Small Autonomous Unmanned Aerial Vehicle

Project Overview

Our goal is to design and construct a prototype of a small, low cost, aerial data acquisition system. UAVs have long been used by the military in reconnaissance applications, but they have yet to trickle down into the affordable consumer market. Team Plane! aims to create a system that will allow companies and individuals, without defense contracts, to perform data acquisition that would otherwise be impossible. Our system is specifically intended for use by the Calvin College Biology Department to aide their research of canopy composition for the Calvin College Nature Preserve. We intend to have a flight time of ten minutes. This will allow the airplane to fly to several GPS locations and return to the launch location. The plane must also be robust enough for repeated use.

We intend to build a remote controlled system with autonomous camera, followed by a fully autonomous prototype if time permits.

Airframe

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The Bellanca and the Super Cub

The first aircraft we chose was the Bellanca Decathlon 480 RTF . It is an electric model airplane. It is a low-cost beginner aircraft with a large fuselage to hold our electronic components. The plane has three control surfaces, two elevators and a rudder, allowing us to use the elevators for stabilization and the rudder separately for navagation. Additionally, spare parts for the Decathlon 480 can also be easily accessed through the provider. If we, or the end user, breaks the aircraft, they only need to order replacements for the broken parts. Unfortunately the Bellanca Decathlon 480 did not have enough power to carry the necessary payload to meet our objectives.

The current model that we are using is the Super Cub. The Super Cub is similar to the Bellanca Decathlon 480 except it has a larger wing span and is made of Z-foam. These extra features allowed the Super Cub to carry the necessary payload. The similarity between the Super Cub and the Bellanca Decathlon helped the pilot easily adjust to the new aircraft.

Navigation

Autonomous navigation will be dependent on a GPS receiver for longitude, latitude, altitude, heading, and velocity. We chose the ET-312 SiRF III. This is a relatively inexpensive module that can lock on up to 20 satellites and has a reacquisition rate of 10 Hz.

Our microcontroller will take the readings from the GPS receiver and use them to determine position and heading. These will be used to compute the desired heading. This desired heading will be fed into a PID feedback control loop. Finally, the output from the feedback control loop will be pulse-width modulated to control the servo for the rudder. We do not intend to use the elevators in our navigation control system. This will simplify the design and help to maintain level flight during operation.

Stabilization

Our design for the stabilization system uses an IR sensor array. The array of IR sensors is used to detect the pitch and roll of the aircraft. It consists of four thermopiles, one each facing forwards, backwards, left and right relative to the center of the aircraft. This is the system that has been utilized in the successful Paparazzi open-source autopilot project. It works on the theory that sky is colder than the ground. Therefore, and infrared thermopile pointed at the sky will read a significantly colder temperature than one pointed at the ground. Therefore, the plane has level roll if the left and right sensors have the same reading. Similarly, the plane has level pitch if the front and rear sensors have the same reading. The differences between these two sensors are then fed back into the feedback control loop to help keep the plane level. In order to obtain a more accurate reading, the signals from the two sensors are averaged. This way, any small error in either of them should be cancelled out by the other. We chose the FMA CDP4 Co-Pilot, sucessfully used in the ArduPilot autopilot. For more information on infrared stabilization see the Paparazzi explanation of IR Stabilization.

While the navigation system utilizes the rudder of the aircraft, the stabilization system utilizes the elevators of the aircraft. To correct an incorrect pitch in the aircraft, the control loop will move the elevators up or down together. To correct an incorrect roll in the aircraft, the elevators will move opposite one another.

Microcontroller

We chose the Arduino Pro Mini. Arduino microcontrollers are commonly used by UAV hobbyists. The Pro Mini has a small footprint while still retaining the power and functionality of other Arduino boards.

Camera

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GE A830 Camera

The GE A830 is the camera that was installed in the airframe. The reason this camera was chosen was because it had 8.0 megapixels and was relatively inexpensive. 8 megapixels allows the ground and trees to be seen clearly so that the biology department can use the pictures for research. The camera was taken apart and only the lens and circuit board. Other components such as the LCD screen were removed to reduce weight. Pictures are retrieved by taking the wings off the airplane and removing the SD card. The lens is pointed out the bottom of the aircraft while the circuit board is pressed against the inside wall of the fuselage. The camera was wrapped in electrical tape after several instances of leads being pulled out and circuit boards breaking from electrostatic discharge caused several cameras to stop working.