Fixed Mounts

Suspended or semi-fixed mounts are not suitable for free-flying, aerodynamic SFAP platforms if they jeopardize the stability of the platform, swing with the platform movements, or take too much room. The autopiloted model airplane and the paraglider (see Chapter 8) feature fixed mounts, because they fly too fast for suspended rigs. Also, a modular plug-in mount would not make sense for free-flying platforms, as it could not be attached after launching.

Two problems need to be addressed for achieving sharp images with a fixed mount on motorized platforms: ensuring verticality or other intended angles of the images and avoiding vibration transmission from the motor. The powered paraglider (Chapter 8.5.3) is an aerodynamic platform with considerable accelerating force and rather variable flight attitude; thus, it calls for a well-damped, self-balancing camera mount in order to avoid heavy vacillations. Figure 7-16 shows the gimbal-mounted system constructed from a suspension staff pivoting on the flight-direction axis (roll) and swinging between double brackets in flight direction (nick). Two oil-pressure shock absorbers (model-making supply) ensure limited and slow swinging, which is especially useful regarding the fitful and jerky flight behavior of the drone. The camera is fixed to the swinging pipe by the tripod screw together with an aluminum bracket supporting a shutter-trigger microservo. Despite the gimbal mount, many instances happen during a flight when the camera is not hanging vertically, and many images turn out as low-oblique shots. This is best compensated for by repeated overflights of the area.

The paraglider is powered by a gasoline engine whose vibrations are inevitably transmitted to the mount and camera, making it difficult to achieve sharp photographs. Vibration absorbers are needed between flying machine, camera mount, and camera. Here, all joints between motor and motor bracket and between frame, shock absorbers, mount, and camera are furnished with small rubber grom-mets. This multiple damping has proven to allow focused images in spite of the motor vibrations, although the number of blurred images remains considerable. As the motor revolution speed and flight attitude change during the flight, so do vibrations, and complete absorption would require much more sophisticated cushioning.

FIGURE 7-17 Foam-padded DSLR camera (Canon EOS 300D with 28 mm Sigma lens) fitted into the body of the autopiloted model airplane shown in Figure 8-42. Port (left) side of plane removed; camera lens pointing through hole in the bottom. Photo by C. Claussen.

For a model airplane, room in the hull is usually too confined for a gimbal mount with pan and tilt functions, so verticality of the images depends on the ability to keep the flight attitude steady. Figure 7-17 is a view into the body of der Bulle model airplane shown in Figure 8-42. The existing hollow in the Elapor material was enlarged to accommodate the DSLR camera damped with foam rubber. The camera is triggered via an electronic shutter release cable by the onboard computer in a pre-defined time interval, which may be adjourned if a chosen tilt-angle limit is exceeded (see Chapter 8.5.2). The camera battery is replaced by a connection to a larger 11.1 V battery that also supplies the electric motors and GPS/INS; this has the advantage of better power management, fewer charging tasks and accessibility of the battery from the airplane cockpit.

Electric motors as used in model airplanes do not cause extreme vibrations if they are well balanced. Because of the appreciable weight of the camera, the foam padding is sufficient to avoid propagation of motor vibrations; however, the smaller airplane with the lightweight compact camera (see Fig. 8-42) is somewhat more prone to vibration-blurred images.

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