«Contents Executive Summary 1 1 Project Motivation 2 1.1 Association for Unmanned Vehicle Systems International (AUVSI) Student Unmanned Air Systems ...»
CUAir: Cornell University Unmanned Air Systems
Stabilized Gimbal Control System
CUAir: Gimbal Project Phillip Tischler Fall 2013
Executive Summary 1
1 Project Motivation 2
1.1 Association for Unmanned Vehicle Systems International (AUVSI) Student Unmanned Air Systems (SUAS) Competition........... 2
1.2 CUAir: Cornell University Unmanned Air Systems Team......... 7
1.3 Stabilized Gimbal System.......................... 8 2 System Design 10
2.1 Project Requirements............................. 10
2.2 Stabilized Gimbal System Overview..................... 11
2.3 System Integration.............................. 11 3 Hardware Design 14
3.1 Physical Gimbal................................ 14
3.2 Electrical Control Board........................... 14 3.2.1 Optical Isolation & Servo Connection................ 14 3.2.2 GPS Unit............................... 16 3.2.3 6-Axis Inertial Measurement Unit.................. 16 3.2.4 Logic Level Converter........................ 18 3.2.5 FTDI & USB Connection...................... 18 3.2.6 Atmega128 Micro-controller..................... 19 3.2.7 Voltage Regulation.......................... 20 3.2.8 Printed Circuit Board Design & Re-ﬂow Soldering Assembly... 21 4 Software Design 24
4.1 Micro-Controller Software.......................... 24 4.1.1 Q Number Format Representation & Math............
Executive Summary This document describes the development of a Stabilized Gimbal Control System for the CUAir team. The Stabilized Gimbal Control System will help the CUAir team compete at the Association for Unmanned Vehicle System International (AUVSI) Student Unmanned Air Systems (SUAS) Competition . The system developed will help the team accomplish the oﬀ-axis target imaging task, accomplish the egg-drop task, and improve the task of imaging targets below the aircraft.
This project consisted of the design and construction of the Gimbal Control Board, and the development of the software that executes both on the micro-controller and on the aircraft’s payload computer. This project did not consist of building the physical gimbal that the Gimbal Control Board will actuate. The Gimbal Control Board contains an onboard 6-Axis Inertial Measurement Unit (IMU), headers for a GPS module, 5 servo connections with optical isolation, voltage regulation, and an Atmega128 micro-controller.
The software developed provides a high performance asynchronous serial communication library, software to read and parse data from the GPS and IMU, software to control the servo signal lines that command the servo to actuate to certain angles, software to stabilize the gimbal system’s pointing angle, and software to point the gimbal at a speciﬁed GPS position.
The ﬁrst section of the document describes the motivation for the Stabilized Gimbal System. This section describes the AUVSI SUAS competition, the CUAir team, and why the Stabilized Gimbal System would be beneﬁcial. The second section describes the overall system design. This includes the project requirements, an overview of the components and how they integrate, and how the system will eventually be integrated into the main CUAir system. The third section describes the design of the hardware.
This includes the custom physical gimbal and the custom Gimbal Control Board. The fourth section describes the software that was developed for the micro-controller and for the host-computer. The ﬁfth section describes the results of the project. Finally, the references and appendices are provided. The appendices include the printed circuit board schematics, the printed circuit board layout, images of the assembled gimbal board, a cost breakdown for the Gimbal Control Board, statistics on the code that was developed, and a breakdown of what tasks were completed by which members of the development team.
1 Project Motivation This section describes the motivation for the Stabilized Gimbal System Project. The ﬁrst subsection describes the Association for Unmanned Vehicle System International (AUVSI) Student Unmanned Air Systems (SUAS) Competition . The second subsection describes the CUAir Project Team, an engineering team at Cornell University that competes in the AUVSI SUAS Competition . The Stabilized Gimbal System described in this document was developed for the CUAir team. The ﬁnal subsection describes the motivation for the Stabilized Gimbal System, and how it relates to the AUVSI SUAS Competition and the CUAir team.
1.1 Association for Unmanned Vehicle Systems International (AUVSI) Student Unmanned Air Systems (SUAS) Competition The AUVSI SUAS Competition is an annual competition in June that takes place at the Webster Field Annex of the Patuxent River Naval Base. The competition focuses on building unmanned air systems that can complete reconnaissance missions with realworld constraints. College teams from around the world attend this competition. Last year over 40 teams registered to compete, about 35 teams attended the competition, and about 32 teams ﬂew their aircraft at competition.
Competition Components. The competition is broken into three components:
the technical journal paper, the ﬂight readiness review presentation, and the simulated mission. The components are worth 25%, 25%, and 50% respectively. The journal paper
is a 20 page paper that focuses on the design and testing of the air system. The ﬂight readiness review presentation focuses on why the team is conﬁdent the air system will perform a safe and successful mission. The simulated mission is a sample mission where students are given mission parameters and expected to perform the mission within the given time-frame and mission parameters.
Figure 3: 2013 AUVSI SUAS Competition: CUAir at the Flight Readiness Review
The Simulated Mission. The simulated mission is broken into eight sections: mission setup, takeoﬀ, waypoint navigation, search grid, emergent target, Simulated Remote Intelligence Center (SRIC), landing, and cleanup. Mission setup involves transporting the competition gear to a designated site within 5 minutes, unpacking and settings up the gear within 15 minutes, and then beginning the mission. Teams are not allowed to turn on aircraft components or wireless gear during this setup phase. After the 15 minutes of setup the mission starts, which means students have 30 minutes to complete all simulated mission components. The ﬁrst component is autonomous takeoﬀ, which is usually attempted once ground checks have been completed. The second component is waypoint navigation, where the aircraft must follow a speciﬁed ﬂight path within a certain tolerance. The third component is the search grid, which is an area of abnormal shape which may contain targets of interest. The air system must stay within the search grid at all times, and must enter and leave the grid at a speciﬁed location. The judges will at some point indicate the location of an emergent target, which is a target of interest with an approximate location. Teams are required to dynamically re-route to this location.
The teams then attempt the SRIC task, which involves downloading information from a remote WIFI network and relaying this information back to the ground system. Finally, the air system lands and data is given to the judges. The air system is tasked with Page 3 of 58 CUAir: Gimbal Project Phillip Tischler Fall 2013 identifying and classifying targets of interests that are located within the mission area during the course of aforementioned ﬂight operations. Teams are judged based on targeting performance and level of system autonomy. Once the mission is complete, teams have 15 minutes to cleanup the area and leave the mission site.
Figure 4: 2013 AUVSI SUAS Competition: CUAir preparing for transport to the Mission Site Ground Focused Imaging. A core focus of the competition is the ability for the air system to take pictures of the ground and identify targets of interest. The air systems must achieve good imagery ground coverage as the target identities and locations are not known to the teams beforehand. Most teams bring ﬁxed-wing aircraft to the competition due to their better performance in long range ﬂight, stabilized ﬂight in wind, and ﬂight with heavy payload components. These aircraft change attitude by actuating ﬂight surfaces to roll or pitch the aircraft. When the aircraft changes attitude, the payload also changes attitude. This means that cameras that point at the ground to take images are no longer pointed at the ground when the aircraft changes attitude from a level position.
The aircraft changes attitude during turns, and in response to wind that moves the aircraft oﬀ desired ﬂight-path. This means that during these events the air system does not take pictures of the ground, which could cause the system to miss targets entirely and hurt mission performance. A stabilized gimbal system can actuate the camera in response to these attitude changes to keep the camera focused on the ground where targets are located.
Oﬀ-Axis Target Imaging. During the waypoint navigation phase of the simulated mission the air system is required to image a target with known location that does not appear directly below the air system’s ﬂight path. That is, a camera system which only points directly down cannot image this oﬀ-axis target. There are two ways to solve this problem: use multiple cameras that are ﬁxed so as to cover any oﬀ-axis target, roll the
Figure 5: 2013 AUVSI SUAS Competition: CUAir settings up for the simulated mission Figure 6: 2013 AUVSI SUAS Competition: Hyperion (CUAir’s Aircraft) preparing for takeoﬀ
Figure 7: 2013 AUVSI SUAS Competition: Hyperion Flying the Waypoint Navigation Section Figure 8: 2013 AUVSI SUAS Competition: Targets that were placed in the mission area
Figure 9: Image taken from Hyperion (left) during a test ﬂight and the targets seen in the image (center, right).
aircraft to align the camera with the target, or use a stabilized gimbal system that can point at the known GPS location as the aircraft is passing the target. Multiple cameras are usually prohibitive due to size, weight, and cost. Rolling the aircraft will cause it to deviate from the required ﬂight-path and may cause the aircraft to exceed the path tolerance. Thus, a stabilized gimbal system is best for a ﬁxed-wing aircraft to image this required oﬀ-axis target.
New Competition Components. The 2014 AUVSI SUAS Competition have a few new components than previous years. The two major components are infrared imaging and egg drop. The infrared imaging task is to identify a target of interest that requires an infrared camera to be seen. Infrared cameras are signiﬁcantly more expensive at higher resolutions, which will require teams to purchase lower cost cameras that have the ability to zoom. Cameras that zoom require a gimbal system to be eﬀective as the probability of a target appearing perfectly below the ﬂight path is very small. The egg drop task is to drop a plastic egg with ﬂour inside to hit a known target. There are many ways to accomplish this task, but most require the actuation and positioning components that are inherent to a stabilized gimbal system.
1.2 CUAir: Cornell University Unmanned Air Systems Team CUAir is Cornell University’s Unmanned Air Systems Engineering Project Team. The team consists of about 40 undergraduate students, up to 1 graduate student, and a faculty advisor. The faculty advisor for the team is Professor Thomas Avedisian of Cornell University’s MAE School. The team is structured into ﬁve subteams: airframe, autopilot, software, electrical, and business. There is a team lead that manages the entire team, and ﬁve subteam leads that manage their respective subteam. Phillip Tischler is a member of the CUAir team. From 2012-2013 he was the full team lead, from 2011-2012 he was the software subteam lead, and 2010-2011 was his ﬁrst year on the team. Phillip Tischler is the single graduate student for the 2013-2014 year.
Team History and Goals. CUAir, Cornell University Unmanned Air Systems, is an interdisciplinary project team working to design, build, and test an autonomous unmanned aircraft system capable of autonomous takeoﬀ and landing, waypoint navigation, and reconnaissance. Some of the team’s research topics include airframe design and manufacture, propulsion systems, wireless communication, image processing, target recognition, and autopilot control systems. The team aims to provide students from all majors at Cornell with an opportunity to learn about unmanned air systems in a handsPage 7 of 58 CUAir: Gimbal Project Phillip Tischler Fall 2013 on setting. The team was founded in 2002. In 2012 the team placed 2nd Overall, and 1st in Mission Performance. In 2013 the team placed 1st Overall, 1st in Mission Performance, and 1st in Technical Journal Paper. The team hopes to continue this success in the 2014 competition.
Overall System Design. Figure 10 shows the design of CUAir’s full system. It is quite complicated and out of scope for this document. From this ﬁgure you can see that there is a message passing layer that can carry data and command messages from various nodes in the system. The aircraft node is the software process located on the aircraft’s payload computer that controls all payload components. This software node can communicate with any onboard gimbal control systems and be a middle-man for any data or command messages that come from the ground system. Any gimbal control system simply needs to be integrated into the aircraft node, and then the gimbal is fully integrated into the rest of the system.