Re: Poor guiding with GM8
I am thinking of doing worm lapping. I see some people had great success using 1-micron diamond paste from mcmaster.
What is the latest wisdom on this subject?
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Re: What result I can get with the current OPW in my old G11?
Hi Andre -
If your mount originally came with stainless worms, from what I
understand it should be a marked improvement.
In my opinion, you ideally want to reduce PE on the RA axis since
that will continually move during tracking/guiding.? Backlash does
not mater as much since you are constantly moving in the same
direction.? Wind handling may come into play, but that can largely
be mitigated with eastward weight bias, or the string trick. ? ?
One the DEC side, PE does not matter much, however you want to
reduce backlash since the DEC will receive small corrections in
both directions.? This is why if it were my mount, I would put the
OPW on the DEC side.
The OPW upgrade is separate from the spring loaded worm
upgrade.?? The SLW upgrade requires the OPW, but it is a
modification? that is only done in house by Losmandy.? That said,
many people have done various DIY interpretations of the spring
loaded worm, with or without the factory OPW.? If youre
comfortable drilling and tapping your mount, adding a spring
should be a relatively simple modification.? Alternately, you
might be able to get creative with some rubber bands or some other
method of applying pressure to the worm block.?? The hole you
mention in the OPW is indeed for the spring mechanism, but
requires drilling and tapping the worm mounting plate.
I am currently using the Wemos R32 and CNCv3 onstep controller.?
I have TMC2130 drivers in SPI mode.? Previously I was using
LV8729s and those worked well too.
I am also using bellows style couplings.? 16mm diameter, 5mm x
6.35mm.? I was concerned the helical couplings might have been
winding up (motor movement without worm movement), so I moved to
bellows just to be safe.? The are less flexible, but as long as
your alignment is good, it should be OK IMO.? Here's the link if
you're curious:?
Good luck,
-Tony
On 7/29/2021 9:27 AM, andre_moutinho
wrote:
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Hello
Tony,
?
The
original mount came with stainless worms.
I
have purchased one OPW and two High Precision worms for both
RA/DEC. I was considering the OPW for the RA axis but will
think about using it in DEC. My OPW came with a hole that
may be used for Sprint loaded, but no spring was included,
just a hole. Thats very strange. Please check this post:
/g/Losmandy_users/message/73027
?
I
have checked your onstep progression. What controller have
you used? What was the tracking microstep configuration? I
have upgraded the stepper controller to TMC 5130.
?
Thanks
for the reduction suggestion. I will think about it.
?
Thanks
Andre
?
De:
[email protected] [mailto:[email protected]] Em
nome de GuitsBoy
Enviada em: quinta-feira, 29 de julho de 2021 10:18
Para: [email protected]
Assunto: Re: [Losmandy_users_io] What result I can
get with the current OPW in my old G11?
?
Hi Andre -?
Did your original mount come with the HP brass worms?? Or were
they stainless?? ?Assuming they were HP brass already, the new
OPW might not offer much less PE than your original ones,
however it should be a whole lot easier to set the backlash.?
And if you ever decided to go DIY spring loaded worms, it
should be a relatively easy mod for you.
Also, I would think you want the High Precision worm to go on
the RA side to reduce periodic-error.? ?Personally, I would
put the OPW on the DEC side with the expectation that I would
eventually do a spring loaded mod to reduce backlash, or at
the very least, make routine backlash adjustment easier.
I also have a ten+ year old G11 that's been converted to
onstep.? ?To give you an idea of how my RMS guide error
progressed:
~ .85 - 1.0 arc-sec RMS:? ?Direct drive 400 step motors and
stock two piece worm blocks
~ .6 - .75 arc-sec RMS:? ?Belt Drive with 16:60 reduction and
stock 2 piece worm blocks
~ .5 - .65 arc-sec RMS:? ?Belt Drive with 16:60 reduction, and
DIY spring loaded worms, new HP worm (old was brass, but high
PE) and bellows style couplings
The above assumes nights of good seeing and little wind.? ?I
am still using a 60mm guidescope, and? I've had 30 lbs of 8"
newt and equipment guiding under .5 arc-sec RMS under perfect
conditions.
I should also note that certain stepper drivers perform better
than others.? The TMC2130 seems to contribute the least
error.? ?Also, mechanical reduction is more accurate than
microstepping for two reasons:? Coarser microsteps are more
accurate and have higher holding torque, and mechanical
reduction also reduces load on the motors, resulting in less
angular error.? If you can move towards mechanical reduction
(planetary gearbox or belt drive) that should give you
additional benefit IMO.? But you have to make sure that the
reduction benefits outweigh the added complexity, friction,
and NVH (noise, vibration, harmonics)
Good luck, -Tony
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Re: What result I can get with the current OPW in my old G11?
Hello Tony, ? The original mount came with stainless worms. I have purchased one OPW and two High Precision worms for both RA/DEC. I was considering the OPW for the RA axis but will think about using it in DEC. My OPW came with a hole that may be used for Sprint loaded, but no spring was included, just a hole. Thats very strange. Please check this post: /g/Losmandy_users/message/73027 ? I have checked your onstep progression. What controller have you used? What was the tracking microstep configuration? I have upgraded the stepper controller to TMC 5130. ? Thanks for the reduction suggestion. I will think about it. ? Thanks Andre ? De: [email protected] [mailto:[email protected]] Em nome de GuitsBoy
Enviada em: quinta-feira, 29 de julho de 2021 10:18
Para: [email protected]
Assunto: Re: [Losmandy_users_io] What result I can get with the current OPW in my old G11? ? Hi Andre -?
Did your original mount come with the HP brass worms?? Or were they stainless?? ?Assuming they were HP brass already, the new OPW might not offer much less PE than your original ones, however it should be a whole lot easier to set the backlash.? And if you ever decided to go DIY spring loaded worms, it should be a relatively easy mod for you.
Also, I would think you want the High Precision worm to go on the RA side to reduce periodic-error.? ?Personally, I would put the OPW on the DEC side with the expectation that I would eventually do a spring loaded mod to reduce backlash, or at the very least, make routine backlash adjustment easier.
I also have a ten+ year old G11 that's been converted to onstep.? ?To give you an idea of how my RMS guide error progressed:
~ .85 - 1.0 arc-sec RMS:? ?Direct drive 400 step motors and stock two piece worm blocks
~ .6 - .75 arc-sec RMS:? ?Belt Drive with 16:60 reduction and stock 2 piece worm blocks
~ .5 - .65 arc-sec RMS:? ?Belt Drive with 16:60 reduction, and DIY spring loaded worms, new HP worm (old was brass, but high PE) and bellows style couplings
The above assumes nights of good seeing and little wind.? ?I am still using a 60mm guidescope, and? I've had 30 lbs of 8" newt and equipment guiding under .5 arc-sec RMS under perfect conditions.
I should also note that certain stepper drivers perform better than others.? The TMC2130 seems to contribute the least error.? ?Also, mechanical reduction is more accurate than microstepping for two reasons:? Coarser microsteps are more accurate and have higher holding torque, and mechanical reduction also reduces load on the motors, resulting in less angular error.? If you can move towards mechanical reduction (planetary gearbox or belt drive) that should give you additional benefit IMO.? But you have to make sure that the reduction benefits outweigh the added complexity, friction, and NVH (noise, vibration, harmonics)
Good luck, -Tony
|
Re: What result I can get with the current OPW in my old G11?
Hi Andre -?
Did your original mount come with the HP brass worms?? Or were they stainless?? ?Assuming they were HP brass already, the new OPW might not offer much less PE than your original ones, however it should be a whole lot easier to set the backlash.? And if you ever decided to go DIY spring loaded worms, it should be a relatively easy mod for you.
Also, I would think you want the High Precision worm to go on the RA side to reduce periodic-error.? ?Personally, I would put the OPW on the DEC side with the expectation that I would eventually do a spring loaded mod to reduce backlash, or at the very least, make routine backlash adjustment easier.
I also have a ten+ year old G11 that's been converted to onstep.? ?To give you an idea of how my RMS guide error progressed:
~ .85 - 1.0 arc-sec RMS:? ?Direct drive 400 step motors and stock two piece worm blocks
~ .6 - .75 arc-sec RMS:? ?Belt Drive with 16:60 reduction and stock 2 piece worm blocks
~ .5 - .65 arc-sec RMS:? ?Belt Drive with 16:60 reduction, and DIY spring loaded worms, new HP worm (old was brass, but high PE) and bellows style couplings
The above assumes nights of good seeing and little wind.? ?I am still using a 60mm guidescope, and? I've had 30 lbs of 8" newt and equipment guiding under .5 arc-sec RMS under perfect conditions.
I should also note that certain stepper drivers perform better than others.? The TMC2130 seems to contribute the least error.? ?Also, mechanical reduction is more accurate than microstepping for two reasons:? Coarser microsteps are more accurate and have higher holding torque, and mechanical reduction also reduces load on the motors, resulting in less angular error.? If you can move towards mechanical reduction (planetary gearbox or belt drive) that should give you additional benefit IMO.? But you have to make sure that the reduction benefits outweigh the added complexity, friction, and NVH (noise, vibration, harmonics)
Good luck, -Tony
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Re: What result I can get with the current OPW in my old G11?
Hi,
My mount had the original steel worm and 492 driver that I recently replaced with onstep with 400 steps motor and using 128 microsteps for tracking.
Here is a video of the g11 mount with onstep:?
The motor is directly coupled into the worm with an aluminum helical flexible coupling. So there exists no Oldham coupler and gear boxes.
You say I need replace the just acquired OPW bearings?
Thanks
Andre
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Re: Poor guiding with GM8
Alex,
Glad you made some improvements. That is still quite a bit of periodic error, and 0.8" guiding for a scope of that FL is sort of marginal. You of course want to get to a point where RA and Dec errors are approximately the same, and both are small. Good luck with the direct drive!
JK
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Re: Poor guiding with GM8
On Wed, Jul 28, 2021 at 05:08 PM, Alexander Varakin wrote:
Alan,
I will check it, but I think it is optical illusion.
What I mean is that it is out of round, due to the set screw mounting, or some other reason.? You should check it with an indicator like John suggested.
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Re: What result I can get with the current OPW in my old G11?
Hi Andre,
Please can you be more specific on the mount you have? Based upon the age I assume this is with the non-tucked motors and a Gemini 1. I have the tucked motors and a Gemini 2, so mine might be too different to advise from. No gear boxes?
Perhaps this video shows your type:
https://www.youtube.com/watch?v=kBi10ztreDw
If you are replacing the worm, you probably should replace the Oldham coupler and the worm bearings at the same time as these will have an effect too. The bearings you might be able to source locally, the Oldham coupler you might be need to get from Losmandy.
The worm and blocks will need to be adjusted to properly mate with the ring gear. I think this Losmandy video is a good guide:
?
Hope this info helps.
John
Note: The first video shows a GM8, which may be different than the 10 year old G11.
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Re: Poor guiding with GM8
Hi John,
I heard about the gauge method and even did some testing. Of course, my worm ring is slightly off round.
I will try to find some info about the worms on this forum, I did not see it before.
I think I am making some progress:
1. I swapped the worms but did not see much improvement, except that the PE curve was smoother
2. I reduced the tension in the belt and saw some improvement: the 480s period reduced from 13" to 7" and rest of the periods were very small, as you can see on the attached image
As a result, my guiding now is about 0.8" vs 1.5" in the past. Not perfect, but useable with my 1150mm scope. Stars are a little eggy, but they can be easily fixed using the deconvolution module of PixInsight.
Based on input from Guilherme, I will be trying direct-drive again.
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Re: Poor guiding with GM8
Alex,
You may benefit by using a run out gauge on your rotating parts. Basically this is a fixed needle point which rides right along the spinning surface and will tell you how far out of round you are. The base of the gauge clamps to some fixed surface which is not moving. Then you should be able to see any variations within 0.001 inches or more. These are common in auto shops and are used when testing brake rotors to see if they are warped out of plane, or are improperly mounted. Perhaps there are higher precision gauges which can better measure the variations in your mount machinery.
The finish of the worm has been discussed greatly here in the past. Each new worm is not perfectly identical and has a certain surface profile on the gear tooth faces. How to best break one in and get the best performance may have to do with wearing it it over time, though some have tried various polishing techniques and other methods. If you think your old ones are damaged you can order new, but don't expect super performance just because it is new. It may take a bit of use and adjustments over time to get it to perform to its maximum.?
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Hi
I have just acquired the OPW amd there exists a hole. Does anyone have purchased it recently? Is it for a spring mechanism??
Thanks
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Re: Poor guiding with GM8
Guilherme,
Could you please share your guide log with guiding disabled or graphs, similar to what I posted?
What kind of worm do you have - is it brass or steel?
Alex
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What result I can get with the current OPW in my old G11?
Hello all!
I live in Brazil and I have a G11 for about 10 years and I never could get really good tracking.?
I finally purchased the OPW (after a long wait) for the RA axis and the new "high precision" worm for the DEC axis.
I would like to hear from members here what result I can wait in terms of PE and guided RMS erros after installing the OPW?
Also does anyone can recommend some instructions on how to install it?
Thanks you so much!
Andre
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Re: Poor guiding with GM8
I use direct drive with my GM8, see in the showcase page. It works just fine with a 400 steps NEMA17 motor, with slews up to 3.5 degrees/s. I also use a spiral coupler instead of the oldham model that came with it.?
The problem with PE is still bad in my case though. I believe it has more to do with the old worm. I recently acquired an OPW with a new high precision worm for the GM8, and will compare the PE before/after.
Guilherme
On Wed, Jul 28, 2021 at 5:09 PM Alexander Varakin < avarakin@...> wrote: Pete,
I also have G11 and I am using Onstep with the direct drive there too.
Unfortunately, GM8 has only 180 teeth on the ring gear vs 360 for G11, so I believe that doing a direct drive for GM8 would be pushing it.
In any case, I did try direct drive and I still saw bad PE.
Let us know how your mod goes, I was wondering about using the Oldham too. I am currently using the spiral coupler, I believe that most folks do this as well.
Alan,
I will check it, but I think it is optical illusion.
John,
Good point, I will try to loosen up the belt a little.
Michael,
Good point too. Is there an article somewhere, describing how to align worm against the ring?
I am reading this forum on a regular basis and did not see a discussion on this subject.
All,
How consistent is the quality of the brass worms? Does it make sense to get a new one?
I guess I can try to pull one from my G11...
Alex
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Re: Poor guiding with GM8
Pete,
I also have G11 and I am using Onstep with the direct drive there too.
Unfortunately, GM8 has only 180 teeth on the ring gear vs 360 for G11, so I believe that doing a direct drive for GM8 would be pushing it.
In any case, I did try direct drive and I still saw bad PE.
Let us know how your mod goes, I was wondering about using the Oldham too. I am currently using the spiral coupler, I believe that most folks do this as well.
Alan,
I will check it, but I think it is optical illusion.
John,
Good point, I will try to loosen up the belt a little.
Michael,
Good point too. Is there an article somewhere, describing how to align worm against the ring?
I am reading this forum on a regular basis and did not see a discussion on this subject.
All,
How consistent is the quality of the brass worms? Does it make sense to get a new one?
I guess I can try to pull one from my G11...
Alex
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Re: Poor guiding with GM8
Alan,? By "main", are you referring to the pulley on the worm?? Given the 480 second PE this seems likely.??
If so, Alexander should check that this pulley is firmly located and tight on the shaft.? There is not much room to make the set screws in the pulley engage with the shaft.
I'm doing an OnStep install on my CG11 and I opted not to do what Alexander has done and use a belt drive.? Instead I am planning to use two new Oldham Couplers to fit the worm shaft in it original position and drill out the 3/16" end of the coupler by 0.235mm to 5mm and then directly mount a 0.9 degree step Nema 17 to that thus avoiding belt drives.? This will be my third OnStep conversion and I hope the best.
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Re: Poor guiding with GM8
Your main pulley is off-center, which gives a 480 s periodic error.
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Re: Changing the servo motor encoders from 256 to 512 or 1024. Any reason not to do this?
The full gory details of how the position counter value is determined are in Microchip document 70208C.pdf (“Quadrature Encoder Interface”): ?
? David ?
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From: [email protected] <[email protected]> On Behalf Of Paul Kanevsky
Sent: 27 July 2021 20:42
To: [email protected]
Subject: Re: [Losmandy_users_io] Changing the servo motor encoders from 256 to 512 or 1024. Any reason not to do this? ? Peter,
Entirely possible and even likely. I'm not arguing with your results. All I was trying to do was to correct some information that was posted earlier on the encoder precision. Gemini PIC controller reads encoders in quadrature, and so the effective resolution is 4x smaller than the (Gemini-addressable) step size.
Regards,
? ? ? -Paul
On Tue, Jul 27, 2021 at 03:32 PM, <pcboreland@...> wrote: Paul,
This is where people are getting confused I think.? The positioning step accuracy is 0.5625". Therefore if you what to make a Dec correction it will be that large. You can not move the motor a 1/4 step.? ?If you install a 1024 encoder you can make a 0.1405" step move. The results are night and day as far as Dec guiding performance. In the chart just posted Dec rms was 0.15", about the same size as the step resolution. There is no point fighting the facts, a higher res encoder will greatly improve your Dec guiding.?
Peter
PS. Before this change by Dec guided at about 0.74" rms.
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Re: Poor guiding with GM8
Alex,
Quite an interesting pic showing your design. If there was ever an arrangement that should remove all gear slop from the stock mounts I would think it would look just like this. Since your deviations are multiples of the worm period, some kind of PEC correction curve should be of benefit. But how to program one into on OnStep I have no idea. You know the brass worms can be bent under the right amount of force, perhaps from your belt tension? If you place a worm in a cordless drill at low speed and stare down the end of the shaft, you should be able to see if the worm end spins in a tight circle, or starts to oscillate out of round. Or some other round piece is doing an ellipse, not a circle.?
You are the trendsetter here, and I certainly hope you can help with a future design model.
Good luck!
John
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Re: Poor guiding with GM8
Alex,
That's a very nice system.
But it is so different from anything "stock" that I'm at a complete loss to advise you.
Your system drive seems sensible, and as the oscillations are at the worm period, so they could be related to anything like the pulley on the worm or anything the worm is driving.? It cannot be anything related to the geared down (by the pulley ratio) in front of the worm.? Those would be at much higher frequency = shorter period.?
Definitely examine the worm center line height vs the ring gear center height.? ?
Best of luck,
Michael
On Tue, Jul 27, 2021, 6:52 PM Alexander Varakin < avarakin@...> wrote: Hi Michael,
Many thanks for the detailed reply.?
Here is my mechanical setup - I have the reverse worm setup with time gear attached directly to the shaft of the worm. The larger gear is 60 and the smaller is 16.
The aluminum parts form an arrangement, which works as OPW. I drilled and tapped the holes in the bearing blocks in order to make the whole thing as one piece.
So I don't have an Oldham coupler and there is no possibility of misaligning the motor and worm shafts.
I have ABEC 7 bearings and I also tried the Belleville spring, it did not help.
I also tried swapping the worms, looks like it does not help, based on few minutes of testing, before clouds rolled in.?
I have brass worms. I wonder if I should buy new worms.
Right now I am running out of ideas...
Alex
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Pete
David C. Partridge
Michael Herman