Package 1

Posted by @ 5:13 pm on Sunday 11th July, 2010.
Categories: Astrostuff, Making stuff
Tags: ,

You'll recall that during my previous observing session the link between my focuser and my SkyWatcher Auto-Focuser stepper-motor broke. Here's a pic showing the setup, the link is the 2-part ally gubbins that links the drive-shaft of the stepper-motor (on the right) to the shaft of the focus-adjuster (on the left):

Here are a couple of shots of the offending article:

It works in a peculiar way... the small end is attached good and proper to the shaft of the focus-adjuster by means of a grub-screw that clamps onto a flat on the shaft. No problems there. The attachment to the drive-shaft of the motor, however, is rather odd. It works by friction, using an internal O-ring that is compressed around the shaft by screwing together the two parts of the link. It doesn't like changes in temperature (too warm and the O-ring deforms and spins, too cold and it contracts and doesn't grip tightly. Oh, and there's always some flex and hence backlash due to the "flexible" nature of the O-ring/shaft connection. It was destined to fail, and indeed did so.

So, a better-engineered solution was required. Something so simple that a child could use it.

Step forward Package 1. This contained a good-old-fashioned Meccano 4-hole brass coupling:

As supplied, the fit to the focus-adjuster shaft was perfect. The motor drive-shaft, however, has a larger diameter, so I had to run a drill-bit half-way down the coupling to open it up a tad. From then on, fitting it was child's play, using proper screws to attach to the flats on both shafts.

Now it's a good and solid link, just as it should be, with no chance of slippage and no backlash due to the motor torquing itself against any resistance from the focuser.

In short, it's a proper job:

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2 Responses to “Package 1”

  1. Ian Aiken says:

    Great advice! The exact samething happened to mine, I was just about to get out the metal epoxy and do some heavy handed gluing, now I dont think I need too! Cheers.

  2. BG! says:

    @Ian Aiken - Such simple fixes are usually the best. I don't understand why designers create complex solutions to simply-solved problems.

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