EQ6, PHD and the 10.2 sec period

[Mike]

Why don't you consider the belt drive mod?

[MarkS]

Have they changed the gearboxes back to the older ones?  Your graph looks like the pre white mount.

I've no idea whether the gearboxes have changed.  But I do know my NEQ6 one is different to and substantially noisier than this EQ6 one.

Thanks for the belt link.  I see it retains the 12:47 gear ratio.  There's a good argument for installing a 12:48 belt kit as long as I never want to drive it from the handset again.

But before doing that I want to see how just far I can push the EQMOD PEC approach.  I think I can get sub 0.5" RMS guiding using a carefully prepared PEC file that works around the limiting assumptions built into the coding of EQMOD's PEC routines.

[Rocket Pooch]

Mark,

I was looking for this page last night, it has a set of EQ6 PE measurements and the measurement dates, you will see why I think they have changed something.

http://demeautis.christophe.free.fr/ep/eq6.htm

And here's a bit list

http://lambermont.dyndns.org/astro/pe.html

[MarkS]

Yes, some of those pre-modification graphs look very similar to mine.

[MarkS]

I've reached the end of the road now regarding PEC.  Two successive PE charts are not sufficiently close to be able to apply any kind of useful PE correction.  Here's a chart showing two successive runs of 6 worm cycles starting at exactly the same place (in terms of motor step count).  Vertical axis is arcseconds, and horizontal axis is motor step count.



The graphs don't lie on top of one another.  Here's a closer up view of 1 cycle:



In some places they line up but in others there is a slight lag.  I'm sure the wobbly idler (transfer) gear is partly to blame.  I've tried generating numerous PEC charts in a spreadsheet but simulation shows there would be almost no improvement in guiding performance.

So I now have an EQ6 belt kit on order.  Thanks for the BeltingOnline link Chris!  

To be honest I don't expect much (if any) difference in overall peak to peak periodic error since I can't imagine that the manufacturing tolerance on the toothed pulleys and toothed belts are precise enough.  However I do expect that the superimposed 10.2 second gear tooth error will disappear and so the remaining periodic error will be much easier to guide out.   If I get no improvement then at least this mod is reversible.

[MarkS]

Wow! The belt kit has arrived already, despite the beltingonline website saying there is a lead time of at least 3 weeks on this kit.

I might be able to find time to fit it at the weekend and then begin testing.

[Mike]

I'm very interested to hear what difference this will make.

[MarkS]

I'm very interested to hear what difference this will make.

You and me both!