FTF3545 Motor drive.

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Some of the motor focusing drives use the larger diameter of the bright section next to the 2nd coarse adjustment knob. [Arrowed] This requires the removal of both focuser knobs and a substitute driving pulley fitted to the shaft. It also robs the user of manual focus adjustment.  

I felt the need to retain manual adjustment until actual practice proves otherwise. Where to hang a motor bracket which would allow manual and electric focus adjustment? A position which would not require the removal of the pretty adjustment knobs? 

The parallel section nearest the black pinion housing looks promising. Rather smaller than the the other cylindrical section, at only 28.5mm Ø x 9mm wide, but still usable. Two immediate problems emerge: Any clamping system would have to be split, or rather, hinged. Otherwise it could not go over the knobs. So a rectangular plate, cut down the middle, will be hinged, by a bolt, at the top of each strip.

At the bottom, a tension bolt will have to clamp it to the bright section of the pinion housing. While I could drill the two parallel plates edgewise, for a long bolt, I'm not sure that wouldn't weaken the plates. A pair of small, projecting studs, drilled for the long clamping screw might be preferable.

There was also the rather large [30mm] overhang beyond the stubby motor shaft to the middle of the fine focusing knob. This meant that the motor must be pushed well outboard of the main supporting plate. Though a stepped timing pulley extension would be possible it risked a gyrating drive pulley.

At first I saw the motor's own mounting plate as a potential site for the hinge pins of the main split plate. Now the hinge pins would have to be carried back to the main supporting plate with pillars supporting the motor plate. The hinge pins are merely supportive until the bottom clamping screw is tightened. A top clamping screw could easily be substituted. It just needs a large enough gap between the plates to clamp firmly onto the pinion housing without closing the gap. Some sort of packing is essential to avoid marring the finish.

After a series of trial positions I favour the motor lying "on its side"  relative to its own mounting plate. Any other position blocks access to the pinion brake thumbscrew.

While it's true that the motor becomes the effective brake I want to retain the pinion brake in case it is ever needed. Any braking by the motor must be applied via the [deliberately] slipping clutch of the drive belt on the slow motion knob. Though I can't imagine slipping is very likely with a toothed belt running over the teeth of the slow motion knob.

I am quite tempted to count the teeth on the gold, fine adjustment knob and work out the pitch for a positive drive. 36 teeth. Which makes the tooth pitch much nearer 3mm than 2mm. 33xPi/36 = 2.7  It might be worth pursuing a 3mm pitch drive belt and pulley. Though I can't believe it is at all critical.

Click on any image for an enlargement.

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