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Sudden 'Jerk' when slewing in RA


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#1 wardr77

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Posted 30 June 2015 - 06:39 AM

A strange issue with my LX90 that only seems to have appeared over the last couple of sessions. After a goto I will often fine slew to get the object dead centred, however if I do this on slew speed 64 (button 5) and press the Right key, the scope will give a sudden sharp jerk before settling to a smooth movement, often resulting in the object disappearing outside the FOV. It does not seem to do this at 16X or slower slew speeds. Just wondered if anyone could offer advice regarding what this maybe, and what if anything could be done to fix?

 

Many thanks



#2 Mark Sibole

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Posted 30 June 2015 - 10:55 AM

when was the last time you have trained and recalibrated the drives?It sounds like they are in need of training and calibrating.


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Mark Sibole
MTSO Observatory
Fife Lake, Mi.

http://astronomy.qteaser.com

#3 wardr77

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Posted 30 June 2015 - 12:10 PM

Hi Mark, no I have not trained the drives, it's something I've been meaning to do, but as the gotos are working well I assumed I did not need to. Out of interest why would training the drives get rid of the sudden movement / jerkiness when slewing?

Thanks you for your response, much appreciated.

Rob

#4 RickScofield

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Posted 30 June 2015 - 05:21 PM

I agree with Mark I would suggest you train your drives. This has always solved my RUBBER BANDING issue which what it sounds like your having happen. Give it a try in fact do it 3 times using your highest power eyepiece and find a distant telephone pole or chimney for centering. Good luck.
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#5 MistrBadgr

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Posted 01 July 2015 - 09:59 AM

Rob,

 

The gear training exercise tells the scope what the backlash (slop) is in the drive trains.  If there is more backlash than the scope thinks there is in a particular direction, the motor and gear train can build up momentum before actually moving the scope and hit it with more force than normal.  This can cause a jerk.  I am sure that is not the only way you could get the characteristic you are experiencing, but it is probably the most common.

 

Hope that is your problem!

 

Bill Steen


Bill Steen, Sky Hunters' Haven Observatory, Broken Arrow, Oklahoma

#6 spiral

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Posted 01 July 2015 - 11:17 AM

One quick question..After training the drives do you have to "park" the scope for it to remember the training? Seems in the manual I read that if you do not park the scope after training it will not retain the info..



#7 Mark Sibole

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Posted 01 July 2015 - 11:30 AM

everything everyone stated above.Drives should be trained and calibrates at least 1ce a season maybe more if the scope it used a lot


Mark Sibole
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http://astronomy.qteaser.com

#8 wardr77

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Posted 01 July 2015 - 12:15 PM

Ok well I trained the drives 3 times, just to be sure, and calibrated the motors but it did not cure the issue. The problem only occurs after a goto and if I select slew speed 64x or greater and only if I click the right arrow first. If I use the up / down or left arrow first and then use the right key no issue at all. If I click right arrow first the RA shifts / jerks approx 0.5 degrees. As I say only happens after a goto. If I manually slew to anything, then select 64x and click on right arrow no problem, very odd. I have also adjusted the RA percentages, but nothing. Not a massive issue I suppose, just an annoyance, I must remember not to click on the right key first after a goto!
I did not put scope into park after training drives, it didn't say to do this in the manual.... ?

#9 RickScofield

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Posted 01 July 2015 - 06:40 PM

You don't have to PARK the LX90 to retain drive training or calibration.
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#10 wardr77

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Posted 08 July 2015 - 07:32 AM

Hi All,

 

Thought I would give an update on this issue in case it helps anyone else out.

 

I mentioned previously that I had calibrated the motors, and trained the drives and it did not cure the described issue.

 

The other night after reading on line advice about training drives I had another go. This time I peformed the task accurately, first calibrating the drives and then training the drives using a 9.7mm EP and Polaris as my point of reference; I also set a slow slew speed (no2) each time to centre the star. This completely cured the rubberbanding, no drift at all when goto'ing an object and no drift after centering. Great!!! Very pleased about this, the reason why it failed the first time, I think, is 1. The terrestrial object was too close 2. I did not select a slow slew speed when centering 3. I calibrated the motors after the train and not before (this was probably the main cause)

 

So all good from a rubberbanding perspective. However the 'jerk' still persists. After further checking I found it does not happen if I centre first on the dec axis and then on the RA. I mentioned this to a Meade service engineer and he suspected that it could be a handset issue so suggested I reset the handset which I did, and at first in max slew during a goto the jerk did not take place but after I put it into quiet slew, the jerk returned, which is a shame. Not a big problem, just an inconvenience. The next thing to look at is the worm/drive gear in the base on the scope, but I doubt very much there will be a problem there. If I ever get to the bottom of the issue I will let you know!

 

Rob



#11 MistrBadgr

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Posted 08 July 2015 - 01:38 PM

Hi Rob,

 

Thanks for the update!  I don't remember anyone asking about the particular jerking problem you are having on this board, but my memory could be bad.  So anything you find out, please post.

 

I do not have an LX 90, nor have I used one.  Therefore, I don't have any more answers than what I have given you.  As with every other time someone has a problem I cannot help them solve, you do at least have my sympathies.....for whatever that is worth to you!

 

Best Regards,

 

Bill Steen


Bill Steen, Sky Hunters' Haven Observatory, Broken Arrow, Oklahoma

#12 mike95376

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Posted 18 July 2015 - 09:16 AM

There may be a bit of junk in the gear drive grease that is getting pushed along fine at low speeds but gets in between the teeth at high speed until the gears bump over it.  Just something to look for if you open it up to take a peek.  Grease that has a lot of small wear particles in it could do something similar.  



#13 MistrBadgr

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Posted 18 July 2015 - 03:18 PM

Given time, some of the filler material they put in the grease to thicken it can settle out and for a fairly tough, clay-like material.  That lump you are talking about could very well be that.  However, I cannot remember how old this scope is.  For the materials in the grease to separate, several years would have to go by.

 

A friend found a bunch of that stuff in an old LX 200 14 inch he bought second hand.

 

Bill Steen


Bill Steen, Sky Hunters' Haven Observatory, Broken Arrow, Oklahoma

#14 wardr77

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Posted 20 July 2015 - 09:08 AM

The scope is 2011. I took the base off and it looks brand new, the gears are well greased without clumps or lumps and there are no obvious mechanical problems. The scope had been used only a handful of times before I acquired it. I think the issue must be firmware or electrical based.
I simply centre the object using the dec arrows before using the RA arrows now and the problem doesn't occur. Quite strange.

#15 MistrBadgr

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Posted 20 July 2015 - 02:34 PM

Yes, that is too new to have the problem of the grease filler settling out.  I guess it might do that in that time frame if it were stored somewhere that was really hot all the time.

 

The behavior is quite strange, but anything is possible.  I had overlooked that you had mentioned that it did this at the 64X speed.  Does this behavior happen at any other speeds?

 

Bill Steen


Bill Steen, Sky Hunters' Haven Observatory, Broken Arrow, Oklahoma

#16 wardr77

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Posted 21 July 2015 - 03:19 AM

Hi Bill,

The issue does not occur at the lower speeds and I have not checked the higher speeds to be honest as they are a bit quick for centering in the FOV, I will have to check this. It is odd, if I use the up/down arrows first or use a slower speed to centre first and then use the right arrow at 64X no problem, its almost as if there is some sort of 'reset' taking place as a result of pressing the other buttons. I've just put it down to a quirk of the scope that I can work around with no problem. Apart from that a fantastic scope!

Thanks again for your support

Rob



#17 MistrBadgr

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Posted 21 July 2015 - 08:59 AM

Hi Rob,

 

If you happen to check out the higher speeds, etc., I would like to try and write all of it down and send the information to someone I know.  The Meade engineering folks go through things on some sort of a long term cycle.  It might be an item for them to check out in the software at that time.  Since the handset is used on a number of different scopes, any problem is probably in one of the subsystems that are in the mount itself.  The handset is the real brains, however, with the processor in the mount taking care of more basic functions.

 

Thanks,

 

Bill Steen


Bill Steen, Sky Hunters' Haven Observatory, Broken Arrow, Oklahoma

#18 wardr77

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Posted 22 July 2015 - 02:43 AM

Hi Bill,

 

After checking last night, I can confirm the issue occurs at speeds of 64X and above. Intensity of the jerk seems to be related to the amount of travel the scope moves during a slew, the greater the slew the more intense the jerk when centering. Issue does not occur in speeds of 16x or less and does not occur in the higher speeds if the right arrow is not pressed first after a slew.

 

Thanks again

Rob



#19 MistrBadgr

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Posted 23 July 2015 - 04:29 PM

Hi Rob,

 

I will pass this on, but it sure sound like the scope does not have the right information about backlash in the right/left drive system.  It learns this with the drive training routine.  Not sure how it could not get the right information when you trained the drive.  You might try that exercise a few times and see if it helps.  On my little DS mounts, I found that multiple training exercises seemed to help, but yours is definitely a better scope.  With my LS 8, it did all of that itself and I never had a problem.

 

Bill Steen


Bill Steen, Sky Hunters' Haven Observatory, Broken Arrow, Oklahoma

#20 wardr77

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Posted 24 July 2015 - 01:53 PM

Hi Bill,

I will do as you suggest and train the drives a couple more times, and see if that does anything. It certainly worked in terms of removing rubber banding, no more drift at all which is good. I have started to wonder after your last post whether something funky is going on with one of the components on the RA board which maybe causing the issue. Interestingly I fiddled with the alt / az percentages but I didn't notice any difference whether I set at 5 or 50%, I suspect these things are not related though.

Regards
Rob




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