FSQ-106 Focuser Modification

I am a big fan of the Starlight focusers and all of my scopes apart from the FSQ 106  have the feather touch focusers on them and I subsequently have a good selection of focus motors that are designed to attach directly to them. The FSQ 106 however when I purchased it did not to my knowledge have any kind of focuser available from this company and the focus motors do not really fit this scope. The only available retrofit focusers were for the older models.

First of all I did try with the smaller of the available stepper motors which did fit although the clearances were a little larger than I would like and making me suspicious that the shafts or gears would become damaged from poor alignment. On top of this the stepper motor could adjust the focus only when the OTA was between horizontal and 30°, any more and it just did not have the torque to move the weight of the draw tube with all the camera equipment on it. What I needed was a bigger motor with a better gear ratio to give the required torque for handling the weight which would be the MSM30 kit.

The problem with that however is that the clamping collar for the stepper motor is much larger than the shoulder on the telescope and the bore of the gear wheel is larger than the diameter of the smaller focusing shaft. The gear was easily bored out and a sleeve installed to reduce the bore from 4mm to 3mm before re-drilling and tapping the hole for the locking screw. I also manufactured a sleeve for the collar on the telescope so that the motor had the correct size of collar to clamp around. This was machined from solid aluminium bar to dimensions of 25mm ID 33.7mm OD and a length of 20mm. In addition there were also 2 holes drilled and tapped at one end for locking screws.

For the installation of the new focuser assembly the knurled knobs of the two speed focuser first had to be removed to expose the shafts and the collar.

The next step was to attach the modified gear wheel on to the central shaft. This had to be as far down the central shaft as possible without touching the outer shaft and the gear must be installed in this orientation to provide the correct alignment to the gear in the stepper motor.

The sleeve is then installed onto the collar at the base and the lock screws tightened to secure it.

Finally the stepper motor is dropped on and the collar tightened before connecting the cable.

With the focuser already at a native 10:1 reduction ratio this arrangement should reduce that even further to around 40:1 from the gearing of the stepper motor giving super fine focus adjustment for truly pinpoint stars!