Slotless, direct-drive motor for Canarian telescope13 August 2020

Schaeffler has provided a rotating direct drive motor solution to a giant telescope located on La Palma in the Canary Islands.

Nowhere else in Europe is the night sky so dark and clear as it is when viewed from the Roque de los Muchachos ridge on La Palma, which rises to a height of almost 2,500 metres. This offers professional stargazers ideal research conditions thanks to the Atlantic island’s extremely low levels of light pollution.

One of the dozen observatories there is the 36-reflector, 10.4m Gran Telescopio de Canarias (GTC), which was opened in 2009 at a cost of 80 million euros.

Giant telescopes such as the GTC operate with extremely high precision. Scientists observing the stars at night or in the early hours of the morning, rely on long exposure times, which means the telescope must be able to move with millimetre precision to compensate for the earth’s rotation, which is challenging given the size and mass of the telescope.

Schaeffler Iberia contributed its specialist engineering expertise in industrial drives to this latest project on La Palma and was involved in developing an instrument rotator for one of the GTC’s focal stations, known as the Cassegrain Focal Station (CG-Set). IDOM, a Spanish company that provides engineering and architecture services, was commissioned to develop this new CG set. Due to a positive experience during its long-standing collaboration with Schaeffler Iberia in various projects, IDOM decided to involve Schaeffler in the development of the instrument rotator drive.

The instrument rotator controls the focal tracking and rapid positioning system that rotates the two-tonne telescopic camera with evenness throughout the entire observation in order to ensure its perfect alignment with the heavens from start to finish. In this specific case, Schaeffler’s special drive solution not only had to ensure the system’s ability to precisely position the camera and regulate its speed, but also had to feature a compact, lightweight instrument rotator.

Schaeffler devised a special solution for the telescope. A segmented, slotless RMF torque motor was developed for the drive of the instrument rotator. Assistance was also provided by Schaeffler during the mounting process in order to determine the motor’s control parameters. The direct drive from Schaeffler Industrial Drives is characterised by highly dynamic yet very even motion, which also takes place with a high level of energy efficiency. The special motor, which is more than two metres in diameter, was developed and built based on a proven drive concept from machine tools for grinding operations that was adapted for the telescope.

This innovative solution also has other advantages. The segmented design of the motor reduced the costs of transportation and mounting. Furthermore, the relatively compact design facilitated the installation process and also helps to optimise the overall system’s performance and maintenance. A particularly important advantage is that only the affected segment – rather than the entire motor – must be replaced when servicing is required.

William Dalrymple

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