From MARHES

Contents 1 Outline of Problem 2 Motivation 3 System Overview 3.1 Features 3.2 Graphical User Interface 3.3 Sensor Suite 3.4 Controllers 3.5 Power Setup 3.6 Locomotion 3.7 Weight 4 Subsections 5 Team Members

Outline of Problem

The Oklahoma State University Multi-Agent, Robotic, Hybrid, and Embedded Systems (MARHES) Laboratory is building a heterogeneous (multiple ground and aerial vehicle) testbed. The lab is in need of an easy-to-use, robust, unmanned aerial vehicle (UAV) to incorporate into the testbed and use for educational purposes in a hands-on embedded control systems class. The UAV should be capable of maintaining an altitude, velocity, and direction and it should contain a Graphical User Interface (GUI), wireless communication system, sensor suit for navigation, camera, and local and remote controllers. The system should also be flexible because MARHES is dedicated to developing easy-to-use multi-vehicle platforms so that researchers can validate innovative motion coordination algorithms with minimal effort. The final demonstration should showcase all the capabilities of the UAV.

Motivation

Defense Industry Daily states that there is a growing US interest in blimps for everything from low-altitude surveillance and communications relay, to air mega-transport, to near space operations. Lockheed Martin Maritime Systems & Sensors in Akron, OH recently received a $149.2 million contract to build and demonstrate the technical feasibility and military utility of a high altitude airship and the U.S. Marines are beginning to use tethered blimps as communication relays in Iraq. The MARHES lab owns an 8 foot blimp that has been underutilized in the lab. For these reasons, the team will use a blimp as the platform for this project.

System Overview

Features

The blimp will:

• Send and receive data over 802.11B.
• Send images from a camera over 802.11B.
• Maintain an assigned altitude, linear velocity, and angular velocity.
• Avoid collisions with local (on blimp) algorithms.
• Be able to execute control algorithms on board the blimp and/or from a remote PC.
• Have a complete C interface for Linux on the blimp.
• Have a complete LabView interface for remote PCs.

Graphical User Interface

Currently, the Labview user interface monitors and displays input from the following components:

• IR Sensors - to indicate to the interface that an obstacle is in view.
• Inertial Measurement Unit - angular velocity of the blimp.
• Battery Voltage Monitor - Displays battery voltage.

The user interface also provides a means to control the blimp. Different types of control measures are presented, ranging from simple on/off fan control to distinct, number based input.

Sensor Suite

The blimp sensor suit will be used for obstacle avoidance and to monitor the status of the blimp. The team incorporated the following sensors into the design:

• [1] Camera (Linksys WVC54GC)
• [3] Multi-LED Sharp IR Range Finders (GP2Y3A003K0F)
• [1] Ultrasonic Range Finder (SRF08)
• [1] Microstrain IMU (3DM-GX1)
• [1] Battery Voltage Monitor

Controllers

The heart of the system is a Stargate system from Crossbow and is supported by an open source community. The SPB400 - Stargate Gateway with Daughter board and 802.11b/g wireless compact flash card will provide a medium for wireless communication to and from the blimp. In addition, the Stargate’s Linux OS allows the flexibility to execute high level control algorithms onboard the blimp.

In addition to the Stargate system, two PIC microcontrollers directly interface with the sensors and actuators. One PIC reads all the sensors and relays the values to the Stargate system via an RS-232 connection and a second PIC generates PWM signals to the H bridges for the three motors. Two PID loops execute on the sensor PIC. These two loops maintain altitude and angular velocity as accurately as the sensors allow. Linear velocity exists as open loop control.

Power Setup

The motors draw approximately 1A at the max desired load and, with three, the full load is about 3A at 3V (average DC value of the PWM signal). The system will use one or two batteries and a DC/DC converter. Testing has proven that the DC/DC converter can provide ample current and voltage when supplied with power from Li-Ion batteries so any of the Li-Ion batteries currently available in the MARHES lab can be used to power the entire system.

• [2] Battery (11.1V Li-Ion 1500mAh)
• [1] DC/DC Converter Datel UHE-5/5000-Q12

Locomotion

The locomotion for the blimp will consist of 3 fans:

• Altitude adjustment (located underneath gondola)
• Forward / Backward Velocity motion (located behind gondola)
• Turning (located on rear fin)

These fans use 6” propellers and DC motors. The platform contains room for propeller and component mounts underneath the blimp and that do not block the ultrasound sensor.

Weight

A digital, high precision scale supplied both balloon maximum lift (~2lbs 6oz without rear fins) information and part weight information so that the system does not exceed the maximum lift of the balloon. Some internal mounting had to be scrapped in favor of a lighter design. The importance of matching weight is crucial and even small amounts of weight can cause the blimp to be uncontrollable. Using sheets of paper to tune the final weight has proven successful thus far.

Subsections

• Specifications
• Hardware
• The Microcontroller Code
• Stargate
• The LabView Interface

Team Members

• Colby
• Matthew
• Michael
• Daniel