Re: Relationship between needle bearing wobble and variable worm mesh and backlash
I am not sure why they used needle bearings in the RA and DEC axes.? Tapered roller bears are really the bearing of choice in this application.? The taper roller bearings combine the function of the thrust bearing and the needle bearing in one, simplifying the design. Pre-loading of the bearings will center both ends of the shaft and take on tremendous axial and radial loads.? Two bearings and you are done.? They are on your car axles and take thousands of pounds of live load and hundreds of RPM.? ?You also don't need a lot of preload.? Even axially capable bearings would be a good alternate (they look like regular ball bearings but the races are purposefully machined to accept a large axial load, again combining a thrust and radial bearing).? Unfortunately, they are all more expensive.??
Regarding the clutches, I agree, putting more pressure on the clutch bearing surfaces invariably puts more pressure on the roller bearings.? Not that the pressure scares me, I just think the necessary slop between the shaft and the needle bearings, and combined functions, makes it difficult to fine tune the mount to the next level.??
I own a G11, well over 20 years old.? Some of my best guiding is around 1" RMS using a 400mm guide scope and a ZWO120.? The graph is ugly (up to 4" peaks) compared to others that have been posted.? I am not sure where to start to fix this.? Currently I am performing the Onstep conversion and I will be rotating the drive to the top to clear the altitude adj knob and I am also spring loading the worm.
Bob
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Re: 76sec error on new OPW-11
Peter,
That's the right side journal that moves to adjust the backlash.
I thought it was funny that it wouldn't be anodized but the cut is definitely not right.
I purchased the OPW as a standalone.
I already purchased the brass worm.
This is on a 2006 (?) G-11 with straight in motors.
I was in the machinist trade over 30 years and this looks like it overlooked somehow during QA.
If I don't hear back from Brian I'll email Tanya tomorrow and show her the picture.
Jim P
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Re: 76sec error on new OPW-11
Jim,
That's not right. It looks all chewed up. They are smooth and black on the bottom. The left hand one has no movement in it's hole. The right hand one can move a little in it's hole. They ought to replace these, or better yet take a look at the entire worm assembly, as there could be other manufacturing issues. What about the hole in the plate?
Peter
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Re: 76sec error on new OPW-11
Brian,
Here's the logs from the other night.
Last night something happened with my NINA sequence and it's all screwed up.
There's also a picture of one of the bearing blocks that came with the OPW from your shop.
It looks like something shifted during the cut and there is a step on the journal that rides in the base plate.
In your opinion, do you think this could lead to problems?
The way it is now, only about half of the journal is in contact with the base at any one time.
Jim P
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Re: 76sec error on new OPW-11
On Wed, Aug 4, 2021 at 09:41 AM, Keith wrote:
Peter:
- The left arrangement in the photo does nothing as it follows the shape of the bearing itself and there is no spring force at all (I noticed this when I first tried the washer as well)
- I really don't think your 80s error is bearing related, and is probably from the McLennan gearbox.? When I used to have the bearing error, it was clearly 76s and not 80s.
- FWIW, I asked someone at Boca Bearings if they thought ceramic bearings would be any better for this application, and they didn't really think so (but of course one can always try)
Keith
Keith, Thanks for this input. You could be entirely right about the 80s error. I too have speculated about this and the McLennan gearboxes. Although its pretty constant in magnitude between the 25:1 and 125:1 models. There are reports of the 76s error moving to 80s with the OPW drive, but there are? reports of people a new mount and OPW with a sizable 76s error. Interestingly I do not have this error. I'm moving in an entirely different direction going with onstep and using servos with high resolution optical encoders to direct drive the worm. No more gears. Of coarse when this is built I will know one way or the other where this 80s error originates. Peter
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Re: 76sec error on new OPW-11
Peter:
- The left arrangement in the photo does nothing as it follows the shape of the bearing itself and there is no spring force at all (I noticed this when I first tried the washer as well)
- I really don't think your 80s error is bearing related, and is probably from the McLennan gearbox.? When I used to have the bearing error, it was clearly 76s and not 80s.
- FWIW, I asked someone at Boca Bearings if they thought ceramic bearings would be any better for this application, and they didn't really think so (but of course one can always try)
Keith
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Re: 76sec error on new OPW-11
Chip,
Just to be clear, the arrangement on the left places pressure directly on the ball race as shown in the drawing, while the arrangement on the right place pressure on the outer shell? You are correct I did follow Michaels drawing detail on this.?
Peter
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Re: G11 Performance Enhancement Criteria - Design Improvements and Ideas to overcome Performance Limitations
Michael B-Y has tallied quite a list of design concerns.??
Comments and known solutions:
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Clutch slippage:
The slippery clutch problem (losing index position relative to motor tick position, and slippage caused by oil contamination of the disk surface) can be solved easily by replacing the slippery disks with a high friction seal type.? ( I do make high friction clutch disks for these mounts. )?
There is a wavy heavy washer in the back of the axis, under the clutch knob, that "preloads" the thrust bearings and the clutch disk.?? ? ?a) on RA this is a static force (from the wavy spring and the entire weight of the scope and counterweights x sine of the polar elevation angle) preloading the axis ? ?b) on DEC this is a variable force, because the weight goes from 100% to 0% as the RA and DEC angles change.? Pointing to zenith gives 100% weight on the clutch and if the CW bar is horizontal the weight is 0%.? If your scope is weightless (say a short 80mm doublet) it won't matter.? If your scope is heavy (12 inch Newtonian) the effect is dramatic. This is why the wide variety of our amateur users have a wide variety of issues...or no issues at all.?
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The needle bearing problems that have been listed affect some mounts and not others.? It was recently reported by Mark Crossley here in email, but not on his website, for his mount of decades ago.? On my own 5 RA and 4 DEC axes, I cannot feel this problem. All shafts are snug in the needle bearings.? My mounts span the production years 1996 to 2016.? It was not felt this week in Vishal's mount of 2021.? But it was also discovered by Peter in his mount... predates tucked motors.??
So this problem is rare but has occurred. This is a production control/ quality control issue and the solution is to have the factory fix it.? The shafts must fit snugly into the cylindrical needle bearings.? If the factory undercut the 1.25 inch shafts, or the bearings have slightly smaller needle rollers, or the outer enclosure race sleeve is larger, then the axis will have excessive play.? That's why the mounts have to be hand fitted at the factory.?
Peter planned to solve his axial play by getting needle bearings with larger roller needles, but this is then a problem for getting the bearing into the mount body, and getting the shaft into the bearing.? Peter did find his cylindrical needle bearings could be popped out on his mount with finger force, but I could not remove my bearings even with hammer blows and a wood dowel.? ?So these needle bearings certainly vary as does everything else mechanical. Peter also is thinking about plating the shafts to increase their OD.? This is more work and then you must ensure perfect plating adhesion.??
I feel that the only viable and correct solution is at the factory. The shafts have to be fitted by the factory and re-worked with the proper diameter shaft.? Or different bearings ... every mechanical thing that is made has an allowed tolerance.? The burden of fitting the parts together properly falls on the mount maker.? They need a quality control checklist and staff to follow it.? ?Chip has told me that the rare cases he has heard of this problem were fixed at the factory, which is nice as he lives near that location.? But these problems should not ever have left the factory in the first place.??
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Worm to ring gear spacing
This is a research paper of its own, but the solutions are: ? 1. Get better quality RA worm bearings. ? ? ? ? Factory bearings are usually nice and smooth rotation.? Unknown quality rating (ABEC bearing quality rating system exists...and there are cheaters everywhere on earth.) ? ? ? ?Owners can buy ABEC-7 quality rated for about $11 each from several suppliers.?? ? ? ? Hugo Garnica extolls these:
G11 Ceramic Bearings for better PE
From Hugo Garnica in Tehachapi California:
??
These are (expensive?) all ceramic bearings and he says they got rid of all his bearing PE problems.? Not cheap and I don't know how they would fit in all bearing blocks, or be able to preload them.? You'd have to likely enlarge the bearing block cylinder.? Anyway I have not yet tried these out.
2. Get rid of the worm axial shift issue. This is only done by preloading the wirm with a spring.? Industry makes precise springs for each bearing type.? The G11 and GM8 use an R4 size Belleville spring.??
3. Align the entire bearing to the worm axis.? This requires a perfect cylinder hole inside the worm block.? Some slight automatic realignment of the bearing can be obtained by polishing down the bearing OD (if it's a metal bearing, not ceramic!) and using a Belleville spring.? The reduced bearing OD can then slightly adjust it's OD axis to follow the worm 1/4 inch shaft.??
But that can only work well if the worm is not pressed firmly into the ring gear.? Why?? If the worm is pressed tightly into the ring gear, the outward force must push the bearing into the wall of the bearing block.? If the bearing block hole is not perfectly aligned with the wirm axis, the bearing must follow the block axus, not the worm axis.? This is why the worm must maintain a slight gap to the ring gear..unless you have perfect worm blocks and an OPW to hold the blocks outer surfaces parallel.
Solution:? Leave a slight worm gap, and hang a weighted cord (a few pounds is usually adequate) around the RA axis with the weight hanging (always) to the East.? This gently preloads the ring gear to the worm gear.? Hanging to the East eliminates a possible "chatter" of the ring gear as friction from the worm gear can vibrate the ring gear.? And use a low friction high pressure capable grease there between the worm and ring gear.??
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Other stuff:
I find the AZ and Elevation locking knobs go too slack when loosened to adjust polar alignment.? So I preload those bolts with 3/8 Belleville spring washers.? Then you get an easily adjustable pressure on these locking points.? Be sure your AZ and Elevation don't wiggle when you are trying to image.
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I'll not go further...here.
I hope I've made helpful comments.? The argument for buying a domestic mount has been that the factory has always supported it's customers with solutions if they discover a manufacturing error. They must continue this tradition. On a new mount the answers must come from the factory, or else replace it.???I think the answers must come from the factory for severe mechanical problems like the 1.25 inch needle bearings fit.? They have the parts to make them fit.??
Have fun and happy imaging!
Michael Herman
I have a hard time believing that there is a 43 minute periodic error
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Re: Wanted High Torque Motor and Gemini 1 or 2 controller.
Hi Rodd,
I do have a Gemini 1 that I believe is in good condition.? I upgraded my Titan to Gemini 2 last year.? No idea of fair value or shipping costs from USA.
Michael
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What are expected RMS arc second guiding numbers? new G11G users are getting?? -and at what focal lengths.
This is for the new G11G with the spring loaded worm.
Thanks for the input everyone!
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Re: 76sec error on new OPW-11
On Wed, Aug 4, 2021 at 08:15 AM, Chip Louie wrote:
This drawing has an error probably because you saw Michael Herman's drawing and don't understand how this is supposed to work.?
The bearing's outer shell is the part that is pressed by the spring disc NOT the inner race which carries the worm!
By orienting the spring disc to contact the inner bearing shell or possibly worse the bearing dist cover you are creating pressure and drag where it should not be and potentially leaving the problem of unloaded bearing balls in the bearing unchanged.?
This drawing needs to be replaced with the correct orientation not just an edited text.?
Chip, OK, since I have gotten several push backs on this, and since I have quite a few guide logs that show a consistence error, I will reverse the washer and report back. I truly hope you guys are right! Peter
Please believe me on this point as was adding Belleville spring discs to HEQ5 and EQ6 mounts before the GOTO computers were standard to solve this issue and the impact of thermal changes. Bearing induced PE is not unique to Losmandy mounts but it is more obvious because there is no threaded cap to retain the bearings which can e used to preload the worm bearings.?
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Re: 76sec error on new OPW-11
On Wed, Aug 4, 2021 at 07:13 AM, Keith wrote:
The washer in the drawing is backwards (should be contacting the outer race).
Keith
Keith, This arrangement produced the lowest PE for me and I think I tried all possible arrangements .? My thoughts as to why this is, is? it is equalizing the pressure why the worm being driven into the bearing.? However my guided PE at 80s is still way too high at 0.7 arc-sec while guiding at Latitude 30 degrees. Michael Herman has suggest that I? try full ceramic bearings. They are expensive so I have opted to buy them in from China at $12 each. Will only use on the Ra axis. Peter
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Re: 76sec error on new OPW-11
On Wed, Aug 4, 2021 at 07:13 AM, Keith wrote:
The washer in the drawing is backwards (should be contacting the outer race).
Keith
Just saw this, 100% correct!? ? -- Chip Louie Chief Daydreamer Imagination Hardware?
? ?Astropheric Weather Forecast - South Pasadena, CA?
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Re: 76sec error on new OPW-11
This drawing has an error probably because you saw Michael Herman's drawing and don't understand how this is supposed to work.?
The bearing's outer shell is the part that is pressed by the spring disc NOT the inner race which carries the worm!
By orienting the spring disc to contact the inner bearing shell or possibly worse the bearing dist cover you are creating pressure and drag where it should not be and potentially leaving the problem of unloaded bearing balls in the bearing unchanged.?
This drawing needs to be replaced with the correct orientation not just an edited text.?
Please believe me on this point as was adding Belleville spring discs to HEQ5 and EQ6 mounts before the GOTO computers were standard to solve this issue and the impact of thermal changes. Bearing induced PE is not unique to Losmandy mounts but it is more obvious because there is no threaded cap to retain the bearings which can e used to preload the worm bearings.?
--
Chip Louie Chief Daydreamer Imagination Hardware?
? ?Astropheric Weather Forecast - South Pasadena, CA?
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Re: 76sec error on new OPW-11
The washer in the drawing is backwards (should be contacting the outer race).
Keith
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Re: G11 Performance Enhancement Criteria - Design Improvements and Ideas to overcome Performance Limitations
I have a hard time believing that there is a 43 minute periodic error
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Re: G11 Performance Enhancement Criteria - Design Improvements and Ideas to overcome Performance Limitations
On Wed, Aug 4, 2021 at 08:15 AM, <pcboreland@...> wrote:
On Wed, Aug 4, 2021 at 02:27 AM, Michael Ben-Yehuda wrote:
Use of axial needle roller bearings for the RA and DEC axis shafts
- ?They are not pre loaded.
- Bearing load is uneven causing uneven wear on the axis.
- required shaft clearance causes mis-alignment of the axis (axis 'sag') and non axial rotation
- ?do not prevent wobble
Michael,
I've said a lot about have to minimizes periodic errors from? the gearboxes and the worm assembly in the past month, and how to and improve Dec guiding performance through using smaller step sizes. Most recently, I've found that the movement in the Dec and Ra axis due to the fit of the shaft and the needle bearings is a foundational problem that leads to worm mesh viability based on rotational position. This creates a low frequency PE (2600s error or larger depending on the thrust bearings used), creates viable backlash as a function of rotation, and effects the 240s error again as a function of rotation.
Further I found that the use of the thrust bearings from McMaster do a better job than the stock bearings as they are more accurately made.
My suggestion is? to first focus on this needle bearings problem. It would certainly be most appreciated by me.
Peter
How would you fix it?? Better thrust bearings are not all that is needed, and it would be good to quantify this. A 2600 s periodic error is easily guided out.? Variable backlash can be fixed by true SLWs.? The variable PA as the axis rotates will affect the guding to some extent but a few " should not be disastrous.? Should we live with the hard to fix axis situation? and ask for better SLW instead? One thought is to add a force sensor on the worm that senses how much friction it is subjected to, and have the position of the outer block be controlled by a motor that backs off the worm position if there is too much friction, and moves it in when there is not enough.? The current SLW apparently suffers from the unavoidable friction of constant spring pressure that causes the worm to run up resulting in wobble.? A motor could adjust the worm just right without adding too much pressure.? Another idea for a sensor would be to have a wheel in the grooves of both the worm and the ring gear both left and right, and produce an electric pressure signal that can be processed independently for the worm eccentricity and the ring gear eccentricity.? Such systems could just be add ons.? Such systems are easier to make than fixing the axes, I think.
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Re: 76sec error on new OPW-11
On Tue, Aug 3, 2021 at 03:31 PM, Jim Pollard wrote:
I purchased the one piece worm from Losmandy hoping to get rid of some of my errors.
So far my 76 sec is worse than ever, and my PHD2 rms got worse.
I snugged the bolts for the worm block to worm housing first, then slightly snugged the bolts to the mount.
I then slightly loosened the worm block bolts to allow them to center with the worm, and then tightened them.
I've tried twice now and still get the same result
There's no noticeable backlash and it seems to run smooth, but obviously something is wrong.
The immediate thought is the worm blocks are "twisting" somehow and putting side load on the bearing.
Since I got almost the same results after R&R the assembly I wonder if the housing was drilled/bored off center.
Appreciate any help and input.
Thanks
Jim P
Jim, As you know this is a bearing problem. Try this arrangement with just the one spring washer.? Also I found that these bearings were much better than the stock bearings:? Also, I just ordered these ceramic bearings to tryout:? Please report back you findings if you decid3ed to make these changes. Peter
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Re: Relationship between needle bearing wobble and variable worm mesh and backlash
I think as a group we have hit upon the loose fit of the shaft in some but not necessarily all cases is perhaps a foundational problem that it is creating a fore-aft force on the ring gear. If this problem is not resolved further improvements like using onstep (direct drive stepper motors) or changing our encoders and or gearboxes will only get you part way. The reason I say this is because is my best performance is achieved above 60 degrees. At 30 degrees guiding is degraded. This is I'm sure due to the atmosphere and seeing, but I suspect also the mount. This slop problem effects Dec backlash, creates motor stall problems, slew pointing accuracy, and PHD2 repeatable due to the lack of indexing and varying thrust bearing pressure.
Is there away to get a close, well centered, axial fit of the Dec and Ra shafts?
Peter??
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Re: Losmandy GM-8: Anomalous wearing of R.A. shaft
Michael's clutch discs are ?material similar to those used in Celestron Nexstar GT, 5/8 and 6/8 models for the last two decades. In the Nexstars they are designed to slip to prevent damage to the drive mechanisms in the event of crashes. The?pressure is maintained by a rather heavy Bellevue washer.
Eventually, they may begin to slip below the loading needed for protection, and cleaning and adjustment is necessary, but they give very long service. I feel the CKS clutch knobs are a bandaid for nylon discs.
As modifications go Mike's friction discs are among the easiest.
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Michael Herman
Chip Louie