imaging in sub zero temperature?

[ONIKKINEN]

1 hour ago, AMcD said:

I wonder whether contraction of the metal parts was my issue.  The DEC motor continued to respond to commands but the DEC axis did not move.  In the circumstances, I wonder whether a set screw shrunk sufficiently to loosen the connection between the motor and the worm shaft such that worm shaft was slipping within the connector.

This has happened to me but in -20 or so weather (45 degree difference in adjustment and use temperature). I had just set my mounts backlash to be perfect so that it barely clears all the tight spots all around the DEC worm. Lo and behold couple hours later in the cold it did not move and i had to relieve the backlash setting a bit to make it work.

[OK Apricot]

2 hours ago, Xsubmariner said:

This was a far cry from a few years ago when I spent a lot of time under the stars with my NEQ6 and laptop. All was well up to -6, then if the temperature dropped further guiding became erratic and the mount sluggish. Found out later the original grease in the NEQ6 was not able to operate at those low temperatures. 

I feel like I want to second this. Most of my sessions, since taking up the hobby in the summer, have seen guiding to be very respectable, as low as 0.26" and averaging 0.4" when balance and cabling is managed properly. The last couple nights have hit -10°C and toward midnight having been out for several hours the guiding starts to suffer. I was thinking maybe the balance had changed, counterweight sliding down the shaft etc, so when re balancing the first thing I noticed was how "sticky" the clutches were which made me think grease. Couple that with thermal contraction and I guess there's your 1.1" accuracy 🤷

[Elp]

I never thought this would be an issue but just brought my rig back in which was cold and now it's sweating like it's under intense interrogation. Need it to warm up so it can be packed away.

[AMcD]

1 hour ago, ONIKKINEN said:

i had to relieve the backlash setting a bit to make it work

Yes, I suspect that this could be my problem.  Over the summer, I installed one piece worm blocks that allow fine adjustment of the backlash and, like you, adjusted it carefully.  It will be interesting to see what happens when the temperature improves.  I suspect we do not know what 'cold' means compared to where you are 🙂

[WolfieGlos]

This may be what's happening for me as well. I only use a Star Adventurer 2i, but Wednesday night I had to scrap 30/55 4minute subs due to trailing even though the guiding was running smoothly. Usually I scrap circa 5%, so this was very unusual.

Thursday night, I shortened my subs to 2 minutes, polar alignment was spot on, levelled, rebalanced to be sure, and guiding ran at total RMS of 0.27px. But similar has happened again; the first 50 subs are fine (none scrapped) but the next 35...every single one was trailing! I then re-checked polar alignment (which was still spot on), recalibrated the guider and tried 1 minute subs. Still trailed. 30 seconds...still trailed. So I gave up. I was imaging NGC7000, started at 6pm so it was way past the meridian, so assume the frost has been kicking in later on, and as the mount has rotated westwards the frost has been making it slip. Strange thing is the guiding graph and results are all very good.

Certainly when I've brought the setup back indoors it has been covered in frost so this is probably the cause, but perplexed how the guider can be running so well.

Really annoying since the cool temperatures helped my DSLR and skies have been crystal clear ! Oh this hobby at times !

Edited December 16, 2022 by WolfieGlos

[ONIKKINEN]

33 minutes ago, WolfieGlos said:

This may be what's happening for me as well. I only use a Star Adventurer 2i, but Wednesday night I had to scrap 30/55 4minute subs due to trailing even though the guiding was running smoothly. Usually I scrap circa 5%, so this was very unusual.

Thursday night, I shortened my subs to 2 minutes, polar alignment was spot on, levelled, rebalanced to be sure, and guiding ran at total RMS of 0.27px. But similar has happened again; the first 50 subs are fine (none scrapped) but the next 35...every single one was trailing! I then re-checked polar alignment (which was still spot on), recalibrated the guider and tried 1 minute subs. Still trailed. 30 seconds...still trailed. So I gave up. I was imaging NGC7000, started at 6pm so it was way past the meridian, so assume the frost has been kicking in later on, and as the mount has rotated westwards the frost has been making it slip. Strange thing is the guiding graph and results are all very good.

Certainly when I've brought the setup back indoors it has been covered in frost so this is probably the cause, but perplexed how the guider can be running so well.

Really annoying since the cool temperatures helped my DSLR and skies have been crystal clear ! Oh this hobby at times !

Skywatcher uses terrible grease in their mounts that doesnt like sub zero temperatures. Could have taken a while to get sticky and when it did your guiding remained bad for the rest of the night. If youre up to a little DIY you would benefit from cleaning the factory gunk and replacing it with a nice white PTFE grease (super lube is great) that doesnt mind the cold.

* Or power supply issues if you run with batteries not suited for cold.

Edited December 16, 2022 by ONIKKINEN
*

[Craig a]

5 hours ago, AMcD said:

I wonder whether contraction of the metal parts was my issue.  The DEC motor continued to respond to commands but the DEC axis did not move.  In the circumstances, I wonder whether a set screw shrunk sufficiently to loosen the connection between the motor and the worm shaft such that worm shaft was slipping within the connector.

It was the dec that was causing my guiding problems the last two nights too, I do think the gear and worm contracted away from each other slightly, won’t know for sure till I get a warmer clear night 

[Xsubmariner]

2 hours ago, ONIKKINEN said:

Skywatcher uses terrible grease in their mounts that doesnt like sub zero temperatures.

This is the reason I changed out my NEQ6 grease for some extreme temperature lubricant and haven’t had a problem since. Not cheap stuff though.

[WolfieGlos]

2 hours ago, ONIKKINEN said:

Skywatcher uses terrible grease in their mounts that doesnt like sub zero temperatures. Could have taken a while to get sticky and when it did your guiding remained bad for the rest of the night. If youre up to a little DIY you would benefit from cleaning the factory gunk and replacing it with a nice white PTFE grease (super lube is great) that doesnt mind the cold.

* Or power supply issues if you run with batteries not suited for cold.

I'm looking into upgrading to a larger mount next year anyway (skywatcher none the less!!), but that's interesting to hear. I will look into replacing the grease, I no idea this could be a problem. Thanks!

Good call on the batteries, my power bank was an issue at the start, it kept turning off so I swapped it for a spare and that then ran fine for my whole session, so that wasn't it. It's also used to power the dew straps, so I know the spare bank was working in that cold!

[ONIKKINEN]

9 minutes ago, WolfieGlos said:

I'm looking into upgrading to a larger mount next year anyway (skywatcher none the less!!), but that's interesting to hear. I will look into replacing the grease, I no idea this could be a problem. Thanks!

Good call on the batteries, my power bank was an issue at the start, it kept turning off so I swapped it for a spare and that then ran fine for my whole session, so that wasn't it. It's also used to power the dew straps, so I know the spare bank was working in that cold!

If you have a multimeter you may want to check the voltage after its been in use in the cold for a while. Its likely it only supplied 11-12v at the end of the night even if it still had most of ita charge left which would affect tracking rates. Cold does that to unregulated batteries, no way around it. Li-ion and other more expensive types are a bit better but still only half a solution. For optimal use you want the voltage to remain between 13-14v, below 12v you run into issues and below 11v your stepper motors will start to slip completely and so it looks like guiding is failing when in reality the guide impulse was never completed by the motors.

Edited December 16, 2022 by ONIKKINEN

[edarter]

I keep the outdoor laptop and dew heater in a plastic container similar to this:
https://www.amazon.co.uk/Wham-Plastic-Stackable-Storage-Containers/dp/B07RF93JB5/ref=sr_1_14?keywords=Plastic+Storage+Container&qid=1671213283&sr=8-14

Laptop is on a wooden standoff I made so that its lifted off the base and is close to the lid. This allows all the other cables etc to be stored in the container when not in use as well as being where the dew heater controller lives. The laptop is then also high enough for the container sides to not interfere with using the keyboard. Once all set up, polar aligned and the session started I close the laptop lid and put the container lid on, the cables coming out at one end leave a little gap but that stops it all getting too warm in there. It stays warm enough in the container that no dew/frost etc form and is nice and dry. I run on mains power rather than batteries and put a polythene bag over the garden extension reel which is next to the container.

The only downside with all this cold weather is the cables are VERY stiff after a session and I'm sure one day I'll experience a failure somewhere that I'll then need to track down. I've searched high and low for silicone sheathed mains cables (as opposed to PVC) but there doesn't seem to be such a thing, a shame as they remain much more flexible in low temperatures. If anyone knows if/where you can purchase them please let me know!

Ed

[dark knight]

Well seems I am not alone.  I set up last night and had nothing but problems, mount not completing goto's, plate solving was a complete failure, dewband cable got so stiff it snapped at the plug/controller junction. It seemed one thing after another and I gave up with not a single sub to show for my efforts. I use mains power to a 12v power supply and run everything from that. I have pi4 at mount running off the mains too via a 5v adapter, and vnc into it from the house. When I looked into the plate solving side of things it seems comparison files had disappeared from the pi4!!! I spent rest of the evening downloading and reinstalling them. Going to have a break from it tonight for my own sanity!

[AMcD]

5 hours ago, Craig a said:

It was the dec that was causing my guiding problems the last two nights too, I do think the gear and worm contracted away from each other slightly, won’t know for sure till I get a warmer clear night 

I went out to check the mount when I got back from work.  The DEC worm was immovable until I ran a hair dryer over the DEC axis, after which it began to loosen.  I guess the grease has become very sticky in the extreme cold.  I plan to reset the seating of the DEC worm tomorrow and will look to clean and re-grease the mount this summer.  @Xsubmariner, what lubricant do you use.

It is interesting that everyone is having issues with the DEC axis but not the RA 🤔

[AMcD]

7 hours ago, WolfieGlos said:

Oh this hobby at times !

Amen to that 😂

[Craig a]

1 hour ago, AMcD said:

I went out to check the mount when I got back from work.  The DEC worm was immovable until I ran a hair dryer over the DEC axis, after which it began to loosen.  I guess the grease has become very sticky in the extreme cold.  I plan to reset the seating of the DEC worm tomorrow and will look to clean and re-grease the mount this summer.  @Xsubmariner, what lubricant do you use.

It is interesting that everyone is having issues with the DEC axis but not the RA 🤔

The Ra is constantly on the move so the gears are  pretty much always meshed but the dec is fixed until a guide command is issued so if the gears have contracted away from each other slightly widening the meshing it will cause problems, that’s my thinking anyway I could be talking absolute garbage and looking for something to blame 😂

[paul mc c]

My gear after a frosty session...no problems at all.

[Elp]

Until you touch it with your bare hands.

[paul mc c]

9 minutes ago, Elp said:

Until you touch it with your bare hands.

You should try your tongue...😜 Lol.

[iwols]

Well guys some great observations/comments thanks

 

[AMcD]

On 16/12/2022 at 10:39, AMcD said:

I wonder whether contraction of the metal parts was my issue.  The DEC motor continued to respond to commands but the DEC axis did not move.  In the circumstances, I wonder whether a set screw shrunk sufficiently to loosen the connection between the motor and the worm shaft such that worm shaft was slipping within the connector.

I dismantled the mount this morning and my initial suspicion was confirmed.   The worm was slipping in the coupler.  The coupler set screws had become loose as the worm / screws had shrunk in the cold.  All working again now 🙂

[Carbon Brush]

On the mains cable. Low temperature mains leads are often referred to a 'arctic grade.

A search on amazon for 'artic grade 3 core cable' gives multiple hits.

Professional/commercial suppliers below also have this type of product.

https://uk.rs-online.com/web/p/power-cable/1964722

https://www.rapidonline.com/Catalogue/Search?Query=arctic grade

https://cpc.farnell.com/pro-elec/pelb0793/cable-3183ya-arctic-2-50mm-blue/dp/CB22804?mckv=s_dc|pcrid|426684131036|kword||match||plid||slid||product|CB22804|pgrid|100371158838|ptaid|pla-1672715869625|&CMP=KNC-GUK-CPC-SHOPPING-9262013734-100371158838-CB22804&s_kwcid=AL!5616!3!426684131036!!!network}!1672715869625!&gclid=CjwKCAiAkfucBhBBEiwAFjbkr4_bNMShVTHv8Jcnzt9kS-0Z8wNIe1SzHo-j714XVgHqrS4GdnbFYRoC11EQAvD_BwE

You have choices of buying short lengths like 5M or 10M. up a 100M reel.