Electronic Design
UAVs Conquer The Skies

UAVs Conquer The Skies

More AUVSI 2010 Coverage

Unmanned aerial vehicles (UAVs) come in all shapes and sizes. They range from tiny microbots to high-flying drones like the General Atomics MQ-9 Reaper, which is ready for reconnaissance or combat (see “Unmanned Military Vehicles: Robots On The Rise”). Remote operation is common, but autonomous and semi-autonomous operation are in high demand since they have fewer technical requirements and often provide more reliable operation than human operators.

The U.S. Air Force uses large aircraft like Northrop Grumman’s Global Hawk for surveillance. It can loiter for more than a day and a half with a ceiling over 65,000 feet. Its high-resolution synthetic aperture radar (SAR) can generate images with 1.0/0.3-m resolution (WAS/Spot). It also can survey as much as 40,000 square miles in a day. It’s more compact than a comparable manned aircraft, but it uses an Allison Rolls-Royce AE3007H turbofan engine. The body is built from high strength-to-weight composites.

Gas and jet engines are common in larger platforms because they offer more power and performance. Very small engines are common on radio controlled (RC) planes flown by hobbyists, but they tend to be rather noisy. Designers can be less concerned about noise with high-flying UAVs, though small UAVs tend to fly closer to the ground where they can be easily heard. One alternative, electric propulsion, has been widely used.

Electric motors have advantages for smaller UAV applications because they can be small and are very reliable. They also eliminate the need for liquid fuel as well as the heat and lubrication issues associated with gas engines. Electric motors are quieter as well, which is an advantage in surveillance applications.

ELECTRIC FLYERS

The Draganfly Innovations Draganflyer X6 is a compact, almost silent electric helicopter (Fig. 1). It has six counter-rotating carbon fiber rotors paired with six very quiet, maintenance-free brushless dc motors. It can fly even if one rotor or motor is inoperable. The system also recognizes when a motor is stopped and will periodically attempt restart while limiting the amount of power used. Noise at 3 m is only 60 dB.

The system is designed to provide a very stable platform. Its SteadyFlight technology (Fig. 2) employs three gyros, three accelerometers, three magnetometers, a barometric pressure sensor, and a GPS receiver for semi-autonomous operation. The flight data recorder uses a removable 2-Gbyte MicroSD memory card.

The helicopter has a ceiling of 8000 ft. It has a flight time of 20 minutes without a payload using a single 14.8-V lithium-polymer 2700-mAh battery. Its maximum speed is 30 mph, with a climb rate of 23 ft/s and a descent rate of 13 ft/s. The Draganflyer X6 can be flown indoors and outdoors as well.

The platform is designed for a relatively calm environment. It can handle 18-mph windspeeds, although Draganfly recommends a maximum of 10 mph for novice pilots. The Draganflyer X6 can hold the payload stable in a 6-mph wind. This allows conventional non-stabilized cameras to be used with the platform. Electronically stabilized camcorders would provide additional stability and operation in higher windspeeds.

Draganfly makes a number of cameras available, including a 10-Mpixel still camera, a 1080p HD camera, a thermal forward-looking infrared (FLIR) camera, a low-light camera, and a micro analog color camera. The camera mount includes a tilt servo and oil-filled, spring-loaded shock absorbers.

Control is maintained using a 2.5-GHz direct sequence spread spectrum (DSSS) data link with a 250-kbit/s bandwidth. The separate video link, which is NTSC and PAL compatible, operates at 5.8 GHz.

The handheld controller (Fig. 3) is designed for ease of use. The SteadyFlight support allows features such as the ability to maintain position using the GPS and simply move up or down within that space. Draganfly provides training and recommends a minimum of two hours of flight time before deploying a Draganflyer X6. The Draganflyer X6 is being used in autonomous and waypoint-oriented flight research with computer-on-module components like those available from Gumstix (see “A Pack of Gumstix”).

The man-portable Draganflyer X6 folds up for carrying. It fits inside a 5.5-in. diameter 28-in. tube. The craft will also fold upon impact to prevent damage. It only weighs 1 kg and has a 500-g payload capacity, which is sufficient for a range of cameras and sensors that can be mounted under the craft. The UAV provides a stable platform, allowing almost any sensor to be used. Carbon fibers and glass-filled injection nylon help keep the weight down while providing a solid airframe. Pricing starts around $10,000.

ELECTRIC PLANE

Planes can loiter but they need to keep moving or come crashing down to earth. They are also more power efficient than helicopters, making them preferable for long-range, long-duration UAVs.

AeroVironment’s man-portable RQ-11 Raven B (Fig. 4) is in high demand with U.S. ground troops. A backpack system includes a pair of aircraft and an 11-lb ground control unit (GCU). It typically is equipped with a color or infrared camera and side-looking camera that can transmit live streaming video via radio. The camera can be swapped out by replacing the nose cone. This hand-launched, 9.25-kg, 97-cm long aircraft has a 1.4-m wingspan.

Like many small aircraft, it lands using a deep stall. Essentially, the nose flips up and the plane lands tail first. It then falls apart by design. Operators just need to replace the battery and snap the unit together before launching it again. Pairs of Raven B’s often are used to provide continuous coverage with the second launched just before the first exits its area of operation. Batteries can be easily recharged from a Humvee’s battery.

The control system utilizes a digital communication system supporting more than 40 channels for control, audio, and video transmissions. This is significantly more than the four channels available with the analog system used before. Digital also handles encryption and Internet Protocol (IP) traffic, making the aircraft a wireless access point. It makes handoff easier as well, allowing an aircraft to fly from one operator to another. The receiver can swap the battery and send the UAV back to its source within minutes.

The Raven B uses a rechargeable (60 to 90 minutes) or single-use (80 to 110 minutes) battery. It powers the motor, the control system, and the payload. The UAV also has a line-of-sight range of 10 km. Its approximately 500-ft ceiling is limited more by the camera optics and resolution. The camera presents a slightly smaller view of what is captured, allowing the system to provide digital optical stabilization as well as pan and zoom. It has been used at locations over 10,000 feet above sea level, including Afghanistan.

The on-board mission control system is designed for RC and fully autonomous operation, which enables operators to specify operation using waypoints specified on maps displayed on a laptop or GCU. The GCU can capture images, while a laptop is normally used to store streaming video.

The Raven B has been designed for rugged environments, so operators can configure or store units while wearing gloves. Training for the Raven B runs about two weeks, but operators are working with a flying plane the first day. Much of the training addresses issues such as safety, maintenance, and proper use. Operators can fly the UAV in real time, though autonomous waypoint operation is used more often so operators can concentrate on the information the UAV can capture.

TACTICAL VTOL

Gas-powered UAVs tend to be larger and provide a wider range of operating parameters. The Aurora Flight Sciences GoldenEye 80 advanced ducted fan VTOL (vertical takeoff and landing) (Fig. 5) weighs around 150 lb with a 30-lb payload. It stands 65-in. high and can hover for three hours. Its typical mission duration is eight hours. Designed for military use, its engine can run on Jet-A, JP-8, and aviation gasoline. It is a derivative of the U.S. Army’s Shadow engine.

The GoldenEye 80 has internal and external payload support. It can handle a range of stabilized eletro-optical and infrared cameras. Its two main internal systems are the flight control system and the mission management system. A 40-MHz microcontroller powers the flight control system. It has access to the GPS and INS (inertial) guidance system. The microcontroller handles the engine and the thrust vectoring system. It also performs real-time stabilization. A system-wide Ethernet network connects it to the mission management system. The network provides payload nodes.

The mission control processor, which is a 1-GHz Power PC, is a bit heftier. The system provides room for growth and allows more sophisticated autonomous operation. It also provides behaviors designed to simplify the user interface. It will eventually permit features such as collision avoidance. The system can already handle loss of communication with the ground station using contingency plans based on the current state of the mission.

External payloads can be mounted on a gimbaled mount. Its heavier payload capacity allows a range of devices to employed from cameras to laser imaging detection and ranging (LIDAR).

GET UP AND FLYING FASTER

Many UAVs are built from the ground up, including their electronic flight control system and mission management system. Cloud Cap Technology aims to deliver this combination in its generic Piccolo system, which can be used on existing or new aircraft. The company also provides stabilized camera systems and inertial measurement sensors.

The Piccolo II (Fig. 6) weighs only 226 g, including a 900-MHz radio transceiver. The compact box is just 142 mm by 46 mm by 62 mm. The Piccolo SL is even smaller at 130 mm by 59 mm by 19 mm. The Piccolo II runs off of a 8- to 20-V dc power source and consumes only 4 W.

The Piccolo’s Freescale MPC555 microcontroller supports five serial ports normally used with payload modules, 16 GPIOs, and four 10-bit analog-to-digital converter (ADC) inputs. It also supports controller-area networking (CAN). An inertial navigation system (INS) and GPS positioning system are part of the package as well. It is designed to hook directly into air sensors mounted on the exterior of the aircraft being controlled.

The software handles RC operation as well as semi-autonomous support. The system provides stability, smooth movements, and full autonomous operation. Failsafe operation accounts for the quality of the remote communication link, enabling the system to switch to fully autonomous mode and potentially a different aspect of the mission plan if the communication link is lost. Likewise, it can easily switch between GPS and INS positioning if all necessary GPS signals are lost. The system also has terrain awareness using data such as shuttle radar terrain map (SRTM) to provide collision avoidance.

The Piccolo is programmed using the Piccolo Command Center (PCC) (Fig. 7), which can control multiple aircraft. It is used for a range of chores from the initial design configuration based on an aircraft’s performance characteristics and its interface to the Piccolo. Cloud Cap developed its own programming language to facilitate customization. Most users take advantage of the PCC using a graphical interface for mission planning, simulation, execution, and analysis.

The Piccolo systems support a range of aircraft configurations including helicopters. Experiments are even underway testing these systems on watercraft. Software options include laser altimeter autoland support, differential global positioning system (DGPS) autoland support, and DGPS and moving net recovery in addition to VTOL vehicle support. The system is so robust and easy to configure that new aircraft have been up and running within a day.

The Piccolo is used in the Optimum Solutions Condor 300 UAV (Fig. 8). The airframe is constructed using advanced composite materials such as carbon fiber embedded in epoxy resin. The wing and stabilizer sections are bonded together into a lightweight structure.

This T-tail aircraft uses a pair of electric motors to drive the propellers. Each motor has a matching gear box designed to provide high torque at low RPMs. A custom-built polymer lithium-ion battery package supplies the power. The system is designed for modularity and redundancy. The battery package has a magazine-style carrier for quick replacement. There are two electrical supply systems within the aircraft so each motor, control surface, and actuator has two power supplies and control subsystems.

The Condor 300 is designed to collapse into a compact package that can be assembled and ready to fly in 10 minutes by two people. The turnaround time on the ground with battery replacement is two minutes. Using the Piccolo, the system can handle autonomous takeoff and landing using a laser-based altimeter.

The aircraft has a maximum speed or 125 km/h with an average cruising speed of 90 km/h. It has a wingspan of 3.22 m and a ground weight of 18 kg. Flight time is up to four hours. The Condor 300 also can handle a 6-kg payload, which typically is a Cloud Cap TASE Duo (Fig. 9).

The Cloud Cap TASE Duo includes a pair of cameras in a 5-in. diameter turret. They feature a 324- by 256-pixel FLIR Photon II IR Camera and an FCB-EX980 Sony Block Camera. The system’s gimbal stabilized package includes GPS and INS support, making it very similar to the Piccolo in functionality.

Given the required functionality for the TASE Duo, it isn’t too much of a surprise that Cloud Cap came up with the TASE LT (Fig. 10). This system combines the Piccolo’s aircraft control with the camera so the control portion is essentially free in terms of space, weight, and power consumption. It employs the same 13-state Kalman filter and neural network as the other Piccolo systems. The single package also makes system design easier.

LARGE PAYLOADS

Northrop Grumman’s Global Hawk is a 32,250-lb unmanned aircraft with a 130.9-ft wingspan and a payload of 3000 lb. Its Allison Rolls-Royce AE3007H turbofan engine enables it to cruise at more than 400 mph. It has a ceiling in excess of 65,000 feet and can stay up for 36 hours. Such a large craft allows more sophisticated systems to be employed for UAV control as well as mission management.

The Global Hawk is designed to support survivability enhancements such as Raytheon’s AN/ALR-89 self-protection suite, which includes the AN/AVR-3 Laser Warning System, the AN/APR-49 Radar Warning Receiver, and a radar jamming system. The UAV can also employ the ALE-50 towed decoy.

Some of the rugged subsystems within the Global Hawk come from Curtiss-Wright Controls Embedded Computing, including the Advanced Mission Management System (AMMS), Integrated Mission Management Computer (IMMC), and Sensor Management Unit (SMU) subsystems (Fig. 11). An IPv6 Gigabit Ethernet network provides the communication between various modules.

The AMMS is the hub for the payload suite with support for Gigabit Ethernet and Fibre Channel. The VPX-based system starts with a 6U VPX6-185 single-board computer (SBC). The SBC runs a dual-core, 1.3-GHz Freescale 8641 Power PC processor. The AMMS can handle up to 21 boards with the base system normally taking up five to 12 slots. The other slots are typically filled with other support hardware such as power supplies and solid-state hard disks.

The IMMC handles flight control and flight-critical chores. It is isolated from other subsystems because of its more stringent qualification requirements. Whereas the AMMS uses more multicore processors, the IMMC uses single-core processors running critical real-time control applications.

The SMU manages sensors and payloads. It also connects the sensor suite with satellite and ground communications systems. The SMU handles legacy interfaces such as 1553 and RS-232 serial ports. Its DSP subsystem allows refinement of sensor data. The subsystem is housed in a rugged aluminum chassis.

All of the systems are linked via Gigabit Ethernet, providing IP-based communication links between applications. This network is additionally linked via radio to ground control systems such as the Ground Sensor Management Unit (GSMU) also provided by Curtiss-Wright. The trend is toward more open, standards-based interfaces for easier connection of new and different subsytems and payloads.

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