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Last night I was autoguiding and DEC started periodic oscillations every 100 seconds or so while RA was fine at 0.5" RMS.? After I loosened the RA and DEC clutches a bit (I like to have them real tight) the vibrations went away and DEC was normal again.? Is this a known phenomenon, and if yes is there an explanation for it?

BTW This is the first time I counterbalanced in RA and I saw the RA error RMS cut in less than half leading to a total RMS of 0.6 to 0.7, sometimes dipping below 0.5.? It is major feat for me, of course I knew this is what everyone does to reduce the RA error.? This is with Ekos and OnStep with a 12" Newt and OAG with DIY SLWs.? I'm finally coming to grips with this modified G11S so I'm looking forward to repeating this on a regular basis.? My goal is to be around 0.5" total RMS.

BTW here's an image of M39 from 20 subs that I took while observing these oscillations, letting DSS select the best 50%.? I think this is a turning point for me.? It proves that Ekos on a Pi with a cheap and simple DIY OnStep controller with no gearbox and simple DIY SLWs performs fine.? Of course the hassle of putting it all together, which takes a major amount of testing time, to get there.? But for me it's part of the fun, and satisfying.

Sorry I'm struggling to download, upload and get a proper resolution.? Here's a link to a better version in an album, I hope this works.

/g/Losmandy_users/photo/266134/3266050?p=Created,,,20,2,0,0

I don't know what to tell you, but I had some spikes in Dec, and I tightened it up and they disappeared. I think that the clutches should be cleaned when they start slipping like this, or you can get the special ones from Michael that handle some grease.?

The onstep sounds like a great and satisfying project!?

Show a screen shot of PHD with these oscillations, and I can tell you.
It could be "forwards-lash" from a too tight worm mesh.
Or axis stiction.

Alan, I tried to search on “forward lash” and all I got was links to custom eyelash extensions !?

What physical cause are you describing with this term??
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Edward