Autopilot DETC2009 87671

Proceedings of the ASME 2009 International Design Engineering Technical Conferences &Computers and Information in Engineering Conference

IDETC/CIE 2009August 30-September 2, 2009, San Diego, USA

DETC2009/MESA-87671

AGGIEAIR: AN INTEGRATED AND EFFECTIVE SMALL MULTI-UAV COMMAND,CONTROL AND DATA COLLECTION ARCHITECTURE

Calvin Coopmans and Yiding Han

Center for Self-Organizing and Intelligent Systems (CSOIS),Electrical and Computer Engineering Department,

Utah State University, Logan, UT 84322−4120, USAE-mails: {cal.coopmans, yiding.h}@aggiemail.usu.edu

ABSTRACTSmall UAV performance depends on an effective and effi-

cient command system architecture. Based on an existing UAVsystem called Paparazzi, AggieAir is a full flight system capableof handling single or multiple UAVs with single or multiple pay-loads per airframe. System-level block diagrams are presentedand specific details about implementation and results are pro-vided.

NOMENCLATUREUAV Unmanned Aerial Vehicle.IMU Inertial Measurement Unit. Typically a 3-axis roll rate

gyro co-axial with a 3-axis accelerometer.INS Inertial Navigation System. Suggests a combination of

IMU and other senors such as GPS via a software filter.

INTRODUCTIONAn Unmanned Aerial Vehicle (UAV) is a complex aircraft

system that is able to navigate without the control of a pilot.The inception of UAVs traces back to the World War I, whichwas primarily for military applications. However, its entry intothe civil/commercial market is barely until the last few decades.There is increasing interest in developing UAV systems for vari-ety of civil applications such as traffic control, border patrol, fire-fighting management [1], agriculture monitoring [2], etc. Differ-

ent sizes, types and configurations of UAV is developed for thespecific application.

Generally speaking, the autonomous UAV system consistsof automatic pilot system, navigation system that includesa widevariety of sensors, on-board microcomputer system as the datahub and ground control station that monitors and changes flightmission in real time.

In the Center of Self-Organizing and Intelligent System(CSOIS) at Utah State University, miniature fixed-wing au-tonomous UAVs are developed for civil applications, such aswa-ter management, irrigation control, highway mapping, etc.TheUAVs we developed are equipped with light-weighted multispec-tral high-resolution optical imager for aerial images within re-configurable bands [3].

This paper presents a novel hardware and software architec-ture. AggieAir is fundamentally based on a proven system archi-tecture: that of a real aircraft. Fig. shows a simplified version ofthis hierarchy, allowing specific mission tasks and goals. On theground, the Flight Commander (a human, in the AggieAir sys-tem), oversees the whole mission as it progresses. The ScienceTeam is also on the ground, monitoring data and controlling ex-periments on the plane in real time.

FUNCTIONALITYAggieAir is a system with many parts and details. Overall,

the aero-team paradigm can be seen illustrated in Fig. 1 Each

1 Copyright c© 2009 by ASME

Proceedings of the ASME 2009 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference

IDETC/CIE 2009 August 30 - September 2, 2009, San Diego, California, USA

DETC2009-87671

Ground Control Station

Airframe

AggieNavIMU, Compass, GPS,

Pressure, Temperature

UART

Payload #1

Payload #2

AggieCap

Ethernet + Local

JAUS

GPos+LPos+Payload

Message Socket Interface

GhostFoto

BlackBox FlightRecorder/

Thermal Camera/Other Payload

{Fractional, Extended}Kalman Filter

GPos+LPos Data Server

GCS + Payload Message

Bus

Gumstix Flight Software (Separate Processes)

AggiePilot (PPRZ)Autopilot + Command and

Control Radio Link+

Standard timebase for all

data

SPI


Bus

GCS Computer #3

• Thernal Camera

Interface

• Etc.

Ethernet + Local

JAUS

GPos+LPos+Payload

Message Socket Interface

GCS C+C

Downlink Radio

UART

PPRZ C+C Link High-Bandwidth WiFi Datalink

GCS C+C Uplink

Radio

GCS Computer #1


Bus

PPRZ GCS +

JAUS

CSOIS AggieAir Software Block Diagram

UART

GCS Computer #2

• GhostEye Interface

• gRAID Interface

Figure 2. AGGIEAIR DETAILED BLOCK DIAGRAM

Payload{1, 2, ...}

Airborne

Ground

Command + Telemetry Link Payload Data Link

AggieCap(Captian)

Papazazzi (Pilot)AggieNav(Navigator)

Payload Team(s)FlightCommander

Figure 1. AGGIEAIR AERO-TEAM BLOCK DIAGRAM

part of the system has its respective role; even the humans ontheground. A much more detailed system block diagram is Fig. 2.

This diagram shows some of the nuances of the AggieAir system.

DATA FLOW

Fig. 3 shows the data flow hierarchy of the system archi-tecture. This allows for many system configurations dependingon the complexity and/or cost demands of the mission at hand.For instance, a particular mission could demand only AggiePi-lot and AggieNav for basic navigation and flight path following.AggieCap and the other parts of the system are not required andcould therefore be left out of the system. One more level couldbe added; AggieCap’s payload management could be demandedwithout the need for the WiFi data link and this could easily beleft out of the mission. The full system could be also imple-mented easily if demanded.


AggieAirGroundstation

AggiePilot

AggieNav

AggieCap

Payload#1

OffboardPayload(s) viaMesh Network

Payload#2

PayloadGroundstation

Increasing System

Complexity

Figure 3. AGGIEAIR DATA FLOW HIERARCHY

2.4GHZ WIFI COMMUNICATION LINK

Figure 4. UBIQUITY BULLET2-HP MODIFIED FOR SMALL UAV

FLIGHT WITH 5.5DBi ANTENNA

CSOIS has developed a high-bandwidth 2.4GHz WiFicomms link for use with single or multiple UAVs and groundstations. Designed to be inexpensive and easily constructed,this link is based on lightweight (80g w/ antenna), high-power(800mW), inexpensive ($70), “carrier-class” WiFi units man-ufactured by Ubiquity Wireless [5], known as the Bullet2-HP.These units are employed on both ends of the data link, and havebeen tested at more than 1 mile range to provide greater than400KB/sec and up to 1.6MB/sec transfer speeds depending onantenna orientation. These Bullets have been modified for flight

Figure 5. WIFI GROUNDSTATION: 14DBi, 160◦ SECTORIAL AN-

TENNA WITH BULLET2-HP

Figure 6. GAIN PATTERN OF SECTORIAL ANTENNA FROM [4]

by the replacement of the heavy integrated N-male RF connectorand plastic case with a hard-soldered, short LMR-400 co-axialpigtail and a standard 5.5Dbi monopole WiFi antenna (Fig. 4).A power-over-Ethernet (POE) splice cable allows the airborneBullet unit to integrate with the onboard UAV Lithium-ion bat-


tery supply as well as the Gumstix flight computer.The ground station network is connected to the WiFi net-

work via a 14Dbi sector antenna [6] (pictured in Fig. 5, givingthe WiFi link a wide horizontal angle, tested to function well at+-80 degrees from center. A vertical gain pattern of 20 degreesallows complete coverage of the long-range UAV area.

The alternative WiFi operating system DD-WRT [7] sup-ports Bullet2-HP units. DD-WRT is a Linux-based operatingsystem with many capabilities, not the least of which is sup-port for OLSR, the Open-Source Link State Routing protocol [8].OLSR creates an Ad-hoc WiFi mesh network by manipulatingthe Linux kernel routing table based on the status of the wirelessnetwork topology, allowing for a flexible UAV flying mesh suchas implemented in [9].

JAUSJAUS, the Joint Architecture for Unmanned Systems, is a

comprehensive, cross-platform command and control architec-ture designed for interoperability and is a standard for US mil-itary unmanned systems. It is ideal for architectures and sys-tems such as AggieAir, and allows for well-tested packet-basedtransmission of critical data such as airframe pose or payloadstatus. Implementations of JAUS vary in price and licensing;the AggieAir system uses OpenJaus [10], a free and open-sourceimplementation of the JAUS system. While JAUS is ideal forcommand and control applications, it is not a particularly goodchoice for transmission of data from sensors or other payloads,and AggieAir therefore uses other protocols (such as rsync)fordata such as aerial images.

RSYNC FOR DATA TRANSFERCurrently the best method for transferring arbitrarily large

data sets over unstable links such as the WiFi link in AggieAiris the rsync protocol. rsync is an open-source utility that allowsfor fast incremental file transfer [11], allowing files transfers tobe interrupted by poor quality data links and resumed later whenthe link as been restored. A simple Bash wrapper script allowsthe Payload Ground Station to asynchronously request the datafiles from the airborne processor and save them on the ground forfurther processing or analysis. In this way, the ground networkcan re-target or change a UAV’s behaviour based on any numberof human or machine decisions.

rsync is currently implemented in AggieAir on the WindowsXP operating system via Cygwin [12], but a small section ofcode changes theping syntax and allows the same script tooperate on multiple Unix variants as well as Windows. The as-sumed behavior of the airborne payload is continuing productionof separate data files (discrete images), however this techniquewill also perform nicely with growing-length data files withdif-ferent options (see below). Although rsync can be used in con-

junction with other protocols such as ssh [13], for reasons of air-borne CPU load and bandwidth the data is sent in an unencryptedstream via the standard rsync protocol.

START

Ping Airframe

2 ICMPResponses?

Sleep 5 Seconds Start rsyncCommand

YesNo

Download Data(delete source)

Sleep 3 Seconds

Figure 7. RSYNC DATA COLLECTION SCRIPT FLOWCHART

Fig. 7 shows the logic flowchart for collection of data viarsync. Note that in this case, rsync has been configured to removethe remote data after downlink to the ground, since each iterationcould take progressively more time to index the source data filesif they are not cleaned each loop iteration. Also, rsync is usedin Backup mode so it will not overwrite files that have identicalnames in case a naming collision occurs (caused by the resettingof the flight computer or crashing of a payload, for instance). Inthis way, we have made a reliable, cross-platform data collectionsystem using established software.

AGGIEPILOTPaparazzi is an open-source autopilot developed by

aerospace students at ENAC University in France [14]. CSOIShas been using Paparazzi for more than two years [15], to muchsuccess. In the AggieAir architecture, the Paparazzi system hasbeen augmented with a JAUS data channel to become AggiePilot,allowing JAUS packets to be transmitted to and from the UAV(s)while in flight. This allows for a useful amount of JAUS com-mand and control data to be sent over the UAV’s normal controllink, up to 10 miles away.

AGGIENAV NAVIGATION SENSOR SUITEAggieNav is a small, accurate, low-cost, tightly-integrated

UAV navigation sensor INS suite [16]. Fig. 8 shows a sys-tem block diagram. AggieNav serves as the Navigator in theaerial team paradigm, and provides the Captain and with real-time global pose data from a 6-DoF IMU, GPS and compassmodule, as well as dual pressure sensors for estimation of alti-tude and airspeed via [17]. AggieNav also serves as a replay


Analog

Devices

ADIS1654

6-DoF IMU

User

Interface

(LEDs,

Buttons)

External

Data

Interfaces

(TTL-Serial;

SPI Slave)

uBlox

LEA-5H

GPS Receiver

Honywell

HMC6343

3-axis

Magnetic

Compass

Atmel

AVR32A256B

Micro-

controller

5.0V; 3.3V

Switching

Regulators

Gumstix

Verdex Linux

System

VTI

SCP-1000

Pressure

Sensors (x2)

Papazazzi

TWOG

Autopilot

Board

Figure 8. AGGIENAV HARDWARE BLOCK DIAGRAM

Figure 9. AGGIENAV HARDWARE WITH GUMSTIX COMPUTER

for filtered data between AggieCap and AggiePilot, with a safetyfallback. As seen in Fig. 9, AggieNav holds and powers theGumstix computer.

AggiePilot

AggieNav Gumstix EKFProcess

Fault Line

Figure 10. AGGIENAV DATA FILTERING FALLBACK STRUCTURE

AggieNav uses some of the Gumstix’ CPU time for an ad-vanced Extended Kalman Filter (EKF), allowing for more ideal

Figure 11. GHOSTFOTO CCD CAMERA, MODIFIED FROM CANON

POWERSHOT SX100 IS

navigation. AggieNav then passes the filtered data along to Ag-giePilot, allowing the system to function with the best navigationperformance, however AggieNav has enough processing power(70MIPS) to allow a fallback/failsafe mode (Fig. 10 if the Gum-stix computer should fail or not be required for a given mission.If, after 1 second (100 packets), AggieNav does not receive datafrom its process on the Gumstix, AggieNav will step in and pro-vide its own data. In this case, the AggieNav processor doessome basic filtering work on the sensor data and passes this datato AggiePilot in the same manner as the normal system opera-tion, allowing a seamless failover, or minimum flight gear con-figuration depending on the scenario.

EXAMPLE PAYLOAD: GHOSTFOTOGhostFoto (GFoto) is a light-weight cost efficient multi-

spectral imager which operates in both visible and near infrared(NIR) light wavelengths. The hardware of this payload consistsof RGB and/or NIR CCD cameras, shown in Fig. 11, and Gum-stix microprocessor on which a program called GhostEye is run-ning for both controlling and configuring the imagers. GhostEyealso provides an interface between the imager payload and UAVsystem, establishing a message and command channel, throughwhich users are able to monitor and operate the payload duringflight.

Another key functionality of GhostEye is geo-referencing ofthe airborne imagery. The orthorectification of the aerial imagesis indispensable for the end users that demand for accurate geo-graphic information. For instance, in applications such astargetrecognition and ground mapping, the geographic coordinates ofany pixel on the aerial image should be able to be retrieved. Byquerying the sensor data, such as the UAV geographic coordi-nates, and pitch, yaw and roll angle of the plane, GhostEye logsthe geo-referencing information for each image so that theycanbe accurately orthorectified. In other word, GhostEye needsto


Figure 12. AERIAL IMAGE AND ORTHORECTIFIED IMAGE

have access to these sensor data from the onboard IMU and GPSmodule.

This access is enabled in the AggieAir architecture throughAggieCap. AggieCap dispatches the EKF filtered flight data toJAUS, from which the payload can query for geo-referencing in-formation. The message and control channel of GhostEye is alsomanaged by AggieCap. The message is sent through AggieNavto AggiePilot, which communicates with ground station, wherethe status of GFoto is monitored.

Airborne imagery can be saved on the memory card in thecameras, or downloaded from the imager onto Gusmtix, andhence sent to the Ground Control Station by rsync through theHigh-Bandwidth WiFi Datalink. This process allows the groundstation to process the acquired imagery in real time, so thatfea-ture based navigation can be implemented in AggieAir architec-ture.

As an example, Fig. 12 shows an aerial image taken overLittle Bear river near the Utah State University (USU) owned

farm (GPS: 41.7978 -111.9296). The image below is orthorecti-fied with the provided geo-referencing data. The image is thenrotated and projected onto globe coordinate with its upper sidepointing North.

CONCLUSIONIn this paper, we have demonstrated a novel architecture for

multiple small low-cost fixed wing UAVs. By integrating subsys-tems including AggieNav, AggiePilot, AggieCap, the AggieAirarchitecture offers flexible and reliable support for UAV airbornepayloads designed for different purposes. On the ground, Ag-gieAir architecture provides real time mission control andmoni-toring of the UAVs, as well as separate payloads. This extensiblearchitecture has been implemented and tested, and has provenitself to be a reliable yet sophisticated solution for smallUAVcommand, control, and data handling.

ACKNOWLEDGMENTThe author would like to thank all of CSOIS, Professor

YangQuan Chen, Austin Jensen, as well as the Association forUnmanned Vehicle Systems International (AUVSI) for their Stu-dent UAS competitions, and the Utah Water Lab. This work hasbeen supported by Utah Water Research Laboratory MLF fund-ing (2006-2010).

REFERENCES[1] Casbeer, D. W., Sai-Ming Li, Beard, R. W., McLain, T. W.,

and Mehra, R. K., 2005. “Forest fire monitoring with mul-tiple small UAVs”. Proceedings of the American ControlConference, June.

[2] Johnson, L. F., Herwitz, S. R., Dunagan, S. E., Lobitz,B. M., Sullivan, D. V., and Slye, R. E., 2003. “Collec-tion of ultra high spatial and spectral resolution image dataover california vineyards with a small UAV”.Proceedingsof the 30th International Symposium on Remote Sensing ofEnvironment.

[3] Chao, H., Baumann, M., Jensen, A., Chen, Y., Cao, Y., Ren,W., and McKee, M., 2008. “Band-reconfigurable multi-UAV-based cooperative remote sensing for real-time wa-ter management and distributed irrigation control”.IFACWorld Congress, Seoul, Korea, July.

[4] Hyperlink Sector Antenna Data Sheet.URL http://www.l-com.com/multimedia/datasheets/DS_HG2414SP-120.PDF.

[5] Ubiquiti Bullet2-HP.URL http://www.ubnt.com/downloads/b2hp_datasheet.pdf.

[6] HG2414SP-120 Setctor Panel WiFi antenna.


URL http://www.l-com.com/multimedia/datasheets/DS_HG2414SP-120.PDF.

[7] DD-WRT.URL http://www.dd-wrt.com/.

[8] OLSR.URL http://www.olsr.org/.

[9] Tisdale, J., Ryan, A., Kim, Z., Tornqvist, D., and Hedrick,J. K., 2008. “A multiple UAV system for vision-basedsearch and localization”.American Control Conference,2008, June.

[10] JAUS Architecture.URL http://www.openjaus.com/trac/openjaus/attachment/wiki/UnmannedSystemsClass/Day_3_(JAUS_Architechture_Messaging).pdf?format=raw.

[11] Rsync.URL http://www.samba.org/rsync/.

[12] Cygwin.URL http://www.cygwin.com/.

[13] Open SSH.URL http://www.openssh.com/.

[14] Paparazzi UAV.URL http://paparazzi.enac.fr/wiki/Main_Page.

[15] Open Source Autonomous Multiple-UAV.URL http://www.engr.usu.edu/wiki/index.php/OSAM.

[16] Coopmans, C., 2009. “AggieNAV: a small, well integratednavigation sensor system for small unmanned aerial vehi-cles”. ASME International Design Engineering TechnicalConferences, San Diego, USA, September.

[17] R. Klopfenstein Jr., 1998. “Air velocity and flow measure-ment using a pitot tube”.ISA Transactions,37, pp. 257–263.


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Autopilot DETC2009 87671