Peje

On 12/09/2019 at 16:13, glowingturnip said:

you could post your guiding log to the phd forum, they're pretty helpful over there.  It's not excessive Dec backlash is it ?

Good suggestion, done

Have attached a screenshot of the output from guiding assistant, other than huge dec backlash I don't see anything interesting.

2 minutes ago, carastro said:

Can't help with actual full time jobs, but there seems to be a gap in the market for some-one to service and repair Astro equipment, particularly mounts, and also doing belt Mods, not every-one is capable of doing it themselves.

There used to be a guy called Graham that did it but had to give it up for health reasons. 

You might like to consider this as a side line.

Carole 

Thanks Carole, it is definitely a good suggestion but not quite the sort of thing I'm after. 

I totally accept this is a weird request for information, it's probably something I'll have to run down myself.

Hi All,

Over the last while I've been considering a slight change in career direction. Currently I work for a global IP camera manufacturer, in the last decade I've gone from a Mechanical Engineering role, to Project Management and now I am an Engineering Manager & Engineering lead for all camera development. I really do enjoy the job I do & work with a great group of people. I have been very fortunate to have been given the opportunity to expand my role in new and interesting areas. I am passionate about my job and my desire for a change is not a reflection on the job I have today.

What has really sparked this off is the realisation that if I can get so much enjoyment from a job that is loosely related to one of my hobbies (photography), how much more satisfaction could I get from something that is actually making a contribution to Astronomy, something that has fascinated me for many years.

The Engineering side of astronomy is something I have no real information on. For example, is it driven by private companies who are contracted by larger Astronomy organisations or do either of these make contributions by themselves?

My plan was that, rather than start talking to recruitment agencies who would inundate me with non-astro jobs and promises of large salaries, I would reach out directly to astronomy related companies who might be interested in someone with my skillset.

The purpose of this topic was to see if anyone had any thoughts on the sort of companies / organisations that I should contact, or even just general feedback on my thought process.

Thanks in advance,
Pete

Updating PHD2 seems like a good idea, I hadn't noticed the flat portion of the line. I can grab the PHD2 debug logs are replot with some time after to see what it later does.

It certainly could be a software glitch, the issue with that is it's unlikely I'll be able to fix it!

20 hours ago, ollypenrice said:

The 'camera heavy' weighting will reduce to zero as you point at the zenith. (The heavy end will be directly below the light end.) Does position in the sky seem to have any connection with the problem? I think it's unlikely that this is connected with your issue but if your camera-heavy weighting is intended to stop the Dec axis oscillating across any backlash there is a better way to achieve that. You can deliberately polar misalign (not enough to trouble your longest subs) and then disable whichever Dec guide direction is not needed to correct for this misalignment. Unfortunately you need to reverse the disabling after a flip. 

Your trace is pretty surprising. Firstly, as it's drifting off, it remains smooth and doesn't look as if it's struggling with a snag (though it might be.) Secondly, when it goes back, it does so without overshooting or oscillating. If you disable Dec guiding what does the Dec trace do? Does it in any way resemble the errant trace?

Olly

I will have to give that a try, one slight issue will be that this often happens when I'm not watching it so I only actually see it from time to time.

18 hours ago, gorann said:

I am no expert at all but I may have an idea. To me it looks like the dec is suddenly not responding to the guide pulses and just slowly drifts off on its own (probably due to a slight polar missalignment), and then suddenly it responds and gets back to where it should be. Would not a lose connection / bad plug be able to do this? Maybe you could try to change the ST4 cable or what ever is connecting your computer to the mount.

You could also wiggle the cable a bit an see if you can induce this behaviour.

Don't think it could be a loose cable, the comms are single Rx & Tx so a loose connection would knock out RA & Dec.

12 hours ago, Whirlwind said:

I would suggest cabling as well.  The feature looks like something is increasingly resisting motion until it snaps back.  That would suggest something is getting caught until such point as it is stretched to far and whatever is resisting it slips over and it releases the pressure.  I'm thinking maybe the spiral wrap is snagging on something (e.g. polar scope cover etc) and it stretches until it is pulled so taught that it slips against whatever is holding it back.

 

 

This does seem reasonable, just need it to stop raining long enough to have a look

7 hours ago, michael8554 said:

Your image reports you were at Dec 39, not that high, so your camera heavy setup should not have allowed the scope to get south at all. 

So maybe it wasn't as camera heavy as you thought. 

And as Olly suggested, a slight PA error that causes the Dec trend to be south will help, about 5arcmins. 

I agree with Olly that the stiction or cable snag behaviour, but without an overshoot on the recovery, is hard to explain, so listen for Dec activity next time as Goran suggests. 

Michael 

It could potentially be explained by a slight slip in the dec but it's hard to explain why this would be happening as it doesn't happy when I extremely unbalance the OTA.

I don't think this can be explained by a neutrally balanced OTA, it's too consistent. It drifts off then snaps back. As you say, it's not very high so I would expect this would happen more readily pointing towards zenith (which it didnt as that where my nights imaging began)

That's interesting, I have my cabling bundled in a loom with spiral wrap. The plus side is that I have RA and Dec as separate pieces so I can look specifically at one piece. 

Not totally convinced this is the issue but I don't have another ideas

As title,

Most nights I get a spot of weird guiding error, normally I only notice it once but it may happen again when I'm in bed. Basically the Dec drifts off really far and then after maybe 5mins it seems to just snap back to what it should be.

The attached image shows the event in PHD and the scope position. Looking at this position I doubt it is related to balance, which is set to be camera heavy.

Anyone ever seen this before? My mount was stripped down during the summer, belt-modded and regreased; no problems with the worm were observed (I did ask the chap to check). This blip has been present for a couple of years so it isn't related to the rework.

Keen to hear any thoughts.
Pete

Looks like everything is fixed

When I got home I refitted the scope and tested the dec to see if I could provoke the slip, even with the OTA being VERY unbalanced I couldn't make it slip. I loosened the belt tension a little and the strange sound went away also.

Once that was complete I removed the dec motor, put thread-lock on the grub screws and refitted it. The borescope makes fitting the motor an absolute gift.  The OTA is still on and I just need to re-attach the cabling over the weekend. which should only take a few mins because it's all tie wrapped together.

Thanks for all the help in diagnosing folks  

Hi All,

Got the mount rebuilt this morning and backlash adjusted. Noticed when I run the dec at full speed I getting a periodic noise, it seems to coincide with the belt moving axially on the pulley (Video attached). It's not moving by very much so probably isn't a problem but I can't figure out what's causing it. I don't get the same movement or noise on the RA.

Any thoughts?

Going to test the slipping tonight and if all is well I'm going to pop the dec motor back out and thread-lock the grub screws. Potentially it could be this rubbing (and therefore vibration) that caused the screw to loosen.

Motor back in, less than 5 mins. I think I've found the solution to getting the belt on the motor... for me it was to remember I bought a cheap (maybe 6quid) usb bore-scope off Ebay a while ago.

It took 3 or 4 mins to figure out the best angle for the camera and maybe 30secs to hook the belt over the motor!

2 hours ago, spillage said:

I would expect you tracking to be bad. But I guess how unbalanced it is. I would imaging that if its slipping on the clutch then it must be very heavily unbalanced.

It's not heavily unbalanced, even the weight of a dew shield was enough to knock it off. Strangely it worked before so I get the feeling something came loose or it is temperature related (cooler temp, tolerances increase)

4 minutes ago, spillage said:

No because the belt system should take out nearly all the backlash, you may find you will have a few millimeters of backlash after fine adjustment of the worm gear spacing but this is normal for this type of mount. I always make sure the scope is neutrally balanced whether its the 130pds or the 8" quattro.

This seems strange, I can't understand how adding belts at the drive end would eliminate backlash at the payload end; but that's a topic for another day

If the mount was unbalanced slightly, what would you expect the behaviour to be? I presume it wouldn't be that the motor would turn but the OTA would not?

1 hour ago, spillage said:

So if it was my call and due to the fact there is not noise made I would be looking at the clutch. I would do up the clutch remove the lever and refit it a couple of cogs over and tighten it back up. A slipping belt or gears make a racket. You say I think you have checked the gears on the motors and worm shaft. But again just to be sure I would remove the panel and worm gear plug just to see what moves. The belt upgrade will mean that you now need good balance.

Slightly off topic but do I not need to have some imbalance to account for the backlash in the worm drive?

8 hours ago, tooth_dr said:

I still think it could that shaft/cog. I think I would have removed it since you went that far anyway. Those bearings are around £3 for SKF ones from a motor factors, and pretty much they won’t break unless you hammer the bearing itself. 

I'm not sure, if it's solid on the shaft I'm not sure what's to be gained from wrestling it out and refitting. Maybe I'm not seeing something, what would you expect to see when it's removed?

8 hours ago, spillage said:

I would remove the cover to the worm shaft and remove the control panel. Using long nose pliers or normal pliers if they will fit manually turn the worn shaft and check that the motor turns without any play. Have you made any adjustments to the clutch lever and what happens if you run the mount without your scope attached, is the same thing happening?

I am sure there should only be one locking nut for the worm shaft.

This slipping only happened when the mount was under big load. It would work OK mostly but every few mins it would slip (motor sounded normal but no dec movement), it would also slip when I unbalanced the OTA to make it camera heavy. This is a good suggestion, similar to one tooth_dr said, with this cover off I can run the mount to see if the worm shaft is spinning when the dec fails to move. This will let me further refine the location of the problem.

7 hours ago, spillage said:

Too late to go out and check but I am sure when I was making adjustments to the worm shaft I kept unscrewing the wrong cap as there was not a slotted nut on one side. It has been a while since I had to touch anything on the mount though. What about the backlash grub screws. If they were too loose would it cause this issue. Did the op say it made a horrid sound? may be the teeth slipping.  Do you not just need to take out any float from the worm shaft? Cogs are tight and in place, belt is not really slack or stupidly tight.

Maybe try moving the dec housing 1/8th or 1/4 of a turn to push the worm gear closer.

No nasty noise, this directed me towards the belt drive end of the system. Something that is earlier in the thread is an image showing one of the grub screws that attach the belt pulley to the dec motor completely loose. 

Sorry, and another weird thing. 

For the shaft bearings, theres only a lock ring on one side. I found that when tapping I had pushed the pulley side bearing out a bit and the pulley fouled the casing. It wasnt difficult to fix though, I found it strange there wasnt a lock ring on both sides

That's a good idea though, I can remove a cap and see what the worm shaft is doing when the scope is doing the 'hopping' thing, this would give me a direction for the issue. 

Just now, tooth_dr said:

When I removed the black cap covering the end of the worm shaft I could see the centre of the shaft spinning for a second before the scope would start moving. I deduced from this that the cog was loose.  

Did you remove the worm shaft?

Didn't remove worm shaft as the pulley was really tight on it, I couldn't slide it off at all. I did a little tapping and got it to slide up a bit but it seemed like too much effort for no real gain and risk of breaking one of the bearings 

Something I maybe didn't say previously, the motor pulley could slip easily when I loosened the second grub screw. 

For the worm shaft pulley, it was tight even after the grub screws were loosened. That said I couldn't get any real grip on the shaft to try and turn it

After looking at the guide, it looks like the clutch is just a grub screw and it's what connects the worm wheel to the saddle part. 

So if it's not after the worm (clutch) then it must be before the worm which leaves me with my 3 original options; Belt Tension, motor pulley or worm shaft pulley. 

Will rebuild it all and retest. 

Just now, discardedastro said:

Very odd. At risk of teaching you to suck eggs, could it be the clutch not providing enough grip? Nice and easy to test, at least...

If the worm's meshing properly and the cog on the worm is happy and being driven by a tight belt then there shouldn't be opportunity for problems mechanically. I'd be turning my attention to the stepper or drive circuits, though that starts to get hard to test...

I was wondering this myself, not so much the clutch but something else in the axis like where the worm wheel engages with the main dec axis up towards the saddle.

Typically I'm thinking about this after I've rebuilt that portion, at least that's easy to pull apart

Are we back to the motor pulley? 

Stripped out the dec axis and no sign of the pullet being loose. It's so tight that I cant get it off. I've the dec refitted to the point where the idler goes in. 

Now I'm really stumped, where could the slip be coming from? The only bit I can see is the belt tension but it felt tight when I poked it with the back of a hacksaw blade. 

Any other thoughts? I cant see how the backlash adjustment could be to blame as that would likely be very noisy. 

Pete

7 hours ago, StarDodger said:

Please keep us posted on how you get on...I have a project of my own, I have bought an EQ8 in mint condition just three years old for a steal of a price so could not resist, but it has the dreaded DEC backlash that has haunted these mounts, (only a bit mind) so I have to make  some minor adjustments and am just plucking up the courage to have a go... 😮

so just recently sold my belt modded EQ6 

The EQ8 is where I wanted to go next too, the main thing holding me back is the talk of backlash issues. To be fair though, I haven't really seen a better alternative option at the same price

Pete

3 minutes ago, StarDodger said:

No, for sure, give  it a good once over while you have it apart...hope you get it sorted...

Me too. If nothing else it gives me a better feel for the design for any challenges that arise later in the season when the stakes are higher. 

I had to redo the worm mesh adjustment from scratch last month so I'm comfortable enough with that, just the motor fitting that I need to get to grips with. Had I been doing the belt mod myself I would have cut out slots in the casing for an endoscope, in theory I could still do this for the dec. 

Pete

Ah well, I partly figured I wasnt going to get off easy so earlier I removed the scope so removing the dec assembly wont be a huge pain. 

I dont fancy going through the pain of getting the motor back in, just to have to take it out again.