Gemini-2 and Gemini-1 Telescope Mount Controllers
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Adapting to Mclennan Gearboxes
By Hilmi Al-Kindy
Please note that the three different motors that Losmandy sells all have different shaft diameters. Please measure the shafts of the motors you intend to use, and order the correct McLennan pinion gear to fit. The High toque motor shafts are 0.125 inches in diameter.

OK, in the interest of benefiting others contemplating upgrading their G11 gearboxes to McLennan gearboxes, I have compiled a shopping list of items to make the transition to these gearboxes as simple as possible. The reason I am posting this shopping list is because I have found that the information available on the web is mostly out of date or provides for a less than ideal solution (for example wrapping tape around the screws to make them a tighter fit).

First of all, you will need to purchase the gearbox. I ordered mine from RS Components. I got two, one for RA and one for DEC. The idea was that if I upgraded both gearboxes then I it is simpler to set up in the Gemini controller
McLennan P5-G11

Next I ordered the gearbox adapter kit on this link. This kit gives you a pinion gear that already has the 3mm bore needed for the latest high torque motors that are fitted on all current models of the G11. DCMotor Gearbox adaptor kit, 12.5:1 - 125:1

3/16" external diameter 0.014" wall thickness brass or aluminum tubing. This can be obtained from many hobby stores. I got mine from ebay. The problem with this is that it is a slightly loose fit, so you will need Red Loctite to make sure it holds.

Red Loctite, I got some other brand of this since I couldn't find red Loctite in retail in Oman.

A 4 - 40 drill and tap set, obtainable from most hardware stores. This is so that you can use the original screws that came with the motor for a secure fit.

A 4 mm drill bit to be used to widen the mounting holes on the ears that stick out of the sides of the gear box.

A Dremel tool with a cutting disk will be useful for cutting the tubing.

Steps for installation:
1) Drill out the mounting holes that stick out of the sides of the gearbox to 4mm. Then clean thoroughly before proceeding to next step so as not to get the gear box innards dirty.

2) Disassemble gearbox cover, taking note of the position of the parts just in case it falls apart and you have to put it back together.

3) Locate the two screw holes used to mount the motor onto the gearbox. Drill and tap these using your drill and tap 4-40 set. This will allow you to use the original screws that came with the motor. Make sure you do this with the plate you are drilling far from the gearbox so as not to drop metal shavings inside. Clean thoroughly when done.

4) Re-assemble gearbox, use Loctite on the screws to prevent them from getting loose int he future.

5) Cut a bit of the brass tube long enough to cover most of the output shaft from the gearbox. This should not be so long as to touch the brass bearing at the base of the shaft. Clean this cut piece of tube thoroughly and file away any burs resulting from the cutting process.

6) Put the sleeve on the gearbox output shaft and glue in place using red loctite, dont drip any into the bearing or you might ruin the gearbox. This tube is used to increase the diameter of the output shaft for a snug fit in the coupler.

7) After curing the glue, drill out a small hole over the flat on the output shaft. This will help secure the coupler by giving the grub screw something to latch onto.

8) Now assemble everything and change the mount type to MI 250 on the Gemini unit (assuming you have changed both)

Pictures coming soon, this website will help you visualize what I said, but it does not match my instructions as I have made some modifications to the instructions.

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