Help please: MESU and PHD2 Backlash does not clear all of a sudden

[kirkster501]

Been imaging and visual with the setup for ages.  All was fine.  MESU mount and PHD2.

Made some tweaks to my rig with a new focuser and the balance is OK but not perfect.  As soon as  I power up the mount the system is solid as a rock.  The mount slews perfectly and up/down movements perfect just as always was.  Platesolves work and puts object bang in the middle.  All good so far. 

I decided to do a new PHD calibration since not done one since Spring.  

PHD2 goes West 12 steps.  Cool.  It then comes back East (in only four steps [why?]), but guide star comes back into the green square in the middle again.  Then its says clearing backlash, one, twice, 110 times.  Eventually gives up and does a North.  Then complains not enough movement in DEC axis.

What the heck.....????  Worked perfectly before....  Uninstalled PHD2 and reset the whole thing.  Rebooted etc.  Still same.  Could it be because the balance is not bang on??????  I thought the friction of the drive would be enough?  When "clearing backlash" does PHD2 tell the mount to "let go" and as a consequence of the imbalance it can never get the backlash cleared?

Thanks guys for any thoughts....  My first thought is to get this slight balance thing sorted.  If mount is no powered it is very, very slightly off balance in the DEC direction.

[david_taurus83]

I thought that type of mount didn't have backlash?

[michael8554]

Returning east in 4 steps? Normal, saves time. 

Don't know why it's taking so long to clear RA backlash. 

Did you nudge north to take up backlash before starting Cal?

As David says, does the mount have backlash?

Are you getting movement in all directions with PHD2 Manual Guide? 

Faulty ST4 cable? 

Michael 

 

[Star101]

I would fix that balance first else you will be avoiding the issue and going in circles.

And when calibrating in PHD2 ....On the "Guiding assistant" Uncheck Backlash and there are no gears ...its friction drive. 

[kirkster501]

Thank you for your thoughts.  I will continue to investigate.

[tomato]

Interesting but, I’m sure, very frustrating. 

Having previously set up and took down every session, I’m sure my balance of the Esprit  150 on the Mesu is not perfect, but PHD2 when calibrating (which I did every session) does 3 “clearing backlash” steps each time them moves on, no problem. I haven’t unchecked the Backlash option, I confess I didn’t know it existed. How are you checking the balance, will the mount “fall” in the Dec axis when powered off? I would certainly get the balance closer if that is the case, also check the connections and test you can move in all for directions manually.

Hope you can get it fixed.

Steve

[Tomatobro]

I saw just this the other night on my EQ6-R where it did just as you describe. I then realised that I had the scope pointing too high so moved it back towards the mid point. It then calibrated as normal.

I don't normally calibrate PHD each session but I had removed the guide camera from the scope. It was replaced at a different position so PHD could not move the scope correctly. I then went straight into calibration and that is when I had the situation you describe. I lowered the scope and it calibrated ok

[mihaighita]

I had the same problem with my Mesu 200 MK1. You need to update software... Also, please remember to initialize mount first (do a offset init)

[kirkster501]

Hi folks,

All slews work perfectly in all directions.

My workflow.  Scope could be pointing anywhere and then I do a blind solve first in SGP. Then I slew to my desired object,  it platesolves and puts object perfectly in the middle of frame.  This would constitute the offset init right?  How do I see the alignment points in Sitech SW?  I then start PHD and try to calibrate and it should pick up the position right? It then does West then East then gets stuck clearing backlash.....  This is a new issue, the above workflow always worked perfectly.

How do you turn off backlash anyway please? MESU has no backlash so where do you do that?  There is no option to turn it off in PHD for RA that I can see.

I am wanting to recheck polar alignment because I think it may be way off after the mount got slightly moved on it's pier that I did in summer.  Not used this rig since then.

I have upgraded sitech software to latest 94N - I was on 91A.  Firmware is ay 9.5 but latest is 9.7.  9.7 does not seem to address any critical issues in this area so would rather leave alone than risk flashing the controller without very good reason.

Thanks.

 

Edited August 31, 2019 by kirkster501

[sloz1664]

Hi Steve,

In the PHD2 "Brain" advanced settings, go to the Algorithm's tab and unclick the Enable Backlash Compensation. 

Although once I have calibrated in PHD2, I save my settings and do not calibrate again for a month or so, unless I alter my rig.

Steve

[michael8554]

IIRC Backlash Comp in PHD2 is for Dec only. 

But I'm never sure if the Clear Backlash after the East steps to the middle are preliminary DEC steps to clear DEC backlash, or to clear RA backlash. 

Ignoring the argument that your mount shouldn't have backlash, try the usual PHD2 advisory, to do some north steps with Manual Guide until you see the guide star move, then Cal, then you can be sure that any Clear Backlash error at the end of RA Cal  is really due to RA. 

Then that would to drive slipping perhaps?

Michael 

Edited August 31, 2019 by michael8554

[vlaiv]

On 26/08/2019 at 12:10, kirkster501 said:

Then its says clearing backlash, one, twice, 110 times.  Eventually gives up and does a North.  Then complains not enough movement in DEC axis.

I think that this is crucial piece of information.

PHD2 will do clear backlash until it sees guide star move on guide command. It is clearing backlash in DEC before doing DEC calibration (RA calibration went ok).

So it tries to clear backlash and does that great number of times, then gives up and and tries going North - and then it complains not enough movement in DEC axis.

This simply means that:

a) for some reason guide commands in DEC axis are not working properly

b) DEC guide rate is set so low that it cannot detect motion of the star even if guide commands are working properly (again very unlikely that 110 moves would not cause guide star to move even if single step was very small).

c) it guides normally but friction drive is slipping in DEC (very unlikely because it slews normally, and it is more likely that it would slip in slew due to torque applied than in simple guide command)

 

[kirkster501]

Thanks chaps.  Will give these steps a try, I have not a had a clear night since my troubles on Wednesday with this issue.  I did uninstall PHD2 and reinstall and I was running at the default settings so it should have worked with that.

I do know I need to do a Polar Align, I forgot about that at the time.  It could be several degrees out.  Even then, backlash should clear I'd imagine........

[kirkster501]

48 minutes ago, sloz1664 said:

Hi Steve,

In the PHD2 "Brain" advanced settings, go to the Algorithm's tab and unclick the Enable Backlash Compensation. 

Although once I have calibrated in PHD2, I save my settings and do not calibrate again for a month or so, unless I alter my rig.

Steve

Thanks Steve,

You can only do that for the DEC axis Steve.  I am getting this on the RA axis after it finishes coming back "EAST".  The appears no option to turn it off on the RA axis where it appears I am having this problem.

[kirkster501]

Ahhh, I read Vlaiv's post properly.......

"PHD2 will do clear backlash until it sees guide star move on guide command. It is clearing backlash in DEC before doing DEC calibration (RA calibration went ok).So it tries to clear backlash and does that great number of times, then gives up and and tries going North - and then it complains not enough movement in DEC axis"

Ah, OK, so the backlash is being cleared from DEC and not RA as I thought.  OK, but I have that box unticked anyway.... ?

Think I need to try a few things then.

[kirkster501]

My list of people who I owe beers to and bottles of gin (like Gnomus) is growing......  

[vlaiv]

8 minutes ago, kirkster501 said:

Ahhh, I read Vlaiv's post properly.......

"PHD2 will do clear backlash until it sees guide star move on guide command. It is clearing backlash in DEC before doing DEC calibration (RA calibration went ok).So it tries to clear backlash and does that great number of times, then gives up and and tries going North - and then it complains not enough movement in DEC axis"

Ah, OK, so the backlash is being cleared from DEC and not RA as I thought.  OK, but I have that box unticked anyway.... ?

Think I need to try a few things then.

In principle you can, and you should for Mesu, as there is no point in clearing backlash on mount that should not have any. I'm not sure it is going to solve your issue, it is just going to skip clearing DEC backlash and go straight into DEC calibration where it will again complain about not detecting any motion in DEC (if everything stays the same).

Could be that software upgrade will solve the issue.

[kirkster501]

1 minute ago, vlaiv said:

In principle you can, and you should for Mesu, as there is no point in clearing backlash on mount that should not have any. I'm not sure it is going to solve your issue, it is just going to skip clearing DEC backlash and go straight into DEC calibration where it will again complain about not detecting any motion in DEC (if everything stays the same).

Could be that software upgrade will solve the issue.

.... indeed Vlaiv, or the DEC balance correction that I have now carried out.  I need a clear night to try out some things now I understand better what is going on.

Many thanks.

[vlaiv]

23 minutes ago, kirkster501 said:

.... indeed Vlaiv, or the DEC balance correction that I have now carried out.  I need a clear night to try out some things now I understand better what is going on.

Many thanks.

This has me worried somewhat. I see myself owning a Mesu 200 in some (distant) future, and it looks like it's a bit fussy with regards to balancing.

How perfect does balance need to be for it to work properly?

[kirkster501]

9 minutes ago, vlaiv said:

This has me worried somewhat. I see myself owning a Mesu 200 in some (distant) future, and it looks like it's a bit fussy with regards to balancing.

How perfect does balance need to be for it to work properly?

I did have it balanced pretty well before my issues.  I then added a new Moonilte Crayford focuser and electronics to my ACF SCT scope which is a total of about 3kg in total to the mirror end of the SCT- the focuser is a very substantial piece of kit.  This upset the balance a bit.  I did tinker with it but the balance was not right when I had the issues the other night and I knew this.  I have since rebalanced it so I need to try again.  And pertinently, the problem I corrected in balance was in the DEC axis, exactly what PHD was complaining about.....  This cannot be a coincidence.

So I would say that the balance does need to be pretty good.  I will know more when I can do more testing because, other than update the Sitech drivers (and redoing Polar Alignment) I have done very little other than rebalance.

I was hoping it was going to be clear last night to do this testing but, alas, it wasn't.  I am in the UK so could be a week or more before a clear sky.  Unless there is another way to test this.

The MESU is the bedrock of my system and I have high confidence in it.  It is a superb piece of engineering and I am 100% convinced this is user error or IT gremlins (or balance).  I would not hesitate to get another one or recommend it to you unreservedly.

[mihaighita]

11 minutes ago, vlaiv said:

This has me worried somewhat. I see myself owning a Mesu 200 in some (distant) future, and it looks like it's a bit fussy with regards to balancing.

How perfect does balance need to be for it to work properly?

Mesu 200 MK2 solves that. With Mk1 there are ways to balance it perfectly. I use a system of pulleys attached to the center of the rotation axis and measure the force needed to pull in any direction. I also have another idea that I need to clear with Lucas first... The dec motor has a tension adjuster on the top that can be loosen and make the dec axis turn extremely easy. I was thinking to use that for balance and then tighten it again to operate the mount. But I need to see that this will not cause any damage to the motor axis. There is also the possibility to monitor the power needed when you are using the handpad to rotate the dec axis. Note that I am speaking only about the dec axis because the Ra axis is easy to balance due to the much bigger centripetal force. 

[Davey-T]

Hope you get it sorted soon Steve 

Also considering the Mesu to replace my obs'y mount and wondering about all these nitty gritty things that need setting for them to work properly, though once permanently setup and sorted I guess it should be fine ?

The fact that the software not being " in house " seems to cause most of the issues, given that all mount control software uses pretty much the same protocol surely it's not beyond the wit of the manufacturer to get a bespoke operating system written, it could then have a built in balancing routine ala 10Micron etal, that would take the guess work out of it as it only monitors the current drawn by the motors how hard can it be ?

Dave

 

 

[mihaighita]

2 minutes ago, Davey-T said:

Hope you get it sorted soon Steve 

Also considering the Mesu to replace my obs'y mount and wondering about all these nitty gritty things that need setting for them to work properly, though once permanently setup and sorted I guess it should be fine ?

The fact that the software not being " in house " seems to cause most of the issues, given that all mount control software uses pretty much the same protocol surely it's not beyond the wit of the manufacturer to get a bespoke operating system written, it could then have a built in balancing routine ala 10Micron etal, that would take the guess work out of it as it only monitors the current drawn by the motors how hard can it be ?

Dave

 

 

10Micron mounts have absolute encoders that help them get the precise position of the axis when they are measuring the current drawn by the motors. It is much more difficult to do the calculation without knowing the axis position. 

[Davey-T]

3 minutes ago, mihaighita said:

10Micron mounts have absolute encoders that help them get the precise position of the axis when they are measuring the current drawn by the motors. It is much more difficult to do the calculation without knowing the axis position. 

Something similar on my iEQ45 that works without absolute encoders, it could include some operator input like asking you to slew to horizontal in RA and Dec then measure current slewing a short distance in both directions maybe.

Dave

[kirkster501]

4 hours ago, Davey-T said:

Also considering the Mesu to replace my obs'y mount and wondering about all these nitty gritty things that need setting for them to work properly, though once permanently setup and sorted I guess it should be fine ?

Indeed Dave (and Vlaiv). Don't let my issue here put you off.  My MESU has been operating flawlessly since I bought it in 2016 and guides and slews beautifully and has never missed a beat.  I am 100% confident this matter is not the mount, it is IT or balance related.  

Some clear patches about at tea time here in Nottingham.  If they hold for tonight I will be able to Polar Align and do some more testing and fiddling.