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The new Alt-AD7 mount from Eckhard Alt arrived finally summer 2008. It is capable to guide about 100kg of equipment. It is filled with proven and modern technology, but without any electronic chip inside. The controller and ports are completely kept outside as it will be described later.

Teeth count in RA = 270
Teeth count in DE = 160
Harmonicdrive gears RA/HDUF70BL3 = 1:70 (germany)
Harmonicdrive gears DEK/HDUF100BL3 = 1:100 (germany)
Escape stepper motors = P530 (switzerland)
= 100 full steps/turn (3.6° step angle)
= 200 half steps/U
= 3200 micro steps/U

Old Controller = Dynostar/Parameter:

Trackingfrequenz = ((Teeth) x (gear/ratio) x (half steps))/(starday)
RAslow = 270 x 70 x 200 /86164 = 43.869829627222505918945267164941
DEslow = 160 x 100 x 200 /86164 = 37.13848010770159231233461770577
RAfast = 700 ; 16x
DEfast = 594 ; 16x
Set Gearing RA = 270 x 70 x 100 x 64 = 120960000
Set Gearing DE = 160 x 100 x 100 x 64 = 102400000
Stepsize = 1/32
Acceleration = 2
Corrfactor/Autoguiding = 1.1825
Voltage = 12V

In the observatory installed Controller = F2 Astro Elektronik Koch

The mount from the back with the locking/slide coupling wheel for the RA axis on the right side. On the left side two counterweights, made of stainless steel (12.5kg each) are visible. They both balance approximatively 40 to 50 kg of equipment.

The DEK axis is normally fixed with an imbus screw and sold in that way. For a little bit more easier handling I modified it with a small selfmade handle, which was permanently fixed with metal glue into the original screw. The top handlepart is fixed by a click on mechanism and may be replaced during goto actions in order to allow the free passage of the gearbox.

The Alt-AD7 is placed on a special adapter (made by Beat Kohler, switzerland) and screwed to the concret tube.

The diameter of the concrete tube is 300mm and at the top 160mm (this smaller part is 250mm in lenght, measured from the adapter plate). The large gearbox of the mount in RA requires this shape of tube and space, as seen in the picture. In order to carry the new Cassegrain it was extended by 700mm.

Three telescopes are mounted on the Alt-AD7 and fixed on a selfmade adapterplate (B.Kohler).

The view from the front.

The view from the back.

The adapterplate was fixed by 6 screws to the heavy metal adapterbar of the Alt-AD7. The overall weight was balanced on the top of the RA axis.
Any various loading on this modifiable adapterplate is thereby adjustable.

The halpha telescope ED100 is freely adjustable fixed in slide tracks and may be even occasionally replaced by other setups.

The same holds true for the Intes-MN61 main telescope and even a cassegrain telescope (300-400mm mirror) may possibly replace in the future the MN61 on this adapterplate.

The handbox of the FS2 controller. The electronic is all included in an external FS2 ontroller made by M.Koch germany. In case of possible elelectronic failures I would have to replace and transport only this small box and not the whole mount.

The two motors inside the Alt-AD7 mount are directly controlled from the outside located FS-2 controller, a handbox and by the serielly linked computer.

And in case of visuell observations here are the tools i.e. in RA... very nice manufactured by Mr. Alt.

The periodic error is about +/-4 arcsec measured in a warm summernight including the seeing of about +/-2 arcsec at its maximum. It is appreciable by comparing the peaks after two turns of the screw in the gear (2 x 320sec/one turn = 640sec). The RA values are corrected for the declination value of the tracking star.

The lower graphic shows the result of the first autoguiding test, where the PE is regulated almost down to seeing. It is remarkable that, due to the harmonic drive gears in the mount, no backlash had to be considered in RA and a minimum value in DE in the parameters of the software K3CCD!

After the corrections for seeing and the deklination of the tracking star, I assume finally an actual periodic error of the noval Alt-AD7 = +/- (2 - 3) arcsec


...and at the day of installing the new mount, I was visited by about 40 storks as seen in the sky.

Some pictures during the production of the Alt-AD7... kindly provided by Eckardt Alt and Rene Rogge..

measuring of central axis error

cutting the toothed wheel

cutting the RA locking tube

the error free harmonic drive