Introduction to Drones and UAVs

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What are they and who uses them? Some call them drones, some apply the label “quadcopters” as a blanket term—though they can have any number of rotors or even be planes—the FAA calls them “unmanned aerial systems” (UAS). I prefer to call them “unmanned aerial vehicles” (UAVs), a neutral term broad enough to safely include pretty much the whole gamut from Hubsan nano drones up to commercial and military aircraft weighing hundreds of pounds and basically the size of small manned planes.

UAVs are and aren't new. Starting somewhere around 2013, a new trend emerged in the tech toy and aerial imaging market—an explosion in popularity of compact multi-rotor RC aircraft, perhaps most notably the DJI Phantom 3, a compact quadcopter capable of flying a GoPro either statically mounted or stabilized with a 2-axis gimbal. RC enthusiasts will, of course, cry foul. They will point out RC—unmanned—aircraft have been around for decades—nay, longer*—not to mention that pilots (“operator” often being the preferred term in RC Land when it comes to highly autonomous aircraft such as multi-rotors) have been equipping them with cameras for FPV since cameras got small and video transmitters got cheap. While this is true, the market was always a niche one, the exclusive realm of dedicated model-builders (a handful of professional users aside) that few on the outside paid much attention to or of whom they were even aware.

A drone with 3-axis gimbal-stabilized camera attached, making aerial images
 

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 props. 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 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

 

UVAs break into seven key components:


Breakdown of the key flight system components found on most multi-rotor UAVs
 

Main Controller (MC)

This is 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 an SDK. In some designs the MC is a separate module with connection ports. On others, especially consumer products, there may be a single PCB (circuit board) that includes the MC, gyros/sensors, ESCs, and other core flight electronics.

The CAN-Bus connection ports depicted here allow connection of peripherals, such as gimbal controllers.
 

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 WooKong-M 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 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.

Weighting in the gimbal keeps its orientation fixed as the quadcopter pitches and rolls. 
Sensors surrounding the gyro tell the MC whether the quadcopter is level or not.
 

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) and one counterclockwise (CCW) rotating motor. 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, as the props are often designated CW or CCW based on which way they screw on, not which way they rotate—which is probably the opposite direction!


 

A typical brushless motor. The threaded part rotates either clockwise
or counterclockwise, depending on the motor's position.
 

Props

Light UAVs use plastic props, which resist breaking on impact because they are flexible, and they are safer. Heaver models use carbon fiber or other more rigid materials (planes frequently use wood or nylon/glass). Carbon fiber props are dangerous, even deadly, and should be used only by experience pilots and well away from people. Unless extreme performance is a concern, the benefits of carbon fiber over plastic are marginal on multi-rotors.

Here are the prop/motor arrangements for a number of  multi-rotor types.
Note the clockwise/counterclockwise pairing of every two motors.
 

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 Futaba receiver you'll probably need a Futaba 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.

Control layout for the Spektrum DX5e transmitter with Mode 2
configuration. Mode 2 puts the throttle stick on the left.
 

Transmitters can range anywhere from simply two-joystick jobs for remote control toys up to highly sophisticated pieces of electronics with advanced programming to support a myriad of 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
  • Telemetry/OSD
  • Ground station

GPS

Once you transcend the toy category, GPS 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, as applied to UAVs, is designed to do indoors close to the ground what GPS does outside at higher altitudes. It implements 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 Vision Positioning, also feature an ultrasonic emitter and microphone to augment vision data à la sonar.

A ground-facing camera uses patterns on the floor to determine its position without
GPS assistance. In some casessuch as the DJI Inspire 1 depicted, this is augmented with ultrasound.
 

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.

In the future, we can expect the capabilities of optical flow to be extended to deliver even greater autonomy, hopefully bringing forth such features as obstacle avoidance. 


  Telemetry/OSD
 

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 on the transmitter. In some cases, the telemetry will operate on its own radio system (900MHz ISM is common for this purpose), so a transmitter with a dedicated telemetry receiver or the ability to install one is required. More recent is OSD (on-screen display), an addition to FPV that superimposes the 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.



 

A video image with OSD telemetry data superimposed
 

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.

Ground stations combine autopilot navigation, FPV, OSD,
manual control, and potentially more into a unified system.
 

Ground station systems are designed mainly for BVR, (beyond visual range flying); particularly planned missions such as aerial mapping and surveying. Currently, the FAA requires that visual contact with the UAV must be maintained at all times, making the BVR aspect illegal in the U.S. For this reason, companies making ground station systems tend to drop the term BVR from their marketing, even though their systems are quite capable of making entirely automated—even unwatched—flights.



 


 

With ground station software, you can define or update an autopilot course
using "waypoint" navigation, as well as see a live FPV image, complete with telemetry overlay (OSD).


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.


  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/entry-level hobbyist
  • Prosumer
  • Professional

Consumer

Here consumer encompasses the “tech toy” category, as well as what we might regard as “starter” hobby aircraft. They are compact, 350-sized, 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.

Hubsan H107C nano-sized  quadone of the smallest consumer drones on the market

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. The most 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.

DJI Phantom 3 prosumer drone with 4K, 3-axis stabilized camera

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.

DJI S1000+ professional drone with Zenmuse Z15 gimbal and Canon 5D Mark III
 

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 pick out 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 much more costly 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 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.

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