Saw toothing with PHD2

[Phillyo]

Hi all,

My setup has been doing this for a while and i've no idea. It hasn't affected my images, yet, but that's only because i'm at such a short focal length I think.

My set up is:

Mount: Avalon Linear Fast Reverse

Scope: WO Star71

Camera: QSI583wsg

Guiding: Lodestar x2 with PHD2

Capture: SGPro

I'm fairly sure i'm balanced as close as i can be. Also I'm pretty damn close to being polar aligned, spent a long time getting it accurate tonight. I think it's just a settings thing, but I can't figure out what.

Clutches are tight, there's no trailing or snagging wires.

Any help would be appreciated.

Phil

[strutsinaction]

Hi Phil

Interesting trace. I have a similar setup to you and haven't noticed anything like that (except the usual spikes when dithering of course and once when I had a loose patio slab).

You RA is fine overall so why is your DEC spiking? It seems quite regular, not random. On closer inspection it also looks like the RA have a brief downward spike just as the DEC spikes upwards but that might just be a coincidence.

Regards

John

[Thalestris24]

Hi Phil

I don't have the mount (I wish!) but I'd suggest a balance or possibly a flex problem. It might be an idea to run PHD2 for a while with guiding off and see what the guide logs say in PHDLab.

Louise

[Phillyo]

Thanks Louise, I didn't know about PHDLab, useful little tool. I've just put in my guide log from that night and (I think) it's telling me I was way out on polar alignment, like 17 arc min. I'm not sure that's right though as I did a drift alignment in PHD2 and I know I was a LOT closer than that. Or so it told me. I'm wondering if a misbalanced mount would think it's out of alignment?

On the whole balance thing, I'm finding it super hard to balance the mount. Firstly, my telescope is SO light that with the slight friction in the movement it doesn't really balance too well? If there's a huge misbalance, like if I put the 6 or even 3kg counter weight on the other end then it will swing down towards the counterweight. However if I remove those and make my own makeshift counterweight and attach that, making the balance a lot closer then it just moves a little bit then sticks. However I can see two things with this, first is as i've just described...it makes it really hard to balance accurately. Secondly, if the balance is so close that the mount sticking is enough to stop it moving then surely that's going to be pretty close to balanced accurately??

I also noticed that when I have the mount locked in RA and free in DEC the telescope will drop slightly to the right...maybe 15-20 degrees. Moving the scope up or down does nothing to affect it. It still drops slightly to the right. I'm wondering if this is because I have an autofocuser on the right of the scope which is slightly overbalancing it in that direction. Maybe that is causing an issue? 

I supppose the best way of finding out is to rotate the scope 180 degrees so that the focuser is on the left side and see if the telescope drops to the left? I might give that a try and see.

Thanks again, and sorry for my rambling!! I'm hoping someone reading this will understand and say "Ah yes, it's because of 'x y and z'" and it'll solve my problems

Also, if anyone knows how to use PHDLab and would be up for looking at my guide log i would VERY much appreciate it. It all looks very baffling to me.

Phil

[Thalestris24]

Hi

It does sound like you may have some balance issues. I know some scopes can be awkward to balance properly and I've read about some creative solutions on here Maybe someone with the same scope as you can advise. I wouldn't take too much notice of PHDLab's PA error calculation - it's based on measurements performed only during the times when there are no corrections being made.

Louise

[libraryman]

Is it possible that you are too well balanced in Dec, allowing a bit of backlash to manifest?

How high were you imaging when the sawtooth came in.

I always unbalance Dec camera heavy just to keep the backlash tamed, it can still be an issue if the scope is pointing at zenith

Ray

[Phillyo]

Hi Ray,

When I had an EQ6 I used to use a little bit of off balance, however with the Avalon mount it has 0 backlash so balance is supposed to be perfect I believe.

Thanks,

Phil.

[Scott]

is cable snagging a possibility? Just throwing a few ideas your way

[Phillyo]

No snagging checked that.

[Bizibilder]

Looks like snagging to me - If you look at the trace and count the horizontal sections from 1-8 you have no saw-tooth in sections 1 or 2, a minor event in section 3 followed by four major "snags" in sections 4-7 and one small snag in section 8.  It looks to me as if something caught, "jumped" four times and then cleared itself?  it is unlikely that you would find any evidence remaining if you look now.

[Phillyo]

Next time I'm out and it's clear I'll stay by the scope and watch the cables with eagle eyes to confirm if it's snagging or not. I kinda hope it is as that's easily solved!!

Thanks Roger.

Phil

[leemr]

Tricky one. Snagging is definitely a possibility as has been mentioned. You can see a recurrent, violent jump followed by a correction. If you continue to have this problem, it might add some value to show the corrections in the PHD graph as well, which will show up as bars on the graph.

[Phillyo]

Right, so it's definitely not snagging. Stood outside watching and checking and as soon as it spiked I checked and no cables were catching, definitely not. I spent an hour doing drift alignment in phd2 to get very accurately aligned and I spent a long time getting balance right.

This is really getting me down. Spent a lot of money and I'm getting worse guiding than on my eq6.

[libraryman]

Hi, i see from your graph, that your min motion on Ra is quite a bit lower than dec, wont matter too much i don't suppose but if you are guiding very tightly, is it possible that on odd occasions; you are getting a seeing related issue?

sorry but most other options seem to have been covered, except possibly a driver update? and fault in the declination mechanics.

Ray 

[strutsinaction]

Hi Phil

A few suggestions:

- Post an image of your setup

- Post all your PHD2 settings

- Post your PHD2 logs to dropbox

- Maybe remove your autofocuser, rebalance, and see if that improves DEC guiding

- Do you balance with all your cables attached?

- Do you balance with the focuser tube withdrawn?

Regards

John

[Phillyo]

Hi John,

I have taken a couple of pictures this morning that I'll upload after work. 

My PHD2 settings are changing daily as I'm trying to figure this out but it's something along the lines of: Guide rate at 0.2, Aggression 90, Hyst 5, min motion 0.05 in RA and DEC. 2000ms pulse. However I have changed these up and down, back, forward and inside out and it was even worse last night. 

I'll pop some logs up to drop box and add a link this evening too.

I will have a try at removing auto focuser, but it'll be a shame if that's causing the issue as that autofocus is incredibly simple and useful. 

I balance with and without cables to see if that made a difference but hasn't; as they're generally supported I didn't think that would add much/any weight anyway?

The camera stays attached to the focuser tube and it doesn't move more than 1-2mm during focus so i don't think that'll make any difference to balance?

Additionally, I was trying to image M81/M82 last night and while pointing north the guiding was truely horrendous!! The graph in DEC looked like a mountain range from the Alps!!

Would that be caused by balance?

I'm finding it really hard to balance the mount accurately because my telescope is so light! (WO Star 71). I'm very new to this astroimaging thing, less than a year, and I'm probably making lots of little mistakes when it comes to simple things like setting everything up. I 'THINK' I'm accurately balanced and polar aligned, but not 100%.

To get my accurate PA I make sure my mount is as level as possible using the spirit bubbles and a spirit level, then I run Alignmaster 2 or 3 times until it's pretty much bang on each time. I would normally then run drift align in PHD2 but when I do that I have to adjust the mount again quite a bit until it thinks I'm polar aligned. I then run Alignmaster once more and it's saying I'm way out again. One seems to be fighting the other.

Ready to sell it all and give up the game!

Thank you everyone that has taken the time to read and reply. It is very appreciated.

Phil

[msh1]

try using phd 1 i couldn't get phd2 to work on my set up, had a similar problem to yours it saw toothed all the time so i went back to phd1 no problems 

mark

[swag72]

Hope that you received the guiding screen grab I sent you Phil, Will show you the settings I use.

A couple of things I'd like to say, but with the caveat that this is what I have and isn't necessarily right!

Balance - I am NOT balanced at all. I won't balance now until I take the RC off and put the Tak on then I will mark the dovetails and weights so that it's fairly easy to swap over.

I do get worse guiding graphs in different parts of the sky. Low south always gives me a pretty poor graph, but the subs are always spot on.

I'm sure that you're checking your subs closely, don't rely on the guide graph for goodness sake ......... again only in my opinion. Others will disagree

[Phillyo]

Hi Sara,

I did!! Thank you very much, I meant to reply last night when I got them but it was clear outside so I was running around like an idiot trying to get everything working.

I'm trying not to get too worked up about the guide graphs, however when you see regular huge peaks going off the top of the graph in DEC above +/ 10", when RA is just wobbling around +/- 2" it makes me worried. Not so much right now when I'm just imaging with the little Star71, but I'm looking at getting an RC8" so I think those peaks are going to be more obvious at 1600mm as opposed to 350mm

I think I'm just a bit dejected when I see other people using the Linear FR with beautiful flat graphs. My EQ6 was getting nice graphs. I spent a fair chunk of money and it "SEEMS" like I've taken a step back.

I shall persevere

Phil

[libraryman]

Additionally, I was trying to image M81/M82 last night and while pointing north the guiding was truely horrendous!! The graph in DEC looked like a mountain range from the Alps!!

Yes that could be balance, as stated earlier, pointing at the zenith could allow some rocking.. "if" ...there is play in the dec axis, however; you say that play is negligible with the Avalon..

To echo Sara's point, the graph is irrelevant if stars are round n tight, but your stars are eggs i believe.

very odd that you PA is in conflict, just use one method..i would suggest PHD drift align since you are guiding with it, in addition, give PHD time to allow a good drift figure, when i am close, i give it a good 5 min's and give in when its telling me i am within 1-1.5 arcmin thats well good enough for guiding.

Ray

[swag72]

When you feel bad, look at my graph, that should cheer you up.... Its not flat!!

[Phillyo]

Don't you use adaptive optics to help though Sara?

It was blowing quite a bit last here too so that might not have helped I guess?

I will do a quick PA with Alignmaster then use drift align to refine then leave it there. Oh to have a permanent set up.

NEXT HOUSE!!

I think I look at the pixels rather than arcmin when I'm doing a drift align. When I get to around 30 pixels (I think) I normally think I'm getting pretty close. That sound about right?

Phil

[swag72]

Nope, haven't used the active optics with the RC.... Its currently up for sale.

I don't know about PA and what's good or bad. Did mine the other night and got it to within 2.8 arc seconds....Good, bad or indifferent? I have no idea!!

[libraryman]

I don't use pixels but if you look at PhD it gives both, eg..0.01 is I believe equal to 6 arcsec.

If you use pixels, it will depend on your pixel size and arcsec pixel ratio.

Eg if your pixel ratio is 3 arc sec pixel then 30 pixels would be around 90 arcsec....good enough for guiding.

Correct me if I am wrong in my understanding of this.

Ray

[Phillyo]

Ok my guidelog can be found here...

https://www.dropbox.com/s/y29ar3k1h3tx2u5/PHD2_GuideLog_2015-03-03_195355.txt?dl=0

Brace yourselves, it's pretty horrible! The 41min log is fairly indicative of what I'm getting.

Images of my setup are here...

https://www.dropbox.com/s/64bivu8q5yrpav8/20150304_072642.jpg?dl=0

https://www.dropbox.com/s/t17xrkffxvkgh2o/20150304_072651.jpg?dl=0

https://www.dropbox.com/s/tygvbsa24hyeqak/20150304_072700.jpg?dl=0

https://www.dropbox.com/s/vxeltcjj9n48idn/20150304_072715.jpg?dl=0

Thanks again guys.

Ray, hopefully it's looking clear again this evening but i'll do a drift align and take a look at the arcseconds.

Phil