Motor drive for the Astro-3 mount

Up one level

I bought the Lidl-refractor in December 2005. The purpose is to use it as a light-weight travel mount, and it served this purpose well under the 2006 solar eclipse. The pictures of the eclipse shown here was taken using this mount. The plan was to use a spare Vixen MT-1 motor to drive the RA axis in the same way as described by Carsten Arnholm here. However, the mount has been changed quite a lot since 2004, so I had to figure out some modifications to the recipe. The picture below shows the mount before modification. I started by removing the big chrome wheel that is used for turning the RA-axis. I also removed the clutch lever just to the left of the wheel.

I designed a motor bracket that will allow use of the mount at relatively low latitudes. I removed the outer cover and made a new bracket from a 2mm aluminum plate.

Brakett for MT-1 motor

Brakett for MT-1 motor

The arrows indicate holes for fastening bolts. These corresponds to the threaded holes in the worm-gear house of the RA-axis of the Astro-3 mount. See below - screws removed.

Screws removed.

A nut (M5) and a washer serves as support for the bracket.

Motor assembly fastened with 3 pcs. M4-bolts.

Motor assembly seen from the other side. We also see the contact for the Boxdorfer MTS-3SDI controller.


The construction can be tilted for latitudes between 8 and 90 degrees. Usable for most destinations. It should be possible to build it for all latitudes by bending the bracket towards the RA-axis.

Drift measurements were made using K3CCDTools. As seen from the graph, the periodic error is in the order of 90 arc seconds. OK for visual use and for eclipse photography, which is my primary use for the mount.

Parameters used for the Boxdorfer MTS-3SDI controller. These may have to be tuned.

Device = MTS-3SXX
RAMG = 11520
DEslow = 11.631772
DEfast = 308.000000
RAslow = 18.584095
RAfast = 308.000000
Corrfactor = 1.875000
Acceleration = 2
Stepsize = 1/64
DEpwm = 47.2%
RApwm = 47.2%
DElimit = 450
RAlimit = 450


The original grease used by the factory is more like glue. I decided to replace this grease. This is a fairly simple operation described here.

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© 2006 Odd Høydalsvik