Stub Mandrel

And the North America Nebula + Pelican: This one suffers from only being 12 subs as well as poor alignment matching! I think it has some fixed pattern noise, too, so maybe I need some supercooled darks!

Finally something that starts to look like success - please excuse double post in the deep sky forum as I want feedback as its my first Ha+RGB (or is that HA+OSC?)image.

After improved, but less than perfect, guiding on the NAN, I've swung lower to the bubble nebula. Watched it like a hawk for my first 5-minute sub: 0.73" in RA 0.72" in DEC! Well buffer me shindigs! Clearly sticking the mount straight up isn't ideal. But I'm formulating a plan to fit a belt drive to DEC by making a new spindle and dovetail mounting plate.

Well struggling again tonight. some improvement, but still a way to go. I don't seem to be able to get the PA far enough out! It insists on drifting north when I want it to drift south so the guide pulses are against the imbalanced OTA. I think my polarscope is out of whack.

That's what I do in Photopaint using 'if darker'. it doesn't seem to work as well in PS, but I only have PS2.

So do I! If I can get a really good result, all this will have been worth it.

On no, it should be way better than that, but if I can get my DEC issue started I will try 5-minute Ha subs on it.

OK, I've done the thrust bearing mod and it looks promising. this isn't a tutorial as (a) I have no idea if this will work and (b) I have reservations about the way I did it. First, remove the DEC work drive by removing four screws and lifting it off to reveal the worm wheel. Look how small it is, the small size is the main cause of all our woes! Now remove the nut inside the polarscope hole, I plugged the hole with felt to catch the nut and washer so they didn't fall down the hole and scratch my polarscope. A skinny spanner helps, but a pair of pliers should do it: Pull the DEC assembly out. If it leaves a red fibre washer behind, remove it: The washer may remain here instead, junk it, fibre washers aren't designed to give free movement. See how we don't have a continuous bearing surface. Clean up the grease on all of both parts: Drop on the big bearing thrust washer and big bearing: Lovely jubbly! Now grease your ralph bearings including the shaft (this will still be running in a close fitting sleeve bearing) with some nice grease. This is much nicer around scopes than lithium grease: ideally a roller bearing shoudl be only 1/3 full of grease, to make sure the rollers don't 'aquaplane' on the grease. Now slip it back in place - the needle roller bearing will run on the (hopefully) unsullied top surface of the worm gear. Bear in mind our rates of <0.1rpm are not going to cause high wear! Feed tehw orm gear with some clean grease too: See how it's m,oved up slightly, but about 2mm? Now at the lower end fit the following onto the screw - the original big steel washer (best looking face downwards), small bearing, small bearing thrust washer. Discard any small black washer that was originally present: Now fit the nut, (I used tweezers to fit get bearing, washer and nut in place). Tighten it until there is no shake, then about 1/8 of a turn more. You want a small amount of preload but not enough to cause drag. You should be able to turn the DEC assembly by hand with virtually no feeling of resistance now. Problem - the nut doesn't go on far enough to engage the nylock part. Solution - I used a blob of silicone sealant/adhesive to help keep things in place. I will watch this and if it loosens put some more up the end of the nut. Why silicone? It sticks, but is easy to undo and less likely to drip on my polarscope than threadlock: Now replace the worm assembly. I fitted two washers to help compensate for the extra depth of the bearing. Unless you lengthen the holes, you won't be able to restore original alignment. I didn't stress over this, as my worm wheel looks worn and a new alignment will use a different part of the gear, although engagement may not be perfect. use the two screws either side and the central screw to take up as much backlash as possible while keeping the worm gear free. this is a mission as using eth two long screws from below to lock it once adjusted, affects the alignment. Just keep tweaking and zero in on a good alignment. My sophisticated test lab showed I hadn't really reduced the backlash, but the unloaded movement of the setup seemed to show much less 'stick slip' at low speeds. Good, that's what this was meant to cure: The other change I made was to swap out the old (printer salvage) stepper for a NEMA 17 one (also printer salvage). That was a good move, the old stepper could be stalled by finger pressure on the wooden stick, with the NEMA 17 stepper I could pull quite hard without stalling. I can now unbalance the mount to reduce backlash - and hopefully more accurate GOTO moves now as well. All I need to do now is test to check the stepper moves the right way then recharge my battery!

Well, thanks to kappa-sigma stacking, this image isn't as bas as I expected, but all the stars are pear shaped as the DEC excursions have given them a little point on top. But anyway, here it is my first proper guided image taken with a cooled DSLR. 90% best of 29 5-minute subs at 800 iso. The cooling (probably down to about -10 or 15) seems to have worked (no darks used), so that's something to celebrate. And one with stars rounded using the 'one weird tip' that works in Photopaint but I can't see how to do in PS: Anyway, the bearings have come (only one washer in each pack, thankfully it look like that will be enough) so off to fit them and document the process. Also a Skywatcher 9x50 finderscope (with a WO end plug!) from the SGL classifieds

Get thee hence to a place of contemplation!

The sawtooth ramp behaviour is exactly what I'm seeing as well, the image on page 12 of this incredibly useful tutorial is the same, only the other way up. Analyzing_PHD2_Guide_Logs.pdf I suggest anyone trying PHD2 takes a look at it.

I'm learning to hate the Crescent Nebula, it's cursed!

No its easy, you just unscrew the four screws to take off the worm gear, undo the nut inside the mount (in the polarscope top hole) and pull out the DEC shaft. Replace the red fibre washer at the top with the big thrust bearing and the washer at the bottom with the small bearing. Clean off old sticky grease and replace with new grease. The worm gear housing will need a simple spacer the same thickness as the top bearing MINUS the thickness of the red washer.

Just calculated my ratio and it's about 2.56:1 My first experiment was a success, it's my tries at real guided imaging which are turning out as failures! I'm trying to pluck up the courage to stack my subs, I know the stars will look like nice biscuits (not even rugby balls!). If my DEC bearing mod works for 'unsticking' it might solve your problems. Hopefully they will arrive tomorrow as Saturday Evening looks promising at the moment. The spec is: ------------------------------------------------------ 1 x AXK2035 Needle Roller Cage 20x35x2mm (AXK2035-MB) = £2.12 1 x AXK1024 Needle Roller Cage 10x24x2mm (AXK1024-MB) = £1.88 1 x Nadella CP1022 Thin Needle Thrust Washer 10x21.5x0.8mm (CP1022-NADELLA) = £1.22 1 x Nadella CP2035 Thin Needle Thrust Washer 20x34.5x0.8mm (CP2035-NADELLA) = £1.24 ------------------------------------------------------ Items Sub Total: £6.46 (Royal Mail 1st Class Post (Ships Friday)): £1.50 VAT: £1.59 Order Total: £9.55 All from Simply Bearings. the thrust washers are packs of 2. Just spotted I hope those 1022mm ones aren't too small I should have got 1024. rats, not impossible to make some though. My worry is that the small end may need me to fit a small spacer to centralise the bearing as the thread is heavily undercut.

Wow, I thought mine was short at 183mm!

The PHD tutorials say less than 1 second will 'chase the seeing'. A 1s exposure will have the same averaging effect as a few shorter ones. I imagine aaveraging is only needed if otehrwise the stars are getting over exposed. What sort of FWHM are you choosing of guide stars (I've gone for stars between about 4.5 and 7.5)

I suspect that the EQ3's main weakness is the DEC arrangement. The wormwheel is quite small, the adjustment arrangements are crude, and there is only a fibre thrust washer at one end! It's clear that the RA isn't too bad as plenty of people are achieving 1-2 minute unguided subs with good polar alignment. The challenge is that for guiding you need to adjust DEC as well. You and me both!

I've found that backing the RS aggression right off gives me guiding better than 1" which is enough to keep me happy, it only goes significantly awry when the DEC does a big jump. I think my DEC problems are largely from two things: 'stick slip' and inability to unbalance enough to remove backlash because of a weak stepper, I've replaced the stepper and ordered a pair of needle roller bearings.

Sorry...

Thanks Nige, I think I have two problems, first is that t 1x sidereal it takes about ten seconds to clear the backlash no matter how well I set up, and second my stepper isn't powerful enough to shift the scope when the mount is significantly out of balance and most of the backlash is taken out. I'm going to try swapping in a bigger stepper (NEMA 17) .

@Nigel G I had another fail last night, entirely down to DEC backlash. I can't adjust the backlash out of my mount without stalling the stepper. I'm getting a minimum of about 10 seconds before a change in direction! What do you do to prevent DEC problems with your EQ3? Do you put it out of balance and guide only in one direction? How do you adjust your PA to get eh direction you want?

There's a campsite on Exmoor that's astronomer friendly. We stayed there and I asked if I could just turn up and pay in they morning, and they said no problem. But I don't get down that way very often! I know a campsite in the Peak District that might be OK.

The eclipse was lost in cloud here :-(

I won't recount last nights nightmare again, but:

That could be related to the stepper motor.