Introduction to Drones and UAVs
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If there is one overwhelming breakthrough that put consumer and prosumer UAVs on the map, it was computerized flight-control systems and multi-rotor technology, the latter not possible without the former. Traditional RC aircraft require skill to fly and many become quite expensive (you may have to remortgage your house to pay for some). Many are powered by tiny gas engines, some even turbines, and fly at scaled speeds competitive with manned aircraft. Multi-rotor UAVs, as distinct for helicopters by virtue of the complexity of their control systems, require a computer to regulate control input. Unlike planes, there is no rudder, no ailerons; just propellers. The only way to modulate flight is by spinning the rotors at different speeds, and there is just no way to do this manually. A side effect of this fly-by-wire implementation is that they can basically pilot themselves, especially when equipped with GPS, optical flow, and other guidance systems. This means just about anyone can fly; though I suppose it’s an open question if just anyone should fly.
Because they can follow very precise flight patterns, as well as hover in a fixed position (assuming GPS or optical flow), it was inevitable that one of the most popular-use cases for multi-rotors would be imaging. And, as luck would have it, at the same time, HD and 4K cameras have gotten really compact and really cheap (compared to the quality that they pump out), making strapping one to a UAV pretty much a no-brainer.
How they work
The heart of the flight-control system, this can be thought of as the “brains” of the UAV. It is an embedded computer (many run Linux) that has custom software for controlling the aircraft, sometimes user-reprogrammable through a software development kit (SDK). In some designs, the MC is a separate module with connection ports. On others, especially consumer products, there may be a single circuit board (PCB) that includes the MC, gyros/sensors, electronic speed controllers (ESCs), and other core flight electronics.
With modular designs, some form of connectivity—analogous to SATA ports inside a computer—is provided, allowing peripherals and user upgrades to be installed. CAN-Bus is widely used. This is an automotive serial interface technology developed in the 1980s that has been repurposed in a diverse range of control-by-wire vehicles including, among other things, combines.
Modular systems have the advantage that they can usually be replaced or upgraded. Early on, a major part of DJI’s business model was selling its Naza-M and triple-redundant A3 Pro flight controllers to third-party UAV makers and individual multi-rotor builders.
Gyros/Sensors
For autonomy to work, the MC needs to track how the aircraft is flying. To accomplish this, some form of sensor array is provided. Generally, it will include accelerometers, inertial measurement units (IMUs), and gyros, and may also work in conjunction with positional data from an optical flow system or GPS/compass. Basically, these sensors tell the UAV how fast its acceleration is changing, in what direction, and whether it is right-side up. Those familiar with motorized gimbal camera stabilizers may recognize the same sensor technology being employed here as in gimbals.
Electronic Speed Controllers (ESCs)
Each motor has an ESC (though some designs put all on one board). In its most basic form, an ESC regulates power going to the motor with which it is paired. More sophisticated systems can also relay data back to the MC, such as vitals about how the motors are performing. With six or more rotors, active feedback makes it possible to keep flying (enough to land safety) if one motor fails.
Receiver
This receiver is for the radio control system. It pairs (“binds”) with the controller the pilot or operator holds, which logically, if confusingly, is known as the “transmitter.” Modern receivers typically operate in the 2.4GHz range (like other license-free radio systems, such as Wi-Fi) and have four or more channels, extra channels enabling custom functionality to be relayed via the control signal, in addition to basic piloting inputs. In the hobby world, these extra channels might be used for anything from retracting/extending landing gear to firing off a smoke generator. In aerial imaging applications, the extra channels can sometimes be dedicated to gimbal or camera control.
Motors
In most cases, these are brushless electric motors. The motors are usually paired, each pair a set containing one clockwise (CW) motor partnered with one counterclockwise (CCW) rotating motor, though they may be sold individually. It is important when replacing them or building your own system to use the correct rotational direction in the correct position. This can get confusing, because the propellers are often designated CW or CCW based on which way they screw on, not which way they rotate—which is probably the opposite direction!
Propellers
Light UAVs use plastic propellers, which resist breaking on impact because they are flexible, and they are safer. Heavier models use carbon fiber or other more rigid materials (planes frequently use wood or nylon/glass). Carbon fiber propellers are dangerous, even deadly, and should be used only by experienced pilots and well away from people. Unless extreme performance is a concern, the benefits of carbon fiber over plastic are marginal on multi-rotors.
Transmitter
This is the radio controller. For an increasing number of tech toy and entry-level UAVs, the “transmitter” is simply the combination of a mobile app and a Wi-Fi-enabled tablet or smartphone (Parrot uses Wi-Fi control for all of its quadcopters). UAVs equipped with receivers, such as Spektrum and Futaba, can work with a range of transmitters. This allows the user to select the best fit, depending on what features they are looking for and what their budget might be. It should be noted: these tend to be proprietary, so with a Brand X receiver you'll probably need a Brand X or, at the very least, a Brand X-compatible transmitter. Systems that include a transmitter (as well as other basic accessories required for flying) are dubbed “ready-to-fly,” and are the simplest to jumpstart the beginner.
When investing in a transmitter, generally, compatibility can be determined by referring to the specs for the receiver. It will need to support the same protocol as the receiver and support at least as many channels as the receiver requires. So, for example, a DSMX 4-channel receiver will work happily with a DSMX 6-channel transmitter. For advanced configurations, one also needs to consider secondary systems that will need to inter-operate with the transmitter, such as a telemetry radio.
Transmitters can range anywhere from simple two-joystick jobs for remote-control toys up to highly sophisticated pieces of electronics with advanced programming to support myriad aircraft configurations, expandable model memory, telemetry displays, audible feedback, and trainer ports. In many ways, high-end transmitters are more complex than aircraft they fly.
Other hardware systems that are not essential to the archetypical UAV but are nonetheless common, include:
• GPS
• Optical flow
• Obstacle avoidance
• Telemetry/OSD
• Ground station
GPS
Once you transcend the toy category, GPS—often generically referred to as GNSS to include GLONASS and other systems—is pretty standard on multi-rotors. By providing (relatively) precise positional data, GPS enables flight modes including fixed hovering, auto return home, orientation control, and safety “bubbles” that limit how close the UAV can get to the pilot. GPS also provides an extra level of granularity to further enhance flight stability. UAVs that are equipped with GPS can generally fly without it, but will lose some of their autonomy. Thus, they are more dependent on the skills of the pilot to stay airborne. For GPS to work, a compass is also required to provide bearing, and compass calibration may involve a baroque but essential pre-flight routine.
Optical Flow
Optical flow—known as Vision Positioning on DJI-based systems—is designed to do indoors close to the ground what GPS does outside at higher altitudes. In classic implementation, there is a camera taking high-frequency still images to keep track of its relative position, using a technique called “motion estimation.” Since current optical flow can only provide relative positional data within limited bounds, it will not give you full autonomous functions, such as return home, but does enable fixed hovering. In addition to optical flow, some systems, like DJI’s, also feature an ultrasonic emitter and microphone to augment vision data à la sonar.
Although designed to promote indoor flying, optical flow does not enable safe operation near, or especially over, people. It relies on an unobstructed view of the floor (or other static surface) and with current systems is only good at heights up to 7' or so, which would put the UAV directly over the average person’s head, not to mention collide with many basketball players. Furthermore, Ultrasonic systems should not be used around animals with acute hearing, such as dogs, as the emissions are audible and can cause discomfort or be frightening.
Obstacle avoidance
While GPS and sensors enable UAVs to basically fly themselves, they work on the assumption of unobstructed air space. Starting in 2015, we began to see the first consumer collision avoidance systems. Yuneec’s adaptation of Intel® RealSense™, for example. Obstacle avoidance provides awareness of the surrounding environment, not only helping the UAV to not bump into anything, but also memorizing a 3D map that can be called up later when updating an autopilot flight line. This technology puts UAVs one frightening step closer to the science fiction/horror nightmare of full vehicular autonomy.
It should be noted that having obstacle avoidance is no reason to throw safety out the window or willfully operate in the vicinity of objects into which one might crash. Hardware and software are fallible, and even with the best systems, the UAV can only react so quickly. With aircraft exceeding speeds of 50 mph and no “brakes,” so to speak, a lot can go wrong—and fast.
Telemetry/OSO
Telemetry is data about your flight—speed, altitude, battery voltage, etc. This can be viewed in several ways. The old-school way is via a display built into transmitter. In some cases, the telemetry will operate on its own radio system with a unique frequency, so a transmitter with a dedicated telemetry receiver or the ability to install one is required. More recent is on-screen display (OSD), an addition to FPV that superimposes select data over the video feed from the flight camera. In this case, an OSD module is required, through which the video feed will pass after leaving the camera, and before arriving at the video transmitter.
Ground station
A ground station is an all-in-one solution for control, FPV, telemetry data, and even full autonomous flying. It may be unified into one air-end and one ground-end component or may require a complex assortment of hardware. Ground stations center around desktop software or an app. In many cases, the software alone is all that is required for operation; though a transmitter can often be tied to it for direct manual control.
In spite of the restriction on BVR, which rules out many commercial applications, for aerial video and photo it is still possible to take advantage of “waypoint” flying to set highly controlled flight patterns for the sake of predicable, repeatable shots, even while keeping the aircraft within visual range.
Safety
UAVs are airborne vehicles that can travel at high speed—up to 50 mph or so for multi-rotor camera platforms, and much faster for fixed-wing planes and RC rotorcraft (i.e., conventional helis). Inherently, they have the potential to be very dangerous. Most safety advice takes the form of common sense, but common sense that all too often gets ignored. Here are some general tips to consider:
• Follow all pre-flight calibration steps very closely, especially compass and GPS calibration
• Maintain visual contact at all times—FPV does not count as “visual contact”
• Stay below 400' above ground level (AGL); in certain locales, even lower
• Do not fly over people, private property, or in urban settings
• Do not fly within 5 miles of airports, in restricted airspace, or near helipads
• Learn how to control your aircraft manually, even if you plan to use autopilot functionality in practice; consider investing in a “starter” aircraft or flight simulator software to get experience flying
Beyond these general tips, your best resource will be other fliers. In particular, consult RC clubs in your local area and contact members of organizations like the AMA for advice. Even if you don’t see yourself as a hobbyist, RC clubs will have the best advice in terms of dos and don’ts, and should be able to direct you to courses, should you wish to learn from an instructor or need assistance troubleshooting.
Beyond multi-rotors
The buzz these days, of course, surrounds multi-rotor configurations, usually quadcopters. But the RC world has known several Jurassic types that long predate these newcomers:
• Planes
• Sailplanes/Gliders
• Helis
Planes
Planes are fixed-wing, usually with a single nose rotor, like a miniature Cessna. The motor may be a small heat engine or, especially in smaller, lighter categories, electric. Jet-inspired turbine engines are also available, but not recommended for the faint of heart.
Sailplanes/Gliders
Once launched—tossed into the air—gliders take advantage of thermals, soaring like hawks. A simple battery-powered rudder/elevator system gives the pilot control, making them true RC aircraft, not simply glorified paper airplanes. Be aware of cheaters, though. Occasionally motorized aircraft will sell themselves as gliders. These imitators feature broad, glider-style flight surfaces, enabling extending glide times with the motors shut off. These fake gliders are sometimes used in commercial applications, such as mapping, due to their long range.
Helis
Do not confuse helis with multi-rotors. Helis have a control surface modeled after real helicopters and, as such, are very difficult to fly. There is one or more main rotor to provide lift, plus a tail rotor to counteract torque from the main rotor. So-called multi-rotors, in contrast, have symmetrical-sized propellers, usually arranged in clockwise/counterclockwise pairs.
Outliers
Not everything fits neatly into a category, of course. The Xcraft X PlusOne, for instance, can’t decide whether it is a plane or a multi-rotor. It features four horizontally-oriented rotors and takes off and lands vertically. But once safely in the air, a transformation happens. The X PlusOne tilts 90-degrees and flies “forward,” a static, wing-shaped body providing lift. This unorthodox arrangement enables the X PlusOne to achieve speeds of up to 60 mph. There are no ailerons, elevons, rudders, or kindred flight surfaces in the usual sense. Instead, variations in motor speed are what maneuver it.
UAV Categories
There are no formal definitions, and if there is one thing we gear heads are known for, it’s endless semantic debates over correct jargon usage. In terms of camera-equipped UAVs and those capable of carrying cameras (excluding the serious RC hobby market), we can roughly break classes down as follows:
• Consumer
• Prosumer
• Professional
Consumer
Here the term “consumer” encompasses the “tech toy” category, as well as what we might regard as “starter” hobby aircraft. They are compact, 350-sized maximum (**), or smaller for quads. While many have cameras, these cameras are primarily for showing off to friends and FPV; they lack stabilization and, therefore, are not suitable for most dedicated video or photo use. They tend not to have GPS or much in the way of autonomy, but offer “fun” features—you decide whether they are gimmicks or not—such as one-button flips and the ability to “easily” perform other acrobatic maneuvers.
Prosumer
“Prosumer,” somewhat nebulously, covers the lower end of aircraft, mostly quadcopter and a handful of hexa-rotors, which are designed specifically with video and photo in mind. A common implementation is to combine a GoPro HERO or similar action camera with a 2- or 3-axis gimbal for stability. I would put these in the “prosumer” category, as some users may be enthusiasts looking for more than what the entry level offers, while others may be shooters who are primarily into capturing great images, as opposed to being RC geeks. Generally, I would hesitate to consider most of these hobbyist vehicles, since virtually all are multi-rotors—and multi-rotors, deserved or otherwise, have a reputation in the RC community of being somewhat graceless—more about enabling VTOL and fixed camera angles and less about performance or skilled technical flying. However, there is nothing stopping hobbyists from tricking quads out and flying them for the sheer enjoyment of flying.
Professional
Professional UAVs will include most hexa-rotors and virtually all octo-rotors and up. These are designed specifically to carry payloads, such as cameras. In terms of platforms that can be purchased through retail outlets such as B&H, pro UAVs max out at about a 25-lb payload in stock configuration. This is enough to satisfy even high-end production requirements. Thanks to compact, high-speed recording media such as CFast and the miniaturization of camera electronics, cinema-quality acquisition is possible in cameras that fall within this weight range.
Which do I buy?
Like anything else, this depends on the intended use. Aerial imagists should see their investment as a tool. In most cases, the choice will come down to the camera(s) and gimbal systems the UAV supports, as well as what features the flight-control system provides; e.g., most GPS-based aircraft can return home automatically; however, not all can track a moving subject by locking-on to the subject’s smartphone or smartwatch. Consider your applications and look for the feature set that constitutes the best fit. Beginners should also consider picking up a consumer copter for the sake of practice. These may seem like kids’ toys, but the basic flying principles will be the same. Plus, if you experience a fatal crash, you aren’t out a whole lot of money. Not to mention, being smaller and lighter, there is less risk that a collision will cause damage or harm someone.
One should also consider completion level. If you are not a dedicated model builder, opt for ready-to-fly. Or at least pick out a fully assembled aircraft and a transmitter, separately, to go with it. Also think about power requirements. Most systems that are hexa-rotor (six-rotor) and up require LiPo batteries that cannot be carried on or shipped via commercial aircraft. They require special hazmat certification to ship. This will limit availability and make spares costlier to obtain. If you are dedicated to aerial production, investment in a professional platform might make sense. However, if you simply want to incorporate some aerial “B” shots, something in the prosumer range probably makes more sense. Finally, if you have a periodic need to fly with something heavier, such as a DSLR/mirrorless or compact cinema camera, consider renting or hiring an owner-operator on an as-needed basis. They will probably be a better pilot, plus you won’t be stuck investing loads of money in a system you rarely use and that will quickly become obsolete.
*The first radio-controlled aircraft on record are novelty airships invented in the late 19th Century. By “radio control,” we are talking spark-gap radio control, by the way. Nicola Tesla, meanwhile, patented the first vehicle radio control system—in this case for boats—in 1898. RC planes with something resembling modern radio control systems emerged in earnest sometime circa 1937.
**Many prosumer level quads are 350 as well—notably the DJI Phantom series. However, 350 is the largest one usually sees in the consumer class. By the same token, prosumer models smaller than 350 are rare, but this will change as technologies like gimbals become more miniaturized.
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