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 Post subject: Wobble with OAG
 Post Posted: Tue Mar 07, 2017 10:28 pm 
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Hi - I already have a 1600mc-cooled for imaging, and today bought a 120mm-s and OAG for guiding.

I'm having problems with getting the X2 driver to work (lots of timeouts), but am also having problems with the OAG.

The connection to the guide camera is very secure perpendicular to the direction of the telescope , but there are noticeable movements (~1mm) parallel to the telescope. I haven't tried guiding with this yet, but previous experience would say that this level of movement would not yield a good result.

Not sure if I'm doing something wrong? I tightened the screws to set the focus and prism depth as tightly as possible.

Any suggestions greatly appreciated.

Thank you,

Colin


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 Post subject: Re: Wobble with OAG
 Post Posted: Fri Mar 10, 2017 9:59 am 
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Hi,mcgillca.Thanks for feedback.
"getting the X2 driver to work" , I don't understand what are you talking about, could you explain?
movement of oag, Is the screw loose?

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 Post subject: Re: Wobble with OAG
 Post Posted: Mon Mar 13, 2017 10:27 am 
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Hi - there are two separate issues.

One is related to getting the X2 driver (software that allows your cameras to work with The Sky X from Software Bisque) to work properly on the Raspberry Pi - currently there are timeouts every few minutes - see this thread.

viewtopic.php?f=17&t=6862&start=10

The second is more fundamental - as I described in my post, the connection from the OAG to the guide camera is on a stalk, fixed to the main body of the OAG via two thumbscrews.

Unfortunately, with this design, it allows movement perpendicular to the thumbscrews (~ 1mm). I haven't had the chance to use this yet, but I would anticipate that this will cause differential flexure between the guidecamera and the main camera, which will mean that the guider will not do a good job keeping the mount pointing to the right position - I might be wrong, but I've had previous experience of this even when the connection appeared to be absolutely rock solid.

If the weather ever improves here in the UK, I'll gather some data to investigate.

It is possible I've missed someway to remove this movement - I'm sure you have tested this out too - if so, it would be great to know.

Thank you,

Colin


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 Post subject: Re: Wobble with OAG
 Post Posted: Thu Mar 16, 2017 8:54 am 
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Thank you for explaining. I will ask our engineer for help :)

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motto:
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Don't know manners, can't be gentle;
Don't know meaning behind the words, can't understand man's heart.


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 Post subject: Re: Wobble with OAG
 Post Posted: Fri Mar 17, 2017 2:56 pm 
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:oops: Well, I might have to eat my words here...

I tested this on Wednesday night. I measured the differential flexure between the camera and guidecamera, and this is essentiallly zero, and this despite having a USB cable and a guide cable.

I found that stacking 20 x1 minute images (without aligning the subs) only increased the size of the stars (FWHM) from 2.2 to 2.4 pixels (about 4.6 to 5") - my scope has focal length of 350mm, so relatively large pixel scale.

So looks like although there is movement of the camera, there is sufficient restraint to stop any serious issues, at least for a small guide camera - I suspect that this would not be true if anyone e.g. used a cooled camera.

I think though, that if your engineer could design out the wobble, it would still be a good thing - though I do like the very compact size of the OAG - it allows me to keep the OAG on the scope in its case.

I may try out with a longer focal length scope and see if this conclusion still holds with more demanding guiding.

Colin


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 Post subject: Re: Wobble with OAG
 Post Posted: Sat Mar 18, 2017 8:01 am 
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Joined: Thu Sep 10, 2015 9:57 pm
Posts: 14
Sam I bought one from ZWO a few weeks ago.
I drilled a hole on guider carrier and the body of the OAG, and added two grub srews to take out the wobble, if you added this to your production it would make a big difference to how stable the unit would be.
cheers
Clive.


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 Post subject: Re: Wobble with OAG
 Post Posted: Sun Mar 19, 2017 9:13 pm 
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I was thinking that if the existing thumbscrew and grub screw were moved slightly off the center-line of the post then they would apply not only force to lock it in place but they would force the post against one side of the supporting structure.


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 Post subject: Re: Wobble with OAG
 Post Posted: Wed Mar 22, 2017 9:05 am 
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elken2004 wrote:
Sam I bought one from ZWO a few weeks ago.
I drilled a hole on guider carrier and the body of the OAG, and added two grub srews to take out the wobble, if you added this to your production it would make a big difference to how stable the unit would be.
cheers
Clive.


we will add one screw to one side of the OAG to avoid wobble problem

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 Post subject: Re: Wobble with OAG
 Post Posted: Thu Mar 23, 2017 8:12 am 
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I actually added one screw to the part that is guider holder and one screw the part that is on main OAG body to stop post from woobling both ends :)
cheers
Clive


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 Post subject: Re: Wobble with OAG
 Post Posted: Fri Apr 07, 2017 6:17 am 
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elken2004 wrote:
I actually added one screw to the part that is guider holder and one screw the part that is on main OAG body to stop post from woobling both ends :)
cheers
Clive

That's a very good news! have a nice day.

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ZWO | Product Manager
Location:lon=120.6 lat=31.3
SuZhou China

motto:
Don't face one's fate, can't be a real man;
Don't know manners, can't be gentle;
Don't know meaning behind the words, can't understand man's heart.


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