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Tuesday, October 22, 2013

Get Above It All

Aerial imaging using consumer-level “drones” is now within reach of any photographer. In this first in a series of articles, we embark on the steps to get started.

This Article Features Photo Zoom

Shooting from the air allows you to get some special perspectives. Here, snorkelers mingle with whale sharks off Isla Mujeres, Mexico.
The Phantom turns on when its 11.1V, 2200 mAh battery is connected. Left alone on a stable surface, it goes through startup calibration and then begins to lock onto GPS satellites. When the multi-color status LED on the back starts to slowly blink green, the Phantom is ready for flight and has locked onto at least 6 GPS satellites, the minimum number required for reliable GPS flight control. The radio transmitter is a standard, 2-stick radio configured in what hobbyists refer to as "Mode 2." One of the great things DJI has done to push quadcopters toward the mainstream is eliminate all such jargon from the Phantom. Turn the radio on, and it just works. The left stick controls throttle (motor power) and yaw (turning left and right), and the right stick controls pitch (forward and backward) and roll (banking left and right). In GPS mode (selectable by a switch on the radio), the Phantom will hold GPS position at the current altitude, so steady hovers are easily achieved, even in wind. I've flown the Phantom in winds as high as 15 knots with 25-knot gusts, and it was rock-solid.

In practice, the Phantom can be flown even by new pilots, but I highly recommend conducting your first few flights in a large field with no trees or power lines around. If you have spectators with you, keep them away from the quadcopter and let them know when you put it up in the air. The one ground truth about these quadcopters is that if you lose control, they likely will crash into things before you even know what happened. Once you can fly figure eights without thinking, you've achieved the first level of multi-rotor pilot mastery.

The ultrawide lens on the GoPro does introduce some distortion, but it can be somewhat corrected in the computer or you can just go with it.
The Phantom has a couple of other flight modes (as do its competitors). Course Lock is a mode where the starting orientation of the Phantom is recorded as "forward." Regardless of how much you yaw the aircraft in Course Lock mode, pushing the right stick forward will make it go in the recorded direction. Home Lock is a mode where "forward" is always a vector between you and the aircraft. At any point, you can pull straight back on the right stick to bring the Phantom home. Speaking of home, one of the greatest features of the Phantom is that it has a powerful failsafe mode. If the Phantom runs low on battery or loses contact with the radio, it simply will fly home and hover at 20 meters in altitude. When the battery becomes completely drained, it will land automatically. Fail-safe is a good last resort, but is something that shouldn't be relied upon during normal flight.

Shooting Stills And Video With The Phantom-GoPro Combination
The Phantom is so easy to fly that most people attach GoPro cameras to them long before they're competent pilots. The two most common recording modes used during aerial imaging are Video mode and Time-Lapse mode. Wide, Medium and Narrow fields of view are all perfectly acceptable, but beginners should probably shoot at 60p (frames per second) for reasons I'll discuss later. In Time-Lapse mode, a 2-second interval is a good compromise between shooting plenty of frames and not coming back with 1,000 pictures to sift through.

Safety First
Check federal and local laws for rules about flying unmanned aircraft (specifically regarding altitude limits, commercial use, and flying near airports and in state and national parks). Spinning propellers and falling UAS have the potential to cause injury, so please fly responsibly.

Also, lithium-polymer (LiPo) batteries can explode and start fires if they're not treated with respect. Always charge batteries in special LiPo-charging bags, and don't leave chargers unattended. Every prospective UAS owner should do a YouTube search for "LiPo fire."
After successfully shooting video and stills during a few flights, you may notice some strange artifacts in your results. In video, you may see waves of horizontal artifacts moving through your frame over time, and in stills, you may have strange distortion in horizontal bands of pixels. These artifacts are commonly called "jello," caused by a combination of airframe vibration and the rolling shutter used in almost all CMOS-based cameras like GoPros. Jello comes from high-frequency vibration originating in the motors and propellers, and not from airframe movement that comes from wind or the automatic stabilization movements during flight. Jello can be prevented by a few tweaks to your Phantom:

1 Shooting at 60p reduces the amount of rolling-shutter artifacts in video.

2 Balance the propellers. Hobby stores sell "prop balancers," which can be used to make sure your propellers are in balance so they don't vibrate back and forth when they're spinning. The best way to learn how to balance propellers is to do a search on YouTube for "prop balance." Note that the Phantom II and Phantom Vision's propeller design has been changed to remove the need for a tightening nut, which may complicate prop-balancing.


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