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Hope I'm missing something obvious here, but my GM811 guiding has recently seemed impossible to get sorted. I have occasionally been able to achieve 0.5" guiding, but more typically 0.7"-1.2" with current configuration. After breakdown of RA and Dec, replacement clutch pads (Hermann), relube of all bearings, adjustment of worm meshes, gearbox, PEMPro RA 2x worm PEC, etc, I still can't seem to dial this in.
A sample screenshot shows a regular whiplash of DEC, with repeating spikes, which to me indicates some regular periodic roughness of worm gear on the DEC axis? DEC is swinging back and forth here. Could DEC also be affecting the RA numbers?
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DEC seems to have slight visible play by hand; clutches are tightened about ? turn past touching. Nothing too different than ever.
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OTA is an SVX140T about 28 lbs with 29 lbs counterweight. Am using an OAG at the scope's FL of about 938mm.
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Is 57 lbs past the limit of the G8 DEC perhaps?
?
Any thoughts on what to try or adjust??
?
Dale
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Some questions for you.? First, what did the PE look like before it started to misbehave?? Generally when a system is guiding well it generally will continue to guide well until you change something.?
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So what did you change?? Different scope?? Different auto guiding system? Different guide camera? Did you change your autoguiding software?? Any software updates?? Update ASCOM?
?
What firmware is your Gemini 2 on??
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Do you have tucked servos and spring loaded worms???
?
--
Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
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On Sun, Mar 2, 2025 at 12:02 PM, DaleN wrote:
<<SNIPPED>>?
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OTA is an SVX140T about 28 lbs with 29 lbs counterweight. Am using an OAG at the scope's FL of about 938mm.
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Is 57 lbs past the limit of the G8 DEC perhaps?
?
Any thoughts on what to try or adjust??
?
Dale
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Definitely not under mounted.? The generally used rules for determining imaging payload for commodity mounts do not apply to better mounts like Losmandy.? The GM811G has a stated saddle payload for imaging of up to 50 pounds.? This does not include any counterweight.?
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I had no issues using my vintage GM8s on a Berlbach Planet tripod with a TEC140, M10" f/6.3 LX200 and NS11 SCTs.? The GM811G has almost twice the payload capability of the old GM8s,.you should be GTG
??
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Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
?
?
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Dale,
?
This seems bizarre behavior. Dec (which should be in red) typically will drift in one direction if PA is off. If seeing is bad it should vary randomly. Having a repeating pattern I think is something software other than hardware as the Dec motor should only be rotating back and forth as corrections are needed.
?
Some random ideas:
-Are RA and Dec cables reversed (probably not)?
-Are you dithering after every frame and is the dither large?
-Have you checked TVC in the hand controller, perhaps too large a value?
-Dec MinMo seems large - I'm seeing changing values from 0.2 to 0.35
-57# on an GM811 seems, like a lot. If a G11 has 60# payload, the 811 is less, I think. Are your counterweights all at the bottom of the CW shaft? Perhaps too much moment-arm the mount can't handle.
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All I could think of for now.
?
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
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On Sun, Mar 2, 2025 at 11:25 PM, John Kmetz wrote:
Dale,
?
This seems bizarre behavior. Dec (which should be in red) typically will drift in one direction if PA is off. If seeing is bad it should vary randomly. Having a repeating pattern I think is something software other than hardware as the Dec motor should only be rotating back and forth as corrections are needed.
?
Some random ideas:
-Are RA and Dec cables reversed (probably not)?
-Are you dithering after every frame and is the dither large?
-Have you checked TVC in the hand controller, perhaps too large a value?
-Dec MinMo seems large - I'm seeing changing values from 0.2 to 0.35
-57# on an GM811 seems, like a lot. If a G11 has 60# payload, the 811 is less, I think. Are your counterweights all at the bottom of the CW shaft? Perhaps too much moment-arm the mount can't handle.
?
All I could think of for now.
?
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
?
John K,?
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Good call on the TVC setting which AFAIK should always be set to zero.?
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The OP's actual payload is only 28lbs. in the saddle not 57lbs which is the TOTAL of his saddle payload plus counterweights.? ??
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Something nobody has mentioned yet is that we don't know if the mount is properly balanced on both axes or not.? As you know it's not just the RA axis payload in the saddle, the weight balanced by the counterweights, but also the balance of the DEC axis, which runs along the axis of the optical tube, that requires good balance.? If the DEC axis is not balanced and there is some backlash the same tooth to tooth bounce can happen on the DEC axis worm and worm gear.?
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The questions in my first post may still hold the answers once the OP posts the answers.? ? ? ?
?
--
Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
?
?
?
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Your DEC may be too perfectly balanced, and your polar alignment may be too good.
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Seems contradictory but if there is any backlash in your DEC then every time you correct (say) a negative DEC error you may overcompensate.
Then you have a positive error, which it then also overcompensates. The cycle continues then, which it looks like what is happening.
?
One thing to try is to reduce the DEC aggressiveness (aka feedback). That may, just may, fix it. I say that because your graph makes it appear your
DEC corrections are overshooting on a periodic basis. PEC is a non-issue with DEC as DEC guiding commands will rarely, if ever, cause a worm cycle.
?
Another thing to try is to turn off Auto DEC and force it to correct in only one direction - namely that needed to correct any (tiny, but not too tiny) DEC drift.
That way it will never reverse so, with a tiny amount of DEC imbalance (in the right direction) the DEC gear will always be engaged.
?
Same idea as RA being heavy east and guiding aggressiveness in the range of 0.5X. Doing that guarantees it will never reverse so any backlash is a non-issue.
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You will need, of course, to figure out which (if any) direction you have DEC drift. But a bit of experimentation will tell you which works for any particular target.
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A tiny amount of DEC drift, together with setting the DEC algorithm so it only goes in one direction, may solve your problem.
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Usually, on most mounts that I've seen, the RA has the larger residual guiding error, not the DEC. Your RA residuals look splendid.
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And, of course, some of this advice is hard to do with remote operations.
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Best regards,
?
Mark C.
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Thank you for the input! Inline answers:
On 3/2/25 8:36 PM, Chip Louie via
groups.io wrote:
?
Some questions for you.? First, what
did the PE look like before it started to misbehave??
Generally when a system is guiding well it generally will
continue to guide well until you change something.
In general, occasionally good (0.41" RA, 0.41" Dec, 0.59" RMS was
best I've seen back in October 2024), mostly so-so to bad PE/guiding
(0.8-1.2" RA and Dec, 1-1.5" combined)
?
So
what did you change?? Different scope?? Different auto guiding
system? Different guide camera? Did you change your
autoguiding software?? Any software updates?? Update ASCOM?
The SVX140 replaces a 102 f7 scope in October 2024. Same basic
system, rotator, FW, focuser, camera, Mele3c, GL.iNet router.
I have used both a 210mm f4 guidescope with ASI290 2.9uM px
binned x2 and binned x11, and a QHY OAG-M with same camera.
Neither seems absolutely better, but I did root out some issues
with the OAG and Rotator interaction for PHD2. Some of my earlier
guiding issues were undoubtedly related to the rotator not
conveying Rot angle to PHD2. This has been fixed.
Always have used NINA, with PHD2 guiding. Always RA is Predictive
PEC at 239.34s fixed, and Resist Switch Dec.
Softwares are current. ASCOM drivers were updated recently
(January) to handle behavior issues with older Wanderer Mini
Rotator.
?
What
firmware is your Gemini 2 on?
HC Firmware 1.61 8/2/23
Mainboard??? 6.02 1/29/24
Servo??????????? RA 3.0 Dec 3.0
?
Do
you have tucked servos and spring loaded worms??
Tucked servos and SLW.
Thanks!
Dale
?
--
Chip Louie
Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
?
?
?
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Thank you John,
These are also some of my thoughts. Moment-arm especially.
RA,Dec cables checked.
Dither is after 6-8 frames, and frequently is RA only, spiral. I
have always (over the life of the mount) had PHD2 timeout waiting
for settle after dithers, so I make them infrequent and mild.
TVC = 0
The GM811 has an instrument carrying capacity of 50lbs imaging,
65lbs visual. I understand that to be exclusive of counterweights,
so I believe well within limits.
However, the moment-arm interests me. The counterweights were
previously 2x11 lbs near the bottom of the CW shaft, and this
particular run I added a 7# CW to the bottom to move the 2 11# CWs
up. They are still not up to top.?
Also, the scope itself is 50" from front edge to camera rear.
That would seem to add a bit of moment arm as well.
I am using an RAEXT, so the Dec axis is also a bit farther from
RA.
RA and Dec are both balanced, slightly East and Camera heavy. Dec
was actually almost too balanced this run.
Thanks!
Dale
On 3/2/25 11:25 PM, John Kmetz via
groups.io wrote:
toggle quoted message
Show quoted text
Dale,
?
This seems bizarre behavior. Dec (which should be in red)
typically will drift in one direction if PA is off. If seeing is
bad it should vary randomly. Having a repeating pattern I think
is something software other than hardware as the Dec motor
should only be rotating back and forth as corrections are
needed.
?
Some random ideas:
-Are RA and Dec cables reversed (probably not)?
-Are you dithering after every frame and is the dither large?
-Have you checked TVC in the hand controller, perhaps too
large a value?
-Dec MinMo seems large - I'm seeing changing values from 0.2
to 0.35
-57# on an GM811 seems, like a lot. If a G11 has 60# payload,
the 811 is less, I think. Are your counterweights all at the
bottom of the CW shaft? Perhaps too much moment-arm the mount
can't handle.
?
All I could think of for now.
?
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
|
Thank you Mark,
Yes, on this particular guiding session, I do recall Dec was
almost perfectly balanced, rather than a little camera heavy. I
was having a bit of trouble getting the balance correct and
finally said "good enough".? I use NINA TPA, and try to get <
0.8", which PHD2 then tells me is 2.0" !? This guiding session, it
started at 2.0" and was 0.2" for the bulk of the guiding.
I will add this to my things to try. Also considering ordering a
21# CW to move up the shaft, to reduce moment arm.
Now the skies are cloudy for a few nights as usual.
Dale
On 3/3/25 11:49 AM, Mark Christensen
via groups.io wrote:
toggle quoted message
Show quoted text
Your DEC may be too perfectly balanced, and your polar
alignment may be too good.
?
Seems contradictory but if there is any backlash in your DEC
then every time you correct (say) a negative DEC error you may
overcompensate.
Then you have a positive error, which it then also
overcompensates. The cycle continues then, which it looks like
what is happening.
?
One thing to try is to reduce the DEC aggressiveness (aka
feedback). That may, just may, fix it. I say that because your
graph makes it appear your
DEC corrections are overshooting on a periodic basis. PEC is
a non-issue with DEC as DEC guiding commands will rarely, if
ever, cause a worm cycle.
?
Another thing to try is to turn off Auto DEC and force it to
correct in only one direction - namely that needed to correct
any (tiny, but not too tiny) DEC drift.
That way it will never reverse so, with a tiny amount of DEC
imbalance (in the right direction) the DEC gear will always be
engaged.
?
Same idea as RA being heavy east and guiding aggressiveness
in the range of 0.5X. Doing that guarantees it will never
reverse so any backlash is a non-issue.
?
You will need, of course, to figure out which (if any)
direction you have DEC drift. But a bit of experimentation will
tell you which works for any particular target.
?
A tiny amount of DEC drift, together with setting the DEC
algorithm so it only goes in one direction, may solve your
problem.
?
Usually, on most mounts that I've seen, the RA has the larger
residual guiding error, not the DEC. Your RA residuals look
splendid.
?
And, of course, some of this advice is hard to do with remote
operations.
?
Best regards,
?
Mark C.
|
My setup is 27Lb, on a G11, and I have it balanced as best I can. I Keep the one 21Lb counterweight as high up as possible. It does seem to help. Same thing for me with NINA TPA and then PHD2 tells me I'm a little higher. Should be no worries on that. Are you doing a Calibration and Guide Assistant before every run in PHD2? You could run a 20-minute Guide Assist and see how it performs over time unguided. Here is a pic of where the 21lLb weight ended up on my setup.?
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On Mon, Mar 3, 2025 at 04:13 PM, David Malanick wrote:
Are you doing a Calibration and Guide Assistant before every run in PHD2?
This can make all the difference. Seems more like a settings or software issue than hardware.
?
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
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Yes, always do calibration and GA each run.
Dale
On 3/3/25 11:08 PM, John Kmetz via
groups.io wrote:
toggle quoted message
Show quoted text
On Mon, Mar 3, 2025 at 04:13 PM, David Malanick wrote:
Are you doing a Calibration and Guide Assistant
before every run in PHD2?
This can make all the difference. Seems more like a settings
or software issue than hardware.
?
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
|
Better! A bit of follow-up to my GM811G with poor Dec guiding for SVX140T:
?
I followed a few of the great suggestions, namely reducing the CW moment arm and Dec guiding aggressiveness.
i ordered a 21 lb CW, and installed it at the top of the shaft, with an 11 lb up against it. A 7 lb midshaft for balancing. So now at 39 lbs CW rather than 29, but much higher on shaft, so moment arm is greatly reduced.
?
dialed back the Dec Aggression to 60, and stretched the guide imaging to 3 sec from 1.5. Got down to ~.45” both RA and Dec for a while, but more generally .7” ish for each for several hours, with low eccentricity. Much better. I’ll see if I can’t dial that in better now.
?
many thanks for the suggestions!
CS, Dale
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On Wed, Mar 12, 2025 at 03:32 PM, DaleN wrote:
Better! A bit of follow-up to my GM811G with poor Dec guiding for SVX140T:
?
I followed a few of the great suggestions, namely reducing the CW moment arm and Dec guiding aggressiveness.
i ordered a 21 lb CW, and installed it at the top of the shaft, with an 11 lb up against it. A 7 lb midshaft for balancing. So now at 39 lbs CW rather than 29, but much higher on shaft, so moment arm is greatly reduced.
?
dialed back the Dec Aggression to 60, and stretched the guide imaging to 3 sec from 1.5. Got down to ~.45” both RA and Dec for a while, but more generally .7” ish for each for several hours, with low eccentricity. Much better. I’ll see if I can’t dial that in better now.
?
many thanks for the suggestions!
CS, Dale
?
There are differing schools of thought on this based on what I have observed others doing and when asked why I got a lot of different answers.? IME ideally you want to use enough counterweight so you can position the counter weight mass up as high as reasonably possible (mechanical interference is the obvious limit and varies based on where you are) and still achieve good balance.? I use the small 7lb. counterweight on the end to make fine adjustments easier.? Using this method requires having the most counterweight available.??Of course the heavier the payload the more counterweights end up on the shaft and they also tend to naturally move up the shaft which is ideal.
?
?
--
Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
?
?
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Here is my eclipse setup, not the heaviest payload in the G11G ever but close.? I had to rebalance by adding an additional 11 lb counterweight, 81 lbs total after adding the 2" AP Maxbright and TeleVue 35mm Panoptic to the M10 f/6.3 SCT.? I almost had to add the 21 lb instead of the 11 lb counterweight to get it to balance, note the 7 lb counterweight on the outside is almost out of counterweight shaft travel.? ?
?
?
--
Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
?
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The SCT as shown must weigh what, 55lbs.?
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On Sat, Mar 22, 2025 at 06:28 AM, George Cushing wrote:
The SCT as shown must weigh what, 55lbs.?
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Hi George,
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I don't know, I didn't weigh the whole kit and caboodle.? But piecing it together I suppose it is about 70 lbs. ++? based on what I have notes for below.? It tracked well though I never really got an actual PA and the moon remained on the ASI2600MC-Pro sensor ROI all night.? It was not being guided and I never bothered with shooting any alignment stars.? Just got lucky as I just used the usual marked spots in the driveway and didn't touch the ALT / AZ adjusters on the G11G.??
?
I know this old LX200 Classic 10" f/6.3 buck naked before even a dovetail or visual? back is added weighs in @ 27+ lbs.? Add the 2.5" Moonlite focuser, old fashioned un-lightened 17" double Losmandy D dovetails and radius blocks, Stellarvue 50mm finder and mount, 2" AP Maxbight diagonal and 35mm Panoptic and it's probably over 42 lbs. or so which is what I have old notes for.??
?
Then add the Askar FRA500 with rings and Losmandy DUP14 and top ultralight V-dovetail weights 15 lbs.? Add to that a Deep Sky Dad Flat Panel, a pair of Stellarvue 50mm optics, a guidescope with the helical focuser and ASI678MM and the finder with RACI prism diagonal eyepiece and mount, as well as an ASIAIR Plus v.3, ZWO EAF, ZWO EFW, ASI2600MC-Pro and various associated Baader M68 extension tubes and adapters to support the Askar f/3.9 reducer.? This rest add maybe 10 lbs??
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And all of this gear is sitting on an original Losmandy Side-By-Side mount with the addition of an ADM MAX ALT/AZ Aiming device.? This configuration weighs a little over 7 pounds.??
?
To really balance it right takes the practical max.? 91 lb combination of counterweights. I tried using a pair of 11 lb. CWs but this left me no shaft room to adjust balance easily.? This is all that.really fits on the CW shaft with an easy to move 7 lb counterweight used as a balance adjuster.? But I couldn't take my last 21 lb. CW off the GM8G which had a load in the saddle that used the 21 lb. and a pair of 11 lb. CWs.? ?
?
--
Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
?
?
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Chip Louie
David Malanick