UAV

Why not design and construct an autonomous unmanned aerial vehicle?

Abstract:

The development and construction of a low cost autonomous unmanned aerial vehicle (UAV) allows for the surveillance and monitoring of remote areas without the need for a human pilot. Various inexpensive sensors can be attached to such a remote sensing platform to perform monitoring of both urban and rural environments. Such a system allows delicate ecosystems to be monitored inexpensively, allowing data to be collected more quickly while at the same time protecting the environment from potentially destructive human and vehicular traffic.

An autonomous unmanned aerial vehicle consists of three parts: an airframe, electronics, and software. In the system designed, the airframe was constructed of economical, environmentally friendly material. The design choice was based on strength and weight since it needs to survive, and not cause damage, in case of malfunction during flight. The electronics consist of low cost sensors to measure attitude and position built around a processing platform of low power microcontrollers and a wireless downlink. These custom electronics are then linked to stock RC electronics and propulsion to move and control the aircraft. The software consists of GPS waypoint navigation, stabilization, and sensor noise removal in order to reliably navigate the aircraft along the specified path while keeping it in the air.

As a result, the aircraft remains inexpensive and can still reliably traverse the predetermined path. Sensors gather data, software processes such data, and then RC electronics move the aircraft. This results in a low cost autonomous unmanned aerial vehicle capable of remote surveillance and monitoring.

Block Diagrams:

Software Setup

Airframe Diagram:

Schematics:

Control Board

Communications Board

Photos:

Discussion:

The first aircraft autopilot was developed in 1912, near the dawn of powered, heavier than air flight. These first mechanical autopilots were limited to the stabilization of the aircraft and could not navigate. After the development of the transistor, autopilots continued to advance and gained navigation capabilities. Modern autopilots are now capable of automating all stages of flight, from takeoff to landing. Autopilot systems currently under development will be capable of automating flight to and from the gate. The problems with all of these systems are size and cost. Current autopilot systems are bulky, heavy, and expensive.

Recent advancements in the miniaturization of electronics and the development of the highly accurate Global Positioning System (GPS) and Wide Area Augmentation System radio positioning systems, have allowed for position and orientation sensing in a small, lightweight package. This, combined with inexpensive, low power microcontrollers, allows for the development of an autopilot that can to be lifted by an aircraft small enough to be carried by a human. Advancement in battery technology allows for an electric propulsion system, removing the possibility of a fuel fire or explosion. Since the plane can be light weight and has no flamable materials, there is a very low probability of injury or damage from a crash. Weight and money can be saved by removing the need for the multiple failsafes of conventional autopilots on manned aircraft.

Such a system was the goal of this project. Two microcontrollers, a GPS module, an accelerometer, an IR range finder, and a wireless module were used. The system is segmented into two parts, navigation and stabilization, and two phases, sensor processing and computation. In the first stage, an implementation of an Extended Kalman Filter removes noise from position and orientation measurements and uses each measurement to correct the other. The Kalman equations filter noise and use GPS data to correct accelerometer data for GPS sensed airframe accelerations, outputting pitch(θ) and roll(φ) data in an earth centered earth fixed frame of reference. Multiple GPS measurements are used to obtain velocity, which is then used to calculate heading(ψ) and find the acceleration to correct the accelerometers. The heading is then used to rotate(r) the GPS acceleration to match the GPS’s frame of reference with the accelerometer’s frame of reference; the measurements are finally combined to form a corrected earth-centered, earth-fixed orientation
measurement.

In the second stage, heading and pitch angles are determined for navigation, and the aircraft is stabilized. To navigate, current heading and altitude are compared to the direction and altitude of the next GPS way-point in order to determine the direction to turn and whether altitude should be gained or lost. In order to navigate, biases are added to pitch and roll data so the stabilization function thinks that the angle of the turn is level and rotates the airframe to said angle. This leads to the other part of the second stage, stabilization. The stabilization function adaptively maps pitch and roll values to servo values such that the stabilization is more sensitive during periods of rapid change in pitch or roll, and is less sensitive during the lack of such changes.

The ground system software allows for course programming and manual control of the unmanned aerial vehicle (UAV). The wireless link between the plane and ground station computer allows for the up-link of GPS way-points to navigate and servo values to control the plane manually. The Google Maps API is used to map out the route for the UAV to navigate. The elevation of each GPS way-point is then queried using the United States Geological Survey elevation service. The user then sets the air to ground level of each way-point to set how far off the ground the plane should fly. The air to ground level of each point is then added to the respective elevation to determine the altitude of the GPS way-point uploaded to the UAV.

There are many potential uses of a small, inexpensive UAV. The main potential use of the UAV is remote monitoring. Due to the size and cost, it is now possible to conduct monitoring previously impossible due to budgetary restrictions or remoteness. Ecological areas can be monitored inexpensively from the air preventing potential damage to fragile ecosystems, at a much lower cost than the use of full size aircraft. With the data gained from the use of a small autonomous UAV, ecosystems can be better studied and understood, the first step in protecting them. Due to the portability and cost effectiveness of a small autonomous UAV, areas that could previously not be studied due to budgetary restrictions or remoteness can now be studied. Advancements in electronics have now allowed an autopilot, something that used to be large and expensive, to become small enough to be fitted on a human transportable aircraft, as well as becoming much less expensive. This opens many new applications for small aircraft. Small autonomous unmanned aerial vehicles have the ability to revolutionize remote monitoring and may come into common use by the hundredth anniversary of the aircraft autopilot in 2012.