degrees of freedom (DoF) inertial measurement unit (IMU). Sensor data is

integrated and processed using a proportional-integral-
derivative controller (PID controller), a feedback loop
maintained by an on-board Atmel microcontroller. All
subsystems of the Quad-Copter are designed to minimize
weight and cost where practical.
Index Terms Kalman filters, Microcontrollers,
Oscillators, Robot programming, Sensor systems and



Fig. 1. Block diagram of Quad-Copter subsystems


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The Quad-Copter is a small lightweight hover-capable
vehicle that can be controlled over a custom wireless
system. The Quad-Copter has a robust sensor suite so that
it can also operate in a more autonomous mode. The
autonomous mode includes subsystems such as a GPS
module so that the Quad-Copter, once given a GPS target
location, can make its own way to the target coordinates
without further human control. This flight mode requires
additional subsystems such as ultrasonic proximity
sensors, so that the robot can detect and avoid obstacles
(including the ground) and a digital compass, so that its
direction can be detected and corrected. All of these
sensors send a lot of data to the MCU, the brain of the
Quad-Copter, which must process the information
according to its algorithms and prompt the appropriate
subsystems to action. An especially complex task assigned
to the MCU is to maintain level flight by varying the
speed of individual motors based upon the calculation of
data received from the IMU (Inertial Measurement Unit).
The IMU combines data from a triple-axis accelerometer
and a dual-axis gyroscope using a sensor fusion algorithm.
The subsystems of the Quad-Copter are interdependent,
linked by the MCU, the physical frame, and the power
system. Power comes at a premium in an aerial vehicle

The Quad-Copter requires several sensors to perform
tasks that range from critical, such as flight stability, to optional, such as the high altitude sensor. Additionally,
sensors are an important part of the Quad-Copter's
autonomous functions such as altitude maintenance, path
finding, and object avoidance. The different sensor
subsystems can be organized into the following
categories: flight stability sensors, proximity sensors, yaw or direction sensor, and the navigation sensor (GPS).
A. Flight Stability Sensors

The flight stability sensors are a critical system for the
Quad-Copter to remain in flight. The system consists of a
triple axis accelerometer and a dual axis gyroscope
combined into a 5 DoF IMU. The accelerometer is the
ADXL335 from Analog Devises, and the gyroscope is the
lDG500 from InvenSense. The outputs from the sensors
are combined using a sensor fusion algorithm, which...
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