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Mar 29, 2011, 05:57 PM
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Onboard Camera. Elimination of vibration and swinging.

Onboard Camera.
Elimination of vibration and swinging

Three types of undesirable oscillation may be singled out in the radio-controlled model, i.e. a) vibration, related with operation of the engine and mechanical schemes; b) jolting, related with the air flows; c) swinging of the model while maneuvering.

Vibration of the helicopter model is the strongest. Seeking for reduction of vibration, it is possible to adapt the shock-absorbers, which are assigned for industrial use. Pay attention to the optimal load, which is usually indicated on such shock-absorber.

It is possible to use the shock-absorbers, assigned for the automobile CD-DVD player, if a small photo-camera is installed. Usually small rubber shock-absorbers with the gel inside are installed in the players.

It is possible to make a sufficiently light shock-absorber out of two plates with the soft rubber, clutched between them; the plates are clenched with the help of the rubber rings from outside. If You are afraid that the rubber will get torn, install the freely hanging safety belts additionally.

Seeking for alleviation of jolting, the shock-absorbers, assigned for the undercarriage of the radio-controlled automobiles, are used. These shock-absorbers consist out of the spring and the pneumatic or oil piston. The freely swinging platform of the camera is underpinned with the shock-absorbers from the opposite sides.

The mechanical gyroscope is used for compensation of swinging. The camera is installed on the freely swinging platform. The heavy mechanical gyroscope is installed together with the camera on the platform. If positioning of the platform is evened with the help of the shock-absorbers, the gyroscope makes swinging more fluent. The effect of precession is the drawback of the mechanical gyroscope. The example of the effect of precession: the inertia pulls the camera to the left, whereas the camera deviates upwards. The gyroscope stabilize the camera efficiently, but it causes strong high-frequency vibrations through insufficient accuracy of production. If there is no possibility to produce the precisely balanced flywheel of the gyroscope, it is necessary to increase its mass and to reduce the revolutions of rotation. The mechanical gyroscope is an ideal solution for stabilization of the camera, if it is not needed to maneuver during shooting. The camera must be balanced in such a way so that the axle of the switched off gyroscope is strictly vertically positioned. If the camera is installed on the inactive object, for example - on the Dirigible balloon, the centre of the platform's mass with the gyroscope and the camera can be lowered for several centimeters downwards as regards the axles of the suspension bracket. The center of the mass must be brought nearer to the axles of the suspension bracket, installed on the movable object, for example, on the helicopter, otherwise the camera will be swinging during the maneuvers as a large and heavy pendulum (fluently, but for a long time). Efficiency of operation of the gyroscope depends upon the mass of the camera and upon precision of balancing. The platform with the gyroscope must be turned around in the horizontal position. If the gyroscope is tilted at the moment of turning around, the camera will also tilt through the effect of precession.

Stabilization of the video-camera with the help of the mechanical gyroscope (1 min 45 sec)

The radio-controlled helicopter is an apparatus, which is too light; it cannot secure ideal stability of the camera. Thus, still persisting vibration is eliminated with the help of the computer filter prior to showing the shot video-stills. The photo-shots with a long exposure rarely work well.

Choosing of the camera for amateurish shooting

Photographers and video operators frequently wish to fix a heavy camera (with a weight about three kg) on a model. For persons who set such serious standard for the image, I'd like to recommend a full-size plane with a live operator on its board. For shooting from a radio-controlled model, a manual camera with the weight up to 1 kg should be fit. If you, for example, remove a telescope from the tripod and hang it with a string, you'll not be able to watch the Moon independently on the price of the telescope (this is to explain figuratively why an expensive camera is not necessary).
The other widely spread objective is usage of sophisticated systems of stabilization hoping their irreproachable operation just after the installation. More reasonable way would be striving to the maximum simplicity of the construction combined with high reliability of it. A photographic camera does not require an active stabilization; it is sufficient to make series of tens of shots and then to choose the best of them. A helicopter needs a scrupulous adjustment of the model, elimination of vibrations in mechanisms and balancing of rotating units. A model of a plane needs good aerodynamics, good weather and correctly chosen speed of flying. However, the most important factor is an ability of smooth controlling of the model.

The following recommendations on choice of the video-camera for the radio-navigated model outflow from my experience:
1. It is necessary to record the video-signal on the board because in any case interferences occur even, if the best samples of radio-transmitters are used.
2. The video-signal should be recorded non-mechanically, i.e. on the Flash-memory card.
3. The wide-angle optics is necessary for better orientation at the locality according to the transmitted image.
4. Vibration of the camera is less noticeable, if the wide-angle objective-glass or "fish eye" objective is used.
5. The camera must be provided with the digital, but not optical stabilizer. I had a certain experience when the lens of the optical stabilizer had been vibrating more violently than the model itself. video:
(2 min 40 sec)

6. It is advisable to set the manual focusing and short exposure.

Choosing and modification of the helicopter for video shooting

The larger the model of the helicopter is, the more stable its flight is. The acrobatic models of helicopters can lift the amount of weight, which is equal to their own weight; however, the weight of the model must not be increased more than half as much again. If the weight of the model has increased half as much again, it is advisable to increase the length of the blades by 15%. The rotor with four blades is more preferable than the rotor with two blades. The profile of the blades must be asymmetric. The symmetric blades are necessary only for the 3-D flights; their efficiency coefficient is lower than the efficiency coefficient of the common profile. The speed of the rotor rotation must be lower than 3-D mode. Seeking for reduction of the RPM, the gear with the number of teeth, reduced by 15-20%, is to be fixed on the engine, as regards the acrobatic variant. Seeking for reduction of vibrations, noise and dirt, it is desirable to select the electric helicopter. The helicopter with the increased load, which does not perform abrupt maneuvers, can and must consume less energy than the acrobatic variant. While selecting the motor and batteries, attention must be paid more towards economy, capacity and weight than towards the maximal power, discharged during a short moment.

A particular attention should be paid to helicopters with several rotors (so called multicopters). As a rule, such aircrafts yield to an ordinary helicopter in some parameters, such as lifting capacity, mobility, and duration of fly. The listed imperfections are bound to a large extent with using fixed-pitch props; however, a probable alteration of the situation is expected in the nearest future. The advantages of these aircrafts include their good systems of electronic stabilization and autopilot for low prices; in addition, they can be more easily operated by a non-experienced pilot as compared to ordinary aircrafts, their exploitation and repairs are simple, they are more safe in a case of a crash and a camera may be placed in the center of the frame such an aircraft.

Many persons are very greedy in respect of technical parameters of a model: they wish it to cover the maximum possible distance on fly, to achieve the maximum possible duration of fly, to carry a large cargo, to have a nice body, to have the autopilot fit in any case and so on. Usually, a list of such requirements is in inverse ratio with the concept of "reliability", so the model will distinguish itself for poor controllability and stability.

Fall of the camera down from the helicopter
(0 min 14 sec)

The camera must be rigidly fixed on the body of the model, if acrobatic flights are performed. This video proves how strong acceleration can be at the moment of gyration of the helicopter. An ordinary camera was installed under the tail rotor; the carbon stanchion of the camera got broken at the moment of the tight turn. Of course, performance of such abrupt maneuvers with the camera is undesirable; however, the reliable fastening must be secured.

Aleksey Zaitsevsky, 2005-2010,
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