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Hi Folks,

I'm new to the G11/Gemini, but not to astrophotography and I have used PemPro previously with great success. ? I'm using Brian's fabulous instructions here:



but, I'm stuck in Gemini PEC setup in the very beginning. ?The problem I can't figure out is that Brian's instructions show that I'm supposed "Choose 2x PEC cycle and press Set", but the pulldown box is empty (see screenshot below). ??

What am doing wrong?

Thanks in advance!

-Bret

On Sat, Aug 27, 2022 at 03:06 AM, Brian Valente wrote:

it guides in one direction all?the time. RA is moving in sidereal speed, so guide corrections are either speeding up or slowing down the RA movement. it's never reversing so backlash during tracking and guiding is not a performance issue

Thanks for the clarification. I really thought that the direction of the arrows you see in PHD2 indicated the turning direction of the RA drive.?

Best wishes,
Daniel

That’s about right. There has to be som movement I remember this has been discussed lots before. ?3mm at the end of the shaft is a lot less at the gear?
--
Brendan

Backlash in Ra is not a thing! My focus would be on Dec. You need an FFT on Ra to understand it's behaviour.

Peter

--

Because it's spring-loaded, you'll see a lot of wiggle if you push moderately hard, but that doesn't mean you have that much backlash during normal tracking.

Even with this backlash, how is your guiding ?? ?Backlash in RA is not a big thing as it tends to guide in one direction most of the time.??

Regards,
Daniel

How much wiggle or movement should there be for the RA axis if the spring-loaded worm and secondary screw are adjusted correctly?? ?I measured the movement of the far end of the counterweight shaft and found 3mm of movement.? This seems excessive.? ?I had less movement but was forced to back off the secondary screw because the RA motor was stalling.? ?Is there something else other than the secondary screw that might be causing/contributing to this 3mm of movement?? ?Is there anything different about adjusting the secondary screw for the RA axis compared to the secondary screw for the DEC axis?? ?The DEC axis had some movement and I was able to significantly reduce it by adjusting the spring-loaded worm and secondary screw for DEC.? ?My mount is a GM811G and is about a year old.? ?I use it a lot, about 130 nights of imaging/testing since purchase.? ?Thanks in advance for any advice.? ? --? Jim?

Danial, please post your PHD2 log file and I'll look at it for glues.

Peter

The spikes I mention can be seen in this excerpt of a PHD2 log:



As you can see the error is most of the time in a band of +-1", but there are occasional spikes. Even without the occasional spikes, I do not like too much the performance, too much oscillations with just 9 lbs of equipment (Sharpstar 76EDPH with all the typical add-ons).? With the 343mm focal length of the 76EDPH? the resulting images are perfect, but? I would like to be able to image with longer instruments (with 1200mm fl as the maximum perhaps).?

I think that oscillations could be related to stiction and may benefit from a fine adjustment of the worm gear.

Best regards,
Daniel

Bob,?

This depends on the total age of the scope, not just idle time. Sitting for 3 years might make the lubes drip through a bit, especially with higher temps. So we know the mount is 3 years + at this point.

If only that old, you can do the basic clean up and relube as in the videos, plus replace or clean the clutch discs which may be worn or oily. If the scope is 5 years plus, you may want to do a full teardown, degrease and relube, but also replace some moving parts like the Oldham couplings, gearboxes and the worm bearings. The thrust bearings and washers should also be inspected at this time as well.

The greases do move away from the gear surfaces with use, and also trap in dust and metal fines from the gears wearing. But make sure to replace with quality lubes like the Jet-Lube MP-50 on the worm and rings, and Jet-Lube Artic or other surfaces (which are the original Losmandy lubes). But I would recommend Mobilgrease 28 over the Artic, as this aircraft-rated grease has very good anti-wear properties.

Wish I could help but I am over 3000 miles away. As mentioned, resetting the worm to ring tension takes some time and patience, if you don't have a Losmandy knowledgeable helper close by.

Regards,

John
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Losmandy G11G2 on pier; SkyShed design roll-off observatory; ZWO ASI2600MM-P; ZWO ASI071MC; Sky-Watcher Esprit 100 ED; Celestron C925 Edge HD with 0.7XFR, William Optics Zenithstar 61 APO; PHD2, Sequence Generator Pro and PixInsight user

PE spikes can be caused by stiction which may be visualized as force ramping upward with a sudden release as the level of force applied overcomes the resistance present. There are two possibilities here, the bottom of the deck plate cap screws are just a smidge too tight or you have a bit too little lift. I would start by adding some additional worm lift using the lift adjustment may fix it but be aware the lift adjustment usually needs to be very small to maintain optimum worm tooth engagement and these are not fine threaded fasteners. So I would make the smallest possible adjustment to the lift adjuster, observe and if needed continue to adjust. It sounds like your worm is close to optimum so with a small adjustment you should be GTG. If you don't see any change the bottom side cap screws are the next place to adjust. I suggest changing the outer or left side first, test, observe and adjust, if after two cycles you see no change try cracking the inner cap screw a smidge.?

You can verify the cap screws are letting the OPW move by wiggling the end of the counter weight and feeling for movement on the outer end of the OPW where the worm bearing block is attached to the OPW. There should be some movement felt on both axis or chances are you need to crack the outer bottom side cap screw a bit. Keep in mind that a little adjustment goes a long way on all of these coarse threaded fasteners.?
?
Keep us posted.?
--

Chip Louie Chief Daydreamer Imagination Hardware?

? ?Astropheric Weather Forecast - South Pasadena, CA?

Vincent has been so kind to contact with me to report that unfortunately he was unable to solve the problem and sold the mount, moving to a CEM60. His mount used a Gemini 1, so either the problem is not tied to the Gemini or the part that causes the problem is present in both generations of the computer (code or electronics).

Thus, the problem is still unsolved and in my case means that PEC is unusable in my mount :-(

Best regards,
Daniel,

Losmandy will do that for you, surely, but maybe they are too busy to do it promptly. Basic maintenance is well covered in their videos (cleaning and re-greasing). Worm adjusting is more intimidating though, but may be you don't need that.??

Best of luck,
Daniel

Did you get those spikes in RA too?? ?I'm considering too slightly loosen the far end bottom screw to try to improve my RA performance. Peak values in RA are over 2.5" and those concern me more than the RMS number.

Best regards,
Daniel

That's exactly what Brian says. He only refers to the far end screw that it is beneath the big spring screw though. Unscrew a little and that should free the worm enough to float over the gear.? However, I'm not sure if I'm going to get much benefit of it. Currently DEC is guiding just under 0.4" RMS over 3 hour sessions and it is the RA axis what is limiting the guiding accurary (I get around 0.6" RMS).

Best wishes,
Daniel

Bob

your the perfect person don’t discredit your skills, attention to detail and analytical skills.?

there are plenty of dissemblely guides ?on the net and attention to order of washers. ?Take photos when taking it apart use this site as a guide



Losmandy sell lubricant kits etc. there are many guides on how to adjust your worm and blocks. ?Many have written them but I like Michael Herman’s guides.?

Maybe look to replace the clutch pads they may clean up ok. ?Be careful of some solvents on the anodising surfaces. ? ?Disassemble clean re-assemble?

Might need new worm bearings or such like ruland coupling. ? Check when taking apart so you can order replacements. There are databases of nuts bolts bearings etc you can use in the files section.?

Remember you cannot wreck it. ?

Maybe try run it prior to dissemble and test PE so you have a base line when put back together to see if something is not right.?

You will learn as you go, best way to do it

cheers

bren




--
Brendan

Bubbles are my thing right now and this beautiful and popular supernova remnant does not disappoint. Two light years across and 1500 lights years away in the constellation of Aquila, which is sadly somewhat barren of DSO objects.?

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Total integration time is 3.66 hrs using an 12" F3.9 truss Newtonian, captured with an ASI 294MM Pro camera using Chroma 3nm narrowband filters. No moon was present. Equal number of Ha and Oiii subs.

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This is a bright object, and I was able to pull out some detail using Pixinsight. Bortle 4/5 sky. Modified Losmandy G11 mount running Onstep.? It's very small for my setup, and I look forward to returning someday with a 3m scope! I was also able to get the little dumbbell (M76) later in the night, so looking forward to seeing how they compare.

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Peter

I don't know that good lubricants would deteriorate appreciably in 3 years.? Does the mount work?

hello Bob Hancey, I am a member of the Sac Valley astro soc. we have a G11 mount (older mount) I am in the start of a rehab project for this mount. My greatest concern is that lubricants on the interior of the mount are no longer qualify as lubricants as the scope sat unused for at least 3 yrs. Will attempt to use soon, but do not have a lot of hope movement from the mount. I will contact Losmandy to see if they do rehabs on their mounts and cost to do so. I do not have the skill set to do a breakdown and rehab (I am a retired ICU RN---not much crossover skills for this project). IF my attempt to have Losmandy to do a rehab is a negative, NEXT best hope is to find a person/business that can do rehab (some funds are available), with a location in central/northern Calif and southern Oregon that the mount can be delivered to. SO, if there is anybody within the Losmandy group has a name of person/business that could be of value in terms of getting this mount back into a reasonable/functioning shape for members/visitors can use, any input would be appreciated, respectfully submitted Bob H.