Tuesday, February 25, 2014
Get Above It All, Part II
This is the second in a series of articles on aerial imaging using drones. In this issue, we look at gimbals, FPV and aerial imaging techniques.
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.
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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