Small DC motors follow the stars at minus 84 degrees.

The maxon DC motor powered Dome C telescope in the Antarctic is constantly in use under some of the harshest weather conditions on Earth.

The Concordia Station (known as Dome C) research station lies in Eastern Antarctica at 3.2km above sea level, one of the coldest places on Earth. In temperatures of down to minus 84 degrees the University of Nice's Astrophysics Laboratory (LUAN) telescope has been in constant use in this inhospitable place 24 hours a day, 7 days a week.

The telescope is mounted on a motorised base (telescope mount) type 3600GTO produced by the US company Astro-Physics. The company develops and produces high-precision telescope mounts and has a wide experience in all kinds of application areas. Various units from the 900GTO and 1200GTO ranges have been in constant use in the Antarctic since the beginning of 2000. This trouble-free and continuous use is of great significance, as maintenance work is extremely difficult and very dangerous. This is because the low temperatures and inhospitable windy conditions make it almost impossible for the maintenance team to work outside and essentially impossible in the Polar night which lasts for six months. This means that the entire system has to run perfectly 24/7 for at least half a year.

It is easy to see why the reduction gearing is one of a telescope mount's key features. This is because it must be continuously manoeuvred, smoothly, without juddering so that the telescope can give a completely consistent view of a particular object in the sky. If not, the object quickly disappears from the telescope's field of vision, making it impossible to plot its trace without disruption. In order to "fix" the object in the field of vision, the heavy mount which weighs around 250 kg, must be motorised accordingly. Wally Piorkowski, Head of Production at Astro-Physics and himself a scientist, speaks from experience: "Because of their high reliability and longevity, Astro-Physics only uses DC motors by maxon for all its telescope mounts". The lubricant used in the motor bearings is ideally geared towards the extreme temperatures experienced at Dome C in the Antarctic. Once mounted, the DC motors from maxon require no more lubrication, but this would be almost impossible anyway, given the ambient conditions.

The motors also have coreless windings and Neodymium magnets to help deliver maximum performance in a compact construction volume. Graphite or precious metal brushes are used for the motors' mechanical commutation. Their linear characteristics make them very easy to implement in telescope mounts.

Every mount has two axes

One - the right ascension axis is set up parallel to the Earth's axis and allows the telescope to move across the Earth's equator. To be precise, the motor drives against the Earth's rotation so that the object in the sky appears fixed. The reduction gearing was developed in-house by Astro-Physics. The second axis, known as the declination axis, is arranged at right-angles to the right ascension axis and maneuvers the telescope intermittently at the object's angular distance to the celestial equator. The DC servo motors of both axes are fitted with 3-channel HEDS 5540 encoders. Orientation in any required direction is possible as the axes are offset at 90° to each other.

"We use maxon A-max DC motors for our smaller mounts and maxon RE 25 DC motors for the telescope mounts, as used in Dome C", continues Wally. The RE 25 motor offers maximum torque and power density in its class. "Another major reason for using maxon DC motors is the fact that they have no magnetic detent" he adds. Detent is described as the jerky, sudden movement that typically occurs with most iron-core motors. By contrast, maxon DC motors feature an ironless core which enables them to run detent-free, even at extremely low speeds. This is a basic requirement in a telescope mount.”

"Mounts are often bought separately from the telescope" explains Wally. "For instance, astronomical associations, colleges, institutes etc. buy telescopic equipment separately from the mount then assemble the two themselves."

 © maxon motor ag

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