All discussed with Doug and John G tonight. A few more things left to try. Gemini and all cables fine. Possible that I might have the wrong guiding speed set in Gemini, but it started at default when I changed the Eprom yesterday, so that should not be an issue. Going to swap the RA and DEC worms with their wormblocks, just in case one of the worms is at fault. I checked the polar alignment and it appears to be pretty well spot on. A and E numbers are a bit of a worry though...the hair tearing continues....
May be worth working through a process of elimination. It now looks like it is a mechanical issue. Swap worms and blocks around, next step would be to check gearboxes and motors, clutch thrust races and backing/tensioning plates. Pay particular attention to the endplay and float of the worms in the worm blocks. Last thing has to be a bearing replacement all round and just check every screw on the mount for tension. You could also try measuring the output voltage from your power supply, a small change in output voltage can make a big difference, particularly if it is getting down into the 12 to 13 volt range.
Peter, I have only just seen this thread. I live in Plympton and if you want to bring your setup here, we can compare directly with my G11/Gemini. We can even swap out various elements to do a direct comparison. I am off work until 12/4 so, if necessary, we can test during the daylight for general setup etc. PM me if you are interested.
Charles
Thanks Charles, Steve came around the other night and we eliminated the Gemini and leads as being the culprits. However, I might take you up on the offer so we can do a direct comparison.
Peter, Marc has repeatedly asked you for the Guide cam image scale and what the graph looks like just tracking. These factors are critical for analysis. Without this info, its just random guessing.
Fred, havent been able to do a thing for nearly a week as the weather has been crud (too windy). As far as image scale goes, not really sure what you mean? I am using just the Tak at F7.7 as the guiding scope, star shoot autoguider, and absolutely nothing else connected. I was not aware that you could get the graph to work with just tracking, so I obviously have not done this one, however, just using the bullseye when not tracking, the star virtually does not move from the centre of the target. I am really beginning to get thoroughly fed up with this, makes one feel like throwing in the towel.
Peter, Marc has repeatedly asked you for the Guide cam image scale and what the graph looks like just tracking. These factors are critical for analysis. Without this info, its just random guessing.
OK, well you originally said the guidescope was an ED80, and Marc then guessed you had a guide scale of 1.8 asp. If the graph is in arc/secs then you certainly dont have a problem, even DEC is only 2 arc secs P/P odd and RA is very good. If its in pixels, then DEC is 3.6 arcsecs P/P, which isnt bad either. The RMS shown Im guessing is RA at 0.21 (and looks like about 1 P/P), which is friggin awesome. I dont know what 0.48 "osc index" means.
Another guess, is the graph is the wrong way round, (RA-DEC are transposed), that would make more sense, the RA as shown is suspiciously low.
The red line looks like the axis is constantly drifting (alignment?) and being periodically corrected with minimum move set to high (not attempting a correction untill its gone too far), and then the correction is too agressive, causeing an overshoot (this could also be backlash).
The "mn mo", which I guess is min move, seems to be a low number, but then I dont know what scale its on. Does "mx dec" mean dec max move?, if so, try lowering that. I cant see a DEC agr setting. Asuming the graph axis are correct, thats a worry, you definitely should be able to set DEC agressivness (or does that come up clicking the RA/DEC button?).
The graph doesnt show what the horizontal timescale is, the oscillation on the 1st graph could even be PE .
All this is based entirely on the graph you have shown (which anyway seems to show no big problem if the scale is as Marc suggested). If you visually get a bad result, then the guide image scale is nothing like 1.8asp.
You can graph whist tracking (I think), just by starting guiding (and the graph) and then pull the guide plug out.
H, when I have disabled the guide output, I assume it stops the DEC, I end up with a straight line in DEC and the RA does its dance. Will see if I can get an example if the bloody cloud will nick off.
Fred, I originally used the ED 80 as the guide scope which is the normal config, however in an attempt to get rid of any possible flexure, I removed it, the Tak guiding mount, the side by side and just left the Tak stand alone to test the guiding with.
Oh yeah, H, I did remove the finder just as a joke, it did nothing...LOL
Although, Let me start this with my thoughts for you Pete and hope a solution is found quickly.
Now my learning. H, by graphing he star in PHD without guiding, I take it your getting shown all of the mount, polar align and balance issues and trying to get the graph as small as you can in this format, will only assist in Guiding?
And Fred, guide scale of 1.8asp?? As I'm using a ed80 guide scope and qhy5, I'd like to know a little more on how you figure out the guide scale and how you use this number to improve your system or reduce guiding errors.
I know I'm a relative newbie at all this, but having travelled an amazing learning curve in the two years since I first looked through a 8 inch Dob, it's amazing how many terms are used on this site that I have no idea what people are talking about.
I have never worked in a field or had a hobby/interest where so many people are willing to give their time and share the experience. Must be we we all get so sucked in..... Oh, and by the way, Good Luck Pete!
Thanks Darren, yep it is great people are interested in helping, I really do appreciate it. Attached is a graph using Steve's Gemini and as you can see it it a real crappy graph. Balance was perfect, polar alignment was good.
And Fred, guide scale of 1.8asp?? As I'm using a ed80 guide scope and qhy5, I'd like to know a little more on how you figure out the guide scale and how you use this number to improve your system or reduce guiding errors.
Darren knowing your image scale on your guider is important because it is the only thing that allows you to quantify your deviation in RA or DEC by looking at your PHD graph. The lines over and under the central lines are pixels on your guider's image. If you use an ED80 (FL 600mm) with a QHY5 (5.2um pixel size) at prime focus your image scale is: 206.265/600mm * 5.2um = 1.78763asp. Now you know what 1 pixel deviation means so you know your guiding is +/- 1.8 arcsec if you stay within the top and bottom line.
Last edited by multiweb; 05-04-2010 at 12:14 PM.
Reason: spelling
Pete,
while no expert in PHD, don't have one, LOL, is that graph so bad? I mean, has it produced images that are substandard? Why I ask is that the little time I have spent with PHD (and going Mac completely means I am likely to spend a LOT more soon), most of my graphs have looked similar, perhaps not quite so wavy, but similar.
"Perfect" balance worries me too, I tend to be east heavy where possible.
Gary
Thanks Darren, yep it is great people are interested in helping, I really do appreciate it. Attached is a graph using Steve's Gemini and as you can see it it a real crappy graph. Balance was perfect, polar alignment was good.
Is this graphed with the same guider on your Tak? What's your Tak FL?
You have a major problem in DEC regardless and that's a clutch/balance issue (side by side). Your RA's not too bad though but DEC should be much less than RA.
There is one thing that didn't make sense by reading all the post in this thread. You are describing a major drift problem during guiding but as Fred mentioned looking at the graph it doesn't show any problem. That's why you need to graph this problem by disabling the guide output in PHD. Forget Gemini or any software for now. What you need to do is get this DEC and RA as close as possible without guiding so you need to polar align very well, pick a star close to the south pole for a start, then get it right. When done pick another star up the meridian and better your balance in RA.
I happen to agree with you Gary, compared to my graph, it doesn't look to bad. Although I spent a few hours last week just refining my polar alignment and getting the balance east heavy and just right, The change in the graph was quite impressive!
At the moment I'm pretty happy getting 10 minute subs with close to round stars but in the future with a better camera, I'd like to push the times out a bit, thus the search for improvement continues!!!!!!
Fred, I originally used the ED 80 as the guide scope which is the normal config, however in an attempt to get rid of any possible flexure, I removed it, the Tak guiding mount, the side by side and just left the Tak stand alone to test the guiding with.
Although I dont know what the graph time scale is, differential flex wont be a problem at such short timescales, with the FL of your refractor, thats not the problem. Flex becomes a problem over say 1500mm at 15min or more, assuming the guide scope is well mounted and the guide cam is not waving in the breeze way out on the end of a dodgy ED80 focuser without being clamped.
Quote:
Originally Posted by desler
And Fred, guide scale of 1.8asp?? As I'm using a ed80 guide scope and qhy5, I'd like to know a little more on how you figure out the guide scale and how you use this number to improve your system or reduce guiding errors.
Darren
Just plug the scope and cam into Ron Wodaskies CCD calculator (free) and it tells you the scale , get its very easy and fast to use.
The scale helps by knowing how just how big a problem is. A graph by itself is meaningless (to see how big the problem is anyway). If Peters graph has graduations at 1 arcsec then theres pretty much no problem, if its in pixels then you need to know the scale in arc/secs/pixel. If say the scale was 4 asp then there is a problem.
Watching how the graph proceeds is also very useful, you can tell PE, backlash, stiction, alignment, seeing, balance, and how stable guide control is (control settings). From my experience, Peters 1 st graph (and it may not be the case here) DEC curve is typical of iether DEC out of alignment with wrong correction settings (slow drift, and wrong/over correction), or a perfectly balanced DEC axis with backlash.
Quote:
Originally Posted by Exfso
Thanks Darren, yep it is great people are interested in helping, I really do appreciate it. Attached is a graph using Steve's Gemini and as you can see it it a real crappy graph. Balance was perfect, polar alignment was good.
Perfect balance is not good generally, especially if you have backlash, both axis should be slightly out of balance so they always drive one way, this eliminates back lash.
I meant to say re perfect balance, that I am just slightly CW heavy and slightly focuser heavy on the scope. I realise if one is perfectly balanced you would get "slop" with the worm and gear meshing, there always has to be a slight load on the worm.
The outcome of all this regardless of the ASP scale and all the dithering about error size is that with this amount of error Pete is ending up with significantly oval stars from a mount and guiding system which didn't suffer the same problem a few weeks ago.
By removing the electronics of the gemini and guider from the list of possibilities, it leaves either, polar alignment ormechanical problems which might well include such things as Motor/encoders, worn bearings, damaged or miss aligned worms or gears or balance.
When it comes down to the mechanical list it is usually a matter of elimination to proove a piece of equipment good or bad.
Comments like that above do nothing but frustrate Pete further than he already is.
Charles, the mount is totally standard except for the latest eprom upgrade for the Gemini.
Marc, not too sure why you responded as you did, I replied to Fred in the thread just prior to yours explaining why I had not supplied the enformation. I am still trying to get my head around this problem and some of the statements being raised are somewhat foreign to me and I need time to work out what you are after. I am after all an old fart and not a guru at this particular stage of fault finding. This is a bit of a long an involved process and a lot of what is being asked has been covered whilst at the SV camp when John, Doug and myself gutted the mount. I do appreciate your input, but please hold back on the sarcasm, OK....
I rest my case. 
