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”).