Re: 76 second RA periodic error fixed with Belleville washer
Magnus,
Measuring the current is easy to do these days of digital ammeters...to tell if a gear is jammed or a motor is bad.? ?I already use one for all my Gemini systems power input monitoring. Ivalsobusevitvyo tell if the scope or counterweights are unbalanced.? Using PHD2 to track a star is easy too.? The laser tester... too much work!
I'm testing someone's damaged Gemini-1 now.? It's running a no load hi torque motor just fine.? I suspect the owner has a bad power supply going into this Gemini, making the Gemini appear faulty....or it could be a bad gear jam.? Right now he cannot tell....needs an ammeter.
As I make these for US customers let me know if anyone is interested in trying one.??
All the best, Michael
On Thu, Apr 1, 2021, 3:37 AM Magnus Larsson < magnus@...> wrote:
I guess it is Holy, not Wholy. Sorry, a Swede here.
Magnus
Den 2021-04-01 kl. 12:33, skrev Magnus
Larsson:
"If only there was a way to test RA PE inside with some kind of
(laser?) alignment procedure, or check if the micro amperage to
the motor is changing in some measurable way :). "
This must be the Wholy Graal of using a mount? :) I for one,
totally agree.....
Magnus
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Hi folks
Many of the readers of this group receive the posts by email. If you edit a
post, the entire thing is emailed again, so if you edit a message twice,
everyone who subscribes by email will receive three emails.
So I'd like to ask that you think twice before editing your posts. If it is
just an obvious typo, maybe just let it be, and if it's something important
for understanding , consider replying to your post with a short message,
quoting ONLY the part of the post you are correcting (i.e. not the whole
message or email chain).
Thanks
David
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Re: 76 second RA periodic error fixed with Belleville washer
I guess it is Holy, not Wholy. Sorry, a Swede here.
Magnus
Den 2021-04-01 kl. 12:33, skrev Magnus
Larsson:
toggle quoted message
Show quoted text
"If only there was a way to test RA PE inside with some kind of
(laser?) alignment procedure, or check if the micro amperage to
the motor is changing in some measurable way :). "
This must be the Wholy Graal of using a mount? :) I for one,
totally agree.....
Magnus
|
Re: 76 second RA periodic error fixed with Belleville washer
"If only there was a way to test RA PE inside with some kind of
(laser?) alignment procedure, or check if the micro amperage to
the motor is changing in some measurable way :). "
This must be the Wholy Graal of using a mount? :) I for one,
totally agree.....
Magnus
|
Re: 76 second RA periodic error fixed with Belleville washer
Very clever way of polishing the worm block ID bore, John.?
I had not thought of using such a small wire wheel on a Dremel tool.?
I had talked myself into the theory that the anodized inside of the block was too hard to try polishing it down.?
But if it really were an anodized surface, your wire wheel should not have cut into its surface.? So much for the hard anodized theory!??
Honestly I never felt any grit in the bearing rotation from my sanding down the?bearing OD.? I use the 3M "wet?or dry" sand paper, and the grit does not come off the?surface of that sandpaper. I used the stuff labelled on the back:..."3M 431Q 150 grit Wetordry paper C wt"? Only the stainless steel from the bearing OD went into the sandpaper grit...no grit came off that type of sandpaper.
The bearings I use are "sealed" R4ZZ.? There is no way for any grit to get into these bearings.? Here they are:
[Edited Message Follows]
Michael and all:
With regard to honing done a surface, I found it was much easier to Dremel tool out the block with a wire wheel head than shave down the bearing. (Please see attached). I tried the bearing route at first and had trouble keeping the sanding debris from traveling inside the bearing. I could feel the grit while turning it no matter how many times I rinsed with solvent. And I found this out the hard way by getting some choppy guiding after my first attempt. Perhaps there is an art to it I'm not getting.
Honing the inside of the block only took a few minutes, versus a lengthy and tedious bearing polish job. Then you can wash away any debris without getting junk into the bearings. And you can also change bearings out quickly from then on. The only drawback is if overdone, you can make the ID too large fast, and the block is ruined. So having a spare block on hand before attempting is a good idea. By the time the anodizing is off, you are at the right size to allow the bearing to easily slip in and out. I started with a used wire wheel which was smaller and duller than when new. (Just wondering now if the anodizing thickness can vary and mess with the ID tolerance).
Also after making any change to the blocks and the block positions, the only way to totally prove out is to reassemble everything and get out under the stars and do some guiding. If not right you have to rebuild again, put rig and camera on mount again, polar align, etc. and repeat until satisfied. If only there was a way to test RA PE inside with some kind of (laser?) alignment procedure, or check if the micro amperage to the motor is changing in some measurable way :).?
John
Regards,
John
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Re: 76 second RA periodic error fixed with Belleville washer
Sorry, but can you please take a minute out of your busy day to link specifically to that article that you have "posted many times".? I did a search and only came up with things saying axial preload was important for stiffness, but did not see anything about periodic errors.
If your claim was that axial preload is all that is needed, I disagree.? Before this fix, I tried many different kinds of axial preload such as:
squeeze the bearing blocks by different amounts
purposely set the blocks too far apart and bias the mount east heavy - this still preloads the bearing
purposely leave the mounting bolt a little loose and squeeze the blocks together with a c-clamp plus rubber padding
None of these fixed the problem.
Another thing - I don't have 76 second "spikes".? I have a very smooth sinusoid with only the tiniest amount of second harmonic.? A bearing ball rolling over a piece of dirt will give spikes and throw out all kinds of harmonics as seen the Fourier transform.? Therefore I buy into the theory that it is due to a misaligned bearing only "leaning on" one ball at a time and the sinusoidal axial modulators are due to the load smoothly transitioning from one ball to the next.
In any case, I don't care that much anymore.? The local witch doctor cured my ailment.
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Re: 76 second RA periodic error fixed with Belleville washer
Michael and all:
With regard to honing done a surface, I found it was much easier to Dremel tool out the block with a wire wheel head than shave down the bearing. (Please see attached). I tried the bearing route at first and had trouble keeping the sanding debris from traveling inside the bearing. I could feel the grit while turning it no matter how many times I rinsed with solvent. And I found this out the hard way by getting some choppy guiding after my first attempt. Perhaps there is an art to it I'm not getting.
Honing the inside of the block only took a few minutes, versus a lengthy and tedious bearing polish job. Then you can wash away any debris without getting junk into the bearings. And you can also change bearings out quickly from then on. The only drawback is if overdone, you can make the ID too large fast, and the block is ruined. So having a spare block on hand before attempting is a good idea. By the time the anodizing is off, you are at the right size to allow the bearing to easily slip in and out. I started with a used wire wheel which was smaller and duller than when new. (Just wondering now if the anodizing thickness can vary and mess with the ID tolerance).
Also after making any change to the blocks and the block positions, the only way to totally prove out is to reassemble everything and get out under the stars and do some guiding. If not right you have to rebuild again, put rig and camera on mount again, polar align, etc. and repeat until satisfied. If only there was a way to test RA PE inside with some kind of (laser?) alignment procedure, or check if the micro amperage to the motor is changing in some measurable way :).?
John
Regards,
John
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Re: 76 second RA periodic error fixed with Belleville washer
Chip & michael
Does the bearing info you are posting apply to the new, tucked, spring loaded, gm8 & g11?
Chuck
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On Wednesday, March 31, 2021, 10:00:37 AM PDT, Chip Louie <chiplouie@...> wrote:
On Mon, Mar 29, 2021 at 02:01 PM, alan137 wrote:
Help me out here with a link to the official cause of the problem, and the official solution.
Sorry but AFAIK there is no official comment or opinion on the source of the 76 second spikes from Losmandy. But the cause it well known and commonly resolved by the use of a light preload axially on the worm bearings and worm using Belleville disc springs. I have been using the parts for the R4 bearings for many years in Losmandy G11 and GM8 mounts and people are happy. Before that I used them for many years in SkyWatcher and Orion EQ6/Atlas & HEQ5/Sirius mounts with similar results. This modification has been around a very long time and for Losmandy mounts at least the periodic spike seen at 76 seconds is the bugger it fixes. in the other mounts the period spikes are different because they have different worm gear tooth counts but the idea is the same. Stiffening up the bearing and worm assembly by removing all axial "play" to minimize any looseness in the assembly makes the balls move with the worm at precisely worm speed and poof - 76 second error is gone.
The white paper posted is very good but Michael Herman's paper is better because Michel shows you how to implement this simple improvement. Michael and I had? several discussions about Belleville discs and how they work to improve bearing action. Michael is a scientist in real life so he felt the need to document what I had already knew from practical experience and the result in writing is Michael's fine article and revisions to the 2014 piece. Look in the group.io Losmandy_users files section for a Michael Herman file titled?Improving the Losmandy G11 V3 Aug 7th 2016?which is the 3rd revision and while it has a couple of mistakes in the document his documentation proves it works. It is important to be aware that some of the illustrations show the orientation of the Belleville discs incorrectly. The Belleville disc must not press on the inner race but only on the outer bearing shell! Some mounts will accommodate using two Belleville discs and if this configuration fits in your mount this is the best way to use them.
As far as the white paper links from bearing manufactures go there are several of them on the web, just do a search for bearing preload then look for the sites, go to the big bearing maker sites, they all have these engineering white papers. They all explain the importance of bearing preload and this is where I learned why you need to preload these critical bearings. The how I already told you so now you have it all.
--
Chip Louie Chief Daydreamer Imagination Hardware
? ?Astropheric Weather Forecast - South Pasadena, CA
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Re: Gemini-2 momentarily went haywire
Separate processor for motor control work makes sense for high-precision.? Especially if the main ARM processor isn't running a real-time operating system (and even there it is hard to bound jitter super tight).??
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Re: 76 second RA periodic error fixed with Belleville washer
On Mon, Mar 29, 2021 at 02:01 PM, alan137 wrote:
Help me out here with a link to the official cause of the problem, and the official solution.
Sorry but AFAIK there is no official comment or opinion on the source of the 76 second spikes from Losmandy. But the cause it well known and commonly resolved by the use of a light preload axially on the worm bearings and worm using Belleville disc springs. I have been using the parts for the R4 bearings for many years in Losmandy G11 and GM8 mounts and people are happy. Before that I used them for many years in SkyWatcher and Orion EQ6/Atlas & HEQ5/Sirius mounts with similar results. This modification has been around a very long time and for Losmandy mounts at least the periodic spike seen at 76 seconds is the bugger it fixes. in the other mounts the period spikes are different because they have different worm gear tooth counts but the idea is the same. Stiffening up the bearing and worm assembly by removing all axial "play" to minimize any looseness in the assembly makes the balls move with the worm at precisely worm speed and poof - 76 second error is gone.? The white paper posted is very good but Michael Herman's paper is better because Michel shows you how to implement this simple improvement. Michael and I had? several discussions about Belleville discs and how they work to improve bearing action. Michael is a scientist in real life so he felt the need to document what I had already knew from practical experience and the result in writing is Michael's fine article and revisions to the 2014 piece. Look in the group.io Losmandy_users files section for a Michael Herman file titled? Improving the Losmandy G11 V3 Aug 7th 2016?which is the 3rd revision and while it has a couple of mistakes in the document his documentation proves it works. It is important to be aware that some of the illustrations show the orientation of the Belleville discs incorrectly. The Belleville disc must not press on the inner race but only on the outer bearing shell! Some mounts will accommodate using two Belleville discs and if this configuration fits in your mount this is the best way to use them.? As far as the white paper links from bearing manufactures go there are several of them on the web, just do a search for bearing preload then look for the sites, go to the big bearing maker sites, they all have these engineering white papers. They all explain the importance of bearing preload and this is where I learned why you need to preload these critical bearings. The how I already told you so now you have it all.? -- Chip Louie Chief Daydreamer Imagination Hardware?
? ?Astropheric Weather Forecast - South Pasadena, CA?
?
?
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Re: 76 second RA periodic error fixed with Belleville washer
Ok. Good conversation.
Paul and John make good points in summary.? Let's go a little further.
All mechanical objects have a dimensional tolerance. See attached PDF.?
If you look at the dimensions of the R4 bearing, you see that it has an OD tolerance. The spec on OD tolerance depends on the quality rating...they are all like +0/-0.005 to +0/-0.008.??
And even if the fit were absolutely perfect at room temperature, the effect of temperature changes the sizes of metal objects anyway.? ?As aluminum expands faster than stainless steel used to make the bearing, in the cold night air, the aluminum block will shrink faster than the stainless bearing, and pinch the bearing OD.
So we may as well conclude all G11 and GM8 bearings act as though they are "pressed" into their aluminum blocks.?
The blocks are cut by the company to fit these bearings.? Some bearings are relatively easy to remove at room temperature, others are near impossible.? (Heating the block with the bearing makes removal much easier.? Using a hot air gun to heat the block in air, while grabbing the bearing with a 1/4 inch diameter tool, works well....when the bearing is loose the hot block can drop off.? )
Any imperfection in tilt of the mounting cylinder hole, vs the outer block surfaces, can cause trouble.? Cutting the block cylinder with a slight tilt in the upward or downward direction can be rectified by the owner shimming under a block edge. Mark Crossley reported such a problem many years ago in his old version G11.? Any imperfection in the side to side "tilt" of the cylinder, when an OPW is involved causes similar tilt vs the worm axis. (The old version with 2 separate worm blocks had no contraint since it had no OPW straight edge.) The flat OPW surface to block edge would have to be shimmed on the side and opposite to the bottom shim.? I think this shimming is unworkable; there is an easier approach.
Much better to "float" the bearing and preload it with a spring.??
To float the bearing, you must reduce it's OD.? If the block has a black inside surface it has been black anodized.? It's surface is Al2O3 and super hard. How could you polish the ID of the block all the way down to the bottom shoulder?? I think that's not workable.??
?It is far easier to polish down the stainless steel bearing OD with fine and extrafine sandpaper, so the bearing can slide (lubed) along the block cylinder.? Then you simply install an R4 Belleville spring washer behind it and voila...the 1/4 inch bearing center is always on the 1/4 inch worm axis, and the bearing OD and contained rolling balls are always aligned with the worm axis too.??
The only questions are: won't the bearing rotate in the worm block, and the bearing move toward and away from the worm?? The only real question is: do these adversely affect? worm performance?
The worm is being constantly forced outward by the pressure from the ring gear (aka worm wheel).? That outward radial force keeps the outer edge of the worm block against the outer edge of the worm cylinder.? Friction there will keep the worm bearing from rotating.? It also keeps the worm bearing from moving in and out radially....it is always pushed out.? So slight undersizing of the worm bearing does no harm, only potential good.??
The data says the reduction of bearing OD by polishing it (by hand, uniformly scuffing the OD circumferentially in polishing it) and lubing it (super lube), and putting in an R4 Belleville spring, show only benefits. (I'm aware of one report of trouble.. one owner said he used a Dremel tool to reduce the bearing OD and he had some issues...perhaps the bearing got out of round? )
I only did this treatment of polishing the far bearing and installing a Belleville spring washer on the far worm block away from the gearbox. I did this on 4 mounts and on both RA and DEC. I had only benefits.?
?I was concerned that putting a spring in the left side bearing nearest the gearbox would allow the worm to shift left or right.? However, this experiment is worth trying...once the Belleville springs are flat there is nowhere for the worm to go laterally anyway.? There could be a pinched ball on the left bearing too....it's a chance.?
More work to do!
If anyone needs a few R4 Belleville springs, let me know.? They are $1 each...and I can mail them in a flat letter envelope.??
All the best, Michael
On Wed, Mar 31, 2021, 7:35 AM Paul Goelz < pgoelz@...> wrote: On 3/31/2021 2:10 AM, John Kmetz wrote:
> Reading through the white paper the following can be summarized:
>
> 1) A 76 second error is due to the bearings hanging up momentarily
>
> 2) A 76 seconds error can't be removed with a PEC curve since it won't
> overlap with the worm period
>
> 3) Some bearings have slightly defective balls or races
>
> 4) Some Losmandy worm blocks have a bearing seat which is minutely
> elliptical to the point where it will deform the bearing causing the
> balls to hang up
I believe another more likely explanation is that the balls are
intentionally slightly undersized for the races to prevent binding.
Under this condition, unless the bearing has some preload AND the load
is exactly perpendicular to the bearing face, the radial load (ie., worm
penetration) will be transferred from one ball to the next as the
bearing rotates.? This transfer causes a slight radial perturbation in
the shaft that translates into unwanted periodic error.
A bearing producing a 76 second signal is quite likely not "defective".
? It is merely operating as designed.... just not optimally installed.
If sufficient axial preload is applied to the bearing(s), all balls will
be in contact with the races at all times and there will be no ball to
ball transfer of load.? Unfortunately, there is no preload adjustment in
the Losmandy worm block design like there is in my venerable LX200 so
the only way to preload the bearings is to squeeze the bearing blocks
together while tightening the cover screws.... and hope that in the
process you end up with the bearing blocks exactly perpendicular to the
shaft.
Paul G.
--
Paul Goelz
Rochester Hills, MI? USA
pgoelz@...
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Re: Gemini-2 momentarily went haywire
that's a reasonably good one.?
is it possible you can try a different power supply?
i had a Pyramid bench power with similar specs just go out on me, surprisingly because it was less than one year old
Pyle PSL92X regulated power supply.? 13.8V @ 5A constant (7A surge).
-- Brian?
Brian Valente portfolio
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Re: Gemini-2 momentarily went haywire
the steps outlined sum it up?
?>>
The diagram is not that useful.? Text is easier if you ask me.??
hehe well, to each his own. We have sent text descriptions, but many people requested?a diagram.?
The diagram is not that useful.? Text is easier if you ask me.??
Step 1.? Turn on mount and see whether RA or DEC has a runaway slew
Step 2.? Swap cables at the Gemini plugs.? RA or DEC?
Step 3.? Swap cables at the motors.? RA or DEC?
That's all the diagram says.? Doesn't actually give the logic for deducing what has failed :-). But that's not hard.
So after Step 2, you know whether or not the motor is at fault.? After Step 3, you know whether or not the Gemini is at fault.??
-- Brian?
Brian Valente portfolio
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Re: FINAL-Definitive Answer regarding Start
>>>
Warm Start?is the best way to go after rotating either axis by hand, while Gemini is turned off.
i agree with Paul, but want to point out two additions:
1. You will want to do a goto, center and SYNC as the first step to re-oriented your model?
2. Warm re/start is only important if you are model building. If you are not, or you are plate solving you do not need to use warm re/start at all
On Wed, Mar 31, 2021 at 6:33 AM Paul Kanevsky < yh@...> wrote: Warm Start?is the best way to go after rotating either axis by hand, while Gemini is turned off.
Regards,
? ? -Paul
On Wed, Mar 31, 2021 at 09:19 AM, <geoffchapman47@...> wrote:
“Warm Start?can be used if RA or DEC were rotated by hand while Gemini was turned off (for example, to balance a scope), but nothing else has changed. Requires mount to start in CWD position. One Sync or Align is required to get better pointing accuracy.“
this is helpful. To verify one of my own confusions: if I am in the middle of a visual session and want to change over to AP and mount a camera to do so and need to re-balance my scope in the process, the best way would be to go to CWD position, turn the scope off, mount the camera, rebalance the scope, go back to CWD, turn the scope on, do a warm start, and then one sync or alignment before going off to my target. Sound good?
-- Brian?
Brian Valente portfolio
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Re: Gemini-2 momentarily went haywire
John please contact us techsupport at losmandy dot com
for support requests, we ask that people open a case so we can track and report on it
On Wed, Mar 31, 2021 at 2:51 AM John Kmetz < jjkmetz54@...> wrote: On Tue, Mar 30, 2021 at 11:57 PM, Brian Valente wrote:
hey are all equally plausible, which is why you want to run the test i outlined to determine which?is at fault. I've read your thoughts about "keeping it at bay" but I really think you are living on borrowed time here. you should determine which part is faulty and replace it (hopefully it's just the cable)
Brian,?
You mentioned a test and a diagram, but I am not seeing them attached anywhere. Could you repost or direct me to where this is?
Thanks,
John
-- Brian?
Brian Valente portfolio
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Re: 76 second RA periodic error fixed with Belleville washer
On 3/31/2021 2:10 AM, John Kmetz wrote: Reading through the white paper the following can be summarized:
1) A 76 second error is due to the bearings hanging up momentarily
2) A 76 seconds error can't be removed with a PEC curve since it won't overlap with the worm period
3) Some bearings have slightly defective balls or races
4) Some Losmandy worm blocks have a bearing seat which is minutely elliptical to the point where it will deform the bearing causing the balls to hang up I believe another more likely explanation is that the balls are intentionally slightly undersized for the races to prevent binding. Under this condition, unless the bearing has some preload AND the load is exactly perpendicular to the bearing face, the radial load (ie., worm penetration) will be transferred from one ball to the next as the bearing rotates. This transfer causes a slight radial perturbation in the shaft that translates into unwanted periodic error. A bearing producing a 76 second signal is quite likely not "defective". It is merely operating as designed.... just not optimally installed. If sufficient axial preload is applied to the bearing(s), all balls will be in contact with the races at all times and there will be no ball to ball transfer of load. Unfortunately, there is no preload adjustment in the Losmandy worm block design like there is in my venerable LX200 so the only way to preload the bearings is to squeeze the bearing blocks together while tightening the cover screws.... and hope that in the process you end up with the bearing blocks exactly perpendicular to the shaft. Paul G. -- Paul Goelz Rochester Hills, MI USA pgoelz@... www.pgoelz.com
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Re: FINAL-Definitive Answer regarding Start
Warm Start?is the best way to go after rotating either axis by hand, while Gemini is turned off (or even when it's on, as long as you pushed the axis by hand).
Regards,
? ? -Paul
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On Wed, Mar 31, 2021 at 09:19 AM, <geoffchapman47@...> wrote:
“Warm Start?can be used if RA or DEC were rotated by hand while Gemini was turned off (for example, to balance a scope), but nothing else has changed. Requires mount to start in CWD position. One Sync or Align is required to get better pointing accuracy.“
this is helpful. To verify one of my own confusions: if I am in the middle of a visual session and want to change over to AP and mount a camera to do so and need to re-balance my scope in the process, the best way would be to go to CWD position, turn the scope off, mount the camera, rebalance the scope, go back to CWD, turn the scope on, do a warm start, and then one sync or alignment before going off to my target. Sound good?
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Re: FINAL-Definitive Answer regarding Start
“Warm Start?can be used if RA or DEC were rotated by hand while Gemini was turned off (for example, to balance a scope), but nothing else has changed. Requires mount to start in CWD position. One Sync or Align is required to get better pointing accuracy.“
this is helpful. To verify one of my own confusions: if I am in the middle of a visual session and want to change over to AP and mount a camera to do so and need to re-balance my scope in the process, the best way would be to go to CWD position, turn the scope off, mount the camera, rebalance the scope, go back to CWD, turn the scope on, do a warm start, and then one sync or alignment before going off to my target. Sound good?
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Re: Gemini-2 momentarily went haywire
No, I’m not referring to the ARM main processer, I am referring to a separate processor that does all the motor control work including the decode of the signals from the motor encoders, and that is a PIC SoC (Microchip) in both versions of the Gemini-2 (G2 used two DSPIC33FJ12MC201 – one per motor (U15, U16) and the G3 uses a single DSPIC33FJ32MC302 (U13)). ? Cheers David ?
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From: [email protected] <[email protected]> On Behalf Of papagordygrapes@...
Sent: 31 March 2021 11:46
To: [email protected]
Subject: Re: [Losmandy_users_io] Gemini-2 momentarily went haywire ? By PIC, I assume you mean the main microcontroller which I understand is based on an ARM SoC?? That would make sense.? I had to Google "GAL" and wow...looks like a precursor to FPGAs!
Amazing what you can do nowadays.? Another?side project I'm working this week is a DIY DSC project for a Dob.? $8 Arduino ESP32 microcontroller that creates a WiFi access point, interfaces with cheap rotary encoders and talks to the SkySafari smartphone planetarium app.? Move the scope and the planetarium on your smartphone updates in realtime! The entire code fits in this guy's message post:
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Re: Gemini-2 momentarily went haywire
By PIC, I assume you mean the main microcontroller which I understand is based on an ARM SoC?? That would make sense.? I had to Google "GAL" and wow...looks like a precursor to FPGAs!
Amazing what you can do nowadays.? Another?side project I'm working this week is a DIY DSC project for a Dob.? $8 Arduino ESP32 microcontroller that creates a WiFi access point, interfaces with cheap rotary encoders and talks to the SkySafari smartphone planetarium app.? Move the scope and the planetarium on your smartphone updates in realtime! The entire code fits in this guy's message post: https://www.cloudynights.com/topic/753765-diy-digital-setting-circles-wifi-bluetooth-with-2-encoders/
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Michael Herman
David C. Partridge
Chip Louie
Paul Kanevsky