?
On topic, without encoders the Moon in eclipse from last night.? (I'm sure there exists better, this shot is mine.)
?
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?
|
I tend to agree with you agree with you Chip - the cost of the encoders is pretty darn steep and the number of takers would likely be low. ? If folks do insist on having high res axis encoders then I guess they are probably going to look at 10-Micron or AP at costs north of about 10k or more. ? Given that a G11 and Gemini combo can deliver approx. 1 arc-seconds RMS tracking error … ? PS Ganymede subtends about 1.5 arc-seconds as seen from here. ? ? D. ? ? ? ? ?
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From: [email protected] <[email protected]> On Behalf Of Chip Louie via groups.io
Sent: 13 March 2025 20:56
To: [email protected]
Subject: Re: [Losmandy_users_io] Encoders, yes or no?? On Thu, Mar 13, 2025 at 03:48 AM, David C. Partridge wrote: As would some other folks, but you have to convince Scott Losmandy to do that.? Ideally this would require a new generation of Gemini (Gemini-3?) with the necessary additional hardware and firmware to talk to the absolute encoders.?? I think it would also be possible to create a smallish additional box that would allow them to be used with the Gemini-2.??? He’d also need to supply the hardware to me as it is likely that I’d end up developing the firmware to support the encoders. ? Adding absolute encoders to an existing mount would be a major exercise involving disassembly of the mount and quite a bit of precision machining. ? So, if it were ever offered, I suspect it would have to be with a new version of the mount, as for most people the cost of shipping the mount back to Losmandy, paying for the work and dealing with the complication of international customs such that you only pay tax/duty on the upgrade charges when it is shipped back to you.?? In the current “trade war” those charges could be huge. ? Please don’t discuss the politics here. ? David?
The problem is not actually building a Losmandy mount with absolute encoders, I have no doubt that Losmandy could design and produce such a mount.? The problem is getting enough people to buy the resulting mount as the cost would be quite high.? Even if you simply added an RA axis encoder ring and the double read heads needed to get the required resolution your talking about doubling the cost of a G11G just for the all new mount hardware design BEFORE you get to the all new controller hardware and new version firmware you will need to run the G11G+Absolute Encoder mount.? So would you pay nearly $8,000 for a 65 pound payload mount with absolute encoder RA?? Would you pay $10,000 for a dual axis absolute encoder mount that did not need guiding for the commonly used short subframe imaging we use today?? I don't think so because in reasonably skilled hands, modern autoguiding on current model G11G mounts is already good enough to produce excellent images for most sub 2,000mm focal length optics.? Not to mention that with all the money you saved you could buy an entire second imaging rig.? ? ??
Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
|
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?
?
?
?
|
On Thu, Mar 13, 2025 at 03:48 AM, David C. Partridge wrote:
As would some other folks, but you have to convince Scott Losmandy to do that.? Ideally this would require a new generation of Gemini (Gemini-3?) with the necessary additional hardware and firmware to talk to the absolute encoders.?? I think it would also be possible to create a smallish additional box that would allow them to be used with the Gemini-2.??? He’d also need to supply the hardware to me as it is likely that I’d end up developing the firmware to support the encoders.
?
Adding absolute encoders to an existing mount would be a major exercise involving disassembly of the mount and quite a bit of precision machining.
?
So, if it were ever offered, I suspect it would have to be with a new version of the mount, as for most people the cost of shipping the mount back to Losmandy, paying for the work and dealing with the complication of international customs such that you only pay tax/duty on the upgrade charges when it is shipped back to you.?? In the current “trade war” those charges could be huge.
?
Please don’t discuss the politics here.
?
David?
?
The problem is not actually building a Losmandy mount with absolute encoders, I have no doubt that Losmandy could design and produce such a mount.? The problem is getting enough people to buy the resulting mount as the cost would be quite high.? Even if you simply added an RA axis encoder ring and the double read heads needed to get the required resolution your talking about doubling the cost of a G11G just for the all new mount hardware design BEFORE you get to the all new controller hardware and new version firmware you will need to run the G11G+Absolute Encoder mount.?
?
So would you pay nearly $8,000 for a 65 pound payload mount with absolute encoder RA?? Would you pay $10,000 for a dual axis absolute encoder mount that did not need guiding for the commonly used short subframe imaging we use today?? I don't think so because in reasonably skilled hands, modern autoguiding on current model G11G mounts is already good enough to produce excellent images for most sub 2,000mm focal length optics.? Not to mention that with all the money you saved you could buy an entire second imaging rig.? ? ??
?
--
Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
?
?
?
|
On Thu, Mar 13, 2025 at 02:20 PM, Chip Louie wrote:
and how it will be used.?
Exactly, practical use of the mount won't improve with more encoders than those already present, unless some use case warrants this.? And most use cases were covered with Gemini.? Given its age and enhancements, it's why it so remarkable.
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On Thu, Mar 13, 2025 at 06:06 AM, WayBack wrote:
Some time ago Gemini and the digital servo made the few remaining advantages for absolutely encoders impractical.?
?
Not really.? The servos just use encoders for the motor position which may or may not be well related to the actual shaft positions.? For real-time position data you need to look at shaft/axle position which the servo motors cannot actually know.?
?
Absolute encoders on the shafts are absolutely possible, I have the 311,000 tic encoders on two mounts right now for use with Nexus DSC and Sky Safari.? To get serious sub arc second resolution gets very expensive depending on how much resolution and how it will be used.??
?
--
Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
?
?
?
|
Some time ago Gemini and the digital servo made the few remaining advantages for absolutely encoders impractical.?
|
As would some other folks, but you have to convince Scott Losmandy to do that.? Ideally this would require a new generation of Gemini (Gemini-3?) with the necessary additional hardware and firmware to talk to the absolute encoders.?? I think it would also be possible to create a smallish additional box that would allow them to be used with the Gemini-2.??? He’d also need to supply the hardware to me as it is likely that I’d end up developing the firmware to support the encoders. ? Adding absolute encoders to an existing mount would be a major exercise involving disassembly of the mount and quite a bit of precision machining. ? So, if it were ever offered, I suspect it would have to be with a new version of the mount, as for most people the cost of shipping the mount back to Losmandy, paying for the work and dealing with the complication of international customs such that you only pay tax/duty on the upgrade charges when it is shipped back to you.?? In the current “trade war” those charges could be huge. ? Please don’t discuss the politics here. ? David
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From: [email protected] <[email protected]> On Behalf Of jim.bachesta via groups.io
Sent: 12 March 2025 17:54
To: [email protected]
Subject: Re: [Losmandy_users_io] Encoders, yes or no?? I use my? upgraded 2010 Losmandy G11G for imaging. The wish list would be to improve guiding using absolute encoders.? If my understanding is correct, the E port on the Gemini-2 is not designed to support that.? With that said, I would pay the dollars to add absolute encoders and placing this on the Gemini-2 road map would be fantastic.
|
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
|
I use my? upgraded 2010 Losmandy G11G for imaging. The wish list would be to improve guiding using absolute encoders.? If my understanding is correct, the E port on the Gemini-2 is not designed to support that.?
?
With that said, I would pay the dollars to add absolute encoders and placing this on the Gemini-2 road map would be fantastic.
?
|
Yes, always do calibration and GA each run.
Dale
On 3/3/25 11:08 PM, John Kmetz via
groups.io wrote:
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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
|
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
|
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.?
|
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:
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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.
|
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 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?
?
?
?
|
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.
|
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,?
?
Good call on the TVC setting which AFAIK should always be set to zero.?
?
The OP's actual payload is only 28lbs. in the saddle not 57lbs which is the TOTAL of his saddle payload plus counterweights.? ??
?
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.?
?
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?
?
?
?
|
Hi Ryan,? Did you get this resolved?? I'm seeing the same behavior - though not quite so bad.? I sent my mount back to Scott due to RA oscillations.? He was able to resolve this, and the mount tracks well now, but my dec backlash is over 4000mS while it was typically under 750mS before sending.? I've historically adjusted the DEC SLW per Scotts video with good success but not having any luck now.? I suspect the screws holding the blocks to the plate might need adjustment (which Scott doesn't touch in his video).? I will look at these next.? I would love to hear what you did to resolve your issue.? ? Best, Jim?
|
On Thu, Jan 16, 2025 at 12:53 PM, crocco1250 wrote:
Hi Ryan,? Did you get this resolved?? I'm seeing the same behavior - though not quite so bad.? I sent my mount back to Scott due to RA oscillations.? He was able to resolve this, and the mount tracks well now, but my dec backlash is over 4000mS while it was typically under 750mS before sending.? I've historically adjusted the DEC SLW per Scotts video with good success but not having any luck now.? I suspect the screws holding the blocks to the plate might need adjustment (which Scott doesn't touch in his video).? I will look at these next.? I would love to hear what you did to resolve your issue.? ? Best, Jim?
|
David C. Partridge
Chip Louie
David Malanick