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I looked again at driving the long throw, 2" helical focuser with the Skywatcher gearbox motor. At first sight seems impossible. The ends of the focuser move 20mm in and out. Perhaps suggesting that a belt drive would be impossible for a fixed motor. 
Then I noticed the knurled focusing ring is also 20mm wide. It just needed the motor [timing] pulley to be in the correct position to align the drive belt with the knurled ring. The belt would then use the full width of the knurled ring as needed without falling off the sides.
I mounted the motor on a bit of scrap aluminium, angle profile. This was needed to get a bit more height for clearance over the etalon housing and focuser assembly. Which the supplied bracket could not achieve.
The alu. motor bracket is held onto the sturdy, AOK Swiss, rear etalon adapter with two 64mm stainless steel, screw clamps. A perfectionists could easily drill the adpater and bolt or screw the bracket on. Avoiding swarf getting into the optical system would then be a high priority!
The long screws could easily be replaced with suitable threaded pillars. Or some sort of tube could be employed to house the screws for a neater arrangement. Nyloc nuts would provide extra security. Or just double up ordinary nuts and lock them together with a spanner/wrench.
The alu. motor bracket is held onto the sturdy, AOK Swiss, rear etalon adapter with two 64mm stainless steel, screw clamps. A perfectionists could easily drill the adpater and bolt or screw the bracket on. Avoiding swarf getting into the optical system would then be a high priority!
The long screws could easily be replaced with suitable threaded pillars. Or some sort of tube could be employed to house the screws for a neater arrangement. Nyloc nuts would provide extra security. Or just double up ordinary nuts and lock them together with a spanner/wrench.
It works perfectly with a 20T timing pulley and 280t 2GT timing belt. A 270T if available belt could achieve a lower profile. I tried a 16T pulley but it was a bit slow. It takes a little over a minute to go from one stop to the other. If different speeds or ratios are desired then larger or smaller motor pulleys could be chosen. The supplied, steel, motor bracket has adjustment slots for the mounting screws. So only plain 5mm holes are required in the angle bracket.
Those with the necessary funds could substitute the Skywatcher DC motor for a stepper motor and control system for repeatable focus position.
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