I have just carefully adjusted both my DEC and RA worms using finger pressure to squash the two ends together and feeler gauges to adjust the gap between the body and the non-motor adjustment block.

Adjustment is very critical 0.002" makes the difference between getting a MOTOR STALLED message and no backlash.? I am coming to dislike the motor / gearbox / worm setup on this mount quite a bit.? I really dislike screwing the motors into the plastic gearbox plates.? They wobble and I am always scared that I'll strip the plastic thread.

My mount has steel worms which seem to work well enough but I cannot do any PE measurement right now for a number of reasons.? I fear that I may have to spring for at least one new OPW and brass worm later this year.? Along with a Gemini 2 upgrade this is getting to be an expensive mount even though I got it cheap.? Honestly, iOptron is beckoning me.

On Sun, Jul 11, 2021 at 02:56 AM, alan137 wrote:

On Sat, Jul 10, 2021 at 12:56 PM, Nick Ambrose wrote:

1. Guide assistant said my backlash was 3500 ms so it did not recommend turning it on. It recommended guiding in one direction which did not work well. Brian V said that PHD cannot accurately measure BL on the spring-loaded worms, so not to enable the comp

I have a very long post describing the DEC axis backlash
/g/Losmandy_users/message/71205

Thanks! I am going to check this out.
Unless DEC affects the RA, then it is less of a concern right now, although might need some attention
When I imaged at DEC=60, RA was insanely good. Last night was DEC=30 and definitely a few excursions

The RA spikes still persisted and I did everything in software I could think of to tweak them, and nothing really had an effect.
Guiding was closer to 0.8-0.9 (DEC=30 not 60). Still OK but for the spikes

Things I can think of?

1. My guider scale is just not good enough and I need (at some point) to upgrade. Definitely possible
2. PHD2 "bug" -> could be just some weird thing. Who knows (somewhat unlikely ?)
3. I did change the weight, moving it further East. Its a 7 pound weight so I thought it would generally be OK to move.
I put it close to the end of the CW bar, and PHD2 kept complaining it could not move the star enough so maybe this has more impact than I thought ?
Maybe check balance again
4. Related to #3 - maybe it's possible Gemini is not getting enough power (since it couldnt move the axis with the weight moved)
I have an 18V power supply but maybe there is some issue here ? (It steps up from 12V)
5. Wires - Next time I will tweak my wires. I think they are tight, but if I try to re-route them and things change, then I will at least have something to look at

Other than that, I guess I don't have much to do except ignore them and assume my images are not affected.
I'm processing one from last night right now, so we will see

It doesn't feel satisfactory but at this point I dont want to tinker, and definitely don't want to void any warranty

I know these things are tough to debug but it doesn't feel super satisfying honestly

Upgrading the guider is definitely a "good thing" though. I think I can easily get an ASI290 and drop it into the current scope, which will help somewhat
Then later I could look into a better scope - but that's going to need a lot better mounting hardware than I have

?Hi Greg,

Surely the bearing blocks are sitting flush on the deck plate and not as is shown in the photos way up off the base deck!?

--

Chip Louie Chief Daydreamer Imagination Hardware?

? ?Astropheric Weather Forecast - South Pasadena, CA?

On Sat, Jul 10, 2021 at 12:56 PM, Nick Ambrose wrote:

1. Guide assistant said my backlash was 3500 ms so it did not recommend turning it on. It recommended guiding in one direction which did not work well. Brian V said that PHD cannot accurately measure BL on the spring-loaded worms, so not to enable the comp

I have a very long post describing the DEC axis backlash
/g/Losmandy_users/message/71205

Please start another thread to discuss this

Totally correct...first thing is re-calibrate the HC screen on boot.? Try this is first.

The fact got past into screens...means it appears to be working so maybe re-seat your HC microSD card.

Dos wiggling the cables cause it to stop?? Clean inspect the sockets and plug pins.

If its a G2 first you can plug it into serial 1 port (but first lower its Baud to 9600bps) and try that port.

It's possible the housing screws but my guess this would manifest in differing issues like slewing HC functions.

Yes it could be a HC or Main unit issue but probably not and no use thinking of this yet.

Lest see how this goes first before looking further
--
Brendan

Past replies on the forum have suggested that if the HC housing screws are too tight the touch screen may not not work properly. Try loosening and re-snugging be hand.?

Did you try re-calibrating the screen? Right before the boot options menu shows up you can press the screen to re-calibrate it.?

开云体育

I have new worms running in both axis. I have no expedience to know how things change as they wear or how long that takes. To what extent are the one PHD2 tracking spikes a function of the worm surface? Does tracking improve or get worse as they wear in? Since I have a few worn worms I thought I might lightly buff one while spinning in an electric drill. I have to assume a polished worm has less friction/stiction.?

Another question I have is what effect do the needle bears have on the system. Do they have a frequency profile? I do have some axis movement. My rig is rather old, and I suspect these have never been renewed. However, it looks like a difficult job, not to be taken on lightly.?

Peter

Peter,?

Not sure if there is a set period for break in, but over time all meshing parts start to wear and smooth down as they loose metal on the tops of the tiny asperities on the surfaces. If you have ever changed the oil in your car after the first 500 miles, you will see the fluid is full of shiny metal fines, shed from the moving parts inside the engine. Same with the worm and rings gears wearing and smoothing over time. Of the worms I have used, my original 3 year old RA worm works the best, and has a noticeable depression in the center where the ring gear has worn it down. How to pre-wear or polish down a new worm is a good question, but doing it evenly and properly would probably involve precise machinist equipment and micro-measurement instrumentation not many have at home. If you polish it unevenly even much less than a thousandth of an inch, you are probably creating new errors. Most I think would love to hear about this if you can achieve it.

The main needle bearings, from my disassemblies, look like they were hammered or pressed into the main mount frames at the factory with perhaps hydraulics or a special knock-in tool which would fit precisely over the bearing races. How to knock the old ones out and replace I have not ever considered yet. With proper lubrication they look like they would last decades, IMHO.

Best of luck,

John??

Sorry about the duplicate / inverted pics. After this point, just tighten left block snug / flush and right block just off snug / flush.

.

On Sat, Jul 10, 2021 at 01:54 PM, <pcboreland@...> wrote:

Nike,

Is this a new or old mount?

That backlash number doesn't surprise me. I worked on and this on and off for months. I spring loaded my worm and decided to just lock things down instead. I get the mesh as tight as possible by rocking the axis back and forth. Don't forget to load the bearings so the worm does not move laterally. I do this with the cover off so I can see if there is any lateral movement in the worm. Then I replace the cover. You may find the motor stalls so you will need to back off the work/gear mesh pressure with the adjustment screw. You should do a full 180 swing to see there is not a stall spot. That said, with all that attention to detail, my backlash is 2500ms, which allows me to guide OK. I've now traced the backlash problem to the slop in the needle bears which is significant and explains I think the whole problem. Also, I found the same issue in the Ra axis.?

Peter

Mount is just a few weeks old. I was hoping not to have to start manually messing with adjustments especially with the new improvements that have been done on the mounts.?

?

Nike,

Is this a new or old mount?

That backlash number doesn't surprise me. I worked on and this on and off for months. I spring loaded my worm and decided to just lock things down instead. I get the mesh as tight as possible by rocking the axis back and forth. Don't forget to load the bearings so the worm does not move laterally. I do this with the cover off so I can see if there is any lateral movement in the worm. Then I replace the cover. You may find the motor stalls so you will need to back off the work/gear mesh pressure with the adjustment screw. You should do a full 180 swing to see there is not a stall spot. That said, with all that attention to detail, my backlash is 2500ms, which allows me to guide OK. I've now traced the backlash problem to the slop in the needle bears which is significant and explains I think the whole problem. Also, I found the same issue in the Ra axis.?

Peter

I moved this discussion to its own thread:

/g/Losmandy_users/topic/needle_bearings_and_axial/84141331?p=,,,20,0,0,0::recentpostdate%2Fsticky,,,20,2,0,84141331

On Sat, Jul 10, 2021 at 12:39 PM, <pcboreland@...> wrote:

Nick,

I looked at your log file. Several things jump out at me.

1. I noticed you have backlash compensation turned off.? Have you run the Guiding Assistant to determine your Dec backlash. I notice there are times when it takes quite a few pulses to make the correct and the pulse width is small at 20ms.?
2, Your pixel scale is 6.45 "/px. By comparison mine is 1.24 "/px.? At this low resolution I'm not sure one can put too much into the guiding numbers, your numbers will look super good as you can not really detect true movement.? But others here are way more experienced on this front and I'm sure I'll get shot down for saying this.. Personally, I think the guide resolution ideally ought to be under 2x the imaging resolution.?
3. Your 240s error is at 4" to 4.5" peak-to-peak give or take. But that is with running the Predictive PEC algorithm. You might what to do a run using say the Hysteresis algorithm with Mount PEC off to get a baseline value. I reduced my native error down to just under 3 arc-sec peak-to-peak by installing a rigid coupler in the Ra. This way the motor shaft and worm are better aligned.? But your number is already low and it guides out really well to around 0.15", so is under control.
4. You have a very large low frequency component at 1100s or so. Not sure what might be causing this?
5. Those spikes are the biggest issue for me, and the elephant in the room is the 76s error, which is surely giving rise to those large transient moves in Ra. PHD2 is only able to reduce it by 2/3rds. There is a lot out there on this problem. With the OPW I do not see this error but I have an equally large one at 80s. Fortunately, I think I can build a PEC curve using PEMPRo to eliminate it. At least that's what I hope.

Overall, this are pretty good results with the caveat that things might look different at a higher guiding pixel scale. Time to take some pictures!

Peter

Thank you so much Peter

1. Guide assistant said my backlash was 3500 ms so it did not recommend turning it on. It recommended guiding in one direction which did not work well. Brian V said that PHD cannot accurately measure BL on the spring-loaded worms, so not to enable the comp
2. Completely agree. I got a small guider setup for my old star tracker as I did not want to have too much weight. I am considering upgrading but mostly only if it will improve my images.?
3. I did a baseline here and it was I believe 7.5 to 7.5 peak to peak (it's in my other thread here). That seems a bit more than expected but Brian V said it was smooth and would guide out as you said
4. I have no clue on the 1100. I tried to get my cabling neat and tidy and nothing snagging etc. I'm on a driveway so cars do sometimes pass by but I am sure they are not coming at exactly 1100 second intervals :)
5. Yeah the spikes worry me but I dont have much recourse here as I am not wanting to muck with the mount and I don't really have a clue where they come from (maybe its the 76-second issue ?)

I'm not letting this stop me imaging, but I dont want to image with poor results. The spikes are my main concern. I will adjust the weight back a bit next time to see if it can help at all

I'm going to look at upgrading the guider. I think I can keep the scope the same and get a better camera and not have to significantly change my attachment to the scope

I'm working on an image now but may have picked something too tough for my gear and skies. Going to give it a few more nights and then consider moving onto a new target

Thanks so much for your feedback !

EDIT (sorry)
This is a brand new mount so I do have all the latest upgrades etc on the hardware side

Nick,

I looked at your log file. Several things jump out at me.

1. I noticed you have backlash compensation turned off.? Have you run the Guiding Assistant to determine your Dec backlash. I notice there are times when it takes quite a few pulses to make the correct and the pulse width is small at 20ms.?
2, Your pixel scale is 6.45 "/px. By comparison mine is 1.24 "/px.? At this low resolution I'm not sure one can put too much into the guiding numbers, your numbers will look super good as you can not really detect true movement.? But others here are way more experienced on this front and I'm sure I'll get shot down for saying this.. Personally, I think the guide resolution ideally ought to be under 2x the imaging resolution.?
3. Your 240s error is at 4" to 4.5" peak-to-peak give or take. But that is with running the Predictive PEC algorithm. You might what to do a run using say the Hysteresis algorithm with Mount PEC off to get a baseline value. I reduced my native error down to just under 3 arc-sec peak-to-peak by installing a rigid coupler in the Ra. This way the motor shaft and worm are better aligned.? But your number is already low and it guides out really well to around 0.15", so is under control.
4. You have a very large low frequency component at 1100s or so. Not sure what might be causing this?
5. Those spikes are the biggest issue for me, and the elephant in the room is the 76s error, which is surely giving rise to those large transient moves in Ra. PHD2 is only able to reduce it by 2/3rds. There is a lot out there on this problem. With the OPW I do not see this error but I have an equally large one at 80s. Fortunately, I think I can build a PEC curve using PEMPRo to eliminate it. At least that's what I hope.

Overall, this are pretty good results with the caveat that things might look different at a higher guiding pixel scale. Time to take some pictures!

Peter

Here is a link to two RAW subs - now we are thinking about "can we see the effect in the images"
This was something David suggested I do to see the effect

You can see in the 90 second sub, the FWHM is lower and the eccentricity higher compared to the 900 second sub
Obviously the 900 is getting more exposure to dim light, but the question David proposed to me was, is the 900 sec sub just smearing the error around a bit, bloating stars and making them appear more round and less eccentric (I measured a bunch of subs and the pattern held for all subs)
Or is the 900 sec sub just bringing in more light, so getting a better image that is more "correct" ?
I don't really know how to answer that.

Some of it may be the duo-band filter, which aren't known for being super high quality filters. I may bite the bullet and remove it and tweak the spacing and see if I get different results.

Part of it is I am not sure what expectations are reasonable and what aren't

On Sat, Jul 10, 2021 at 09:51 AM, Chip Louie wrote:

This issue is part of what the Belleville disc springs resolves by taking up all backlash axially. the worm axels are sized as they are for the real world and ease of maintenance and replacement. These bearings are consumables and as such are replaced as they get dirty and noisy. For visual users none of this makes any difference at all as you can barely even measure a difference in PE using PHD2. But it is there if you want to "fix" it.? ? ?

--

Chip Louie Chief Daydreamer Imagination Hardware?

? ?Astropheric Weather Forecast - South Pasadena, CA?

Thanks Chip. I only want to fix it if it will help my images and I have no idea if it will. Also, not being mechanical, I am more likely to do harm than good most likely

Peter,?

What do you mean by "hammer action"?

--

Chip Louie Chief Daydreamer Imagination Hardware?

? ?Astropheric Weather Forecast - South Pasadena, CA?