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The latest thing in UAVs RPAs . . . Remotely Piloted Aircraft (RPAs) are on the threshold of a major explosion in design, operation and areas of deployment. Leading the way in this revolution is a style of helicopter best known as a Quadcopter or Multi-rotor Copter. By Bob Young MULTI-ROTOR HELICOPTERS I n recent years, we’ve looked at Licence) but some classes of RPAs the review of the Parrot elsewhere in several of the developments in will need to be controlled by those this issue) through to large, complex UAVs (or now, officially called with the equivalent of either private machines intended for “serious” applications such as filming, surveying RPAs) and the technology used in or commercial pilot’s license. Fortunately, we believe that the and military uses. these machines. This type of vehicle is absolutely However we are now entering a fun police won’t be looking at small new era in RPAs, driven by the fact “hobby” quadcopters (which are ideal for use in urban environments that in the USA the Federal Aviation referred to as SGMAs, or self-guided in that it is small, light, extremely manoeuverable and relatively quiet. Authority (FAA) has been instructed model aircraft). There is a wide variety of these by Congress to integrate RPAs into the machines ranging from three rotors US National Shared Airspace within Electric power One of the machines featuring heav- through to eight or more rotors (even 90 days for emergency services and by 2015 for civilian use. This is expected ily in this new upsurge of interest in sixteen in the case of the man-carrying to result in an explosive growth in the RPAs is the Electric Powered Multi- e-volo multi-copter, as we shall see). rotor Helicopter. Some have four arms with eight motors use of RPAs. They range from fun “toys” (see mounted in pairs, one above the other. Here in Australia, CASA, having Others have eight arms originally led the world with fitted with a single motor. an operational regulation (isRPAs? What happened to UAVs? Each has advantages and sued in 2002), is now working The ICAO (International Civil Aviation Organisation), the disadvantages. to bring an improved alignment international aviation governing body, has recently “tidied The media has recently between technology advances up” their acronyms and have decided that the terms for discovered the advantages and aviation safety. UAV operations are to be re-designated Remotely Piloted One outcome of the legisla- Aircraft, or RPA. Thus we have RPL (Remote Pilot License), of these machines, leading tion (due early next year) is that RPA (Remotely Piloted Aircraft) and so on. Over the years to a class of journalism now entitled “Drone Jourcommercial RPA “pilots” will we have gone from RPV to UAV to UAS and now RPA! And don’t forget that CASA have decreed that only nalism”. need to be just that – licensed A camera-equipped pilots. Some will only need an commercial aircraft can be called “RPA” – hobbyist models are to be called self-guided model aircraft, or SGMAs! multi-copter which fea“RPL” ticket (Remotely Piloted 18  Silicon Chip siliconchip.com.au tured in an incident at the Christmas Island Detention Centre last year caused quite a stir and has since brought to the fore all sorts of questions, not the least being privacy. After taking photos of the Detention Centre, it crashed into the Indian Ocean, giving rise to rumours that it had been shot down. The Author has since had it confirmed that it was not shot down but even so, Christmas Island Authorities were indeed quite upset about the whole incident, stating that “it instilled fear for all concerned below” with many of the detainees having first-hand experience of what RPAs are capable of doing from their years in Afghanistan. However there are even more serious aspects of “Drone Journalism” to be considered. For example it is now quite feasible for a quadcopter fitted with a camera and real-time video downlink to fly up to a window and quite literally look through that window – or indeed, if the window is open, fly right through the window into the room. If some of the over-achieving drone designers have their way, RPAs the size of cockroaches or household flies will be sitting on the wall or walking across the desk listening in to any conversation in the room. The Civil Libertarians are going to go nuts over this stuff and it is here now. However, for military people they are a Godsend as they can completely remove any mystery from entering a room, peeking around a corner or looking over a hill without risking any soldier. So what is a quadcopter and how does it work? Two early rotor craft: the Oehmichen No.2 (top), said to be the first successful design and uderneath is the deBothezal machine developed for the United States Air Service. Both are from the early 1920s. (Photos courtesy Wikipedia). in the horizontal plane, stabilised the machine laterally. Another propeller was mounted at the nose for steering with the remaining pair of propellers being used for forward propulsion. The aircraft exhibited a considerable degree of stability and controllability for its time and was the first helicopter capable of reliably carrying a person. The No.2 made more than a thousand test flights during the middle 1920s. By 1923 it was able to remain airborne for several minutes at a time, and on April 14, 1924 it established the first-ever FAI distance record for helicopters of 360m. Later, it completed the first 1km closed-circuit flight by a rotorcraft in 7 minutes and 40 seconds. (Source: Wikipedia) Dr George de Bothezat and Ivan Jerome developed an aircraft for the United States Air Service with six bladed rotors at the end of an X-shaped structure. Two small propellers with variable pitch were used for thrust and yaw control. The vehicle used collective pitch control. It made its first flight in October 1922. About 100 flights were made by the end of 1923. The highest it ever reached was about 5m. Although demonstrating feasibility, it was underpowered, unresponsive, mechanically complex and susceptible to reliability Origins of multi-rotor helicopters The Frenchman, Etienne Oehmichen, experimented with full size manned rotorcraft designs in the 1920s and demonstrated the first successful helicopter on February 18, 1921. Among the six designs he tried, his helicopter No.2 achieved considerable success. This machine had four rotors and eight propellers, all driven by a single engine. The Oehmichen No.2 used a steeltube frame, with two-bladed rotors at the ends of the four arms. The pitch of these blades could be varied by warping. Five of the propellers, spinning siliconchip.com.au Dave Jones, an American pioneer in multi-rotor craft whom SILICON CHIP readers may remember from earlier model aircraft and radio control articles. August 2012  19 Definitely not an RPA, nor a “quad”copter! This is the e-volo Multi-rotor, a 16-motor monster multi-rotor capable of manned flight. Indeed the designer, Thomas Senkel, is shown here in the world’s first manned electric multi-rotor flight – October 21 2011 in southwest Germany. (Photo: Wikipedia) problems. Pilot workload was too high during hover to attempt lateral motion. (Source: Wikipedia) An early pioneer in the model quadcopter field in America is Dave Jones of AUAV in Florida USA (featured in SILICON CHIP DSS [February 2009] and Flamingo [June 2010] articles). Dave experimented with R/C quadcopters in 2003 and he is shown overleaf with one of his quads. While flown quite successfully as a radio-controlled quad, Dave’s machine lacked the finesse found in modern quads. Time and technology have combined to completely sort out these shaky beginnings to the point where we now see tiny little unmanned quadcopters small enough to fit into the palm of a man’s hand (usually referred to as na- Here’s a DJI Flamewheel airframe with DJI 30A opto and DJI Nava stabilisation. The motors are 928kV DJI. This quadcopter has the familiar “X” pattern of rotors. The alternative is the “+” pattern which behaves quite differently. Both are explained in the text. 20  Silicon Chip nocopters), flying fully autonomously in formation using swarm technology. How times have changed. Manned multi-rotors So what then of manned multirotors, have they been left behind? By no means, as the photo above shows. German aircraft developer evolo has developed a manned multirotor that it calls a multi-copter. While the company has previously demonstrated unmanned drones, on October 21st 2011 it accomplished what it claims is a world first – a manned electric multi-rotor flight. It took place at an airstrip in southwest Germany and lasted one and a half minutes. Thomas Senkel, a physicist and designer/builder of the multi-copter, piloted the aircraft from a centre-mounted seat, using a handheld wireless control unit. The flight consisted mainly of manoeuvering the multi-copter around within a fairly small area – no sense in getting cocky. “The flight characteristics are good natured,” Senkel said afterward. “Without any steering input it would just hover there on the spot.” According to e-volo, its multi-copter is simpler in construction and mechanics than a helicopter and safer - it can reportedly land even with up to four of its motors failed, and its propellers experience much less wear. siliconchip.com.au Onboard computers running custom firmware control the rotational speed of the propellers, dictating the attitude (horizontal orientation to the ground), altitude and direction of travel of the aircraft. Once again potential flight times are limited and range from 10 to 30 minutes, depending upon battery capacity and payload. As in most aircraft, payload and endurance fight with each other for supremacy with the mission requirements deciding the final outcome: long endurance, small payload; high payload, short endurance. Lithium polymer batteries There is an enormous amount of technology and development that has needed to come together to make these tiny fully autonomous machines possible. From the satellite-based GPS system through micro-miniature electronics to tiny electric motors and batteries, all have played their part. However, from a purely practical, operational viewpoint the underlying technology which has made the Nanoquads possible is the lightweight, high energy density lithium polymer battery. These batteries have completely altered the miniature aircraft landscape. For the first time, electric powered model aircraft are successfully challenging the internal combustion (IC) motor’s position of supremacy; at least in the field of short endurance flying operations. This is the “Achilles heel” of electric powered aircraft; endurance! Until battery manufacturers manage to produce batteries or power sources with energy densities similar to liquid fuels, electric powered flight will remain the “country cousin” of IC engines. That said, however, even a twofold or better increase in battery energy density will open up all sorts of possibilities for electric powered flight. That is how close the battle is balanced. As an example, almost half Modern RPAs have only become possible with the miniaturisation (and power) of today’s computers. The computer makes all the adjustments necessary (to motor speed especially) to actually keep the thing in the air! of the models used in the recent World Aerobatic championships, a typical short endurance event, were powered by electric motors. The author, given equality in energy densities, would use electric power exclusively in his company’s RPAs for a host of reasons including lack of vibration, reliability, low noise and ease of handling (starting and stopping the motor in flight, fuel cartage and storage etc). In short, in many areas electrics leave ICs for dead but for long endurance RPAs at the moment electrics just simply do not cut it. Thus we see that from the outset the electric powered quadcopter is primarily a short range and short endurance vehicle thus ideal for line of sight operations. How does it work? The quadcopter is quite different from both helicopters and fixed wing aircraft. With no fin, rudder, elevators, ailerons, collective or cyclic pitch, just how do these things work? In the following explanation the description will concentrate on a simple quadcopter on the understanding that the same basic principles apply to all multi-rotor craft. Basically they consists of series of rotating propellers, some rotating clockwise and some rotating counterclockwise. The reaction between the thrust and torques generated by these propellers (or rotors) are used to stabilise and manoeuvre the machine as well as provide the lift required for vertical ascent. For hovering flight, the torques must be in equilibrium and the thrust must equal the weight. Any imbalance in this equilibrium will result in a change in attitude or altitude with a resulting change in position. As well as this the quad can be configured in the “X” or “+” configuration, completely altering the control Diagrams showing the effects of torque and thrust. Diagram on the left shows the effect increasing thrust on one motor and reducing thrust on the opposite motor. Diagram right shows reducing thrust on the opposite pair results in a rotation around the Z axis. siliconchip.com.au August 2012  21 It’s not all fun and games: this RPA (equipped with camera) is relaying – in real time – close-up shots of this 50m mobile phone/microwave relay tower to the video operator on the ground (inset below). This operation requires two controllers – one “piloting” the plane with the second controlling the camera direction, zoom and focus while capturing the images required. This system also has huge potential in the movie/TV /advertising and commercial production area, too. inputs required to stabilise or move the aircraft. The “+” configuration requires the control of two motors at a time for a change in horizontal position. If motor one decreases RPM and motor two increases RPM then the quad will move off in the direction of motor 1 (top of the page) due to the vectored thrust. Likewise left, right and backwards movements are achieved with the appropriate thrust vectors. On the other hand X configuration requires less thrust on the two front rotors and more thrust on the two rear rotors to move forward. Both configurations then require Z-axis compensation to correct for the rotation induced by these thrust (torque) changes. The quad therefore must be controlled in the X, Y and Z axes for positional placement as well as controlled to prevent rotation around these three axis. The rotation around the X, Y and Z axes roughly equates to the control of an aircraft in the Pitch, Roll and Yaw axes. However, there is one very powerful difference. Any rotation around the X or Y axis will result in a thrust vector which will move the quad left, right, forward or backwards in the horizontal plane. Any imbalance around the Z 22  Silicon Chip axis will result in a rotation clockwise or anti-clockwise around that axis. Thus control of all four rotors simultaneously is required to maintain the correct orientation of the quad in relation to the nominated reference point (eg, front of the quad). For example, if a camera is mounted on the front of the quad with a simple Here’s the hi-res image transmitted from the RPA: crystal clear, perfect sharpness. Sure beats climbing a ladder! single axis horizontal-to-vertical camera mount, the camera can be swung left or right by inducing a rotation around the Z axis by a change in the balance of torques. Programming one of these little devils is not for the faint-hearted but fortunately most of the delicate control inputs required to hold equilibrium No, it’s not a computer simulation: it’s a swarm of tiny RPAs, flying indoors, in a controlled formation with no risk of collision. . . siliconchip.com.au Fig.2: this diagram shows the conditions for hovering flight. with no rotation around the Z axis. All motors are equal in RPM with two rotating clockwise and two anticlockwise and thrust equal to weight (not illustrated). can now be taken care of automatically with modern inertial management unit (IMU) sensors. Fortunately, with modern sensors, all of the corrections required can be programmed in as automatic responses. The overall effect in a correctly set-up quad is for a very stable camera platform, free of vibration and able to fly forward, backwards, sideways, up or down and rotate around its own axis. Thus the requirement for a complex gimbaled camera mount can be reduced to a simple single axis mount moving the camera from horizontal to vertical, resulting in a great saving in weight and complexity. We’ve focused on the small electric-powered quad-rotor but these machines can be quite easily fitted with standard IC engines and built to any size, as we have seen from the early efforts undertaken in the 1920s although the thought of starting and tuning four model-sized IC motors is quite daunting. Just what the future holds for multi-rotor machines remains to be seen but you can rest assured . . . we ain’t seen nuthin’ yet! SC A tiny video camera can be fitted to all but the smallest RPAs to relay images back to earth. It’s shown here (left) mounted in the end of one of the radial arms. By contrast, the large RPA shown above left was fitted with the latest Canon EOS 650D digital camera, complete with 1855mm zoom lens, on a tilt and pan gimbal. All aircraft and camera functions are controllable from the ground. NEXT MONTH: We’ll look at another RPA, an electric Piper Cub, fully kitted out for remote piloting and photography. We’ll also look at some “real world” flying situations. siliconchip.com.au RPA OPERATIONAL GUIDELINES The instruction issued by the US congress to the FAA states that RPAs under 55lb (25kg) are to be allowed into shared US airspace by 2015 with small RPAs under 2kg, later upgraded to 11.3kg) operated by emergency services to be given permission within 90 days. This is expected to lead to an explosive growth in people and companies queuing up for Company Operating certificates and Remote Pilot Licenses (RPL). In the US, the 90-day set of FAA rules will apply only to Police and other first-responder RPAs smaller than 25 pounds (11.3kg) that are flown in daylight below 400 feet, and that stay within line-of-sight. There are several police forces here in Australia investigating RPAs and the multi-rotors are of great interest to the TV media. Of special interest in this stampede towards RPAs is the quadcopter. Here in Australia, the Author has been a part of the team developing the CASA Level 1 RPL and it has been a very interesting project indeed. The Level 1 license covers operations carried out below 400 feet, visual line of sight (VLOS), Day Visual Meteorological Conditions (VMC), 3nm from an aerodrome and not over populous areas. There is also talk of a weight limit of 55lb, certainly in the USA, while in Australia at the moment that current limit is somewhat higher. The aircraft that fits most easily into these regulations and with the widest application is the small multi-rotor and thus the majority of people lining up to be issued for the RPL Level 1 are multi-rotor operators. For the hobbyist SGMA (self-guided modeal aircraft) operator, the Model Aeronautical Association of Australia (MAAA) has proposed a set of guidelines (MOP067) for what they term SGMA. Briefly, these guidelines propose a weight limit of 5kg with motor size limits (Electric and IC) and operations carried out below 400 feet, VLOS, Day Visual Meteorological Conditions (VMC), and on MAAA approved flying fields. For the complete MAAA policy follow this link: www.maaa.asn.au/maaa/mop/ policy/MOP067%20-%20Policy%20SGMA It is interesting to note here the MAAA definition of line-ofsight. The MAAA specifies that the pilot must be able to tell the model orientation at all times, should he be forced to resume manual control as below. MAAA SGMA VLOS Definition: the maximum range at which the Pilot in Command can clearly determine the orientation and also manually control the Model Aircraft in sustained flight. CASA CAR (1998) Part 101 states that “a person may operate a model aircraft only if the visibility at the time is good enough for the person operating the model to be able to see it continuously” (101.385). For those interested in the differences between SGMAs and RPAs from CASA’s perspective, this link tells the story: http:// casa.gov.au/scripts/nc.dll?WCMS:STANDARD::pc=PC_100375 Of particular importance for all RPAs and SGMAs is a return to launch (RTL) feature which is initiated automatically upon loss of the data link or manual control. Also the autopilot should automatically return the aircraft to launch should the RPA or SGMA exceed an operator predetermined distance from home (eg, the pre-determined MAAA defined VLOS distance for that particular model). All small commercial autopilots also have an added legislated, anti-terrorist feature built-in, that being a RTL if 300km distance from home is exceeded. August 2012  23