Eq6r worm gears

[Wonderweb]

Hi. 

Just wondering if there are better quality worm gear sets or drive motors that can be fitted to an eq6-r to improve tracking accuracy? Mine seems to have a performance range between 0.7 and 1.2 rms but I hear people getting crazy figures like 0.3 out of their eq6-r.  I have recently changed the bearings and tuned out as much backlash as possible (I have a maintenance engineering background so I know my way round drives/gears/belts etc) but it hasn't really improved things. When I ran PEC training, the curve seemed to be all over the place which lead me to think maybe the gears are poor quality. I have zero binding anywhere in the drive train so I can't really think what else it could be. Would lapping the gears help? T.I.A

[omo]

Something like this possibly:  Rowan Astronomy Zero Backlash Worm Mount

Needs the Rowan Belt drives as well. No idea how well it performs, but everything i have had from Rowan Astro has been very very good.

[wookie1965]

https://www.astrofriend.eu/astronomy/projects/project-eq6-dismantling-rebuilding/02-eq6-dismantling-rebuilding.html

Dont know if this is any good to you. 

[Stuart1971]

13 hours ago, Wonderweb said:

Hi. 

Just wondering if there are better quality worm gear sets or drive motors that can be fitted to an eq6-r to improve tracking accuracy? Mine seems to have a performance range between 0.7 and 1.2 rms but I hear people getting crazy figures like 0.3 out of their eq6-r.  I have recently changed the bearings and tuned out as much backlash as possible (I have a maintenance engineering background so I know my way round drives/gears/belts etc) but it hasn't really improved things. When I ran PEC training, the curve seemed to be all over the place which lead me to think maybe the gears are poor quality. I have zero binding anywhere in the drive train so I can't really think what else it could be. Would lapping the gears help? T.I.A

Before you start spending a ton on money on that mount, just to get you RMS down by .2 or .3 RMS, ask yourself a few questions, forget what other people say they get with this mount, as people will always quote those low figures, as they have seen them for 10 mins on one night,  I have had 0.2 RMS from my mount, for an hour or 2 on the odd night when seeing was really good, and in certain parts of the sky,  but mostly it’s around 0.6 to 0.9 which for my imaging scale of 1.4”/pixel is perfect.

So ask yourself, what is you imaging scale, and your seeing, in the UK the seeing at best is probably around 1.5”, so really your guiding does not need to be any better than that in theory, as you are seeing limited, and if you imaging scale is lower, you are still seeing limited, so guiding at 0.7 to 1.2 RMS would be fine…

I think some people get too hung up on getting there RMS figures as low as possible, if you ]r images are good and the stars are round then just enjoy, all what is more important is to keep your RA and DEC rms figures as close to each other as you can, as if you have one that is double the other then you can get elongated stars no matter what your guiding is like, so that is something else very often missed..

[Wonderweb]

38 minutes ago, Stuart1971 said:

Before you start spending a ton on money on that mount, just to get you RMS down by .2 or .3 RMS, ask yourself a few questions, forget what other people say they get with this mount, as people will always quote those low figures, as they have seen them for 10 mins on one night,  I have had 0.2 RMS from my mount, for an hour or 2 on the odd night when seeing was really good, and in certain parts of the sky,  but mostly it’s around 0.6 to 0.9 which for my imaging scale of 1.4”/pixel is perfect.

So ask yourself, what is you imaging scale, and your seeing, in the UK the seeing at best is probably around 1.5”, so really your guiding does not need to be any better than that in theory, as you are seeing limited, and if you imaging scale is lower, you are still seeing limited, so guiding at 0.7 to 1.2 RMS would be fine…

I think some people get too hung up on getting there RMS figures as low as possible, if you ]r images are good and the stars are round then just enjoy, all what is more important is to keep your RA and DEC rms figures as close to each other as you can, as if you have one that is double the other then you can get elongated stars no matter what your guiding is like, so that is something else very often missed..

Hi Stuart. Thanks for the info. I totally agree that the limiting factor is probably the seeing, but I was curious as to what was available and above all, if maybe an engineering solution (lapping the gears) would improve my tracking accuracy rather than relying on a pec training to make the best of a bad job. 

Depending on which camera scope combo I use my pixel scale can be anywhere from 1.7"/pixel down to 0.4"/pixel (although i dont often attempt the lower end). I mostly operate at around 0.75"/pixel so would like to try and get things as stable as possible. 

Edited Wednesday at 08:43 by Wonderweb

[malc-c]

My suggestion would be to simply upgrade the mount to belt drive and then see what you get from that.  Once you have done that and adjusted the backlash on the worm you may find the reduction in RMS is within the range you are looking for with out the need to strip the mount and spend a fortune updating the bearings etc.

[Wonderweb]

On 25/09/2024 at 11:10, malc-c said:

My suggestion would be to simply upgrade the mount to belt drive and then see what you get from that.  Once you have done that and adjusted the backlash on the worm you may find the reduction in RMS is within the range you are looking for with out the need to strip the mount and spend a fortune updating the bearings etc.

Hi malc. The mount is already belt driven. I spent a lot of time tuning out backlash when I changed the bearings. Since I did this, I have seen very little improvement in performance. Its very frustrating.  

[Tomatobro]

are the stars nice and round for the exposure times you use?

[Ardsley Astro]

I've just been speaking with some of the engineering guys where I work about backlash. They said they would normally expect something like a PTFE coating on worm gears. It's soft and slippy so should take up backlash and reduce sticktion at the same time. Bare in mind these guys don't know anything about EQ mounts, but I find it a interesting idea. If I had an old out of warranty mount I'd have a go with it. Should be easily removed if it becomes problematic. I'm actually using PTFE tape as a fix for stripped threads on the tube ring of my OTA. 

 

[vlaiv]

On 25/09/2024 at 10:01, Stuart1971 said:

Before you start spending a ton on money on that mount, just to get you RMS down by .2 or .3 RMS, ask yourself a few questions, forget what other people say they get with this mount, as people will always quote those low figures, as they have seen them for 10 mins on one night,  I have had 0.2 RMS from my mount, for an hour or 2 on the odd night when seeing was really good, and in certain parts of the sky,  but mostly it’s around 0.6 to 0.9 which for my imaging scale of 1.4”/pixel is perfect.

So ask yourself, what is you imaging scale, and your seeing, in the UK the seeing at best is probably around 1.5”, so really your guiding does not need to be any better than that in theory, as you are seeing limited, and if you imaging scale is lower, you are still seeing limited, so guiding at 0.7 to 1.2 RMS would be fine…

I think some people get too hung up on getting there RMS figures as low as possible, if you ]r images are good and the stars are round then just enjoy, all what is more important is to keep your RA and DEC rms figures as close to each other as you can, as if you have one that is double the other then you can get elongated stars no matter what your guiding is like, so that is something else very often missed..

Mount performance always adds up to seeing to increase FWHM and reduce sharpness of the image - no matter what the seeing is.

If one is disproportionally large compared to the other - sure, other will not have much effect, but do keep in mind that FWHM to RMS of Gaussian curve is x2.355 - so seeing that is 2" is the same as guiding that is 2 / 2.355 = ~0.85" RMS - as you can see, they tend to be rather similar and have similar impact on star size in the end.

On 25/09/2024 at 10:39, Wonderweb said:

Hi Stuart. Thanks for the info. I totally agree that the limiting factor is probably the seeing, but I was curious as to what was available and above all, if maybe an engineering solution (lapping the gears) would improve my tracking accuracy rather than relying on a pec training to make the best of a bad job. 

Depending on which camera scope combo I use my pixel scale can be anywhere from 1.7"/pixel down to 0.4"/pixel (although i dont often attempt the lower end). I mostly operate at around 0.75"/pixel so would like to try and get things as stable as possible. 

I would always take reported RMS figures with a grain of salt. It really depends on guiding parameters and guiding sensitivity is much less with higher DEC. Most accurate figures for mount guiding performance come from:

- guiding near meridian

- guiding with enough resolution (meaning low enough guide resolution to give precise measurements)

- when the seeing is taken out of the equation - by using longer exposures (at least 2 seconds) and multi star guiding (in best case at least dozen stars).

It is also worth remembering that it is not all down to mechanical precision. There is also part of precision that depends on electrical side of things.

Stepper motors are all more or less rated to +/- 5% accuracy in full step position. This figure is worth remembering and comparing to actual step size in arc seconds.

For EQ6 mount that is: 720:1 is mechanical reduction, further 200 full steps per revolution gives us 360 degrees / (720 * 200) = 9 arc seconds per step.

You will hear that precision of EQ6-R is 0.140625" - but that is with 64 micro steps or 9"/64 = 0.140625". Let's calculate actual error that is 5% of one step or 5% of 9 arc seconds = +/- 0.45".

+/- 0.45" is declared error on stepper motors in EQ6 - and that alone prevents the mount from being guided below 0.5" RMS consistently.

We are guiding at ~15"/s - so above deviation happens about every one and a half second. It won't always be exactly + or - 0.45 but it will be in that range.

Then there is matter of stepper motor drivers and precision of micro stepping. This depends on electronics but also on the power supply. "Dirty" power supply will cause larger error by introducing noise into voltage itself if electronics is not properly filtered with capacitors.

Final remark - you are over sampled at 0.75"/px. You want your sampling rate to be around FWHM/1.6 - so measure FWHM that you can achieve and divide with 1.6 and then aim for that resolution / bin accordingly (prefer binning in software as it is more flexible).