Tuck-in motor modification for the classical Losmandy GM8 equatorial mount

This is a tuck-in motor modification for the classical Losmandy GM8 equatorial mount.

Losmandy mounts are all well designed for easy service & maintenance. However, for those vintage mounts, their servo motors are extruding outwardly and making them to be easily bumped upon accidentally. Losmandy has manufactured tuck-in version of mounts nowadays, but there are no tuck-in modification kits available for users to install by themselves.

The tuck-in modifications for both GM8 & G11 are similar. The modification for the DEC of G11 is straightforward. With the tuck-in adapter plate, one can complete the modification via either the pulley transmission method (with two GT2 T48 pulleys & one GT2 belt 172mm in length, please see the following for more details.  https://www.printables.com/model/936574-dec-transmission-axes-cover-for-losmandy-g11t-equa ) or the  gear transmission method (via two 0.4 MOD T95 gears, one has center circle diameter 10mm, and the other has center hole diameter around 4.78mm).

However, the modification for GM8 is a little bit trickier, since the G11 tuck-in adapter plate will cause installed motors to interfere with the GM8 mount. One solution is to rotate (around the worm rotation center) the adapter plate upwards at least 15 degree, nevertheless , after the rotation only one cover screw can be applied (due to the interference between one plate fixing hole & one cover fixing nut) . Here I decided to rotate 18 degree.

Furthermore , the modification for the RA of GM8 involves dismantling the RA part & carefully drilling 3 extra holes (that are 120 degree apart around a  circle with 25.4mm radius, please see the photo for more details) on the original connector plate.

Note that a ball bearing (with outer diameter 16mm & center-hole diameter 8mm, thickness 5mm) is also selected & installed to provide better supporting strength & rotation smoothness.

Also, the rotation axis is made from a 8mm-diameter brass cylinder bar with 36mm in length. Lathe it to 4.78mm-diameter with 5mm in length & adjacent with 8mm-diameter with 31 mm in length.

So the following items are required:

• Brass rotation cylinder bar for each worm gear.

• 16x8x5mm ball bearing for each axis.

• GT2 T48 pulley: 2 are needed for each axis. One with 8mm center-hole diameter & the other with 5mm center-hole diameter.

• GT2 pulley belt: 1 is needed for each axis. Belt length is 172mm (or 86 teeth).

• Screw & washer: M3 screws & square M3 nuts are selected. The washer diameter is around 7mm. The length of cover fixing M3 screws is about 30mm.

Note: 

1. the axis-diameter of the reducer gearbox is around 4.7625mm, however, the diameter of the selected pulley center-hole is 5mm, therefore, some lining is required for perfect fitting. 3 layers of aluminum foil seems do the job.

2. It turns out that the first matching cover design (with only 1 fixing screw) can not provide enough strength to counter the motor vibration (due to the only 6mm-thickness adapter plate printed from PETG), a new design of tuck-in adapter & cover set, which will cover the whole tuck-in adapter area with 3 fixing M3 screws, is added.

3. A stiffer tuck-in adapter plate (8mm thickness) that supports M4 screws and nuts is added. However, to apply M4 screws & nuts, Some M4 threading or hole enlargement are necessary. The length of cover fixing M4 screws is about 25mm.

4. A updated tucked-motor base (version 3) is added This version applied two flange ball bearings (NSK MF148ZZ) on each side of the adapter plate.  It provided a more steady rotation of the brass cylinder bar for the worm gear.

5.  A cover with 20mm height is added. It is suitable for gear-drive modification and require 3 fixing M4 screws (20mm in length).