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|The future is bright for aerial imaging using small unmanned aircraft systems. With just a little bit of effort, a photographer can have a flying, stabilized camera with a real-time video feed coming out of it. There's still a learning curve, and any new drone pilot will experience setbacks and frustrations, but this is an exciting new world for enthusiasts.|
In the article about aerial imaging using drones in the December 2013 issue of OP, we discussed how to take your first pictures in the air using GoPro cameras and entry-level quadcopters like the DJI Phantom. In the last year, aerial imaging products have become accessible to just about everyone, providing opportunities to capture perspectives that were previously out of reach without large budgets. In this article, we'll talk about how to be successful in capturing images by using modified, mainstream quadcopters.
Virtually every multirotor aircraft with 8-inch or larger propellers is capable of lifting a GoPro camera, which is by far the most popular camera used in unmanned aerial imaging because of its extraordinary quality to size-and-weight ratio. Homebuilt multirotors can easily be adapted to hold GoPros, and mainstream quadcopters like the Phantom actually come with GoPro mounts so they're ready to lift one right out of the box. This article will focus on the use of GoPro cameras in the air, but most of the techniques and tips discussed can easily be applied to any camera you choose to put in the air, including the built-in camera in the new Phantom 2 Vision. For the purposes of this article, we'll refer to the original Phantom as "Phantom" and the new offering from DJI as the "Phantom 2 Vision."
Note also that, at the moment, just about anything you decide to change or add to an off-the-shelf quadcopter like the Phantom immediately thrusts you headfirst into the remote-control (RC) hobby world. Aerial imaging is developing very quickly, but we're currently only at the very edge of mainstream solutions.
Image Integrity: Getting Rid Of Jello
All aircraft that use propellers have the potential to introduce high-frequency vibrations into camera systems. In the last article, we talked about artifacts that appear when the rolling shutter in the GoPro (and similar cameras) is subjected to these unwanted vibrations. Commonly called "jello," these artifacts cause annoying horizontal shearing in both video and still images.
To remove jello, you must eliminate the high-frequency vibrations, which can be accomplished by balancing all of the propellers and installing a vibration isolator between the camera and airframe. Prop balancing is relatively simple and is aided by special prop balancers that are sold in hobby shops and online. The basic idea is that a propeller should be perfectly balanced, meaning that both sides are the same weight. When a balanced propeller spins around its center, it doesn't introduce any vibrations into the system. Clear tape is often used to add weight to one side of a propeller, although using a file to remove material from the heavier side of a prop is also common.
Dedicated vibration isolators are also common and usually consist of four or more silicone balls that sit between the airframe and the camera mount. You can purchase or build a vibration isolator, but I recommend skipping this step altogether and getting a brushless gimbal, which includes built-in vibration isolators.
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Framing And Composition
The first time I put a camera up in the air on a quadcopter, I was elated, but I also felt totally blind. I was successfully taking aerial pictures and video, but I couldn't control the camera and couldn't see what it was capturing. To apply your photographic eye to aerial composition, you'll want two important upgrades to your aerial imaging rig.
The first is camera-orientation control. Fortunately, all gimbal controllers have this sort of control built in, and if you have a radio transmitter with an extra channel, all you need to do is connect an output from the flight controller or radio receiver to the appropriate input on the GCU. If you went with the Zenmuse and Phantom Upgrade Kit, you're in luck. The kit includes hardware to provide access to the transmitter channel that controls pitch (tilting the camera up and down), and the Zenmuse gimbal will just work when you start using the new control on the transmitter. If you're mixing and matching your own hardware, you'll need to work out your own solution. Luckily, much of this is documented online, and with a bit of web research, you'll find instructions on how to do it (wiring and soldering skills are required). You can also have your local RC dealer do the installation for you.
The second part of successful aerial composition is real-time framing via a video signal from your multirotor's camera. This is commonly called "first-person view" (FPV), and the incoming video signal is displayed on LCD monitors (typically, 7 to 10 inches) or LCD glasses, allowing a pilot to fly as if he or she was looking out of the front of the aircraft. Flying FPV is very similar to playing a video game using a joystick, and it's not uncommon to feel like your aircraft is a flying avatar capable of capturing images from anywhere!
Getting an FPV setup working can be complicated, but the principles are simple. Find your camera's analog video-out signal and connect it to a video transmitter (websites like ReadyMadeRC sell GoPro cables for this purpose). On the receiving end, use a compatible video receiver, and plug its video output into your chosen display device. Common consumer brands for FPV are Fatshark and ImmersionRC, and companies like DJI also offer FPV solutions.
Both of these aircraft upgrades are currently firmly planted in the hobby world. It can take a lot of research to understand how exactly to perform these modifications yourself, but if you enjoy building things, it can also be a lot of fun. As mentioned previously, you can also just buy an off-the-shelf dealer package that incorporates everything we've talked about so far.
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Settings For Success
Once your aerial imaging platform is set up for FPV and vibration-free image capture, you're ready to begin to optimize the images captured by your flying camera. One reminder about aerial imaging is that piloting skill is absolutely the most important variable in the equation. This will likely change in the future, as aerial platforms focus more and more on autonomy and safety, but in the near future, your images are only going to be as good as your piloting skills are. Practice safely, and practice often.
Capturing still images using a GoPro on a Phantom is straightforward, since there aren't very many options you can set. I commonly use my GoPro HERO3 Black Edition in time-lapse mode at 2-second intervals. This gives me hundreds of pictures per flight, but storage is cheap, and I'm happy to throw away most of the images that are captured, keeping only the best. The other reason 2 seconds is the magic number is that the GoPro won't output real-time video when it's shooting at 0.5- or 1-second intervals. Shoot any faster than 2-second intervals, and FPV goes dark.
Getting good exposures from an aerial GoPro can be tricky at certain times of day. Shooting midday in bright, sunny conditions doesn't usually pose a problem, but if it's cloudy, the dynamic range necessary to capture both sky and ground is too large for GoPros (and most cameras on the market). In this case, angle your camera down to get the camera to expose for the ground. You'll blow out the sky, but your subject is most likely terrestrial, and you'll probably want to optimize for that.
New quadcopters like the Phantom 2 Vision have integrated cameras, which allow for camera control during flight. The well-designed iOS app for the Vision lets users switch between still and video modes, start and stop the camera, set exposure, and more. It's a little awkward to have to remove one's hands from the sticks in order to adjust the camera and take a picture, but one can either have a second person control the camera or set the camera to video/time-lapse mode and focus on flying. Note that the Phantom 2 Vision's gimbal is pitch-only and uses a servo. This effectively makes it a composition tool (camera angle up and down) and not a stabilization tool.
In the previous article in this series, I recommended shooting video at 60p (frames per second) to minimize jello. However, if you've balanced your props and are using properly tuned vibration isolation to mount your gimbal, you should have no jello in your video, even at 24p. It's important to note that some tuning still may be required even in ready-to-fly solutions. Almost all gimbal manufacturers ship gimbals with multiple vibration isolators, suggesting that there's no catch-all solution to eliminating jello. In my case, I had to swap out the silicone balls in my Zenmuse H3-2D gimbal with softer ones (included) before jello disappeared from my setup, even though my propellers are perfectly balanced.
In my aerial video pursuits, I typically set my GoPro for Protune with manual white balance in one of the following video modes: 2.7k/30p Wide, 1080/60p Wide or 1080/30p Medium. I like the less-distorted look of Medium FOV, but shooting in 2.7k is flexible because I can crop and still have plenty of data to output 1080p. I shoot at 60p when I want to slow down footage a lot in post, but even at 30p, you can slow footage down to 24p, which is a pleasing effect.
Eric Cheng is an award-winning underwater photographer, publisher and technologist. Caught between technical and creative worlds, Cheng holds bachelor's and master's degrees in computer science from Stanford University, where he also studied classical cello performance. He's the founder of Wetpixel.com, the premiere community website for underwater image makers. See more of his work at echengphoto.com and skypixel.org.
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For many years, gimbals in the RC hobby world used servos in order to rotate cameras around pivots, but in mid-2013, brushless motors were adapted for consumer gimbals. The rise of the inexpensive brushless gimbal has been an incredible thing to behold and is an example of how fast this space is evolving.
Brushless gimbals for small cameras are typically 2-axis gimbals, which means they stabilize a camera in roll and pitch directions, leaving only yaw unstabilized; 3-axis gimbals exist, but typically have only been used in large-camera applications. Luckily, 2-axis stabilization is sufficient to keep the horizon level and in the same vertical location in the frame. The way a brushless gimbal stabilizes a camera is very similar to the way a multirotor stabilizes itself in the air. Sensors on a chip are mounted on the camera platform and report movements to a gimbal controller, which tells the gimbal's brushless motors to counter the detected movement. This happens many times a second, and in practice, video recorded using cameras on brushless gimbals looks like it was captured using a floating Steadicam.
DJI makes a gimbal called the Zenmuse H3-2D, which is designed for GoPro HERO3 and HERO3+ cameras (which are identical in shape when outside of the underwater housing). Although the Zenmuse can be attached to any platform, it works particularly well on the Phantom and is shallow enough to be used with the stock landing struts. The Zenmuse H3-2D requires a power management unit (DJI Naza PMU v2, $65) and gimbal control unit (GCU, included with gimbal), but if you're flying a Phantom, you can also purchase the Phantom Upgrade Kit, a $69 replacement main board with integrated PMU and GCU. This saves a huge amount of weight, and when used with the replacement board, the Zenmuse H3-2D is the smallest, lightest brushless gimbal you can get for a GoPro. Small gimbal size is important because every third-party GoPro gimbal I've seen requires raising the body of the Phantom for gimbal clearance, which is done by altering the existing landing gear or by replacing it with a third-party solution. My favorite replacement landing gear is the Simensays Landing Gear, which is 3D-printed and sold by Shapeways for around $40. The Simensays Landing Gear is designed to use any 6mm tube as legs, so you can purchase your own carbon-fiber tubes and cut them to your desired lengths.
Six months after the Zenmuse H3-2D was announced in April 2013, the market was flooded with inexpensive 2-axis brushless gimbals. At the time of writing, the Zenmuse H3-2D costs $699 (without PMU or Phantom Upgrade Kit), and decent third-party gimbals like the Tarot T-2D can be purchased for $200. All current gimbals require soldering and complex installation, but many dealers will do the installation for you or sell you a quadcopter package with a gimbal preinstalled.