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Re: Need alignment/modeling help

 

Dear Brian,

Given the changes of daylight savings time starting date over the years, it's easy to get the hour off by 1 hour...at least that's my theory.? ?

The solution is this: only enter the UTC time, which is exact.? To do that, set the time zone offset to zero.? (That is, don't try to enter your local time...it is unnecessary and prone to error).? ?Then enter the UTC time.? Then enter your latitude and longitude.

Then Cold Start from.CWD position.? (Not Quick Start!).? Cold start erases any data in the "model" as these model terms are actually "error" terms.? It is easy for one if these to be wrong and throw your mount pointing into error.

Try those things and report back what you get!

All the best,
Michael

On Thu, Jul 29, 2021, 8:18 PM brianm <bkmiller4463@...> wrote:

Hi all, great forum. I¡¯m not sure if what I¡¯m experiencing is normal, hence the post. I have a new G11G/Gemini 2. PA to start is decent but not perfect, probably within a dozen arc minutes of where it should be.

Mount level, CWD down, Quick start. Mount type, location, time and offset all correct. Finder and OTA aligned with each other. Start the model, slew to (in this case) Spica, and Spica isn¡¯t anywhere to be found in my Meade 7x50 finder. After some major centering gymnastics, I do the usual model-align-back routine and go to Arcturus. Same issue, rinse, repeat. Try something in the east - same problem. I¡¯ve been using a 55 Plossl just to make things easier, then fine centering with a 9mm. The same routine is necessary on subsequent gotos; it¡¯s a night-long struggle.? I have had some success synching, but it¡¯s still not nailing the gotos.

I MUST be missing something. Any ideas?

Thanks!
Need alignment/modeling help

brianm
 

Hi all, great forum. I¡¯m not sure if what I¡¯m experiencing is normal, hence the post. I have a new G11G/Gemini 2. PA to start is decent but not perfect, probably within a dozen arc minutes of where it should be.

Mount level, CWD down, Quick start. Mount type, location, time and offset all correct. Finder and OTA aligned with each other. Start the model, slew to (in this case) Spica, and Spica isn¡¯t anywhere to be found in my Meade 7x50 finder. After some major centering gymnastics, I do the usual model-align-back routine and go to Arcturus. Same issue, rinse, repeat. Try something in the east - same problem. I¡¯ve been using a 55 Plossl just to make things easier, then fine centering with a 9mm. The same routine is necessary on subsequent gotos; it¡¯s a night-long struggle. ?I have had some success synching, but it¡¯s still not nailing the gotos.

I MUST be missing something. Any ideas?

Thanks!
Re: What result I can get with the current OPW in my old G11?

 

On Thu, Jul 29, 2021 at 08:50 AM, andre_moutinho wrote:
You say I need replace the just acquired OPW bearings?
Andre,

Most people who do a mount rebuild usually replace the bearings at the same time. They are inexpensive and therefore disposable. If you just ordered new ones from Losmandy, you should be OK. When inserting into the worm block, use care to press in evenly with pressure or gently tapping on the outside race only. If you press on the inside you can bend them, or if inserted on an angle, they can be warped out of round, and you can create the dreaded 76 second error, where the balls are not riding smoothly between the inner and outer races.

Also the bearing should slide smoothly with finger pressure over the brass worm and should not be forced in or hammered in. One new brass worm I received was very slightly oversized, and I used 400 mesh sandpaper to gently twist and polish the end down until the bearing would fit over.?

Usually I have several new bearings on hand, just in case of any mistake, or possible damage during insertion, or guiding errors that could develop later.

Best Regards,

John
Re: Poor guiding with GM8

 

On Fri, Jul 30, 2021 at 06:36 AM, <pcboreland@...> wrote:
I'm hard pressed to see the larger periodic error being ?associated with the worm. You might be looking in the wrong place. May I suggest you change the the thrust beings. I would recommend buying them from McMaster, not Losmandy.
The largest component of my PE is 480s, which is exactly the worm rotation period, so it must be something with the worm.
Before doing lapping with diamond paste, I think I will start with natural polishing - crank up the sidereal speed of Onstep to 100x and run the mount like this for a few hours.?
BTW, the main issue is not really the PE itself:? +-8 for 480s worm period is like +-4 for 240s period of G11 and guiding should be able to correct such slow-moving errors.
The main issue is that there is a lot of noise and spikes in the guiding graph and lapping should smooth things out.
Re: Poor guiding with GM8

 

Alexander,

I'm hard pressed to see the larger periodic error being ?associated with the worm. You might be looking in the wrong place. May I suggest you change the the thrust beings. I would recommend buying them from McMaster, not Losmandy.

Peter
Re: Poor guiding with GM8

 

On Thu, Jul 29, 2021 at 12:08 PM, alan137 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.
Makes sense, will check it out.
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?
Re: What result I can get with the current OPW in my old G11?

 

¿ªÔÆÌåÓý

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:

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?

 

¿ªÔÆÌåÓý

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
Re: What result I can get with the current OPW in my old G11?

 
Edited

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
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
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.
Re: What result I can get with the current OPW in my old G11?

 
Edited

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.
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.
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.?
OPW with a hole?!

 

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
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
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
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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