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Astrophotography and Sketching >> Beginning and Intermediate Imaging

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Clumpybug
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Reged: 12/03/11

LXD75 Autoguiding Problems
      #5755847 - 03/25/13 10:34 AM

Howdy folks,

I have a 8-inch Newtonian that I use with my Meade LXD75 mount. I try to autoguide using an Orion Starshoot autoguiding camera. About half the time it works great, but lots of times, it won't track in the declination direction. It almost always tracks in RA, but a lot of times, it simply won't even calibrate in the Dec direction. Sometimes even in the same session it will work for a while, then I'll go to a different part of the sky, try to re-calibrate, and the Dec direction is useless. My computer is communicating with the mount, it can move the mount in the Dec direction, and the weights are slightly unbalanced. I don't even know where to begin troubleshooting. Does anyone have any thoughts about why it wouldn't work?

Thanks


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Cliff Hipsher
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Reged: 12/31/08

Loc: North Chesterfield, VA
Re: LXD75 Autoguiding Problems new [Re: Clumpybug]
      #5755858 - 03/25/13 10:39 AM

C'mon Dude. I've already told you. If you do a drift alignment you do not need to guide the DEC axis.

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michael hester
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Reged: 11/28/08

Re: LXD75 Autoguiding Problems new [Re: Cliff Hipsher]
      #5755988 - 03/25/13 11:39 AM

The LXD 75 has a ridiculous amount of backlash in the DEC axis. Backlash is what happens when the worm gear doesn't perfectly mesh with the drive gear on a particular axis. It will never be perfect. The problem with backlash is corrections in autoguiding are so angularly small that it will take time for them to go through the backlash and your mount won't actually guide during that time. PHD still thinks it's sending guide commands and the mount is reacting. It can take up to 2 minutes to clear through the backlash. Here is what to do about this.

1. Watch PHD guiding's graph. In the tools menu click "enable graph".
1b. Activate guiding.

2. In the graph at the bottom find the minimum motion setting. It defaults to .15. This is frankly observatory quality guiding and you can't expect that on an LXD75 under most conditions. Set this to .5. My CGEM DX can't handle that strong of a minimum motion setting.
3. Set the maximum dec correction to 500 or higher. 150 will make it take too long to fix anything.
4. Watch the graph drift and wait for it to correct. You'll see the red line drift up or down. Once it corrects you're ready to shoot, this means it ate through the backlash.

Additionally you should do a drift alignment. The easiest way to understand what happens is to follow a guide I had for drift alignment with a laser pointer.

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/5423247/Main...


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JoseBorrero
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Reged: 09/04/09

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Re: LXD75 Autoguiding Problems new [Re: michael hester]
      #5755998 - 03/25/13 11:46 AM

Actually the best drift alignment is here: http://tinyurl.com/bnzll7z

is a ppt presentation easy to understand



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Clumpybug
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Reged: 12/03/11

Re: LXD75 Autoguiding Problems new [Re: michael hester]
      #5756015 - 03/25/13 11:54 AM

I know you already suggested DEC drift alignment, and I plan on trying the drift alignment, but since I've got an autoguider, I'd like it to work. Otherwise, what's the point of having one?

Michael, can I do this graph method or do the drift alignment the way you describe it without calibrating in the DEC direction? Sometimes it won't even get past the calibration stage.


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Cliff Hipsher
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Re: LXD75 Autoguiding Problems new [Re: Clumpybug]
      #5756072 - 03/25/13 12:19 PM

OK, so if you're having trouble with the guide package, why not contact the vendor? Same goes for the guide software.

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jgraham
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Re: LXD75 Autoguiding Problems new [Re: Cliff Hipsher]
      #5756120 - 03/25/13 12:42 PM Attachment (18 downloads)

I used an autoguider on an LXD75 for several years with veryy good results. Drift alignment is nice, but not necessary. I never use drift alignment, just the polar scope after making sure that the polar scope was aligned properly with the mount. As Michael described it is common for the LXD75 to have problems with backlash and gear lash, particularly with the dec axis. (The R.A. axis can be slightly east-heavy to reduce the problem with this axis.) Adjusting the gear lash is fairly simple and doing a Google search should give several good sites. OPT used to have a set of tuning notes on the LXD75 that described the process. Another trick with the LXD75 is that once the guider is calibrated apply dec corrections in only one direction, the gears are rarely tight enough to allow the corrections to switch back'n forth. If the response is sluggish you can also try increasing the dec% in the handbox or through Remote Handbox on your computer (part of the Autostar Suite).

My ol' LXD75 set up for guiding...


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zerro1
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Re: LXD75 Autoguiding Problems new [Re: Clumpybug]
      #5756137 - 03/25/13 12:49 PM

Quote:

Howdy folks,

I have a 8-inch Newtonian that I use with my Meade LXD75 mount. I try to autoguide using an Orion Starshoot autoguiding camera. About half the time it works great, but lots of times, it won't track in the declination direction. It almost always tracks in RA, but a lot of times, it simply won't even calibrate in the Dec direction. Sometimes even in the same session it will work for a while, then I'll go to a different part of the sky, try to re-calibrate, and the Dec direction is useless. My computer is communicating with the mount, it can move the mount in the Dec direction, and the weights are slightly unbalanced. I don't even know where to begin troubleshooting. Does anyone have any thoughts about why it wouldn't work?

Thanks




OK So I have two LXD75 mounts and fought the battles and have succeeded in getting very good guiding result. That said; without having performed a hypertune or at the very least a cleaning, greasing and adjustment of the mount you are flying blind as to how well you can expect it to perform. An SN 8 is a lot to ask of it but when everything is dialed in, you should be able to pull it off.


Questions:
how many steps does it take to calibrate the RA axis?

What is the setting under the brain(advanced settings) for "calibration steps ms"?

Have you made sure that the Polar Scope is aligned with the RA axis?

I've self hypertuned both of my LXD75's and can easily get 10 minute subs with an AT6RC. what I'm hearing in your post is that it's not moving enough in DEC to calibrate before it times out in the Step Count. This means you need to increase the "calibration step ms". In a perfect world you want calibration to succeed at 15 to 25 steps. if you are going to 40 steps in RA before it moves 24.5 pixels on the guide camera it's not moving enough during each step. I like to see mine calibrate by moving almost 1 pixel if not a touch more, per step.

Here is an explanation of PHD's settings

http://www.astronomyforum.net/astronomy-software-forum/112778-stark-labs-phd-...


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DaemonGPF
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Re: LXD75 Autoguiding Problems new [Re: zerro1]
      #5756270 - 03/25/13 02:14 PM

An autoguider won't solve all of your guiding problems. It can only compensate for so much. As a prior LXD-75 owner as well, I can tell you the mount is not without its personality. Like Robert mentioned, there are some minor mechanical improvements that can be made to help it along - i.e. adjusting and regreasing, or go as far as a Hypertune. Otherwise, getting that mount to mesh correctly requires proper balancing (notice I didn't say perfect balancing, you need some offset to apply a little counterweight to the gears) and dialing in the settings on both the mount and your autoguider to match. It took me several outside sessions with my LXD-75 to finally get it to play nice when autoguiding. Once it was dialed in though, it worked great. The guys on here are giving some really good recommendations. Robert and John have been using their LXD-75 mounts forever. They can tell you a TON about dialing it in.

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nine44
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Reged: 01/19/13

Re: LXD75 Autoguiding Problems new [Re: Cliff Hipsher]
      #5756397 - 03/25/13 03:17 PM

Quote:

OK, so if you're having trouble with the guide package, why not contact the vendor? Same goes for the guide software.



Cliff--how are you adding to the conversation? This IS the Beginning imaging forum, isn't it? Let the man ask his question and let others respond to it--even if you 'think' you have already answered his question.


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fetoma
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Reged: 09/26/06

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Re: LXD75 Autoguiding Problems new [Re: nine44]
      #5757244 - 03/25/13 11:32 PM

Agree...

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Cliff Hipsher
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Reged: 12/31/08

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Re: LXD75 Autoguiding Problems new [Re: nine44]
      #5758429 - 03/26/13 03:15 PM

Quote:

Cliff--how are you adding to the conversation? This IS the Beginning imaging forum, isn't it? Let the man ask his question and let others respond to it--even if you 'think' you have already answered his question.




I'm butting in because the OP asked this same exact question in another thread. I and several people replied, and to my knowledge he did not indicate that he had tried any of the suggestions.

In similar venues this type of behavior would be considered "trolling".

Here is the OP's thread in Mounts: Mount


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jgraham
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Reged: 12/02/04

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Re: LXD75 Autoguiding Problems new [Re: Cliff Hipsher]
      #5758469 - 03/26/13 03:33 PM

No under-bridge dweller here. Someone suggested on 3/23 that he ask this question here, and on 3/25 he did. No probleemo. Politely repeating responses or providing a link to responses is also okay IMHO.

Having thought about this a bit more I have seen this type of behavior with the LXD75 dec axis when the Dec% was set too low. The easiest fix is to try increasing the Dec% and see what happens. You gotta be careful though as it's easy to go from no response to way too much response fairly quickly. I try to keep mine as low as possible, which for me runs about 60% but I've run it as high as 80% before.


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Clumpybug
member


Reged: 12/03/11

Re: LXD75 Autoguiding Problems new [Re: jgraham]
      #5762977 - 03/28/13 06:59 PM

I don't remember off-hand what the settings were (I'll have to take a look later), but I do remember that I increased both the Dec and RA axes calibration step ms value to something like 1500. The RA moved its 25 pixels in maybe 5 or 6 steps. The Dec axis would move a few pixels in the right direction, then just kind of waffle back and forth without making any progress, and then konk out when it had gone its max of 50 steps. Again, the strange thing is sometimes it works perfectly, and sometimes it does what I just described.

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zerro1
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Re: LXD75 Autoguiding Problems new [Re: Clumpybug]
      #5763161 - 03/28/13 08:50 PM

5 or 6 steps is too few of steps; to get a good calibration. It needs to be at least 15 steps.

What is the guide scope??? if it was a mini guide scope/modified finder 1500ms may work. If you are using an 80mm guider scope then you probably need to drop the ms down to 750 or 800ms

But it does sound like you also need to do some evaluation of what's going on with the DEC. try weigting it a bit heavy (or heavier than you have)on the counter weight end of things so there is always pressure on the drive. watch the calibration process and take notes:

It wouldn't hurt to look at the dec% in the handbox as was suggested.

If nothing helps on the DEC, I would consiider looking at the gears on the motor and on the end of the worm to see if the set screws have worked loose. it is a known issue on these mounts. I've encountered it a couple times my self.


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jgraham
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Re: LXD75 Autoguiding Problems new [Re: zerro1]
      #5763785 - 03/29/13 07:51 AM

Good point about checking the set screws. That is another easy fix and a common problem. This happened to one of my LXD75s. If the set screw has come loose I'd clean any grease and oil from the gear and shaft, align and snug the set screw, apply a drop of Locktite to the set screw and a dab of lithium grease to the gear. It should never come loose again.

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Clumpybug
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Reged: 12/03/11

Re: LXD75 Autoguiding Problems new [Re: jgraham]
      #5766879 - 03/30/13 01:24 PM

Cool, thanks folks! I'll give these things a try and see if I can get things working better. I like the LXD75 - it seems like a pretty good mount for the price. I think I just need to keep figuring out its quirks.

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jgraham
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Re: LXD75 Autoguiding Problems new [Re: Clumpybug]
      #5767113 - 03/30/13 04:21 PM

Absolutely. My Atlas is a fantastic mount, but I still enjoy using my LXD75s.

Have fun!


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