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Atlas/EQ6 Back lash settings...???

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#1 Sky Captain

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Posted 29 August 2009 - 12:45 PM

Can someone explain these settings and how they affect the mounts operation?

These are the settings in my hand controller:
RA=0 02' 00"
DEC=0 02' 00"

Do I need to make any adjustments? I'm not doing any AP, just visual and a little astro-video, but that's only 2 sec. of integration.


#2 Skylook123



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Posted 29 August 2009 - 02:22 PM


I followed the user manual instructions and started with zero in both, then started with one axis and started looking through the eyepiece and performing short manual slews in each direction. If there was a jump in the view at either end of the slew, in either direction, I increased the backlash for that axis by a small amount. Eventually I got to something close to your numbers. HOWEVER, I found the manual incorrect in one sense; the manual said that too much correction was not a problem. For me, if I entered too much backlash, it wasn't apparent in the manual slews but it played havoc with GOTOs, where there would be an almost hysteritic wobble at the end if too much backlash was set. In one case I meant to enter 0 00' 07" in one axis, and I entered 7 00' 00" instead. Not much of a problem on the manual slew check, but on the next GOTO it went nuts at the end, slewing back and forth heavily until I hit the ESC key.

Contrary to my usual behavior, I'm avoiding the answer that I don't really know; what is the effect of the backlash setting coupled with autoguiding. Since I only do eyeball visual, I'm not sure if there is any influence of the backlash settings and the autoguiding inputs.

The last couple of updates to the firmware have left the HC backlash settings at 0 00' 00" in both axes; I haven't renewed the settings, but I've only seen any backlash issues when fine tuning alignment with a reticle eyepiece. In that case, there will occasionally be a detectable jump in the final (Rate=2 or 3) manual centering. Not often, though.

#3 Charlie Hein

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Posted 29 August 2009 - 02:23 PM

This is from the manual: "For better pointing accuracy, it is important that the backlash value is set to be equal or greater than the real amount of backlash between the gears. The default setting of the backlash is 10' 00" (10 arcmin. and 0 arcsec.)"

On mine I never did anything other than to make certain that the value in there was a non-zero number. One of the firmware updates a long while back corrupted the data in that register and if you didn't set the backlash to something other then zero you could find yourself with a mount that acted very strangely.

I'm sorry that I can't remember which way this went, but if the software uses this data to compensate for backlash at all times and not just when it's doing a go-to then it should be a simple enough thing to monkey with the values until the mount immediately changes direction (without a jerky motion) when you press the manual slew buttons and immediately stops when you release the button (instead of drifting until the gears catch up). If the software doesn't use that data during manual slews then this could become a little more involved.

My opinion is that if the backlash that you have isn't an issue that is already bugging you then I'd leave well enough alone. If you're not aware of a problem then you probably don't have one, or else it's small enough to be inoffensive.

#4 Skylook123



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Posted 29 August 2009 - 03:23 PM

It was that "equal or greater" comment that got my attention, so I was surprised when it behaved so badly when I screwed up the entry.

My experience is that the backlash setting is taken into account when doing manual slews. I just get too lazy (since every use for me is a fresh setup) to fool around with the backlash settings every time I upgrade the firmware and I keep forgetting what works best; for me, somewhere around 02' in each axis. When I have nailed down the setting, then even the small, low rate manual moves are smooth. If I leave it at all zeroes, then there is an occasional hiccup, but not objectionably so.

So, I guess that means I'm following your advice!

#5 hudson_yak


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Posted 29 August 2009 - 10:21 PM

Agreed, the manual doesn't seem right on that point and there seem to be changes in the behavior with firmware versions. I never had any problems with the settings at 0, and that's how I preferred it. For GoTos the mount does its own backlash take-up at the end regardless of those settings.

Affects of the backlash settings are most obvious if you have set a slow manual slew rate (eg. speed 1 or 2). You can hear a faster slew speed (seems to be something between speed 4 and 5) for a period of time depending on your setting before it resorts to your selected slew rate. For RA slew it only does this in the direction opposite the tracking direction, then takes up backlash in the tracking direction upon button release. For Dec slew it does the backlash take-up either way, with nothing upon button release.

So it seems like it's intended for guiding use, so you don't have to wait for backlash take-up when changing direction. I didn't see much point in it for visual object centering use, where I was using speed 4 or 5 anyway, so it didn't save any time.

An aspect of it perhaps unique to the SVP was the gear backlash wasn't all that consistent at all points on the worm wheel or pointing direction or ambient temps so there wasn't one good setting that worked well.


#6 Sky Captain

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Posted 30 August 2009 - 09:18 AM

Thanks guys!!!

I think that clears up my assumptions on its effects. I may just leave it as is, since its working great.

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