Mount Backlash Settings

[mj.w...@gmail.com]

Page 14 of "PHD2 Best Practices" says "Don't use backlash settings in the mount".

Is this only RA, or does it include Dec?

(According to GA my wedge-mounted LX200GPS has 9208mS of Dec backlash (with the Mount's Dec Anti-backlash at zero). I was advised on a LX200 forum to "Train" the mount's drives (which gives the mount a figure for the amount of backlash to include in GoTo's), and then to enter this figure in the mount's separate Dec Anti-backlash.)

Michael

Wiltshire UK

[Brian Valente]

Hi Michael

 

Backlash is DEC only

 

Does your mount have an RA backlash setting?

 

 

Thanks

 

Brian

 

 

Brian Valente

Brianvalentephotography.com

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[bw_msgboard]

Hi Michael.  You certainly don’t want to use backlash compensation for RA.  As long as you’re guiding at 1x sidereal or less, RA backlash is irrelevant.  As a general rule, backlash compensation implemented in the mount is going to lead to very bad guiding results – you will typically get oscillations in Dec that never stabilize.  The mount backlash settings and “training” are really intended for visual use, primarily to help with pointing accuracy and centering of an object in an eyepiece field of view. 

 

Most Meade fork mounts have large amounts of backlash like yours.  If you’re currently set to guide at 0.5x sidereal, you could try increasing that up closer to 1x sidereal.  That will normally reduce the backlash by a proportional amount.  In all likelihood, you’ll be better off guiding in only one Dec direction with this mount, an option that’s described in the PHD2 help guide.  But if you want to experiment, you could try a couple of things:

 

1. Increase the guide speed as mentioned before and see if you can get the measured backlash down below 5 seconds.
2. Try setting Dec backlash correction in the mount to 1-2 seconds – nothing higher
3. Do some guiding with PHD2 and see if you end up with Dec oscillations

 

If this fails (I think it probably will), you could then reset the mount backlash settings to zero and try PHD2 backlash compensation - assuming you’ve already reduced the backlash below 5 seconds.  Even if the Dec behaves better, you’re likely to see poorer RA guiding because of the long delays when the Dec guiding reverses direction.  

 

Hope this helps,

Bruce

 

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From: open-phd...@googlegroups.com [mailto:open-phd...@googlegroups.com] On Behalf Of mj.w...@gmail.com
Sent: Wednesday, February 28, 2018 5:08 PM
To: Open PHD Guiding
Subject: [open-phd-guiding] Mount Backlash Settings

 

Page 14 of "PHD2 Best Practices" says "Don't use backlash settings in the mount".

 

Is this only RA, or does it include Dec?

 

You certainly don’t want to use this for RA.  As long as you’re guiding at 1x sidereal or less, RA backlash is irrelevant.  As a general rule, backlash compensation implemented in the mount is going to lead to very bad guiding results – you will typically get oscillations in Dec that never stabilize.  The mount backlash settings and “training” are intended for visual use, primary to help with pointing accuracy and centering of an object in an eyepiece field of view.

 

(According to GA my wedge-mounted LX200GPS has 9208mS of Dec backlash (with the Mount's Dec Anti-backlash at zero). I was advised on a LX200 forum to "Train" the mount's drives (which gives the mount a figure for the amount of backlash to include in GoTo's), and then to enter this figure in the mount's separate Dec Anti-backlash.)

 

Michael

Wiltshire UK

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[mj.w...@gmail.com]

Hi Brian, Andy

Yes the LX's have antibacklash on RA.

My RA antibacklash is on zero and I have no problem with RA guiding 10 minute exposures.

The default guiderate is 0.66 and I tried to up this to 0.8 as an experiment, but even with a new Profile the setting kept returning to 0.66 - Ascom problem?

My PA is about 5 arcmins and I usually guide Dec in one direction, or even off !, and switch to Auto just before dithers, but it would be nice to leave it on auto :-}

I have experimented with the antbacklash, but not at the setting arrived at by the Train Drives procedure.

So to answer my question, yes the advice in Best Practises is to not use mount antibacklash in RA.

Thanks

Michael
Wiltshire UK

[bw_msgboard]

Hi Michael. I think you may not quite understand how the mount guide speed
setting works. That isn't something controlled from PHD2, PHD2 never sets
that value. You change it using the hand-controller on the mount - PHD2
will see whatever value you specify there.

I used a Meade LX200GPS fork mount for a number of years, but maybe
something has changed since then. The 'train drives' procedure available to
me was essentially useless for guiding purposes, I think you will find it
troublesome. As I said in the earlier message, I think these features were
implemented for visual use. If you increase your guide speed and then
measure the backlash with the latest dev build of PHD2 (2.56.4dev8), you
will probably get the best measurement of the backlash.

Good luck,
Bruce

-----Original Message-----
From: open-phd...@googlegroups.com
[mailto:open-phd...@googlegroups.com] On Behalf Of mj.w...@gmail.com
Sent: Thursday, March 01, 2018 2:53 AM
To: Open PHD Guiding

[mj.w...@gmail.com]

With respect Bruce, I'm aware that the guide speed isn't controlled by PHD2.

I upped the guide speed in the handset, but PHD2  continued to show the old setting, so I suggested Ascom might be fighting my selection?

Train Drives is for improving GoTo's, but Dec Antibacklash was suggested by a respected LX200 expert as the first step to improve the Dec backlash.

I have previously tried using Antibacklash, and as you predict it didn't improve matters, but on that occasion I wasn't aware that a possibly sensible setting was available from the Train Drives result.

The 9208ms figure was reported by dev 7, I'll report back what dev 8 and antibacklash does !

Thanks

Michael

Wiltshire UK

[bw_msgboard]

From: open-phd...@googlegroups.com [mailto:open-phd...@googlegroups.com] On Behalf Of mj.w...@gmail.com
Sent: Thursday, March 01, 2018 10:53 AM
To: Open PHD Guiding
Subject: Re: [open-phd-guiding] Mount Backlash Settings

With respect Bruce, I'm aware that the guide speed isn't controlled by PHD2.

I upped the guide speed in the handset, but PHD2  continued to show the old setting, so I suggested Ascom might be fighting my selection?

 

It’s possible the ASCOM driver interface allows the setting for guide speed or it may not be reporting the value set by the handset.  The easiest way to know what value is actually being used in the mount would be to set it in the handset, then do a fresh calibration in PHD2.  Even though PHD2 might continue to read a bogus value, the computed RA and Dec rates would tell the correct story, and the bogus value wouldn’t matter.

 

[mj.w...@gmail.com]

Thanks Bruce

I will try cals on 0.66 and 0.8 and look for changes.
I don't have access to a log at the mo, which parameter should I look at ?
Regarding the backlash box in algorithms, is the figure in the box in ms?
If I go to zero mount antibacklash, is it worth putting a compromise figure in the algorithms box, to get Dec moving?

Michael
Wiltshire UK

[bw_msgboard]

 

 

-----Original Message-----
From: open-phd...@googlegroups.com [mailto:open-phd...@googlegroups.com] On Behalf Of mj.w...@gmail.com
Sent: Friday, March 02, 2018 2:45 AM
To: Open PHD Guiding
Subject: RE: [open-phd-guiding] Mount Backlash Settings

 

Thanks Bruce

 

I will try cals on 0.66 and 0.8 and look for changes.

I don't have access to a log at the mo, which parameter should I look at ?

 

It’s probably easier to do a ‘Review Calibration’ from the ‘Tools’ menu.  Then look at the measured RA and Dec rates and compare those to the expected guide rates.  1x guiding is 15 arc-sec/sec, 0.6x guiding is 9 arc-sec/sec.  Since your mount has a lot of backlash, you’ll probably need to move it north as the last thing before starting the calibration.  Otherwise, if you calibrate close to the celestial equator, the RA rate will give you a good indication.  It will never match exactly but it should be fairly close.

 

 

But if you have to get the info after the fact from a log file, use the LogViewer and look at the heading block at the start of each guiding section.  On the ‘Mount =” line, there are entries for xRate and yRate.  Those are in units of pixels/sec.  So multiply them by the “Pixel scale” value in that header and that gets you to arc-sec/sec.  Then you can do the same comparison with the 1x sidereal rate.

 

Regarding the backlash box in algorithms, is the figure in the box in ms?

 

Yes, in ms.  That info should be in the tool-tip but I see it isn’t, so we’ll fix that.

 

If I go to zero mount antibacklash, is it worth putting a compromise figure in the algorithms box, to get Dec moving?

 

You can certainly give it a try.  We have a new dev build coming out shortly that gives you a bit more control over this, including a ceiling level.  As long as you know what to look for – Dec oscillations that won’t stabilize – you should be able to stay out of trouble.

 

Good luck,

Bruce

[mj.w...@gmail.com]

Dug out a log, and X and Y rates times pixel scale = 10.76 and 9.6, which is 0.66x or thereabouts.

The UK is snowed in at present - 6 inches and a few 3 foot drifts and everything grids to a halt !

So will be a while before I can try 0.8, and then some backlash figures in Algorithms.

Thanks again

Michael

Wiltshire UK

[Andy Galasso]

On Fri, Mar 2, 2018 at 11:18 AM, bw_msgboard <bw_m...@earthlink.net> wrote:

We have a new dev build coming out shortly that gives you a bit more control over this, including a ceiling level.

I uploaded 2.6.4dev9 last night with the backlash ceiling.  You can upgrade with the menu option: Help > Check for updates. (PHD2 will notify you automatically anyway next time you start it unless you have disabled the automatic update checking option.)

Andy

[bw_msgboard]

Hi Michael, sounds good.  If you can increase the guide speed successfully and re-calibrate, I’d suggest re-running the Guiding Assistant backlash test.  That will presumably give you two different measures of the backlash so you can go from there.  We recently made some changes in the measurement process (2.6.4dev8) and we think the results will be better than in earlier releases.

 

Good luck,

Bruce

 

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From: open-phd...@googlegroups.com [mailto:open-phd...@googlegroups.com] On Behalf Of mj.w...@gmail.com

Sent: Friday, March 02, 2018 9:39 AM
To: Open PHD Guiding

Subject: Re: [open-phd-guiding] Mount Backlash Settings

 

Dug out a log, and X and Y rates times pixel scale = 10.76 and 9.6, which is 0.66x or thereabouts.

[mj.w...@gmail.com]

Thanks for the heads-up for dev9.

I can't be the only one using a guiding laptop that is never connected to the internet, so I'm usually only aware of a new dev if I spot a higher number mentioned in a reply to someone's problem.

I'll check out dev 9 as soon as I see some clear sky.

Michael

Wiltshire UK

[peter wolsley]

Good point Michael,

Maybe a new topic could be created by the authors when a new release occurs.

Peter

[Andy Galasso]

On Sat, Mar 3, 2018 at 11:59 AM, peter wolsley <wols...@gmail.com> wrote:

Maybe a new topic could be created by the authors when a new release occurs.

Fair enough, we can do that.

Andy

[mj.w...@gmail.com]

I moved over to the ASCOM Talk forum, where I got a load of help from Dick and Andrew.

The conclusion was that as soon as PHD2 connects to the Mount with the ASCOM LX200GPS driver, ASCOM resets the custom guide rate back to 66% with a        :Rg10.0#         command.

I have tried setting the guide rate in the handbox to 80% AFTER connecting to the mount, and I get the required result in the guidelog, the guiderate goes up to 11.69 arcsecs per sec, or 78%.

I also used the Calibration Calculator with 0.80 entered, the 700ms result is shown in the log to have been used for Cal.

I also tried 1500ms in the new Dec Backlash Compensation, I will experiment more with that setting.

It's hard to be certain when UK seeing is involved, but the combination of custom guide rate and Dec Backlash Comp has given a noticeable improvement in Dec guiding.

Dec was 1.06 RMS, now 0.55 RMS (PA is 2.3 Arcmin).

I also noted that after doing a DITHER in Manual Guide, that the log shows a "Settling Complete" comment - is that shown anywhere while guiding?

Thanks

Michael

Wiltshire UK

[bw_msgboard]

HI Michael, see below.

 

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From: open-phd...@googlegroups.com [mailto:open-phd...@googlegroups.com] On Behalf Of mj.w...@gmail.com

Sent: Wednesday, March 14, 2018 7:02 AM
To: Open PHD Guiding

Subject: Re: [open-phd-guiding] Mount Backlash Settings

 

I moved over to the ASCOM Talk forum, where I got a load of help from Dick and Andrew.

 

Yes, they also contribute heavily on the LX200GPS forum and definitely understand how these mounts work.

 

The conclusion was that as soon as PHD2 connects to the Mount with the ASCOM LX200GPS driver, ASCOM resets the custom guide rate back to 66% with a        :Rg10.0#         command.

 

I have tried setting the guide rate in the handbox to 80% AFTER connecting to the mount, and I get the required result in the guidelog, the guiderate goes up to 11.69 arcsecs per sec, or 78%.

 

I also used the Calibration Calculator with 0.80 entered, the 700ms result is shown in the log to have been used for Cal.

 

I also tried 1500ms in the new Dec Backlash Compensation, I will experiment more with that setting.

 

It's hard to be certain when UK seeing is involved, but the combination of custom guide rate and Dec Backlash Comp has given a noticeable improvement in Dec guiding.

Dec was 1.06 RMS, now 0.55 RMS (PA is 2.3 Arcmin).

 

We can look at your guide logs to get a sense of what’s going on with your Dec guiding.  The change in the guide speed setting could account for maybe 20% of the improvement.  I guess you’ll have to decide whether that’s worth the nuisance of having to reset it manually after the PHD2 connection has been made.  I can’t remember if the source code for this driver is available – if so, this behavior could probably be changed.

 

I also noted that after doing a DITHER in Manual Guide, that the log shows a "Settling Complete" comment - is that shown anywhere while guiding?

 

It isn’t shown in the UI, if that’s what you’re asking.  But it’s always shown in the guide log regardless of how the dither was initiated.  So the LogViewer tool, for example, will show it.

 

Bruce

 

Thanks

 

Michael

Wiltshire UK