2012 AUVSI SUAS Student Competition Journal Paper. Kansas State University Salina UAS Club. Prepared By: Mark Wilson Coby Tenpenny Colby Walter

Transcription

1 2012 AUVSI SUAS Student Competition Journal Paper Kansas State University Salina UAS Club Prepared By: Mark Wilson Coby Tenpenny Colby Walter May 14, 2012

2 Willie Abstract The Willie Unmanned Aerial System (UAS) was designed, built, and tested by the UAS club at Kansas State University Salina. The aircraft was built with the intention of competing in the AUVSI student competition in Maryland. It has been designed to fly a fully autonomous mission while collecting surveillance information. Based on an Align T-Rex 700 series RC helicopter, the aircraft has been outfitted with a Piccolo SL autopilot and surveillance hardware powered by ViewPoint GUI imaging software. All test flights have been carried out inside of a restricted airspace with a Certificate of Operations (COA 2012-CSA-1) granted by the FAA. The KSU Salina UAS club relishes the fact it operates at all times within federal regulations. The setup of the Willie is capable of meeting the entire list of threshold mission requirements, and has been flight tested numerous times with success. The KSU UAS club expects an impressive flight demonstration at competition. Willie Helicopter Before Test Flight With Painted Cowling -2- Page

3 Table of Contents Abstract...2 Table of Contents...3 Description of System Engineering Approach...4 Mission Requirements/Analysis Design Rationale Expected Performance Description of UAS Design...5 Air Vehicle Ground Station Data Link Payload Mission Planning Data Processing Method of Autonomy Test and Evaluation Results...11 Safety Considerations/Approach...12 Airframe Mission System Redundancy Conclusion...16 Appendix P a g e

4 Description of Systems/Engineering Approach The Kansas State Willie helicopter was designed to be capable of vertical takeoff and landing (VTOL) with the ability to accomplish autonomous flight, including autonomous takeoff and landing, while operating a payload capable of targeting an object s location with ± 100 accuracy. The use of a rotor-wing aircraft was decided early in the design process. There are several characteristics of a VTOL aircraft that were thought to be beneficial during competition. A feature rotor-wing aircraft boasts over fixed-wing is maneuverability; this is valuable in reconnaissance type missions since the aircraft is able to move three dimensionally at low speeds and low altitudes. Above all other advantages, a VTOL aircraft has the ability to hover. When surveying targets with the intent of gathering actionable intelligence, hovering over an object can supply a much more stable look at a target rather than passing over without stopping. While building the aircraft, the competition objectives and parameters were addressed during design. The method of autonomy was addressed by implementing a commercially available autopilot. Simple navigation tasks are accomplished by plotting waypoints the aircraft will follow. Re-tasking is as simple as adding additional waypoints for the aircraft to track to. With the VTOL ability of the aircraft, autonomous takeoffs and landings are an unassuming task carried out by the aircraft slowing down, and making a gradual vertical decent onto the landing platform. The imagery system was critical in the design process. The stable platform of the rotorwing aircraft was the base for the imagery system with its ability to stop and hover over any desired target. A video based system with the ability to take still shots of targets that included embedded telemetry data was used. A camera with a narrow angle lens was chosen to narrow the field of view for more detail on the target. Mounted on a two axis gimbal, the camera is able of being pointed in any direction addressed by the payload operator. All images gathered by the imagery system are transmitted in real time back to the ground station for evaluation with location data for the operators. Performance of the system was streamlined by integrating the imaging system with the autopilot system. The autopilot chosen works seamlessly with the imaging software that powers the camera setup. By integrating these two systems, the issue of complexity by adding extra hardware for camera control and stabilization was eliminated. Advantages that came P a g e

5 with this included reduction of weight added by payload, reduced chance of component failure, and overall cost of the system is reduced. Parameter Threshold Objective Autonomy Navigation Take-off & Landing Imagery 2 Target Characteristics 5 Target Characteristics Target Location Within 250ft Within 50ft Mission Time Within 40 Minutes Within 20 Minutes Operational Availability 50% 100% In-Flight Re-tasking Additional Waypoint Additional Search Area Performance Goals, Green Indicates Expected Capabilities In the design process of the aircraft, the competition rules and objectives were constantly kept in mind. The rules list a number of parameter thresholds and objectives, and with the ongoing flight test, the aircraft consistently shows that it can operate at the threshold parameters and most of the objective parameters. It is anticipated that the majority of the 40 minutes will have to be used for the mission. The relatively small endurance of the aircraft means at least one change in batteries to complete the mission. Target imagery and location continue to be tested, and with more time spent, it is anticipated that the objective parameters will be met in time for competition. Descriptions of UAS Design Air Vehicle The Kansas State University Salina UAS Club selected an Align T-REX 700 RC Helicopter named Willie as the base platform for the 2012 AUVSI suas competition. The durability of the aircraft is very important in case of a complete system malfunction. The club chose T-REX 700 airframe as the base platform for integration because of the quality/durability of the airframe and the availability of the parts. The airframe and components are made of carbon fiber and machined aluminum. If the T-REX 700 was recovered from a system malfunction the airframe and components on board the aircraft may possibly be re-used because of the durability of the materials used to build the airframe and components. Willie utilizes the V-TOL method which allows the helicopter to be launched from almost anywhere with ease. The main power plant is a brushless AC motor the Scorpion HK III Kv. Willie operates on a fully electric system utilizing four six cell 5,000mAh Lipo batteries that is electrically equivalent to one 12 cell 10,000 mah Lipo battery for flight and three 2,200 mah three cell batteries to operate the P a g e

6 camera, autopilot, and servos. Willie has endurance on 14 minutes. During the competition the helicopter will be brought back to land and flight batteries will be replaced to allow 28 minutes of total flight time. An onboard systems diagram is listed below Flight Batteries Camera/Wi-fi Battery Power Connection Power and Data Connection ESC AXIS WI-FI 5.8 GHz Camera Data connection Motor Servos Gimbal GPS Servo Power Out Servo Battery 900 MHz Piccolo SL autopilot Servo Power In Power Regulator Power Block AGL Sensor Magnetometer Autopilot Battery Willie Systems Diagram P a g e

7 Ground Control Station All flight operations are carried out through the ground control station (GCS). The GCS is operated by the use of two laptop computers connected to the Piccolo portable ground station. Each computer has an assigned purpose for each mission. One computer is always designated to operate the Piccolo Command Center Software for aircraft navigation and operation. From this computer, the pilot/operator inputs commands and monitors telemetry and flight data. The second computer operates the ViewPoint GUI software that controls the video payload of the aircraft. This station is manned by the payload operator who positions the gimbal mounted camera to obtain desired intelligence. Both computers have external monitors with large screens connected to allow easier data acquisition. The Piccolo Portable Ground Control station (PGCS) is a transceiver enclosed in a protective case. Here, all appropriate cables and antennas are connected to facilitate communication between the aircraft and the ground station. The PGCS connects to the ground station laptops through serial cables. Since the laptops used do not have a serial port, a USB to serial adapter must be used. Two antennas are connected to the PGCS and then mounted on the outside of the trailer, one 900 MHz for transmitting and receiving data, and one GPS antenna for location data. KSU Salina s Ground Control Staion Piccolo Portable Ground Station (PGCS) 900 MHz Antennas P a g e

8 Ground Control Station System Diagram The ground control station is powered by a fuel burning generator that can supply electricity as long as it is fueled. In case of fuel exhaustion, the systems are backed up by a 30 minute Uninterruptable Power Supply (UPS) battery backup in addition to the internal batteries of the laptop computers and PGCS transceiver. Additional features of the GCS include the trailer that ground operations are conducted in, it provides protection from sun glare that would inhibit viewing computer screens, an air conditioning unit for the comfort of the crew, a ladder to allow the placement of antennas on roof, and a weather station that provides real time weather data. Data Link Effective communication to and from the aircraft is paramount. Without the ability to send and receive data flying the aircraft would simply be a folly since there would be no way to control its operations or collect any type of intelligence necessary for reconnaissance operations. 5.8 GHz Transmitter Mounted - on 8 - Aircraft P a g e

9 Willie The autopilot transmits on a 900 MHz ISM band frequency between the aircraft and the ground control station. This requires two antennas for operation, one on the aircraft and one on the GCS. This link allows two-way communication; it transmits flight data including altitude, attitude, GPS location and waypoint information from the aircraft, while sending commands from the operator in the control station. The imagery data is sent by a 5.8 GHz Wi-Fi modem capable of two way communication though it is only used for transmitting a signal one way. This provides long range transmission of data from the aircraft to the receiver. Images are sent real time to the GCS where the laptop computers can display the image. 5.8 GHz WiFi GCS Transceiver Payload Gimbal In order to obtain imagery up to 60 degrees FOV in all directions from vertically below the air vehicle, an ultralight weight two axis ball turret camera was selected. In order to utilize the pan/tilt functions and image stabilization, two spare servo PWM ports were configured through the autopilot for pan and tilt. To stabilize the image for pitch and yaw variations, the IMU gyros inside the autopilot that are used for flight stability are also utilized to stabilize the gimbal by sending control commands to the servos. In order to independently stabilize the camera from the airframe the gimbal is attached to a plate mounted on top of vibration isolators, which connect to the airframe. This minimizes the amount of vibration seen through camera image. To find the target location, we calibrated to the gimbal at the 0 position. To Camera Gimbal Mounted on Aircraft find the target position the auto pilot uses the azimuth, angle of the camera and height above the ground to calculate the position. -9- Page

10 Camera A Sony IX-11A block camera was selected for the video. The camera composite video signal is converted to IP format using the Axis M7001 Video Encoder. This encoder is connected to an Ubiquiti Networks Bullet wireless transceiver that transmits live video to the ground station via a 5.8 GHz Wi-Fi network. This camera is capable of 10x optical zoom and 4x digital. The zoom feature of the camera is controlled via an RS-232 connection to the autopilot. This camera was chosen mainly for its size, its dimensions allowed it to fit perfectly into the gimbal installed on the aircraft, and weighing only 3.4 ounces meant that added payload would be very small. The camera also boasts a 2.1 Watt power consumption that allows several flight operations on one battery charge. Viewpoint Viewing the live video feed from the camera is achieved by a Cloud Cap Technology ground based control software called ViewPoint. The reason for selecting this software was because we knew that it would be compatible with the current set up of our platform, it allows us to view target location when pointing our camera at a specific location on the ground, and it supports IP video input through the Axis video encoder and Bullet Wi-Fi transceiver. In addition, it also allows image mosaicing and target tracking functions for easier target acquisition and identification. Data Processing All data processing is accomplished by the ground control station via the onboard autopilot. All flight data is processed through the onboard autopilot. Method of Autonomy Avionics The T-REX 700 is capable of autonomous takeoff, landing, altitude changes and waypoint navigation. To complete this, the team selected a Piccolo SL autopilot for the autopilot integration. This is a proven commercial autopilot distributed by Cloud Cap Technologies that was ideal for our VTOL system because of its size, capability of waypoint/altitude navigation, and support of VTOL aircraft via the onboard internal GPS and inertia sensors, a data link radio, rotary wing flight controller firmware, and electromagnetic P a g e

11 interference (EMI) shielded enclosure. The EMI shielded enclosure is particularly important due to the close proximity of all the sensors onboard the helicopter. The autopilot fits perfectly in between the frame of the T-REX 700. Due to the high frequency vibration of the rotary wing platform, the autopilot is positioned on top of four vibration isolators to minimize the amount of vibration in between the airframe and the autopilot. The use of the pitot/static capability of the Piccolo SL was not practical, due to the fact that a pitot tube would have to be extended past the rotor blades to prevent the rotor downwash from interfering. Therefore, to provide accurate altitude sensor data to the autopilot, a laser altimeter provided by latitude engineering was integrated. This improves the accuracy of autonomous take off and landings. Test and Evaluation Results Flight testing has been uneventful and free of malfunction Payload Testing The payload was found during the initial RC flight testing. The rotor head was governed to 1,600 RPM through the ESC because the rotor head when under autonomous control is governed to 1,600 RPM. Then utilizing a qualified RC pilot weight was added to the aircraft until the RC pilot no longer felt comfortable flying the helicopter. The helicopter was capable of lifting 10lbs. Imagery System Testing The imagery testing began during the final phase of our flight testing. Minor adjustments continue to be made after each test flight to improve image quality. Vibration of the camera is an issue that is constantly addressed and changes to the airframe have reduced the problem to manageable levels. Operation of the Imagery payload is practiced during every test flight to insure the highest experience level come time for competition. Target Location Accuracy Piccolo SL Autopilot Mounted on Aircraft P a g e

12 According the rule book s key performance parameters the objective is to find the target within 50 feet. To meet this objective the club took target data from practice mission and compared this data to the actual location of the target. The first tests of our target location showed that the location of the majority of the targets were 50ft-100ft from the actual position of the target. After inspection the club found the camera mount had been 8 degrees lower than the airframes level position. In order to fix this the gimbal calibration setting needed to be adjusted in PCC. Flight testing As of May 24 th, 2012 a total of minutes of flight including 15 autonomous takeoff and landing cycles were accomplished by the club. Throughout the flight testing Willie has shown the ability to take off in winds up to 15kts, maintain a forward velocity of 10kts, and demonstrated a climb rate of 7, and a descent rate of 5kts. During an early test flight Willie showed an oscillation in flight, this was quickly remedied by resetting the neural network and the oscillation was never encountered again. To complete autonomous take off and landings an AGL sensor was installed to assist the autopilot, from the first test flight autonomous takeoffs and landing have been carried out with less than 5 feet of error from the designated landing area. When testing the waypoint tracking feature of the Piccolo, a qualified external pilot is on standby in case the aircraft performs undesirably. During test flights the aircraft is commanded through the PCC to fly to assigned waypoints, and consistently carries out the function with no measurable error. Endurance Willie has a usable flight battery capacity of 8,000mAh. The first 50% of the battery amperage is equal to 70% of the total flight time. The last 50% of usable battery capacity is equal to 30% of the total allowable flight time. This allows approximately 14 minutes of endurance. Safety Considerations In the Kansas State UAS department, safety is applied intrinsically. By the use of checklists and redundancy in its systems safety is constantly monitored and addressed. This type of safety carried over to club operations, and is applied to all components of our missions. For this competition, safety was addressed in three parts: Aircraft, mission and redundancy. Safety is always the most important consideration during all phases of UAS operations. During design, assembly, testing and mission, safety will always be addressed by our club P a g e

13 Aircraft During the assembly phase of the Willie helicopter, close attention was paid to insure the aircraft was properly assembled as per the instructions. The torque specifications were checked, Loctite was used where applicable, and torque seal was used as a visual indicator of insuring all screws stayed within specification. Also on the aircraft, special attention was paid to making sure all loose Torqe Paint, Wire Sleeves, Zip Ties and High Visibility Paint cables and components are properly secured to reduce the risk of unintended movement during flight operations. To prevent wires from abrasion every wire on the system was wrapped flame retardant braided shielding. Additional safety precautions that were taken on the aircraft included high visibility paint. Wherever possible, metal components were painted a high visibility orange, and the batteries are wrapped in a bright blue to promote high visibility to both operators and onlookers. Before integrating the autopilot system, several external pilot test flights were conducted on the aircraft to insure functionality of the helicopter, along with payload and endurance tests mentioned in the design portion. Mission A risk assessment tool designed by KSU Salina s safety officer is used before every flight. After completion, this tool gives the operation a go/no go decision based on mission type, environmental factors, and crew readiness. The risk assessment tool relies on a point system where low numbers represent small risk, and larger numbers represent high risks. When added together these points help decide a go/no go decision P a g e

14 Attenuation is also taken into consideration before each mission. Since amplitude of a signal is typically lost when passed through a medium, a test is performed by passing the signal through an attenuator to insure the best signal quality is being output. Likewise every mission performed by the Willie Helicopter always begins and ends with a checklist. A point is made to never commit anything to memory so that no item is ever missed. Before the flight portion of the mission begins, a crew briefing is held, here the crew assignments are verbalized along with type of takeoff, mission objectives, emergency procedures, and recovery methods. In the event of an emergency or unintended movement, the crew is instructed to take shelter inside, or behind the GCS to prevent being struck by the aircraft. Fire extinguishers are on hand in case of fire to the aircraft or GCS. Crew assignments are a very important part of mission safety. It is imperative that every person participating in a flight test is given an assignment to keep crew focused on the task at hand, and know what their role is in case of an emergency. The ground control station consists of the parts of the crew who conduct the autopilot and payload operations. It is their job to conduct the checklist before the flight, and commanding operations during flight. The ground station crew is responsible for all operations of the aircraft, unless operations are transferred the external pilot. In the event of an emergency, the GCS crew is required to stay inside the station to prevent injury. Ground crew members are responsible for the handling of the aircraft when not flying. They are tasked to transport the aircraft, charge batteries and test systems before each flight. Once all checklists are complete, the ground crew must move to inside or behind the ground control station during flight operations. The safety pilot s responsibility is to handle the external pilot transmitter at all times. When necessary the safety pilot assumes control of the aircraft, and is ultimately responsible for the safety of flight operations. While in flight, the safety pilot operates as a spotter to insure clearance from danger. Redundancy Redundancy begins in our ground control station (GCS). The Kansas State University GCS boasts a triple redundant power system. Since UAS operations cannot be carried out P a g e

15 without the GCS, these redundancies are very important. The entire electrical system is powered by a gas burning generator that can supply power as long as it contains fuel, if the generator fails an uninterruptable power source with an internal battery that lasts for 30 minutes takes over. Once that fails the system relies solely on the laptop batteries that also last approximately 30 minutes. So the GCS is capable of operating without the generator for approximately 60 minutes, which is more than enough time considering the flight time of our aircraft is only 15 minutes. The Piccolo autopilot system also boasts redundancy. During any phase of flight the abort function can be initiated. Depending on what phase the aircraft is in, this feature can safeguard the aircraft and its surroundings. If abort is selected during rotor spin-up or liftoff the rotors will spin down and the aircraft will kill the motor and put itself into prelaunch mode. At any time during flight operations abort is selected, the aircraft will decelerate to zero airspeed, and begin a controlled decent and land directly below its flight path. This is a great benefit of having an aircraft capable of vertical takeoff and landing (VTOL). Where a fixed-wing aircraft needs a large area for emergency procedures, a VTOL aircraft can simply land in almost any area with little risk to damaging the aircraft or onlookers. If at any moment communication is lost, the remote flight plan programmed into the aircraft for lost communication goes into effect. Before the mission, the operator chooses what the lost communication procedure will be. In our operations, lost communications always results in the aircraft initiating its landing flight plan, and executing an autonomous landing wherever it was programmed to do so. This eliminates any possibility of loss of aircraft due to communication error P a g e

16 Willie Conclusion With careful design considerations and extensive testing of systems on the ground and in flight, the Willie helicopter will be a system capable of carrying out all threshold requirements of the competition. The fully autonomous flight capability, and the integrated imaging payload matched with a talented team of operators are likely to perform exceptionally at this year s competition. Willie Performing a Fully Autonomous Landing P a g e

17 Appendix Operations Risk Assessment Form P a g e