Re: G8 DEC axis backlash, fixing, questions
On Tue, Apr 6, 2021 at 04:09 PM, Henk Aling wrote:
Does this mean that the back-off screw is meant to keep the worm from riding up the ring gear because if it does, the assembly wobbles?? That would be disappointing.
I have never seen the Losmandy spring loaded worms in detail other than the assembly/adjustment video.? If it has a wobble problem, would it help to pull the block down at the pivot by applying a (Belleville) spring underneath it?? An old design by Chip on CN had springs at the bottom IIRC.? In the worst case add a brace around the worm assembly that provides a pivot at the top to keep it from wobbling.? Pivots on both sides should greatly reduce the wobble.
It's the preload from the regular screw (with spring) that keeps the worm from riding up. I tried putting an o-ring underneath the allen head for the block bolts, but it didn't make a difference.
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Re: Nice discussions leading toward perfection...
On Tue, Apr 6, 2021 at 10:16 PM, Tom & Barbara Coverdale wrote:
Mike et al,
This is a very interesting discussion and I am following?every comment.?But as a noob I often have more questions than answers! The one?question thats nags me thru these guiding and technical discussions is "when does one need to be this technically?sophisticated
with their guiding?" For instance I have a GM-8 and a Stellarvue 102mm and generally do not guide since I?fail in so many ways to get guiding to work for me.I?typical shoot 30sec to 3 min exposures depending on?targets and "seeing" from Atmospheric. I like my images and am learning both the?nuances of imaging but the workflow and challenges of Pixinsight. So at what focal length, exposure time etc does guiding become?truly?necessary??Thanks. Tom
Tom, Most people use PHD2 or another app for correcting their guiding unless they are very happy with the tracking of their mount. Super steady tracking allows for sharper and rounder stars and can be used for much longer exposure times for your subframes. More advanced astroimagers are willing to pay a premium for the best possible tracking and are willing to buy mounts which can approach $10K or even much more. The tech discussions you see here are mostly centered around squeezing the maximum performance out of the moderately priced Losmandy mounts.? So you will see much about fine tuning the mechanical drive train, or using various software settings to gain the most advantage. The longer the focal length of your scope and the smaller the arcsecond diameter of the astronomical target of interest, the more accurate the guiding needs to be.? If you are happy with your images, then you are good. The tech talk from all the scientific and engineering folks is more an expression of interest in the topic, and their willingness to apply their talents to maximizing operation. It can be overwhelming and you don't really need to absorb it all to enjoy the basic use of your mount. John
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Re: G8 DEC axis backlash, fixing, questions
>>>Won't the Losmandy / PHD2 Anti-TVC Gods come down and zap me for using it?????
haha no. not anymore! it's a slightly different approach than before. Before I think people were trying to eliminate backlash, and it was not a good approach
you can try TVC 10. if it's working well, you should see backlash amount decrease (but not be eliminated)
if it's too much your DEC will oscillate. it will be pretty obvious. just drop it by a point or two.?
10 is pretty low. you could also increase it if you want to see more improvement. I probably wouldn't go past 25 for now
Won't the Losmandy / PHD2 Anti-TVC Gods come down and zap me for using it???? Sure; I am willing to try.? I need to order some but I want to try using?NyoGel 774 Damping Grease on some of the DEC gear to gear surfaces to see what happens (Not on the worm).? I DO NOT recommend anybody do this.? Let me try it first. I will supply before and after PHD2 logs.?
I will try setting TVC to 10 first and supplying the before and after PHD2 logs also.? How would I know that PHD2 is having an issue with this - TVC set to 10?
For me and I suspect many other DEC backlash it the weakest point in the Losmandy design.? I am not sold on the SLW being the fix for this issue.??
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Jim W
Phoenix, AZ. USA
-- Brian?
Brian Valente portfolio
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Re: G8 DEC axis backlash, fixing, questions
Won't the Losmandy / PHD2 Anti-TVC Gods come down and zap me for using it???? Sure; I am willing to try.? I need to order some but I want to try using?NyoGel 774 Damping Grease on some of the DEC gear to gear surfaces to see what happens (Not on the worm).? I DO NOT recommend anybody do this.? Let me try it first. I will supply before and after PHD2 logs.?
I will try setting TVC to 10 first and supplying the before and after PHD2 logs also.? How would I know that PHD2 is having an issue with this - TVC set to 10?
For me and I suspect many other DEC backlash it the weakest point in the Losmandy design.? I am not sold on the SLW being the fix for this issue.??
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Jim W
Phoenix, AZ. USA
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Re: G8 DEC axis backlash, fixing, questions
Henk, et al,
Just a quick overview...
The thread here has focussed attention on the newest version GM811 units with tucked motors and spring loaded worms.??
The major problem reported by many is a high hysteresis? meaning a long time lag between telescope movement and a worm direction reversal. This is making autoguiding difficult or ...PHD2 fails.?
Several possible causes must be ruled out one at a time.? Here is a checklist of tests and procedures:
1. Make the worm to ring gear mesh tight and look for a loose dovetail or slipping clutch disk.? ?How: On the DEC axis drive, back out the "back off" small bolt near the spring, until the worm will not turn.? Do not run the motor.? Grab the dovetail and try to wiggle it.? It should be completely immobile.? If it wiggles, suspect the dovetail bolts are either loose or bottomed out.? If bottomed out you must file the end down to shorten the bolt. Get the dovetail to be tightly held.
2. The GM8 clutch disks are small 3.0 inch OD and 1.25 inch ID.? Does the DEC axis clutch slip?? If so the disk may be oily.? Take the DEC axis apart and clean the plastic and mating metal surfaces. See attached PDF about alternative clutch pads.?
3. Now the worm still will not turn because we jammed it.? But the worm might still shift left to right.? Let's look at the chance the worm assembly can shift around.? How: when you grab the dovetail and try to rotate it, the worm is attached.? See if you notice the worm OPW assembly shift while you are wobbling the dovetail around in the DEC direction.? If the OPW can shift, then extra time will be needed for the autoguide system to respond.??
See if you can determine the cause of the shift.? You can first tighten the left pivot point block bolt.? Now wobble the DEC axis.? Do you see the worm move?? If the worm moves then the end block is not tight enough toward the left bearing block.? ?Perhaps the bolt holding the far block has loosened or shifted.? Fix this (or add a Belleville spring...some work here to remove and undersize the bearing, do the spring will work).??
4. If the worm won't move by wobbling the DEC dovetail, great.? Next step is to see how much the transfer gear on the gearbox needs to move before the DEC axis responds.? How: remove the DEC motor.? This allows the gearbox output shaft to freely turn.? Try to rotate the gearbox output gear back and forth.? How far can you rotate that before it feels the jammed worm?? If it rotates a lot, sustect a loose Oldham coupler metal part.? To get to that, bolt down both left and right bearing blocks.? Then remove the thick aluminum OPW cover.? Now you can see the Oldham coupler completely. Ensure both metal ends are tight.? (I often take out the tiny grub setscrews, and drill and tap to install 4-40 setscrews.? Those enable me to use a larger hex socket wrench.? If you need some if those set screws contact me.)
5.? Also check to see that the 2 transfer gears setscrews are firm.? (Sometimes these have tiny setscrews and can't be loosened or tightened!)..See note above about? replacing them with better 4-40 setscrews that can more easily be removed or tightened.
6.? Now that every item has been checked for hysteresis with the worm locked into the ring gear, there will be too much friction. You can't leave it like this in the evaluation condition with the worm jammed.? ?The next step is to drive the "back off" bolt in to relieve the heavy spring pressure forcing the worm into the ring gear.? ?Use just enough bolt inward movement so the worm will turn by hand using the gearbox transfer gear.? (The DEC motor is still off!).?
7. Now put the motor back on and run the Gemini DEC axis in both directions.? There should be no Lags or Stalled messages.? If you get a stalled message try reducing the digital setting for max Slew rate motor speed.? If that won't solve it you must back the worm off more with the back off bolt, but be careful...the more you back that off the more time there will be when it switches direction.?
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I'm done....I hope this step by step investigation will turn up good suspects and close the mystery case for you.
Best, Michael?
On Tue, Apr 6, 2021, 4:13 PM Henk Aling < haling@...> wrote: On Sun, Apr 4, 2021 at 10:21 PM, alan137 wrote:
I also tried a configuration with a very soft spring and no back-off bolt for a truly spring-loaded worm.? With this set up it is very important to have a hard stop that prevents the worm from lifting up and skipping over the ring gear.? I found that twisting the axis one direction lifts the worm up, and the other direction pulls it down into the gears, so there must be some kind of asymmetric shape to the ring gear tooth profile.? Anyway, I could sometimes also get a very low backlash, but this system was too unreliable in terms of always getting a low backlash.? I think the low spring force makes the worm block "wobbly" and it doesn't seem to sit on the ring gear consistently.? Too bad.? And if there is too much axis friction, a turning worm gear will try to "ride up" on the ring gear, whereas in a system where the worm is locked in place, it would be forced to push the ring gear along.?
Does this mean that the back-off screw is meant to keep the worm from riding up the ring gear because if it does, the assembly wobbles?? That would be disappointing.
From my own experiments (DIY v3 see the other thread), I have no trouble pushing the worm into the ring gear without the motor binding up.? However since both bottom screws are loose (by slightly loosened screws), the worm assembly can tilt and it does - mainly because I have steppers attached with a flex coupler.? Because the motor and worm are slightly misaligned the left block wobbles.? I will attempt to fix that by applying a Belleville washer at the bottom of the bottom screw of the near block so it pulls the near block down, hopefully tight enough to level it (and thereby the whole worm assembly) against the bottom. If that works I still have to worry about the block staying in place horizontally (the spring pushes it to the far side of the hole for the near bottom block) so in the worst case I have to build a stop so the block can't travel within its hole.
I have never seen the Losmandy spring loaded worms in detail other than the assembly/adjustment video.? If it has a wobble problem, would it help to pull the block down at the pivot by applying a (Belleville) spring underneath it?? An old design by Chip on CN had springs at the bottom IIRC.? In the worst case add a brace around the worm assembly that provides a pivot at the top to keep it from wobbling.? Pivots on both sides should greatly reduce the wobble.
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Re: G8 DEC axis backlash, fixing, questions
HI Jim
nice to see you here :)
can you upload a guidelog?to see how it's going?
one additional thing you might try is increasing the TVC. you might try a value of 10 and see how that goes. we used to steer people away from TVC because it could potentially fight with PHD, but now we are more thinking it can help take the edge off the backlash in certain circumstances
I need to read through this entire post but for me a lot of my GM811G DEC backlash was caused by one of the screw holes on my DEC gear box being stripped.? The motor would rock back and forth when changing DEC directions.??I purchased another gear box, disassembled the DEC worm assembly, adjusted stuff and put it back together. Worm mesh is critical and you need to play around with it.
Its manageable now but I have to keep on top of things.? I still have more DEC backlash than I would like.? The PHD2 dither 'settle time' is better.? Before I would get dither settle time errors and my error value was set to 16 seconds - if I recall correctly.
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Jim W
Phoenix, AZ. USA
-- Brian?
Brian Valente portfolio
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Re: G8 DEC axis backlash, fixing, questions
I need to read through this entire post but for me a lot of my GM811G DEC backlash was caused by one of the screw holes on my DEC gear box being stripped.? The motor would rock back and forth when changing DEC directions.??I purchased another gear box, disassembled the DEC worm assembly, adjusted stuff and put it back together. Worm mesh is critical and you need to play around with it.
Its manageable now but I have to keep on top of things.? I still have more DEC backlash than I would like.? The PHD2 dither 'settle time' is better.? Before I would get dither settle time errors and my error value was set to 16 seconds - if I recall correctly.
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Jim W
Phoenix, AZ. USA
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Re: Nice discussions leading toward perfection...
Mike et al, This is a very interesting discussion and I am following?every comment.?But as a noob I often have more questions than answers! The one?question thats nags me thru these guiding and technical discussions is "when does one need to be this technically?sophisticated with their guiding?" For instance I have a GM-8 and a Stellarvue 102mm and generally do not guide since I?fail in so many ways to get guiding to work for me.I?typical shoot 30sec to 3 min exposures depending on?targets and "seeing" from Atmospheric. I like my images and am learning both the?nuances of imaging but the workflow and challenges of Pixinsight. So at what focal length, exposure time etc does guiding become?truly?necessary??Thanks. Tom
--- mherman346@... wrote: From: "Michael Herman" <mherman346@...> To: [email protected]Subject: Re: [Losmandy_users_io] Nice discussions leading toward perfection... Date: Mon, 5 Apr 2021 02:59:52 -0700 This is a nice forum (especially for us insomniacs) to discuss improvement and diagnostic ideas.? I'm sure all the other owners are busy using their mounts to get great images.? That's the "silent majority"!??
I had great results from my G11T the other night when shooting M81 and M51.? Of course those are less of a challenge for tracking since they are close to the NCP.? Still, I was shooting at FL of ~2850mm.? I felt that I really didn't need auto guiding, though I was using an OAG in case my polar alignment was not perfect.? My 300 sec exposures were perfect...stars were all round dots.??
That G11T has been souped up.? I put on a 1:2 ratio belt drive, and McLennan 25:1 gearbox, so it is operating as a? 50:1 gearbox providing double the torque.? And any variation in the gearbox or belt is cut in half too.???I shimmed the RA worm case by very thin brass shims, to try and get the center of the worm exactly centered on the ring gear center.? I also just installed a?pair of back to back Belleville washers (30mm OD for the large worm bearings of the Titan) at the screwcap end of the RA worm, do the worm is not going to shift during temperature changes.? I reduced the weight hanging to 1 pound on the East side RA cord.? And I changed from Superlube to CRC caliper grease with MolyD, graphite, and teflon on the RA worm and ring gear.??
The system is running very smoothly.? The load is a 14 inch C14EdgeHD (~62 lbs) the 0.7 FL reducer (~5 lbs) QHY168C camera (~4 lbs), nautilus filter wheel, Celestron big OAG, and a heavy 80 mm refractor on rails on the top.? And 82 lbs of counterweights.? The total motor current running sidereal was ~ 0.25 amps at 17 volts into a high torque motor.? It's driving a total weight on the RA of about 165 lbs...well balanced but for the 1 pound hanging weight.?
Incredibly, I could still see M81 center in the camera image through opaque sky clouds.? It was enough to test the mount and get the camera imaging working.? Here is a picture of the rig and sky conditions before I shut it down.? Anyone sensible would have packed up earlier.??
As soon as you get your system working perfectly, it acts like a magnet for clouds.? Better than iodide cloud seeding!??
All the best, Michael
My opinion is that you need just enough clearance to allow the bearing to tilt inside the block by a tiny bit.? Maybe about 0.001 - 0.002" clearance
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Re: G8 DEC axis backlash, fixing, questions
I have found through trial and error, that erring on the side of loose worm adjustment gets the best performance. I also found that the best performance happens where ease of movement of the motor aligns with tightness of the worm mesh (of course). To be able to easily adjust things I made a gear cover that can flip up so that I can quickly adjust the gears and feel how easy the motor turns:
One thing that I noticed is that the ease of movement of the motor changes with different clutch tightness. When I tighten the clutches I flip open the gear covers and tighten the clutch to the place where the gears move the easiest.? I have a GM811G, so my DEC is the same as the GM8. I've found that a fairly tight clutch makes the best setup for DEC motor ease of movement. The RA (G11) axis seems to prefer a looser clutch.?
I've kept my notes here:?
Jamie
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Re: G8 DEC axis backlash, fixing, questions
On Sun, Apr 4, 2021 at 10:21 PM, alan137 wrote:
I also tried a configuration with a very soft spring and no back-off bolt for a truly spring-loaded worm.? With this set up it is very important to have a hard stop that prevents the worm from lifting up and skipping over the ring gear.? I found that twisting the axis one direction lifts the worm up, and the other direction pulls it down into the gears, so there must be some kind of asymmetric shape to the ring gear tooth profile.? Anyway, I could sometimes also get a very low backlash, but this system was too unreliable in terms of always getting a low backlash.? I think the low spring force makes the worm block "wobbly" and it doesn't seem to sit on the ring gear consistently.? Too bad.? And if there is too much axis friction, a turning worm gear will try to "ride up" on the ring gear, whereas in a system where the worm is locked in place, it would be forced to push the ring gear along.?
Does this mean that the back-off screw is meant to keep the worm from riding up the ring gear because if it does, the assembly wobbles?? That would be disappointing. From my own experiments (DIY v3 see the other thread), I have no trouble pushing the worm into the ring gear without the motor binding up.? However since both bottom screws are loose (by slightly loosened screws), the worm assembly can tilt and it does - mainly because I have steppers attached with a flex coupler.? Because the motor and worm are slightly misaligned the left block wobbles.? I will attempt to fix that by applying a Belleville washer at the bottom of the bottom screw of the near block so it pulls the near block down, hopefully tight enough to level it (and thereby the whole worm assembly) against the bottom. If that works I still have to worry about the block staying in place horizontally (the spring pushes it to the far side of the hole for the near bottom block) so in the worst case I have to build a stop so the block can't travel within its hole. I have never seen the Losmandy spring loaded worms in detail other than the assembly/adjustment video.? If it has a wobble problem, would it help to pull the block down at the pivot by applying a (Belleville) spring underneath it?? An old design by Chip on CN had springs at the bottom IIRC.? In the worst case add a brace around the worm assembly that provides a pivot at the top to keep it from wobbling.? Pivots on both sides should greatly reduce the wobble.
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Re: Nice discussions leading toward perfection...
Yes...you have to experiment.? The external reflective insulation may not have a clear effect...depends too on what type of tube you have.? Carbon fiber or fiberglass might not be much affected but my thick aluminum tube (12 inch for a 10 inch f/6 mirror) certainly changes dimension from hot to cold during a night.?? If you are imaging with your Newtonian then keep the fan on the back of the mirror on,? in a low speed, and look for optical fluctuations from tube currents with the fan on vs off.? Since the Newtonian tube is open (most are open anyway), there might be an airflow even without a fan.??
Having a slow constant fan going probably makes the imaging conditions more consistent.? Just beware to isolate the fan to allay any vibration.??
Have fun, and good luck imaging,
Michael
On Tue, Apr 6, 2021, 2:01 PM wa1vta01452 < loeblt@...> wrote: Makes sense Michael. I use a fan on the back of the mirror and I place a small fan at the mouth of the OTA? (my park position is with the tube horizontal to the south) about an hour prior to imaging. I will give the insulation a shot to both the OTA as well as the guide scope.
Tom
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Gracias Brian, me pondre en contacto. ?
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Re: Nice discussions leading toward perfection...
Makes sense Michael. I use a fan on the back of the mirror and I place a small fan at the mouth of the OTA? (my park position is with the tube horizontal to the south) about an hour prior to imaging. I will give the insulation a shot to both the OTA as well as the guide scope.
Tom
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Hi David
Please write to Tanya here tanyak@... with exactly the products what you want and your full shipping address. she can give you an accurate quote for delivery to spain
On Tue, Apr 6, 2021 at 1:26 PM Davidspain via <algayaterro80= [email protected]> wrote: Brian, he enviado varios mensajes a losmandy ventas sobre el coste del envio de una montura a espa?a o si seria mejor pedirla a un distribuidor en mi pais, por que el cambio del dolar al euro hay un importante ahorro.
-- Brian?
Brian Valente portfolio
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Brian, he enviado varios mensajes a losmandy ventas sobre el coste del envio de una montura a espa?a o si seria mejor pedirla a un distribuidor en mi pais, por que el cambio del dolar al euro hay un importante ahorro.
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Claro, tambien pensando para astrofoto, antiguamente tenia la mitica celestron G11 y los goto no los dejaba dentro del ocular con el 300mm, con el otro telescopio 200mm f / 5 era diana en el centro. Asi que la G11T lo manejaria muy bien el 300mm f/4. En precio no hay mucha diferencia entre las dos monturas, 700 euros es asumible y con la G11T podria poner en el futuro telescopios mas pesados
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Re: Is the Titan Mount still being made?
Si, responde a mi pregunta. Muchas gracias!! ??
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Re: Is the Titan Mount still being made?
Hola David
I understand you are asking if we have an option to update a G11T to a Titan mount?
We do not currently offer that option. The G11T supports weights up to 75lb, it is a very capable mount
I hope this answers your question
Brian
On Tue, Apr 6, 2021 at 11:58 AM Davidspain via <algayaterro80= [email protected]> wrote: Brian, teneis pensado en el futuro un eje de AR como actualización de la G11T, para asi tener el titan completo ?. Ya teniendo en mente hacerme con una G11T es una actualizacion que sin duda me haria con ella
-- Brian?
Brian Valente portfolio
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Re: Is the Titan Mount still being made?
Brian, teneis pensado en el futuro un eje de AR como actualización de la G11T, para asi tener el titan completo ?. Ya teniendo en mente hacerme con una G11T es una actualizacion que sin duda me haria con ella
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Re: Nice discussions leading toward perfection...
Since this thread turned to temperature equilibration, I've always wondered why the SCT/Mak's are traditionally in enclosed tubes while other compound?scopes are not (like RC's, DK's, Newt's, Cass, ...). And since temperature equilibration is such a large issue with these SCT's, it would seem reasonable to un-enclose them. I guess the same could be said for refractor's, but I thought that protecting the glass takes precedence.
-yurij
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Michael Herman
Jamie Amendolagine
Davidspain