Alt-azimuth Mount of the 110 cm Cruxis Telescope (Part 1)

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Design and Construction of the Alt-azimuth Mount (Part 1)

Ground board

The ground board is a 1000 mm (39.4") diameter 18 mm thick plywood disk with the following add-ons:

Three 32 mm track rollers on which the drive board will rotate, positioned exactly above three 76 mm (3") diameter feet.
A central 25 mm (1") bearing positioned exactly in the center of the ground board.
An aluminum strip on the side of the disk that will be the driving surface for the azimuth rim drive.

Weight is 10.6 kg (23 lbs); this could be reduced by making some cut-outs (not sure whether it will be worth the effort).

Drive board

The drive board is a 1000 mm x 1150 mm rectangular double layer (36 mm thick) plywood plate:

Four bearing assemblies for the altitude trunions - one of them is driven by the altitude servo motor. The azimuth rim drive has a tensioning device for controlling the friction of the rim drive.
For more details on the motor drive system see the motor drive page.

Four steel beams (60x20x2 mm rectangular profile) add sufficient stiffness for the 200 kg (450 lbs) OTA:

Bottom view of the drive board with the ground board and the 4 castors used for rolling the telescope:

Remove the castors... and the drive board becomes a very low profile altazimuth platform for a huge telescope.

The four 160 mm (6.3") castors provide plenty rolling capacity for a 270 kg (600 lbs) telescope. The castors can be attached and removed with large knobs.

Weight of the drive and ground board combined is about 50 kg (110 lbs), to which the castors add another 10 kg (22 lbs). The weight could be reduced by making some cut-outs in the plywood, but I'm not sure whether it will be worth the effort.

Drive board Finite Element Analysis

A finite element analysis of the stiffness of the drive board has been executed. The design goal was to limit the maximum deflection to about 0.2 mm (0.008") for the 200 kg design weight of the OTA.
Finite Element Mesh of the drive board of the 110 cm telescope. Deflections are magnified 300 times.

Finite Element Mesh of the drive board of the 110 cm telescope. Deflections are magnified 300 times.

Deflections of the drive board of the 110 cm telescope. Deflections are magnified 300 times.

Stresses of the drive board of the 110 cm telescope. Note the action of the steel stiffeners.

Finishing touches

The finishing touches and the operational mount are shown on the Alt-azimuth Mount Design and Construction (Part 2) page.