Anthonyexmouth

These 3 screws? 

Having a bit of a Frank Spencer moment here. 

I've read the astro baby section on worm adjustment but getting nowhere

Yesterday I fitted a belt mod and noticed a bit of play in the RA, now I should have left it alone, but I tried to adjust it and last night had worse guiding than I ever had before. 

My problem is I don't know where my starting point should be for the grub screws now. I release the 3 hex bolts a turn each, adjust the grub screws as described but finding I can get rid of the play and rotating in one direction is smoother than the other.

Is there a way to effectively start this procedure from scratch? Is guiding at the night the only way to truly test everything is working and backlash is minimised?

20 minutes ago, Stub Mandrel said:

There's a relatively new feature in PHD2 - you need the latest version - called 'predictive PEC' or PPEC. It 'learns' your system's behaviour over the first few cycles and then applies it, and  it constantly refines its model of the PEC. It does appear to work and I use it all the time now.

Does that augment Sidereal+PEC in EQMOD or do you turn it off there? 

OK, now this bloody mount is just trolling me. I'm opening up a bottle or port, i'll drink most of it and the rest im drowning the mount in. 

1 minute ago, vlaiv said:

I don't think tight belts will cause this - I have mine really tight. When I first did my mod, I thought I had them tight, but it turned out that I need them like really, really tight - so now they are as tight as they can be - motor can't move any further.

But worm gear tension can be issue, and also I would look into end float. The graph shown in EQMod window represents one revolution of worm gear - that means big gear that belt is put on and one that you adjust end floats for (from the link I posted). Above graph shows two tight spots - exactly half way around - I would say that end float is to blame.

Did you check all your gears by hand? By actually turning gears with your fingers you can sense a lot of issues with it - just do it slowly and feel their motion under your fingers.

Yeah, i ran it a few times with my hand with the belt off while adjusting the tension. Luckily global warming gave us one of the hottest feb days today, hopefully another one tomorrow so i can sit in the garden at my pier and try again. 

1 minute ago, vlaiv said:

Yes that would be perfect example of "sticky" graph - mount nearly stops (slope goes almost vertical) - and then it continues "like nothing happened" at perfect speed - slope horizontal.

Is that likely to be caused by my blundering around with the worm gear tension? or maybe tight belts?

Are these 2 almost right angle steps in the PEC gragh places it's sticking? 

1 minute ago, michael8554 said:

Doesn't the "High-frequency Star Motion in GA tell you the seeing conditions ?

Michael

Hope that wasn't directed at me. At this point i'm doubting I know what a telescope looks like. 

Should the setting in PHD match this? 

Also, how do you estimate your "seeing" 

Sky looks crystal clear and cloudless. 

Just checked EQMOD, should my RA / Dec rates be .50ish? Sure thats what I changed the to, if so should they be the same in PHD" or is that something different?

Its disabled, I'll do a new one right now. 

Do I disable guide output in PHD2? 

Graph is worse than before the belts added. I was better off before building this pier and doing the mod. 

Results after the belt mod and a first attempt at adjusting the RA worm gear

Backlash chart is closer to what it should be but its gone all jumpy. 

This doesn't look much better

1 hour ago, vlaiv said:

Above two items that I've pointed out are related.

Stock mount can have P2P Ra error as much as 40-50". This is "leading and trailing" error combined - meaning mount is a bit faster than it should be for some part of worm revolution and then it is slower than it should be for other part of worm revolution. This happens because mechanical parts are not perfect circles, but rather "egg shaped". In practice it means that if you leave your mount unguided, during the course of one worm cycle stars will drift in RA that much - P2P value. It also means that if you do one full worm period single exposure - star streaks will be that much arc seconds long.

With PEC applied this P2P error should be significantly reduced - order of 5" and that is because of fact that PEC is compensating for part of that "egginess", but it can't do it perfectly. You should also note that there won't be two exactly same worm periods with respect to star position deviation - P2P error will change from period to period and that is caused by longer wavelength errors of the mount - like RA gear being slightly out of shape. RA period is 24h so you won't be able to see that period unless you record for couple of days - which is not possible.

Rate of change is "slope" of PE curve and has direct impact on how "guidable" your mount is. It is usually reported as maximum rate of change - where the curve is the steepest. If you want to guide out all periodic changes in your mount - you should choose guide period such that it can guide out even when the position error is changing the fastest - to be able to react to that change.

P2P error is not very important in it self if slope of it is small - or rate of change is small - there is low speed change in star position - this guides out easily. Problem is of course that worm period is fixed, and higher P2P implies faster rate of change with even perfect sine wave, and period is never perfect sine wave as it consists of different harmonics. This is why you want both of these to be as small as possible.

thanks, still a bit confusing but starting to get my head around it. cycle up to FLO tomorrow and collect my belt kit and baader click lock. Reducer is now fitted. 

Forecast is clear all tomorrow night so fingers crossed. 

On 21/02/2019 at 23:05, vlaiv said:

I marked out bad:

P2P error is large - you want that to be smaller - with guiding you want your p2p to be less than 2".

Second thing marked is max drift rate - you want it to be lower, so that drift limiting exposure is something like 8-10s. You want to guide at about half to full drift limited exposure. Meaning that your guide exposure should be anywhere from half to full max drift rate. Longer guide exposure helps with seeing, but you can't have it be larger than drift limited exposure (about half is max really when you have "smooth" mount).

Belt mod should sort both of these issues, and a bit of backlash as well.

Getting the belt mod tomorrow so all of this might be redundant, but it would be nice to understand this a little better. Just doing another guide assistant and right Ascension P2P after is now 32.22 arc seconds and drift limiting exposure is 0.6 sec. I take it this is worse than the other night. What causes this? 

I should probably leave well alone until i do the belt mod, but i just downloaded phd2 log viewer and it says my polar alignment error last night was over 5 arc mins and yet the guide assistant said it was 0.2 when i ran it last night. 

Belt mod is waiting to be collected from FLO, will grab it Monday and try the PEC training again when that's done. Field flattener arriving Monday too. Xmas in February. 

3 minutes ago, Demonperformer said:

Sorry, realise yours is permanent and wasn't trying to hijack the thread (much!), but the process obviously takes a significant amount of time and was wondering if it was still a worthwhile option when all the gear is put back together each session in not necessarily exactly the same relative positions. If PEC is working out of step it would be likely to cause more problems than it solves?

it's all staying together, hopefully the days of setups are over. 

It is a permanent setup, just built a pier and trying to get everything dialled in

Calibration was done about 5°

Dec compensation is on

this is the graph after changing to .5x and recalibrating

Camera gain was set to 95. I am using the zwo driver. Would the ascom driver be better?

1 minute ago, vlaiv said:

Change both to x0.5 or x0.4 - you will need to recalibrate your PHD2 after that.

Yeah, phd just got proper annoyed. Might wrap it in soon. Getting cold and not run all the wiring into the workshop yet. Waiting until everything is working. 

Just checked and I think I'd updated eqmod and it looks a little different to what I remember. 

Is it the ascom pulse guide settings? Ra and Dec were set to .9 so I've just changed the Ra to .5

1 minute ago, vlaiv said:

Your RA graph shows quite strong 13.8s period - and this is motor gear meshing period - it looks like motor gear on RA is not meshing properly. You can try to adjust this by changing how the motor is seated in housing.

Because of this, you need lower guide exposure 1s or 1.5s. What sort of gain are you using with your camera? Can you increase it? Maybe use ASCOM driver instead of native one in PHD2 and select 16 bit output and higher gain.

Also, your RA corrections are rather small - I can hardly see them on the graph. Not sure why is that. What guide rates do you use on your mount? x0.5 of sidereal or less (down to x0.3) should be good.

Do I increase the gain somewhere in phd2?

Pretty sure it's set to .5x but I'll check. 

Just ordered the belt mod, late night shopping is expensive,  so will that eliminate the meshing issue?

While I was at it I also ordered a baader click lock and Altair flattener/reducer