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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!

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.?

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

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?

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?

The washer in the drawing is backwards (should be contacting the outer race).

Keith

I have a hard time believing that there is a 43 minute periodic error

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

1. ?They are not pre loaded.
2. Bearing load is uneven causing uneven wear on the axis.
3. required shaft clearance causes mis-alignment of the axis (axis 'sag') and non axial rotation
4. ?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.

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

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??

On Wed, Aug 4, 2021 at 05:01 AM, Henk Aling wrote:

About mechanical indexing, are you referring to encoders?? If you just want to get the ring gear roughly in a predetermined position, cut the top off the cover plate, this exposes the ring gear, and mark it.? That way you can position the ring gear in a deterministic manner.?

Henk,

I do not believe that this will help you for the reason that the tightening of the clutch creates a variable fore-aft force on the ring gear due to the the axis shaft being off center. This off? "centerless" varies based on each given mount (production run) and the weight of the equipment being carried by the mount.?

Peter

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

1. ?They are not pre loaded.
2. Bearing load is uneven causing uneven wear on the axis.
3. required shaft clearance causes mis-alignment of the axis (axis 'sag') and non axial rotation
4. ?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

I don't see how one could preload the RA bearings with all the weight on it.? Can you be more specific and point out what could reasonably be done while keeping the system simple?? Preloading these bearings does not seem realistic to me.

If you release the clutch you will lose all references, this is normal, is it not?? Or do you expect external encoders to keep track.? I don't? know systems that do this, can you name an example or suggest a fix?

About mechanical indexing, are you referring to encoders?? If you just want to get the ring gear roughly in a predetermined position, cut the top off the cover plate, this exposes the ring gear, and mark it.? That way you can position the ring gear in a deterministic manner.? To keep things simple, motors with internal encoders or stepper motors are preferred I think.? External encoders would just overcomplicate the system IMHO.

About software based motion correction, Ekos provides adaptive PEC and PHD2 does too if I am not mistaken.? Non-adaptive PEC is hardly used so I would not make a point of this.? To me it does not seem critical but opinions may difffer.

For a discussion with Losmandy we should condense and prioritize the list to the most realistic, common and important ones and present clear suggestions.

I would suggest adding the worm bearing alignment to the list, this is something that can be preloaded easily, like how Chip and Michael proposed this.

On Wed, Aug 4, 2021 at 04:26 AM, Michael Ben-Yehuda wrote:

Hi Henk
I'll try and address your questions

Don't the "touch points" as per Peter's drawing, depend on how the scope is balanced? If the scope is balanced towards the counterweight, these touch points would be just opposite.? And if the balance were perfect the touch points would be on the same side (low).Based on a deviation of 0.004" and a 16" distance between the bearings (just guessing), worst case, the angle between the shaft and the axis could be off by plus or minus (2×0.004/16)×(60×180/pi)=1.7'.? ?After a 180 degree rotation the polar alignment would be off by 3.6' if it were 0 at the CWD position.? So much for the arc second accuracy of polar alignment.? Frankly I doubt if it were that much.

The touch points don't change by balancing the scope. The total mass of the DEC axis, telescope and counterweight system is supported by the RA shaft and bearings. Even if there were no gap there would be uneven pressure on the needle bearings. The bottom half of the upper bearing and because it acts like a lever, the upper half of the lower bearing carry the load. The only way to equalize the load on the bearings is to pre-load the system with an opposite force.? The counterweights balance off the force on the worm gear and drive train.?

You are correct, the play in the system is far less than 0.004"? I don't have an easy way of measuring it, but i suspect it's around 0.001"

I see, it's just the DEC axis that has counterweights, my reasoning does not apply to the RA axis.

The number of 2' is normal for my AVX.? If I rotate it manually 15 seconds east then 15 seconds west while taking a 30 second image at 6400 ISO using a DSLR with the scope's RA center of rotation in the FOV, I see 2 star trail circles on the LCD with centers that are about 2' apart.? That's because the manual rotation positions the axis in different directions going one way vs the other because of friction.? I have not tried this with my G11S yet but that would be a simple test to measure the effect of the gaps between the shaft and the needle bearings.If the scope were perfectly balanced when tightening the clutches the touch points would be at the same side and the angle between the shaft and RA axis would be zero but the center would still be offset by 0.004" so the rong gear might still bind up unless using true SLWs or unless adding enough slack

The error from the required clearance of the RA shaft to be able to pass it through the needle bearings does not create the kind of error you describe. Peter has tuned his G11 to achieve sub arc-second RMS guiding accuracy. He posted it in one of the other threads. He was at the step limit of? 0.56 arc-seconds until he installed a higher ration gearbox which brought him down to the 0.14 arc-second guiding range.?

It's easy to lose perspective about the level of precision and accuracy being discussed.

I'm not losing perspective of that.? I started a thread on the OnStep board about this.? I am running TMC2130 steppers for 0.9 degree motors at 64x.? The step angle is 50.625".? ?I want to get to 256x but when I try that, the slewing stops working for some reason.? I will try to find the bug because I know the TMC2130 is capable of that.? At 256x the step would be 12.5", albeit at 4x lower torque.? It's a delicate balance but I don't want to add a belt if I can avoid it.

Having said that, the test I suggested has nothing to do with guiding just mechanical, and I will try to illustrate it once I get back from my road trip.

?

Looking for one Losmandy High Torque motor. This is for a Titan mount but I've been told that they are the same motor as the G11.
Also looking for either a Gemini 1 or 2 controller at a reasonable price.
--
Geelong Australia. G11, Titan project

1. Use of axial needle roller bearings for the RA and DEC axis shafts
   1. ?They are not pre loaded.
   2. Bearing load is uneven causing uneven wear on the axis.
   3. required shaft clearance causes mis-alignment of the axis (axis 'sag') and non axial rotation
   4. ?do not prevent wobble
2. Thrust bearings are not implemented properly
   1. Bearings are not pre-loaded.
   2. Bearings are loaded based on clutch operation not on proper setting for shaft rotation dynamics
   3. Bearing pressure not consistent. RA axis drag and dynamics not predictable or repeatable.
   4. Thrust bearings do not prevent non axial movement of the axis
   5. Bearing are exposed to the elements.
3. Clutch functionality
   1. Lack of mechanical indexing makes it impossible to recover from
      1. Releasing the clutch to perform required operations such as balancing disrupts the mechanical adjustment and calibration of the drive.?
      2. Clutch slip can occur and it is impossible to identify or quantify the loss of mechanical alignment calibration and adjustment
      3. It is impossible to accurately restore positional orientation after releasing the clutch.
   2. Operation is neither repeatable or reproducible
   3. Clutch pressure setting determines axis shaft thrust bearing load. Undesired cross effects
   4. Unloaded bearings can become misaligned.
   5. Thrust bearing load impacts drive motion dynamics and alignment.?
   6. No indicator or way to consistently set the clutch pressure
   7. Unwanted negative impact on drive performance.
   8. Clutch action is unpredictable
4. No indexing of mechanical components
   1. Impossible to maintain repeatability or reproduce performance.
   2. Mechanical alignment and adjustments are lost during the course of normal operations.
   3. impossible to reproduce mechanical alignment and adjustments.
   4. Inconsistent results even when following the same procedures.
5. Software based motion correction
   1. Software based motion correction gets out of sync with the mechanical position of the drive.
   2. Due to lack of indexing it is impossible to resync the software with the mechanical system.?
   3. Out of sync condition is only discovered by degradation of collected data and changes in guiding performance.
   4. Must eliminate other causes of poor data and guiding.
   5. Time consuming and data loss.
   6. Impossible to recover error correction data and apply it or re-apply it accurately.??
   7. There is no way to determine if the software motion control corrections are correct without fully testing and calibrating the drive.
   8. Fully testing the existing corrections takes as much or more time or more than starting over and collecting new data.?
   9. Stored PEC makes the guiding worse if it's out of sync by interfering with auto-guiding applications
6. Gear reduction ratios causes un-correctable PE errors
   1. Gear ratios are not even multiples so the periodic error is also not an even multiple. It is 'out of phase' so shifts over time
   2. Alternative gear box from McLennen has same 25:1 ratio but the intermediate ratios are even multiples and can be corrected with PEC.
7. Worm adjustment and mounting

This is a list of issues. I will try to bring forward ideas that are posted in other threads about solutions and link them in this thread.

Regards,

Michael

Hi Henk
I'll try and address your questions

Don't the "touch points" as per Peter's drawing, depend on how the scope is balanced? If the scope is balanced towards the counterweight, these touch points would be just opposite.? And if the balance were perfect the touch points would be on the same side (low).Based on a deviation of 0.004" and a 16" distance between the bearings (just guessing), worst case, the angle between the shaft and the axis could be off by plus or minus (2×0.004/16)×(60×180/pi)=1.7'.? ?After a 180 degree rotation the polar alignment would be off by 3.6' if it were 0 at the CWD position.? So much for the arc second accuracy of polar alignment.? Frankly I doubt if it were that much.

The touch points don't change by balancing the scope. The total mass of the DEC axis, telescope and counterweight system is supported by the RA shaft and bearings. Even if there were no gap there would be uneven pressure on the needle bearings. The bottom half of the upper bearing and because it acts like a lever, the upper half of the lower bearing carry the load. The only way to equalize the load on the bearings is to pre-load the system with an opposite force.? The counterweights balance off the force on the worm gear and drive train.?

You are correct, the play in the system is far less than 0.004"? I don't have an easy way of measuring it, but i suspect it's around 0.001"

The number of 2' is normal for my AVX.? If I rotate it manually 15 seconds east then 15 seconds west while taking a 30 second image at 6400 ISO using a DSLR with the scope's RA center of rotation in the FOV, I see 2 star trail circles on the LCD with centers that are about 2' apart.? That's because the manual rotation positions the axis in different directions going one way vs the other because of friction.? I have not tried this with my G11S yet but that would be a simple test to measure the effect of the gaps between the shaft and the needle bearings.If the scope were perfectly balanced when tightening the clutches the touch points would be at the same side and the angle between the shaft and RA axis would be zero but the center would still be offset by 0.004" so the rong gear might still bind up unless using true SLWs or unless adding enough slack

The error from the required clearance of the RA shaft to be able to pass it through the needle bearings does not create the kind of error you describe. Peter has tuned his G11 to achieve sub arc-second RMS guiding accuracy. He posted it in one of the other threads. He was at the step limit of? 0.56 arc-seconds until he installed a higher ration gearbox which brought him down to the 0.14 arc-second guiding range.?

It's easy to lose perspective about the level of precision and accuracy being discussed.

I keep pinching myself that I finally own this level of gear having rehabbed and hypertuned Celestron and Meade mounts.? Those designs have some good things about them. but this is a different beast.

I may be able to call in to get the date of manufacture of my G11 but it has a black ring gear and is a gem-1 with the last version of the hardware. Standard un-tucked motors.
I'll confirm the worm gear and bearing arrangement tomorrow. It does NOT have space for a wavy washer between the clutch plates.

Does that put it in the 2005 time frame.??