Outline Plan UAV with stabilized camera

Transcription

1 Outline Plan UAV with stabilized camera Version 1.0 Author: Therese Kjelldal Date: December 5, 2010 Status Reviewed Approved

2 Project Identity Group Homepage: Orderer: Customer: Course Responsible: Project Manager: Advisors: Per Skoglar, Linköping University Phone: , David Törnqvist, Linköping University Phone: , David Törnqvist, Linköping University Phone: , Erik Lindén Sina Khoshfetrat Pakazad, Linköping University Phone: , Group Members Name Responsibility Hamdi Bawaqneh hamba208 Olof Bäckman Tests oloba221 Magnus Degerfalk magde580 Fredrik Eskilsson frees868 Per Johansson perjo871 Erik Jonsson Holm Designer erijo975 Therese Kjelldal Documents thekj512 Erik Lindén Project Manager erili277 Gustav Öst Information gusos234

3 Document History Version Date Changes made Sign Reviewer First draft. TKL Therese Kjelldal Minor changes. TKL Therese Kjelldal

4 Contents 1 Introduction 1 2 Definitions 1 3 System Overview Airplane Gimbal Communications Camera Xbee RC controller Implementation

5 UAV 1 1 Introduction The purpose of the project is to modify an existing control system for an autonomous unmanned aerial vehicle (UAV) and to steer and stabilize a camera placed on a gimbal on the UAV. The camera shall be able to look at specific points on the ground. The camera image is sent to a computer via a wireless modem. The platform that is used in the project is the airplane Multiplex Easystar and the control system Ardupilot. The positioning system of the UAV will be based on a GPS and an IMU. The gimbal will be build by the group members and equipped with an IMU to make it possible to compensate for the movements of the UAV. 2 Definitions ArduPilot - Open source control system for model airplane Xbee - Wireless modem from airplane to ground IMU - Inertial Measurement Unit RC - Radio Communication GPS - Global Positioning System UAV - Unmanned Aerial Vehicle

6 UAV 2 3 System Overview The UAV will be equipped with a GPS, an IMU and a gyro for determining the position and to calculate the movement of the UAV. The camera on the UAV shall be able to follow a target on the ground. It is possible to choose autonomous or manual mode of the UAV. Switching from autonomous to manual mode is possible throughout the whole flight. The centre of the system is the ArduPilot. When in manual mode it forwards the signals it receives from the receiver to the different servos and throttle that makes the UAV fly. When in auto-flight mode it receives flight orders from the Xbee module. A battery is connected to the throttle, and feeds the whole system. To be able to tell where the UAV is, and at what angle and height it s currently flying it uses a GPS together with ArduIMU-1. The information received from this GPS is also transmitted via ArduPilot to ArduIMU-2, which controls the two servos connected to the gimbal to get an accurate centering over the target on the ground. Figure 1: System overview The system can be divided into two subsystems: The Airplane The Gimbal

7 UAV Airplane The airplane used in the project is Multiplex Easystar with the control system ArduPilot. As the diagram shows, there are three loops that makes the UAV reach it s goal in a smooth way. The biggest loop controls the heading, and makes sure that we are indeed heading towards our goal. Banking is controlled by the middle loop, which together with the first loop keeps us in the air while heading the right way. The last loop is for quick changes in the servos, to manage disturbances and to make sure the UAV is able to manage the references given by the two other loops. The UAV can either fly by GPS coordinates supplied through the Xbee receiver, or in two different manual modes. When flying in autopilot ArduPilot calculates the flight data and controls the servos and throttle to reach the coordinates. In manual mode we can switch between having the ArduPilot just forwarding our commands straight to the UAV, or to fly-by-wire. With fly-by-wire turned on, ArduPilot assists with stabilizing the plane, while following the commands from the RC-controller. Figure 2: System overview of the airplane

8 UAV Gimbal The camera is placed on a gimbal that is to be constructed. The gimbal shall be able to move in tilt- and pan-direction to make it possible for the camera to look at a specific point on the ground. The gimbal will be equipped with an IMU to measure the movement of the gimbal. The IMU is useful when eliminating disturbances. In the control system of the gimbal feed-forward will be used to get high performance, since it will measure the disturbances and directly compensate for it. If we look at the chart, we see that we get a reference from ArduPilot. We can calculate the difference in position between the UAV and the target, and together with the current flight angle and angle of the gimbal (given by the gimbal s IMU) we know how to adjust the gimbal to center in on the target. These values are then translated into panand tilt-angles for the servos controlling the camera. Figure 3: System overview of the airplane

9 UAV Communications The plane has to communicate with the ground station in three ways. It also uses a GPS receiver to determine its position and altitude Camera The camera transmits a videostream to the ground via a wireless analogue interface so the stream can be viewed on the ground Xbee To be able to change the planes route during a flight, a wireless serial interface, Xbee, connects the plane to the ground computer. The system is totally transparent and acts like a serial cable RC controller When the ArduPilot is in manual or fly-by-wire mode it is controlled by the RC controller manually, either in total manual mode or a stabilized fly-by-wire mode where the ArduPilot only stabilizes the plane. (a) Xbee (b) RC Controller Figure 4: Communications on the UAV 3.4 Implementation The code to the autonomous UAV will be implemented in C. A simulation environment will be developed in Matlab, containing models for the airplane and the gimbal.