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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.

Labels: Gear
This Article Features Photo Zoom
Image Stability: The Rise Of The Brushless Gimbal
Gimbals are special mounts that rotate a camera around one or more axes, most often for stabilization. A camera mounted directly onto a multirotor is certainly capable of capturing still images and video, but the camera's orientation will be tied directly to the orientation of the aircraft. In this configuration, it's nearly impossible to keep the horizon straight, and video footage will be shaky as the multirotor automatically stabilizes itself in the air.

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.


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