Re: PEC with GM8 492 Controller
Thanks for the info and confirmation George and Mark.?
?
Avi?
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Re: PEC with GM8 492 Controller
Meade had PPEC, but I think first with the the 1992 LX200, which used a Motorola 68000 type MCU. Pin INT2 got a signal from a Hall effect IC on the RA worm. It was processed and stored in an external 4092 BIT EEPROM. The Ultima used Hall effect feed back to monitor motor speed, but the Celestar Deluxe used SAIA step motors and no other sensors..
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Re: PEC with GM8 492 Controller
The 492 was a development of the Celestron 1990 Ultima PEC System. It was a microprocessor quartz controlled closed loop system. For the G11 and Celestar Deluxe mounts the feedback loop was dropped and step motors were employed. All three mounts had PEC, but I don't believe they were PPEC (permanent PEC) with a memory. The Celestar Dlx was notorious?for failing to even record the?error stream. PPEC requires about 1-2K to store.
As you can see the 492 has an Intel 80C52 MCU. IIRC it had 256 bytes of internal memory and could support up to a 16K EPROM. The 64K EPROM couldn't be used for on-board programming.?
When I look at the 492, I remember?the first mainframe I worked on in the late '60s, it also had 64K main memory. That required 30+ ferrite bead plates each with 4,092 hand woven iron beads, more than 6 months work for a weaver. And barely over 20 years it's all reduced?to this.
The I-8051/2 design is still widely?copied, used and greatly?reduced in size and flash memory is now up to 2T in SD and smaller formats.
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Re: PEC with GM8 492 Controller
Avi,
?
Your understanding is correct: The PEC table evaporates when the power is cycled. So you must redo the PEC each session.
?
Part of the reason is because of the memory technology used in the older drives.
?
Another part of the reason is that the 492-equipted mounts do not have any feedback from the motor/worm assembly (aka encoder or PEC sensor).
?
At one point Meade and Celestron (if my old memory isn't failing) used the term PPEC for Permanent PEC.
?
Best regards,
?
Mark Christensen
|
Re: Irregular lurches in RA -- what to look for?
Right, those are basically all the things to check!? It will be a
week before we have another clear night for testing.? I was
wondering if any specific cause jumped out at anyone, and in
particular if it was associated with the firmware upgrade
(although I can't see how a firmware problem would cause random
lurches).
Could it be too little DC voltage (12.6 V)?? My main power supply
has to stay under 13.0 because that's the limit for my Altair
camera.? I do have a 19-volt power supply I can use with the
GM811G.
It may still have been cable management -- something dragging
that I didn't catch.? In that case it won't recur next time.
On 2025-04-30 09:08, Paul Kanevsky
wrote:
Hi Michael,
?
Difficult to diagnose from a distance. A 12" jump sounds like
something beyond seeing conditions, unless you had clouds
passing through. Here are the things I'd check, in this order:
?
1. Check that everything is tightened down, nothing is loose
in the imaging/autoguider system
2. Check motor cables, make sure they are clean and making
solid contact
3. Reset Gemini to HGM default settings, to clear out any odd
settings, then reenter all the correct settings
4. Check for backlash in RA worm/gear, adjust if necessary to
reduce (adjustment depends on whether you have spring-loaded
worm or not). Large temperature swings can also result in some
issues with both, binding, and increased backlash.
5. Try moving to a different part of the worm-wheel: start in
CWD. Loosen the clutches, move the RA axis 90 degrees by hand,
tighten the clutches. Then, using Gemini HC arrow buttons,
rotate the axis back to CWD, or -90 degrees. Restart Gemini
using cold start from CWD position. This should move the mount
to use a different portion of the worm wheel, just in case there
were some problems or dirt on the part where you had trouble.
6. Check that your gearboxes are attached properly, possibly
swap gearboxes to see if the RA problem goes away
7. Check the oldham coupler and tighten the screws on both
sides if anything is loose
8. Check/clean/relube the worm -- there may be dirt or
particles that are in the way that are causing sudden jumps.?
9. Try reverting to a previous version of firmware to see if
that would make a difference
?
Regards,
?
? -Paul
?
?
On Tue, Apr 29, 2025 at 10:26 PM, Michael A. Covington wrote:
Last night my GM811G gave really poor autoguiding
with a setup that had
previously worked very well all the time.? C8 EdgeHD, iGuider
guidescope
bolted to the side of the mount saddle, PHD2, NINA.? Normally
this setup
gives me approximately 0.7" RMS guiding at my site.
Last night, though, there were frequent large irregularities
and lurches
(2" to 12"), mostly in RA, somewhat in declination too (enough
to
deflect suspicion away from the RA drive but not totally
exonerate it).?
They were at very irregular intervals, 30 to 90 seconds apart,
and a few
were bad enough to produce multiple images of stars.
My first thought was that a cable was dragging, but
rearranging the
cables a couple of times didn't fix it.? Nor did the
guidescope or guide
camera appear to be loose in any way, though I'm going to take
them off
and put them back on carefully the next time I have the mount
out.
I had just upgraded the Gemini firmware, and I made sure that
its PEC
was turned off.
I made sure the RA clutch was tight enough but not too tight.
I had PHD2 recalibrate, just in case it had been mistaken
about the
guidescope, and tried a couple of different guiding
algorithms.
The air didn't *look* unsteady, but could this be an
atmospheric problem
after all?? An effect of the slight east breeze (4 mph)?
Or does my RA drive require cleaning and lubrication or
something?? The
mount is 3 years old and has been used lightly.
Thanks!
--
Michael A. Covington, Ph.D.
Consultant, Covington Innovations, Athens, Georgia, USA
--
Michael A. Covington, Ph.D.
Consultant, Covington Innovations, Athens, Georgia, USA
|
PEC with GM8 492 Controller
Hello All,
?
I have a non-goto Losmandy GM8 with the 492 digital drive that is working quite well for me.?
?
I have been running some guiding "tests" over the past week just to see what kind of tracking performance I get w/ and w/o guiding, w/ and w/o PEC etc. I am actually quite happy with the results and I am seeing further improvements with PEC applied.?
?
My assumption was that once generated the PEC is stored within the 492 and would automatically get applied to the next session. But from what I can tell, that does not appear to be the case. Is that true? Does the PEC generation protocol need to be re-run each time I start up the controller??
?
Sequence of events:
?
1. After successful guide calibration with PhD2, I started autoguiding
2. After ~10 mins of autoguiding, I hit the PEC button on the 492 panel and the red LED started flashing telling me that it was in recording
3. After ~8 mins (worm period on GM8), the red LED stopped flashing telling me that the PEC had been applied.?
4. I continued autoguiding with PEC turned on and I saw an improvement to an already good tracking performance.
5. After wrapping up my tests, I turned the 492 unit off and turned it on again.?
6. PEC light was off by default (I was thinking it would remain ON since I had already gone through PEC generation). When I hit the PEC button, it started flashing again.....so effectively restarting PEC generation?
?
I really don't mind redoing it (I need to redo guide calibration each time anyway, so an additional 8 mins is no big deal), but just wanted to understand how the system works. The manual does not provide much information about this.?
?
Many thanks!
?
Avi
?
?
|
Re: Problem with Gemini 1
?Hi John,
?
Did you ever get your G1 servo motor issues resolved???
?
--
Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
?
?
?
|
Re: Irregular lurches in RA -- what to look for?
Hi Michael,
?
Difficult to diagnose from a distance. A 12" jump sounds like something beyond seeing conditions, unless you had clouds passing through. Here are the things I'd check, in this order:
?
1. Check that everything is tightened down, nothing is loose in the imaging/autoguider system
2. Check motor cables, make sure they are clean and making solid contact
3. Reset Gemini to HGM default settings, to clear out any odd settings, then reenter all the correct settings
4. Check for backlash in RA worm/gear, adjust if necessary to reduce (adjustment depends on whether you have spring-loaded worm or not). Large temperature swings can also result in some issues with both, binding, and increased backlash.
5. Try moving to a different part of the worm-wheel: start in CWD. Loosen the clutches, move the RA axis 90 degrees by hand, tighten the clutches. Then, using Gemini HC arrow buttons, rotate the axis back to CWD, or -90 degrees. Restart Gemini using cold start from CWD position. This should move the mount to use a different portion of the worm wheel, just in case there were some problems or dirt on the part where you had trouble.
6. Check that your gearboxes are attached properly, possibly swap gearboxes to see if the RA problem goes away
7. Check the oldham coupler and tighten the screws on both sides if anything is loose
8. Check/clean/relube the worm -- there may be dirt or particles that are in the way that are causing sudden jumps.?
9. Try reverting to a previous version of firmware to see if that would make a difference
?
Regards,
?
? -Paul
?
?
On Tue, Apr 29, 2025 at 10:26 PM, Michael A. Covington wrote:
Last night my GM811G gave really poor autoguiding with a setup that had
previously worked very well all the time.? C8 EdgeHD, iGuider guidescope
bolted to the side of the mount saddle, PHD2, NINA.? Normally this setup
gives me approximately 0.7" RMS guiding at my site.
Last night, though, there were frequent large irregularities and lurches
(2" to 12"), mostly in RA, somewhat in declination too (enough to
deflect suspicion away from the RA drive but not totally exonerate it).?
They were at very irregular intervals, 30 to 90 seconds apart, and a few
were bad enough to produce multiple images of stars.
My first thought was that a cable was dragging, but rearranging the
cables a couple of times didn't fix it.? Nor did the guidescope or guide
camera appear to be loose in any way, though I'm going to take them off
and put them back on carefully the next time I have the mount out.
I had just upgraded the Gemini firmware, and I made sure that its PEC
was turned off.
I made sure the RA clutch was tight enough but not too tight.
I had PHD2 recalibrate, just in case it had been mistaken about the
guidescope, and tried a couple of different guiding algorithms.
The air didn't *look* unsteady, but could this be an atmospheric problem
after all?? An effect of the slight east breeze (4 mph)?
Or does my RA drive require cleaning and lubrication or something?? The
mount is 3 years old and has been used lightly.
Thanks!
--
Michael A. Covington, Ph.D.
Consultant, Covington Innovations, Athens, Georgia, USA
|
Irregular lurches in RA -- what to look for?
Last night my GM811G gave really poor autoguiding with a setup that had previously worked very well all the time.? C8 EdgeHD, iGuider guidescope bolted to the side of the mount saddle, PHD2, NINA.? Normally this setup gives me approximately 0.7" RMS guiding at my site.
Last night, though, there were frequent large irregularities and lurches (2" to 12"), mostly in RA, somewhat in declination too (enough to deflect suspicion away from the RA drive but not totally exonerate it).? They were at very irregular intervals, 30 to 90 seconds apart, and a few were bad enough to produce multiple images of stars.
My first thought was that a cable was dragging, but rearranging the cables a couple of times didn't fix it.? Nor did the guidescope or guide camera appear to be loose in any way, though I'm going to take them off and put them back on carefully the next time I have the mount out.
I had just upgraded the Gemini firmware, and I made sure that its PEC was turned off.
I made sure the RA clutch was tight enough but not too tight.
I had PHD2 recalibrate, just in case it had been mistaken about the guidescope, and tried a couple of different guiding algorithms.
The air didn't *look* unsteady, but could this be an atmospheric problem after all?? An effect of the slight east breeze (4 mph)?
Or does my RA drive require cleaning and lubrication or something?? The mount is 3 years old and has been used lightly.
Thanks!
--
Michael A. Covington, Ph.D.
Consultant, Covington Innovations, Athens, Georgia, USA
|
Re: Off Topic: Convert PT Pier into something more permanent.
Simpler yet, drill and tap some holes at the top and as far down as you can and still hit the inner square tube. Four bolts per side. Then screw in clamp bolts. That way you still have the option of moving it up and down later on. Dunno how thick the aluminum is so best maybe to use a fine thread. And small bolts. Like 1/4" x 28. As many threads engaged as you can.
?
Also has the option that it's cheap and easily reversible. 16 bolts and maybe an hour with a drill and tap. Or give it to me! (Grins).
?
Mike
?
|
Re: Off Topic: Convert PT Pier into something more permanent.
Weren't those adapted from telescope lifts for the '50s? How big did those cat tubes get - 36"? Lot of leaded?glass to shield the viewer electron beam.?
Think they have a threaded?actuator. I'd imagine there's a bit of play inherent in the mechanism. Think the two sections telescope. Pick favorable elevation and weld at the?overlap.
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Re: Losmandy G11 bearing question
IF there is any need for a more bearing surface it would seem that the best approach would be to obtain a bearing with a longer cage. It would also?seem that the machinist, knowing the length of the intended bearing might not bother doing precision?machining of the bore beyond that needed for the intended bearing. I'd be sure to gauge the bore before any proposed?bearing seat before malletizing a bearing in place.
|
Re: Losmandy G11 bearing question
Of all the things we do to bearings, asking them to carry our telescopes?is probably the least burdensome. We want them to carry a modest oscillating radial load, at very low speeds with minimal vibration and mild environmental conditions. Without doing the math, it doesn't surprise me that early mounts resorted to plastics. In some applications, thermoplastic bearings withstand nearly 200,000 psi before failing. Steel alloys are overkill.
The static capacity of roller bearings is the maximum load that can safely be applied to a non-rotating bearing that will not cause subsequent bearing operation to be impaired . For roller bearings that's 580,000 psi. Bearings are generally spec'd at half their capacity.
If you want to worry there is the problem of not providing the bearings?with enough work to do.? They require a minimum loading so they immediately start rolling as the shaft starts to rotate.?
I'm not saying go out and machine some?PEEK, PE, PP, PVDF or PTFE or what have you to replace the SKFs, but understand this ain't rocket science. The designer callsan engineer he knows at his bearing supplier and says he's putting a 2" by 12" steel shaft into a machined 6061 alloy billet that will operate in various positions at low loadings and he needs some off the shelf recommendations for thrust?and radial roller bearings. He adds that it would be nice if they were bearings that his company already?stocks.?
Keep it dry, clean and lubricated and it will outlast humanity.
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Re: Losmandy G11 bearing question
On Fri, Apr 25, 2025 at 10:13 AM, Laurel O. Sillerud wrote:
I added a third bearing simply by lubricating it slightly, inserting it part way, sliding the shaft into the center, and gently tapping the third bearing into place.
All went very smoothly this way and there was no chance of misalignment.
Laurel
On 4/25/25 9:43 AM, Paul Kanevsky via groups.io wrote:
? [EXTERNAL]
On Fri, Apr 25, 2025 at 10:09 AM, Chip Louie wrote:
Binding due to misalignment is one of the problems I found as a potential way to screw up my perfectly good G11 mount as I contemplated this modification.? To get that perfect non-binding installation the additional bearing would need to be supported on a shaft that is in alignment with the other two bearings as the 3rd is pressed into place.??
?
So when I looked at the distance between the bearings and the very short length the axle? is unsupported at the end of the body I figured it should make no difference.? My guess was it would not improve performance even if the 3rd bearing was installed perfectly.? But if not installed perfectly or the axle was not perfectly straight the slight misalignment could be the source of a slight, regular binding as the axle rotated.? So I passed on that modification.??
?
The possibility of screwing up the mount is very real, as my first-hand experience made painfully obvious... at least to me :)
?
There is no mechanical advantage in doing this if the mount and bearings are in spec.? That said this is the method I suggested if for some reason a person feels compelled to do this.??
?
--
Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
?
?
?
|
Off Topic: Convert PT Pier into something more permanent.
I have a PT (1 or 2) that I purchased many years ago. It is the the type that can go up and down. Still works but with my permanent observatory, I have not needed to use that feature in many years (still works though).?
?
What I do not like about this setup is the minor movement (even when the pier is all the way down) you can put your finger on the scope mount and 'shake' it scope.?
?
I am trying to figure out how to 'convert' this into a permanent mount; ie...fill it with concrete, rocks, sand...etc to help stabilize it. I wont ever need to raise it again so I don't care about the guts on the inside of the pier.
?
Any thoughts/recommendations??
?
|
Re: Losmandy G11 bearing question
I added a third bearing simply by lubricating it slightly,
inserting it part way, sliding the shaft into the center, and
gently tapping the third bearing into place.
All went very smoothly this way and there was no chance of
misalignment.
Laurel
On 4/25/25 9:43 AM, Paul Kanevsky via
groups.io wrote:
toggle quoted message
Show quoted text
? [EXTERNAL]
On Fri, Apr 25, 2025 at 10:09 AM, Chip Louie wrote:
Binding due to misalignment is one of the problems I
found as a potential way to screw up my perfectly good G11
mount as I contemplated this modification.? To get that
perfect non-binding installation the additional bearing
would need to be supported on a shaft that is in alignment
with the other two bearings as the 3rd is pressed into
place.??
?
So when I looked at the distance between the bearings
and the very short length the axle? is unsupported at the
end of the body I figured it should make no difference.?
My guess was it would not improve performance even if the
3rd bearing was installed perfectly.? But if not installed
perfectly or the axle was not perfectly straight the
slight misalignment could be the source of a slight,
regular binding as the axle rotated.? So I passed on that
modification.??
?
The possibility of screwing up the mount is very real, as
my first-hand experience made painfully obvious... at least
to me :)
|
Re: Losmandy G11 bearing question
On Fri, Apr 25, 2025 at 10:09 AM, Chip Louie wrote:
Binding due to misalignment is one of the problems I found as a potential way to screw up my perfectly good G11 mount as I contemplated this modification.? To get that perfect non-binding installation the additional bearing would need to be supported on a shaft that is in alignment with the other two bearings as the 3rd is pressed into place.??
?
So when I looked at the distance between the bearings and the very short length the axle? is unsupported at the end of the body I figured it should make no difference.? My guess was it would not improve performance even if the 3rd bearing was installed perfectly.? But if not installed perfectly or the axle was not perfectly straight the slight misalignment could be the source of a slight, regular binding as the axle rotated.? So I passed on that modification.??
?
The possibility of screwing up the mount is very real, as my first-hand experience made painfully obvious... at least to me :)
|
Re: Losmandy G11 bearing question
?
?
Hi Paul,
?
Binding due to misalignment is one of the problems I found as a potential way to screw up my perfectly good G11 mount as I contemplated this modification.? To get that perfect non-binding installation the additional bearing would need to be supported on a shaft that is in alignment with the other two bearings as the 3rd is pressed into place.??
?
So when I looked at the distance between the bearings and the very short length the axle? is unsupported at the end of the body I figured it should make no difference.? My guess was it would not improve performance even if the 3rd bearing was installed perfectly.? But if not installed perfectly or the axle was not perfectly straight the slight misalignment could be the source of a slight, regular binding as the axle rotated.? So I passed on that modification.??
?
--
Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
?
?
?
|
Re: Losmandy G11 bearing question
On Thu, Apr 24, 2025 at 06:31 PM, fetoma wrote:
I'm doing a deep dive into my G11 and replaced all the bearings. One thing I noticed is while replacing the inner needle bearings is that one end of the RA and Dec axis housings have enough room to fit two needle bearings. See photos. Do you think it would help in any way to add another bearing in this space?
Hi Frank,
?
Just as Laurel, I added a third bearing to a G11 more than 20 years ago, when I was planning to put a 10" SCT on it side-by-side with a small refractor. The thinking was to stabilize the axis, fix it so there's little chance of a wobble. It took some effort to install the third bearing -- I didn't have any specialized equipment to do so.
?
What was worse was that it became nearly impossible to push the axis through the three bearings. With three bearings that are properly sized, you'll need to make sure that all three are aligned very precisely, that none are even slightly tilted relative to the others. Any slight tilt of the new bearing will surely help secure the axis better, but will also make it nearly impossible to get the axis threaded through all three of them! :( It took me nearly a day to rectify a slight tilt I introduced with the new bearing. The one I installed fit very snuggly into the axis tube, so making adjustments to its position was not easy.
?
I can't say for sure that it improved anything with the mount, but after all the pain and suffering, the G11 performed well for years, and I still have it and use it on occasion when I need a portable set up :)
?
Regards,
?
? ?-Paul
|
Re: Losmandy G11 bearing question
Yes,
??? Years ago I added a third bearing to the axis and it markedly
stabilized the tracking.? If you search the archives you will find
a lively discussion about this and how to do the addition.
Laurel
On 4/24/25 4:31 PM, fetoma via
groups.io wrote:
? [EXTERNAL]
Folks,
?
I'm doing a deep dive into my G11 and replaced all the
bearings. One thing I noticed is while replacing the inner
needle bearings is that one end of the RA and Dec axis
housings have enough room to fit two needle bearings. See
photos. Do you think it would help in any way to add
another bearing in this space?
?
-Frank
?
|
Chip Louie
Paul Kanevsky