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I've had a heck of a time understanding where I might be getting RA - and only RA - spikes from.? My setup is a Celestron 9.25"Edge HD with an OAG, sitting on a Losmandy GM811 mount, using Gemini II, N.I.N.A and PHD2 to control everything.? Calibration looks good (See the PHD2 log) and tracking is generally very good - nearly always within 1" ...except for occasional non-periodic spikes in RA which randomly occur a few times an hour, always in the same direction.
?
?
?
?
All gearing and bearings have been thoroughly cleaned but I suspect something in the RA train is binding up, then suddenly releasing.? I keep the clutches relatively loose.? No real differences between East and West guiding.? Alternatively, maybe it's the power supply (but then, why only RA)?? Or a corrupted signal from PHD2? One of these days I'll try swapping motors but because tracking is generally really good I don't want to fool around with the drive train until I absolutely have to.
?
Regardless, I should be grateful - I typically get at least 9 good images out of every 10 - but those spikes just bug me because I can't determine root cause.? Have any of you dealt with this in the past, and if so, I'll take as many recommendations as I can get.
?
?
Paul
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Hi Paul, my first suggestion would be to use the frequency analysis on that session to see if there’s any give away. Other than that I’m not of much help, I can only think of some dirt in some areas around the worm gear, or the worm, or even the gearbox and transfer gears.
?
sorry, people with more experience might chime in :)
?
Jonathan
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First things first, if you are getting 9 out of 10 good subexposures at 2350mm, then you are good. Guiding and imaging over 2 meters focal length is always a challenge. Second, in the calibration plot there are a lot backlash clearing steps. I've confronted the same situation a weeks ago and the solution was to clean the clutch discs. The DEC one was very oil stained and that was the cause of a too much backlash clearing steps even if I cleared backlash using the calibration assistant.? But prior to checking the discs try simply with a little more tightening on both RA and DEC clutches (but not overtighten!). Last, check cables, they are the usual culprit of non periodic spikes (along with windy weather).
?
Regards,
Daniel?
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Thanks Jonathan and Daniel.
Aperiodic errors will generally not be found in a (periodic) frequency chart as they are, well, not periodic.? I always check anyway, since my original goal was to suppress the usual 240-sec, 76-sec and 32-sec perturbations common to Losmandy mounts.? I found nothing unusual and in fact, the common periodic spikes at 36, 76 and 120/240 are very small indeed.
Just prior to this post I had replaced the Ethernet connection between my laptop and the Gemini II controller, in the hopes that I had a cable issue.? No dice there but a great suggestion nonetheless.? I had also just cleaned the clutches so no oil/grease issues there.
As for the guiding at 2350 mm:? Yeah, it's a great challenge and I'm proud?of accomplishing that quality imaging feat.? Only took about 4 years.? I am well aware of the DEC backlash in my rig and continue my attempts to control it but this post was specifically about the RA spikes which affect imaging much more than the slightly sloppy DEC control that I'm experiencing. Tonight I will try tightening the RA clutch a bit more to see if that makes any difference.
Paul
First things first, if you are getting 9 out of 10 good subexposures at 2350mm, then you are good. Guiding and imaging over 2 meters focal length is always a challenge. Second, in the calibration plot there are a lot backlash clearing steps. I've confronted the same situation a weeks ago and the solution was to clean the clutch discs. The DEC one was very oil stained and that was the cause of a too much backlash clearing steps even if I cleared backlash using the calibration assistant.? But prior to checking the discs try simply with a little more tightening on both RA and DEC clutches (but not overtighten!). Last, check cables, they are the usual culprit of non periodic spikes (along with windy weather).
?
Regards,
Daniel?
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Hi Paul,
?
By cable issues I mean cable management problems (dragging, tension, etc).? Anyway tell us if still have RA spikes after tightening the clutch.
?
Regards,
Daniel
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On Fri, Aug 23, 2024 at 04:28 PM, Paul Buckley wrote:
All gearing and bearings have been thoroughly cleaned but I suspect something in the RA train is binding up, then suddenly releasing.? I keep the clutches relatively loose.? No real differences between East and West guiding.? Alternatively, maybe it's the power supply (but then, why only RA)?? Or a corrupted signal from PHD2? One of these days I'll try swapping motors but because tracking is generally really good I don't want to fool around with the drive train until I absolutely have to.
?
Regardless, I should be grateful - I typically get at least 9 good images out of every 10 - but those spikes just bug me because I can't determine root cause.? Have any of you dealt with this in the past, and if so, I'll take as many recommendations as I can get.
?
?
Paul
Paul,
?
This is not normal even for a long local length - I have the same scope. I take it you are seeing this over multiple nights, not just on one occasional with passing clouds or variable seeing. When you cleaned and lubed your bearings did you use the HGM inhouse lubricant - the Jet-Lube MP-50? Few other greases have the same extreme pressure additive composition, and your ring and worm contact could be chattering - building up tension and then releasing. Since your RA spikes are all in the same direction, this could be the case as the worm motion always pushes the mount westward. Your worm spring tension could also be set a bit too tight and the smooth sliding between the gears is not happening. Perhaps try backing off a bit without creating too much backlash.?
?
Good luck,
?
John
--
_____________________________________________________________________________________________________________________________________________________________________________
Losmandy G11G2 on pier; refurbed Losmandy G11 with OnStep controller; SkyShed design roll-off observatory; ZWO ASI2600MM-P; ZWO ASI071MC; Sky-Watcher Esprit 100 ED with field flattener; Celestron C925 Edge HD with 0.7XFR, William Optics Zenithstar 61 APO; PHD2, NINA, Sequence Generator Pro and PixInsight user
|
All,
After an additional night?of observation and a slight tightening of the RA clutch, the random spikes are still there, not frequent but consistent.? I'll check the lubricant that I used (actually two lubricants, a molybdenum based lube for the ring/worm gears and a different one for the needle bearings - I don't have access to them right now but will check later to get their?exact names. I know that my choices were carefully selected based on the Losmandy group's recommendations and I was satisfied with the research that was done.? As for my worm gear, it's a pre-spring-loaded worm so no "backing off" in that suggested manner, but I could increase the gap slightly between the worm's support posts and the mount - I think that would be equivalent, and it will certainly trade off gear mesh for backlash.? I currently have the RA standoffs gapped to 0.76mm for any of you that?also do this.? Not sure that increasing the gap is going to be a good thing during a meridian flip, though, as more backlash will amount to slop during that transition.? But it's certainly worth a try.??
As per John Kmetz' suggestion that worm gear "chatter" could cause this:? Wouldn't that result in a periodic error?? It's the aperiodicity that has me hunting for and understanding root cause.
I'll swap the gear motors tonight to see what happens.?
All of this problem-solving would normally take me weeks to resolve, but Western New York is enjoying an unheard-of string of 5 clear nights in a row, so with each night I can tweak something to see what effect it might have on tracking.
Paul ?
On Fri, Aug 23, 2024 at 04:28 PM, Paul Buckley wrote:
All gearing and bearings have been thoroughly cleaned but I suspect something in the RA train is binding up, then suddenly releasing.? I keep the clutches relatively loose.? No real differences between East and West guiding.? Alternatively, maybe it's the power supply (but then, why only RA)?? Or a corrupted signal from PHD2? One of these days I'll try swapping motors but because tracking is generally really good I don't want to fool around with the drive train until I absolutely have to.
?
Regardless, I should be grateful - I typically get at least 9 good images out of every 10 - but those spikes just bug me because I can't determine root cause.? Have any of you dealt with this in the past, and if so, I'll take as many recommendations as I can get.
?
?
Paul
Paul,
?
This is not normal even for a long local length - I have the same scope. I take it you are seeing this over multiple nights, not just on one occasional with passing clouds or variable seeing. When you cleaned and lubed your bearings did you use the HGM inhouse lubricant - the Jet-Lube MP-50? Few other greases have the same extreme pressure additive composition, and your ring and worm contact could be chattering - building up tension and then releasing. Since your RA spikes are all in the same direction, this could be the case as the worm motion always pushes the mount westward. Your worm spring tension could also be set a bit too tight and the smooth sliding between the gears is not happening. Perhaps try backing off a bit without creating too much backlash.?
?
Good luck,
?
John
--
_____________________________________________________________________________________________________________________________________________________________________________
Losmandy G11G2 on pier; refurbed Losmandy G11 with OnStep controller; SkyShed design roll-off observatory; ZWO ASI2600MM-P; ZWO ASI071MC; Sky-Watcher Esprit 100 ED with field flattener; Celestron C925 Edge HD with 0.7XFR, William Optics Zenithstar 61 APO; PHD2, NINA, Sequence Generator Pro and PixInsight user
|
UPDATE on my RA spike issue:? I swapped RA and DEC motors but the spikes stayed with RA, so I've ruled out the motors.? There are no more clear nights for the time being, but my next experiment will be to back off the RA worm blocks a couple hundredths of a millimeter at a time to see what that does.? I'm?pretty?confident that it will make a difference, just not sure about the resulting backlash.? My last resort will be to bite the bullet and degrease/relube the worm/ring gears and use John Kmetz' suggested in house HGM lubricant.? I'm currently using Stalube?Synthetic Brake & Caliper Grease (Moly?+ PTFE?+ graphite).
Paul
On Sun, Aug 25, 2024 at 11:00?AM Paul Buckley via <paulbuckley14059= [email protected]> wrote: All,
After an additional night?of observation and a slight tightening of the RA clutch, the random spikes are still there, not frequent but consistent.? I'll check the lubricant that I used (actually two lubricants, a molybdenum based lube for the ring/worm gears and a different one for the needle bearings - I don't have access to them right now but will check later to get their?exact names. I know that my choices were carefully selected based on the Losmandy group's recommendations and I was satisfied with the research that was done.? As for my worm gear, it's a pre-spring-loaded worm so no "backing off" in that suggested manner, but I could increase the gap slightly between the worm's support posts and the mount - I think that would be equivalent, and it will certainly trade off gear mesh for backlash.? I currently have the RA standoffs gapped to 0.76mm for any of you that?also do this.? Not sure that increasing the gap is going to be a good thing during a meridian flip, though, as more backlash will amount to slop during that transition.? But it's certainly worth a try.??
As per John Kmetz' suggestion that worm gear "chatter" could cause this:? Wouldn't that result in a periodic error?? It's the aperiodicity that has me hunting for and understanding root cause.
I'll swap the gear motors tonight to see what happens.?
All of this problem-solving would normally take me weeks to resolve, but Western New York is enjoying an unheard-of string of 5 clear nights in a row, so with each night I can tweak something to see what effect it might have on tracking.
Paul ?
On Fri, Aug 23, 2024 at 04:28 PM, Paul Buckley wrote:
All gearing and bearings have been thoroughly cleaned but I suspect something in the RA train is binding up, then suddenly releasing.? I keep the clutches relatively loose.? No real differences between East and West guiding.? Alternatively, maybe it's the power supply (but then, why only RA)?? Or a corrupted signal from PHD2? One of these days I'll try swapping motors but because tracking is generally really good I don't want to fool around with the drive train until I absolutely have to.
?
Regardless, I should be grateful - I typically get at least 9 good images out of every 10 - but those spikes just bug me because I can't determine root cause.? Have any of you dealt with this in the past, and if so, I'll take as many recommendations as I can get.
?
?
Paul
Paul,
?
This is not normal even for a long local length - I have the same scope. I take it you are seeing this over multiple nights, not just on one occasional with passing clouds or variable seeing. When you cleaned and lubed your bearings did you use the HGM inhouse lubricant - the Jet-Lube MP-50? Few other greases have the same extreme pressure additive composition, and your ring and worm contact could be chattering - building up tension and then releasing. Since your RA spikes are all in the same direction, this could be the case as the worm motion always pushes the mount westward. Your worm spring tension could also be set a bit too tight and the smooth sliding between the gears is not happening. Perhaps try backing off a bit without creating too much backlash.?
?
Good luck,
?
John
--
_____________________________________________________________________________________________________________________________________________________________________________
Losmandy G11G2 on pier; refurbed Losmandy G11 with OnStep controller; SkyShed design roll-off observatory; ZWO ASI2600MM-P; ZWO ASI071MC; Sky-Watcher Esprit 100 ED with field flattener; Celestron C925 Edge HD with 0.7XFR, William Optics Zenithstar 61 APO; PHD2, NINA, Sequence Generator Pro and PixInsight user
|
On Tue, Aug 27, 2024 at 06:37 AM, Paul Buckley wrote:
UPDATE on my RA spike issue:? I swapped RA and DEC motors but the spikes stayed with RA, so I've ruled out the motors.? There are no more clear nights for the time being, but my next experiment will be to back off the RA worm blocks a couple hundredths of a millimeter at a time to see what that does.? I'm?pretty?confident that it will make a difference, just not sure about the resulting backlash.? My last resort will be to bite the bullet and degrease/relube the worm/ring gears and use John Kmetz' suggested in house HGM lubricant.? I'm currently using Stalube?Synthetic Brake & Caliper Grease (Moly?+ PTFE?+ graphite).
?
Paul
?
?
Wait, before you bother to strip the mount think about what the mount is doing as it gets cold acclimated.? Your classic Losmandy 2-piece worm drive system mount will never have as low backlash as the newer spring loaded OPWs. This is a fact and nothing is going to change that.? That said backlash on the classic Losmandy drivetrains is your friend in the dark especially as the night air gets colder and the winter moves in.? The thing to know is that with the classic drivetrain Losmandy GM8 and G11 mounts backlash shrinks as the air temp drops. If your mount has minimal backlash in a warm room it will stall once it shrinks in cold air. Ideally you should set your backlash up on a fully cold acclimated mount. Once it warms up it will seem to have a ton of backlash but that's okay because you don't use it to capture images when it is warm. There is no grease made that can overcome the sliding friction of a worm with no backlash with the low level of torque the Gemini drive systems produces. You MUST have some backlash or stall the drivetrain.?
?
--
Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
|
Chip, interesting comment.? I habitually readjust worm?block spacing outdoors every October and March (or thereabouts) because of the seasonal changes here in?WNY. I may have had this RA spiking issue all along but it was always masked by the "bigger holes in the sieve" problems, so to speak. As I've become more technically proficient and have better mastered the mount, other sources of error have fallen away or are controlled to the point that these RA spikes are next on my list of issues to resolve.??
Except for a few experiments I have never stalled the mount, at least not during an observing session.? I will incrementally back off the worm blocks next time the skies are clear.? My current RMS errors are generally right around 0.5" so my goal will be to keep them in that range without those occasional spikes.
Paul
On Tue, Aug 27, 2024 at 06:37 AM, Paul Buckley wrote:
UPDATE on my RA spike issue:? I swapped RA and DEC motors but the spikes stayed with RA, so I've ruled out the motors.? There are no more clear nights for the time being, but my next experiment will be to back off the RA worm blocks a couple hundredths of a millimeter at a time to see what that does.? I'm?pretty?confident that it will make a difference, just not sure about the resulting backlash.? My last resort will be to bite the bullet and degrease/relube the worm/ring gears and use John Kmetz' suggested in house HGM lubricant.? I'm currently using Stalube?Synthetic Brake & Caliper Grease (Moly?+ PTFE?+ graphite).
?
Paul
?
?
Wait, before you bother to strip the mount think about what the mount is doing as it gets cold acclimated.? Your classic Losmandy 2-piece worm drive system mount will never have as low backlash as the newer spring loaded OPWs. This is a fact and nothing is going to change that.? That said backlash on the classic Losmandy drivetrains is your friend in the dark especially as the night air gets colder and the winter moves in.? The thing to know is that with the classic drivetrain Losmandy GM8 and G11 mounts backlash shrinks as the air temp drops. If your mount has minimal backlash in a warm room it will stall once it shrinks in cold air. Ideally you should set your backlash up on a fully cold acclimated mount. Once it warms up it will seem to have a ton of backlash but that's okay because you don't use it to capture images when it is warm. There is no grease made that can overcome the sliding friction of a worm with no backlash with the low level of torque the Gemini drive systems produces. You MUST have some backlash or stall the drivetrain.?
?
--
Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
|
On Tue, Aug 27, 2024 at 09:37 AM, Paul Buckley wrote:
UPDATE on my RA spike issue:? I swapped RA and DEC motors but the spikes stayed with RA, so I've ruled out the motors.? There are no more clear nights for the time being, but my next experiment will be to back off the RA worm blocks a couple hundredths of a millimeter at a time to see what that does.? I'm?pretty?confident that it will make a difference, just not sure about the resulting backlash.? My last resort will be to bite the bullet and degrease/relube the worm/ring gears and use John Kmetz' suggested in house HGM lubricant.? I'm currently using Stalube?Synthetic Brake & Caliper Grease (Moly?+ PTFE?+ graphite).
Hi Paul,
?
The caliper greases work but start to get very tacky over time as they lose their solvent content. Please send me a PM and I can send you a sampler of MP-50 at cost (the smallest can online is ~$100). The reported chatter doesn't occur at regular intervals, just when spring tension lets go. If you take the mount apart again, you may wish to replace the worm bearings, thrust bearings and needle bearings too if you are so motivated. But you will need a bearing puller to get the needle bearings out, which I can also loan to you. It sounds like something is catching and grabbing - you'll just have to go through the process of elimination. I have a parts list as well.
?
Regards,
?
John
--
_____________________________________________________________________________________________________________________________________________________________________________
Losmandy G11G2 on pier; refurbed Losmandy G11 with OnStep controller; SkyShed design roll-off observatory; ZWO ASI2600MM-P; ZWO ASI071MC; Sky-Watcher Esprit 100 ED with field flattener; Celestron C925 Edge HD with 0.7XFR, William Optics Zenithstar 61 APO; PHD2, NINA, Sequence Generator Pro and PixInsight user
|
On Fri, Aug 23, 2024 at 04:28 PM, Paul Buckley wrote:
Celestron 9.25"Edge HD with an OAG
Observing the guiding, one might contend that it resembles the primary mirror support. An Off-Axis Guider (OAG) would detect when starting friction permits a minor deviation in the optical path.? However, correcting this deviation takes time, resulting in our rapid observable motion followed by a gradual adjustment. This movement is somewhat evident in the declination too, manifesting as a shift in one direction, followed by a realignment, but without the oscillation characteristic of a windup effect.
?
Slippage appears to be random in occurrence. Considering the duration, it only disrupts the maximum peak. It's also unlikely to be evident in an exposure as others noted. ?Could be the primary or the secondary and behave this way if true.
?
?
?
?
?
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On Tue, Aug 27, 2024 at 06:07 PM, Paul Buckley wrote:
Chip, interesting comment.? I habitually readjust worm?block spacing outdoors every October and March (or thereabouts) because of the seasonal changes here in?WNY. I may have had this RA spiking issue all along but it was always masked by the "bigger holes in the sieve" problems, so to speak. As I've become more technically proficient and have better mastered the mount, other sources of error have fallen away or are controlled to the point that these RA spikes are next on my list of issues to resolve.??
?
Except for a few experiments I have never stalled the mount, at least not during an observing session.? I will incrementally back off the worm blocks next time the skies are clear.? My current RMS errors are generally right around 0.5" so my goal will be to keep them in that range without those occasional spikes.
?
Paul
On Tue, Aug 27, 2024 at 06:37 AM, Paul Buckley wrote:
UPDATE on my RA spike issue:? I swapped RA and DEC motors but the spikes stayed with RA, so I've ruled out the motors.? There are no more clear nights for the time being, but my next experiment will be to back off the RA worm blocks a couple hundredths of a millimeter at a time to see what that does.? I'm?pretty?confident that it will make a difference, just not sure about the resulting backlash.? My last resort will be to bite the bullet and degrease/relube the worm/ring gears and use John Kmetz' suggested in house HGM lubricant.? I'm currently using Stalube?Synthetic Brake & Caliper Grease (Moly?+ PTFE?+ graphite).
?
Paul
?
?
Wait, before you bother to strip the mount think about what the mount is doing as it gets cold acclimated.? Your classic Losmandy 2-piece worm drive system mount will never have as low backlash as the newer spring loaded OPWs. This is a fact and nothing is going to change that.? That said backlash on the classic Losmandy drivetrains is your friend in the dark especially as the night air gets colder and the winter moves in.? The thing to know is that with the classic drivetrain Losmandy GM8 and G11 mounts backlash shrinks as the air temp drops. If your mount has minimal backlash in a warm room it will stall once it shrinks in cold air. Ideally you should set your backlash up on a fully cold acclimated mount. Once it warms up it will seem to have a ton of backlash but that's okay because you don't use it to capture images when it is warm. There is no grease made that can overcome the sliding friction of a worm with no backlash with the low level of torque the Gemini drive systems produces. You MUST have some backlash or stall the drivetrain.?
?
--
Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
?
?
?
With an average PE in the 0.5" RMS range and lower the spikes are not likely from worm to worm gear backlash. Have you checked your worm axial end play? This one is easily resolved in the old 2-piece worm blocks by adding Bellvue disc springs which minimize worm shaft end play and also prevents the bearing balls from.causimg the start / stop bumps in tracking error. Michel Herman and I worked on this and he wrote a nice note about the problem, it's here someplace. Just Google Michael Herman and how to improve Losmandy mount or something like.it.?
?
This issue could also be contamination in the drivetrain or axel bearings, it could be anywhere. Servo pinion, hearboxes, loose or missing set screws to Oldham couplers (there should be 2 per coupler), Oldham parts, worm or worm gear faces etc.?
?
It sounds wacky but have you lubed your Oldham couplers to see if this has any impact??
?
Being desperate early in my Losmandy ownership more than a few moons ago discovered that using heavy grease on the Oldham couplers can sometimes have a positive effect on PE smoothness. I don't know if they were just dirty, worn out, had some kind of a hitch or damage in the plastic sliding piece or just made them move easier smoother or what but it helped my PE curve. I have only done it twice and only saw an improvement on one mount.
?
I replaced the Oldhams on that GM8 mount and it was not an issue anymore but then I sold it. I still put a tiny toothpick daub of Superlube with Teflon on the Oldhams after cleaning them when I reassemble Losmandy mounts. Just sort of a religious thing as I can't proove one way or another if it really works or not LOL.?
?
--
Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
|
Chip,
I keep worm?end play controlled by manually pushing the outside worm block toward the motor as hard as I can while tightening the block with my other hand. Michael Herman's paper is this one, I believe:??.? It's full of interesting information and something that I will seriously consider the next time I take everything apart. Adding a Bellvue?spring looks straightforward.
I never considered the Oldham couplers as a possible source for errors. I did replace them this spring so they are new, but not lubed.? Nevertheless I will put a little bit of SuperLube on them.??
The learning experiences?I've had with my mount remind me that this is not so much a lesson in technical, incremental improvements but rather, attempts to wrestle the beast into submission.
Paul
On Tue, Aug 27, 2024 at 06:07 PM, Paul Buckley wrote:
Chip, interesting comment.? I habitually readjust worm?block spacing outdoors every October and March (or thereabouts) because of the seasonal changes here in?WNY. I may have had this RA spiking issue all along but it was always masked by the "bigger holes in the sieve" problems, so to speak. As I've become more technically proficient and have better mastered the mount, other sources of error have fallen away or are controlled to the point that these RA spikes are next on my list of issues to resolve.??
?
Except for a few experiments I have never stalled the mount, at least not during an observing session.? I will incrementally back off the worm blocks next time the skies are clear.? My current RMS errors are generally right around 0.5" so my goal will be to keep them in that range without those occasional spikes.
?
Paul
On Tue, Aug 27, 2024 at 06:37 AM, Paul Buckley wrote:
UPDATE on my RA spike issue:? I swapped RA and DEC motors but the spikes stayed with RA, so I've ruled out the motors.? There are no more clear nights for the time being, but my next experiment will be to back off the RA worm blocks a couple hundredths of a millimeter at a time to see what that does.? I'm?pretty?confident that it will make a difference, just not sure about the resulting backlash.? My last resort will be to bite the bullet and degrease/relube the worm/ring gears and use John Kmetz' suggested in house HGM lubricant.? I'm currently using Stalube?Synthetic Brake & Caliper Grease (Moly?+ PTFE?+ graphite).
?
Paul
?
?
Wait, before you bother to strip the mount think about what the mount is doing as it gets cold acclimated.? Your classic Losmandy 2-piece worm drive system mount will never have as low backlash as the newer spring loaded OPWs. This is a fact and nothing is going to change that.? That said backlash on the classic Losmandy drivetrains is your friend in the dark especially as the night air gets colder and the winter moves in.? The thing to know is that with the classic drivetrain Losmandy GM8 and G11 mounts backlash shrinks as the air temp drops. If your mount has minimal backlash in a warm room it will stall once it shrinks in cold air. Ideally you should set your backlash up on a fully cold acclimated mount. Once it warms up it will seem to have a ton of backlash but that's okay because you don't use it to capture images when it is warm. There is no grease made that can overcome the sliding friction of a worm with no backlash with the low level of torque the Gemini drive systems produces. You MUST have some backlash or stall the drivetrain.?
?
--
Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
?
?
?
With an average PE in the 0.5" RMS range and lower the spikes are not likely from worm to worm gear backlash. Have you checked your worm axial end play? This one is easily resolved in the old 2-piece worm blocks by adding Bellvue disc springs which minimize worm shaft end play and also prevents the bearing balls from.causimg the start / stop bumps in tracking error. Michel Herman and I worked on this and he wrote a nice note about the problem, it's here someplace. Just Google Michael Herman and how to improve Losmandy mount or something .?
?
This issue could also be contamination in the drivetrain or axel bearings, it could be anywhere. Servo pinion, hearboxes, loose or missing set screws to Oldham couplers (there should be 2 per coupler), Oldham parts, worm or worm gear faces etc.?
?
It sounds wacky but have you lubed your Oldham couplers to see if this has any impact??
?
Being desperate early in my Losmandy ownership more than a few moons ago discovered that using heavy grease on the Oldham couplers can sometimes have a positive effect on PE smoothness. I don't know if they were just dirty, worn out, had some kind of a hitch or damage in the plastic sliding piece or just made them move easier smoother or what but it helped my PE curve. I have only done it twice and only saw an improvement on one mount.
?
I replaced the Oldhams on that GM8 mount and it was not an issue anymore but then I sold it. I still put a tiny toothpick daub of Superlube with Teflon on the Oldhams after cleaning them when I reassemble Losmandy mounts. Just sort of a religious thing as I can't proove one way or another if it really works or not LOL.?
?
--
Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
|
Would there be any harm done in simply running the mount back and forth a bunch of times to its East and West limits on both sides of the Meridian?
This might smooth-out whatever is causing the spikes in RA. ’Work out the kinks’, so to speak, like someone doing some warm-ups and stretches before a run.
|
On Thu, Aug 29, 2024 at 06:17 AM, <kevinwalsh324@...> wrote:
Would there be any harm done in simply running the mount back and forth a bunch of times to its East and West limits on both sides of the Meridian?
This might smooth-out whatever is causing the spikes in RA. ’Work out the kinks’, so to speak, like someone doing some warm-ups and stretches before a run.
I'm sure doing this is fine but I'm not sure what you think is going to happen.
?
If there is debris somewhere in the drivetrain or there are sticky bearings due to contamination or using the wrong grease this won't do anything significantthat I can see. It won't hurt anything if the limits are set correctly for your rig but I doubt it will give any benefits either.?
?
--
Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
|
Latest Update 9/3/24
Last night I had exceptionally good seeing conditions, so I lubed the RA Oldham coupler and backed off the outside worm gear block just a tad (0.05 mm) from the ring gear. This made a noticeable difference in reducing?the number of spikes, literally to zero.? There are still a few spikes but they look different and could be due to other factors like a slight breeze or a nosy raccoon.
Most of the advice that you all provided has come in handy, both in helping to eliminate possibilities?and eventually, to reduce the impact on imaging.? Last night I imaged the Bubble Nebula and obtained 155 clean 3-minute images out of 170 taken, and most of the ones that I threw away were due to issues completely unrelated to those RA spikes.? For this set of images the RA/DEC RMS errors were generally less than 0.5".? Tracking was incredibly consistent all night on both sides of the?meridian.
When I do my cold weather adjustments next month I'll look into a few more tweaks, like adding a Bellvue?washer to the worm gear block.
Paul
Would there be any harm done in simply running the mount back and forth a bunch of times to its East and West limits on both sides of the Meridian?
This might smooth-out whatever is causing the spikes in RA. ’Work out the kinks’, so to speak, like someone doing some warm-ups and stretches before a run.
I'm sure doing this is fine but I'm not sure what you think is going to happen.
?
If there is debris somewhere in the drivetrain or there are sticky bearings due to contamination or using the wrong grease this won't do anything significantthat I can see. It won't hurt anything if the limits are set correctly for your rig but I doubt it will give any benefits either.?
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Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
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Chip Louie