This chapter is from the book
This chapter is from the book
This chapter is from the book
Using Gimbals
In early 2013, getting stabilized aerial video from small consumer drones was almost unheard of. By the end of 2013, two-axis stabilization (roll and pitch) via brushless gimbals had become standard, and these days, three-axis stabilization is required—and, expected—to capture usable aerial video. Luckily, most popular camera drones work well with modern three-axis gimbals, both integrated and stand-alone, and the silky-smooth video that comes from using them is not very difficult to get (FIGURE 4.3).
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FIGURE 4.3 A 2-axis Zenmuse H3-2D gimbal keeps a GoPro level during a flight with DJI Phantom 2.
Gimbal Modes and Control
Gimbals that are used in the air have a few main operating modes that are useful.
- Follow Mode, in which the gimbal’s roll and pitch (tilt up and down) are fixed in orientation, but yaw (pan side to side) is allowed. Follow Mode is the default mode for most gimbals and is the only useful mode found on camera drones with fixed landing struts, such as DJI Phantoms. In Follow Mode, a pilot can fly the drone around and expect the camera to follow as the drone turns. All pitching and rolling of the aircraft due to stabilization or navigation are completely removed, and abrupt yaw motion is smoothed out, allowing only large yaw motions (navigation panning). The vast majority of drone videos are shot using Follow Mode.
- Free Mode, in which all three of the gimbal axes are fixed in orientation. In Free Mode, the gimbal prevents all aircraft movement from reaching the camera platform, regardless of aircraft orientation. Video footage captured in Free Mode from a nonmoving camera drone often looks like it was captured using a tripod. Free Mode is the most common gimbal mode for dual-operator flights, during which piloting and camera operations are separate duties, each controlled by a dedicated operator and remote controller. See http://ech.cc/gimbal-free-mode for an example of how effective a DJI Inspire 1’s Free Mode stabilizes its camera during aggressive flight.
- Advanced gimbal modes tied to smart flight modes. One example of a smart flight mode is Point of Interest, or Region of Interest, during which the gimbal is kept oriented toward a fixed point in space (such as a person standing on the ground). Another is Follow Me, during which the camera drone can be asked to keep a moving subject in frame using a combination of drone and gimbal orientation. DJI’s FPV Mode is used to simulate fixed-wing flight and to allow a pilot to see the roll orientation of the drone. In FPV Mode, rolling your drone to the side will result in rolling the gimbal (and the horizon will no longer be straight).
Some camera drones include custom buttons on the remote controller that can be mapped to useful gimbal shortcuts. The 3DR Solo features two custom buttons on the front of the remote controller that are designed to be mapped to flight modes. Its remote also features dedicated gimbal controls. DJI remote controllers feature similar custom buttons that are most typically used by operators to control gimbal features (FIGURE 4.4). In dual-operator mode, the pilot and camera operator can each map their own custom functions to the custom buttons.
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FIGURE 4.4 Some camera drone remote controllers feature custom buttons that can be mapped to gimbal modes, flight modes, and other useful settings.
The DJI Inspire 1 is a common camera drone for dual-operator flights because the landing gear retracts, giving the camera an unrestricted 360° range for panning. The versatility in motion gives the gimbal additional modes of operation, and custom buttons become extremely useful for accessing features that are used often.
I like to configure my Inspire 1 custom buttons so C1 resets gimbal yaw and C2 toggles between Free Mode and Follow Mode (FIGURE 4.5). In typical use, I might fly in Follow Mode with the camera pointing forward until I see a subject I want to film. I will yaw the aircraft and pitch the gimbal until my composition is roughly where I want it to be. From here, I’ll sometimes press C2 to toggle from Follow Mode to Free Mode, which locks the gimbal orientation in place. This leaves me free to fly the Inspire 1 however I’d like to, and the camera orientation will never change. When I’m done, I can use C1 to reset the gimbal yaw so it’s facing forward again and press C2 to get back to Follow Mode.
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FIGURE 4.5 Mapping remote control custom buttons C1 and C2 for use with a DJI Inspire 1
Another commonly used custom setting is Gimbal Pitch/Yaw, which toggles the gimbal rocker wheel so it controls either pitch or yaw, so you can move the camera up and down or side to side (but not both at the same time).
If you need to control both pitch and yaw at the same time and don’t want to pilot the drone to control yaw while using the gimbal wheel for pitch, you can also tap and hold your finger down on the FPV display in the DJI GO app (FIGURE 4.6). You’ll see a white dot where you initially tapped and a turquoise circle at your finger’s current position. By dragging your finger around on the screen, you can move the gimbal in any direction, with its velocity controlled by the distance between where you originally tapped and your current finger position. This feature also works if you are using a DJI Phantom 3, but only pitch control is supported.
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FIGURE 4.6 In the DJI GO app, tapping, holding, and dragging is an effective way to change the orientation of a DJI gimbal.
Camera drones that do not have retractable landing gear have fewer options when it comes to gimbal operation, but software is starting to evolve to compensate for the lack of gimbal freedom in the yaw direction. Some drones abstract the experience to simple camera control; the actual aircraft orientation becomes irrelevant to the pilot, who needs only to think about what camera movements are required. These control schemes are still in their infancy in the consumer camera drone market but are sure to develop quickly as demand escalates for simpler interfaces.
Gimbal Speed
Obviously, the quality of camera movements is extremely important when shooting video. Most movements should be slow, smooth, and considered, with fast movements used only when necessary (for example, in an action scene, when you might want to purposefully create excitement or discomfort). Manual gimbal controls are still fairly simple, with position-sensitive rockers and wheels that allow for variable-speed movements. These have not yet been tuned to the complete satisfaction of serious filmmakers who are accustomed to using dedicated remotes for gimbal control but are a huge step forward when compared to some of the first attempts, which used simpler mechanical controls or buttons on a screen. These older interfaces were impossible to use to create pleasing movements.
Most single operators using DJI products elect to turn down the maximum gimbal speed (FIGURE 4.7). This is known as the maximum rate in the RC world. This decreases the movement speed of the gimbal across the full range of the control wheel, giving pilots more gimbal control but removing the ability to turn a camera quickly. I like to set mine at somewhere between 30 and 50 (out of 100).
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FIGURE 4.7 DJI GO allows pilots to limit the maximum speed a gimbal can move.
Dual-operator setups also support advanced customization of gimbal control, allowing for the control rates of various axes of movement to have curves applied to them (as opposed to a enforcing a linear response). These settings are usually labeled as “EXPO,” which is short for exponential curve, and are typically used to increase or decrease stick sensitivity near the center of a stick’s range and change responsiveness based on the selected curve when a stick is farther away from the center. Tuning EXPO is beyond the scope of this book, but there is plenty of online material that discusses EXPO and how to use it.
Automatic gimbal controls are starting to appear in smart flight modes and mobile apps released by both manufacturers and third-party app developers. Features designed for aerial videography use smooth, natural gimbal movements, with easing applied at the beginning and end of all movements. These new apps and flight modes will help new drone pilots execute the kinds of camera movements that experienced drone teams achieve through countless hours of practice and experience.
Gimbal Tuning and Calibration
Gimbals are complex systems and are comprised of a gimbal controller, inertial measurement unit (IMU), camera platform, electronic speed controls (ESCs), and brushless motors. Their components are similar to what comprises a drone, only instead of stabilizing an aircraft while flying, a gimbal stabilizes a camera platform. Gimbals work well only when they’re tuned to a particular configuration that includes the weight of the stabilized payload. Furthermore, balance is critical, and pushing the center of mass too far off any single axis can cause failure, sometimes resulting in a motor burning out.
Most gimbals currently in use either were designed as part of an integrated camera drone or were made specifically for one camera model (such as a GoPro) or a narrow range of camera types. These gimbals are typically pretuned at the factory and do not need any additional calibration or tuning to work well. However, a gimbal might sometimes need calibration, especially if it was bumped hard in a crash or during transit. Gimbals all ship with calibration tools, which range from being nearly unusable to being really simple to use.
There are two kinds of gimbal calibrations that aerial videographers might need to do in the field.
- Gimbal IMU calibration (usually just called gimbal calibration), during which a gimbal’s IMU measures acceleration and motion in all directions and declares, “I am now level.” This levels the gimbal and also prevents it from drifting. Early gimbals required special mounts to perform IMU calibration because the IMU had to be positioned exactly level, but newer gimbals are able to autocalibrate in a wide range of environments. The latest DJI camera drones can be auto-calibrated with a single tap, using the DJI GO app from a smartphone or tablet.
- Gimbal roll adjustment, during which an operator manually adjusts gimbal roll in order to level the horizon (FIGURE 4.8).
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FIGURE 4.8 Manually adjusting the gimbal roll position during a DJI Phantom flight via the DJI GO app
Most gimbals that are purchased ready to use can be calibrated by users, but more serious tuning usually requires a trip to the manufacturer for repair. Homemade gimbals can be built using a variety of third-party gimbal controllers like SimpleBGC (FIGURE 4.9). These gimbal controllers have entire guides dedicated to tuning, and one can spend many hours to ensure perfect operation of such custom setups.
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FIGURE 4.9 A BaseCam SimpleBGC gimbal controller and IMU
Gimbals and Filters
As I have mentioned, when using accessories such as lens filters on gimbaled cameras, you need to be careful that you are not upsetting the balance too much. There are a couple ways to help figure out whether a filter or other accessory will work well on a particular gimbal.
- If it’s made by the same manufacturer for use on an integrated gimbal, it is probably OK.
- If it’s made by a third-party manufacturer specifically for use on a gimbaled camera, it might be OK. Do a web search and read reviews to see whether others have had success.
In general, gimbals are built with a bit of latitude when it comes to payload weights and will support lightweight accessories, especially if they’re close to the centers of rotation. Because of mechanical advantage, a lightweight accessory far away from a center of rotation will require a lot more force to move than an accessory close to the center of rotation.
If you’re worried about gimbal balance, you can try to compensate by adding weight on the other side of the imbalance. Many hobbyists did this, for example, when adapting gimbals made for the GoPro HERO3 to work with the HERO4. They glued a single penny to the side of the gimbal’s pitch motor, which seemed to balance the 14-gram weight difference nearly perfectly. A word of warning: Making these modifications will likely void your warranty, so proceed with caution.