Posts tagged 'Focuser'

Package 1

Posted by on July 11th 2010 in 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:

Scope focuser upgraded

Posted by on September 10th 2008 in Astrostuff, Shiny new kit

I'd been considering upgrading the scope's basic rack & pinion focuser for some time. After various bouts of tinkering, I'd managed to reduce the "Synta Slop" image-shift in the original focuser as far as I could without major surgery, and was fairly happy that it was the best that I was going to get, the other option being to shell out £100+ on an upgrade that I couldn't justify.

Then I chanced upon a bargain Crayford-style focuser at a keen price from Astronomica. After a few emails to check that the thing would fit with the minimum of hassle, I took the plunge and ordered one.

And guess what? It's a little gem. OK, it's unbranded, but I'm not one for paying for a label. Silky-smooth action with no discernible image-shift, plenty of travel, enough friction to lift the D50, and the Skywatcher Auto-Focuser fits it as well. The only butchery required was the elongation of two of the mounting-holes in the scope OTA, but it was easy with the right kit.

 

 

I'll give it a thorough workout next time we get a clear night. Don't hold your breath, though - last night was the first (partially) clear one since we got back from Denmark, and the forecast says that it'll get worse before it gets better.

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