Antenna motorisation is being repaired

The parabolic antenna can be moved along two main axis,  Right Ascension (RA) axis and  Declination axis (DEC), using three different electrical motors.

Antenna motorization is composed of three motors :

  • mono-phase tracking motor, 25 t/mm, tracking 0,25°/min
  • three-phase clock motor, 180 t/mn, 30° mn, 45 t/mn, 6°/min, from -4h to + 4h
  • declination three-phase motor, 45 t/mn, 6°/min, -30° à 55°

The equatorial mouting allows targetting objects in the sky according to its two coordinates RA and DEC, then follow the object while the Earth is rotating, using a low speed movement toward west to compensate the rotation.

Antenna movements can be initiated by pushing buttons on the command panel or by giving orders from a remote site using an astronomy software application that sends the coordinates of the object to be targeted.


Software driver computes the movement orders to be transmitted for motor activation. Several speeds and directions are available.  Movements toward east or west at low or fast speed or very low speed tracking toward west ; and positive or negative declination movements.

Reductors gears are positionned between the antenna wheel and the motors like in a clock mechanism or on a bicycle to reduce the actual rotation speed of the antenna.


The above picture shows declination axis motor and reductor. They have been removed in order to be repaired.

Close view on gears covered by rust to be soon cleaned.

Command panel is displaying slow speed toward west direction activated by sofware remote control. Local-remote switch is in remote position and selector of local commands is in neutral position.

Absolute optoelectronic coders are connected to both rotation axis and transmit RA and DEC angles with a high precision (12 bits – 1/4096).

KK6MK-F1EHN-F6BSV interface card has been moved out of the rack during remote control tests. LED display reads Az for RA and El for DEC angles. A new interface card equiped with an Arduino micro controler is under development. This new card will replace the old one that could only handle four commands of low speed movements. It also includes more commands in order to be able to switch ON and OFF some radio devices.


View on the RA axis motor.


Ellyan, François and Steve from Electrolab « rescue team » came to work at La Villette and the antenna was soon well secured. This preliminary work was necessary in order to be followed by the motor reductors removal.


While opening the second motor reductor cover, a mixture of oil and water came out. The picture shows inside that the axis is invaded by rust.


The radiotelescope antenna is presently on security position aiming at the zenit.


The main declination axis wheels are being cleaned while rust is removed using a metallic rotating brush.

Intensive efforts have been accomplished in order to remove the cover of second reductor after removing appropriate bolts and using a dedicated extractor manufactured by the colleagues from Electrolab. Inside the cover one can see the Archimede screw that was connected to the primary declination moto reductor. The lower ring gear used to step-up the rotation with vertical gear was very difficult to remove from the rotation axis. A specially designed extracting tool has been used for removing the corona wheel.20190516_143949 - Copie

20190516_143921 - Copie

20190516_144117 - Copie

The 25 Tons extracting tool has been designed by Steve at Electrolab (Nanterre) mechanical department. This tool was successfully used to extract the remaining coronal wheel attached to the declination axis of the radiotelescope for further service of reductor to be repaired.

Night work for removing the declination moto-reductor
Extractor instrument specially built
Remaining hardware finally removed
Electrolab received the new parts for reductor restoration

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