The Dwingeloo Radio Telescope is mounted in such a way that it can move in two directions:
- in azimuth (= compass direction): a horizontal rotation of tower and mirror together around a vertical axis;
- in elevation (= height above the horizon): a vertical rotation of the mirror about a horizontal axis.
With the help of pointing and tracking equipment, the radio telescope can be directed at a position on the starry sky and during the observation the telescope continues to follow the star or the radio source by a continuous slow motion in azimuth and elevation.
During the building, the pointing and tracking equipment consisted of the pilot (coordinate transformer), pointing and tracking motors and the associated electronic control (servo system) and gearboxes.
The pilot or mechanical electrical coordinate transformer was an extremely advanced and vulnerable system of brackets, axes and gears. Together with a sidereal time clock, the pilot functioned as an analog computer and calculated how the radio telescope had to move with the rotation of the starry sky. The sidereal time was calculated with very accurate quartz clocks. In 1993, the pilot was removed from the radio telescope and his function was taken over by computers.
Pointing and tracking motors
The function of the pointing motors was to bring the mirror quickly close to the correct position in the sky. Thereafter the tracking motors automatically switched on to ensure the radio telescope accurately moved with the chosen point at the rotating starry sky. On several occasions, stronger tracking motors replaced the older ones.
The tracking accuracy of the radio telescope due to inaccuracies of the pilot, the electronic control, the gears and the deflection of the telescope together resulted in an average angle deviation of 0.05 degrees in the sky. In comparison: the moon takes an angle in the sky of 0.5 degrees.
In 2007, CAMRAS replaced all motors with one type of motor suitable for both fast pointing and slow tracking.
Azimuth drive equipment
The azimuth drive is located in the engine room in the control house. A large bull gearwheel with a diameter of 2.5 meters with spindle and bearing is fixed to the concrete foundation. Two small gearwheels (pinions) run around this sprocket, each of which was connected to the differential via its own gearbox. The differential distributed the forces of the pointing and tracking motor equally over the two pinions. The differential was replaced in 1966 by two torsion axes, which greatly benefited the zero-backlash of the pinions and the stability of the servo system. The pointing and tracking motor was replaced in 2007 by one motor. The original azimuth pointing motor has been preserved in its original position in the engine room.
A special oil circulation circuit with a pump ensures that all gears are lubricated with thin oil.
Elevation drive equipment
The elevation drive consists of two similar parts at the top of the tower. On each side a gearbox is mounted with the pointing and tracking motor (from 2007 one engine on each side). The movement is transferred to the mirror via two quadrant bull gears with a radius of 1.8 meters, which are attached to the frame of the mirror and with bearings on the two elevation axes. The mirror construction with very high torsion rigidity forms the mechanical coupling between the two axes. The power supply of the motors works as an electric differential.
Because all axes in the elevation drive are horizontal, oil bath lubrication is applied.