HEQ5 and inconsistent N/S movements

[swag72]

I am hoping someone can give me some thoughts on this as my whole guiding and mount system has come crashing down around my ears over the last couple of weeks!

The HEQ5 has finally been sorted, with masses of thanks to Mel (Astrobaby) and the HEQ5 strip down guide. So the large amount of play I had in the DEC axis has gone and it's running very smoothly indeed. It was so bad that you could physically see the scope juddering at some points. So out for a play last night, and I finally worked out that my ST-4 cable is on it's way out and so by 0200hrs I was guiding using ASCOM pulse guiding.

Anyway I digress. I am yet to check the backlash on the mount, which I aim to do tonight using PEMPro. But I do still have a bit of an issue with my DEC axis.

When I manually move the mount in EQMOD or the handset using the arrows, the E / W movement is instant and can be seen on the camera capture screen straight away. With the N/S movements (DEC Axis) it can not move for a while, then move lots - This is generally on the slower slewing settings, but I need it to be working in order to get the mount back to the same position night after night. I can not determine whether the issue is worse in N or S as it happens in both. It is equally as bad starting from a stationary mount as having just finished some degree of N/S movement. There's just no consistency to the DEC movement at all.

Nothing is binding, nothing is too loose as far as I can ascertain. There is a very small amount of play in DEC, but it's always been there I think and shouldn't be causing me issues.

So if it is backlash - Is there some setting that I can use to tweak backlash during manual slewing? I know that there are backlash settings for guiding.

Or perhaps, you have some other idea what this may be. Either way, I'm a cheesed off bunny!!!

[swag72]

No one any thoughts on what the issues could be? It's nice and clear tonight to I will be out later and could really do with some help - Please!!!!

[nightvision]

I think my new NEQ6 does something similar, no obsy yet so not managed to confirm. I did read that the scope should be positioned to ensure it is not balanced but is always pressing against the drive direction, not sure if this would help on the DEC.

[ncjunk]

Sorry, cant help you as I am having a nightmare with my eq6. i have a lovely oscillation in the guide trace so even though i have it adjusted and no slack it's still.playing silly persons....

I turn guiding off in one direction on the Dec so it only corrects for errors one way. I have very slight drift in the dec so this means i dont end up correcting for an error one way then re-correcting it for the other, reverse direction. i.e. i keep nudging the dec only in one direction. this means over corrections are euled out and backlash becomes less of an issue. my dec works blindingly well....shame the RA doesnt take a leaf out of the decs book...blumming RA...

of course i have waffled about a completely unrelated topic...i'll re-read and see if i have anything usefull to add...probably not!

[ncjunk]

whats it like on a long slew?

the only thing i'd be looking at is if there was a consistancy of positioning when you move between targets i.e. does it consistantly get to within a few minutes of the target everytime?

[swag72]

Cheers Neil, hope your EQ6 gets sorted soon, although when is that MESU due?

Quick update - Weight is not the issue. I have loaded and unloaded the East side and regardless I get the same.

When I move N on speed x8 slew speed, the star hangs for about 2 seconds before moving. It will then move North. If I leave it and move N again, it will move straight away. Then when I move to South, I get the same issue - Hangs for a couple of seconds then moves. Also tried it after an E/W slew and I get the same.

So once I make a N/S move AFTER I have made a slew in any OTHER direction it hangs and waits, then moves. If it's in the same direction it moves straight away.

[Spikey]

I'm sure my HEQ5 mount used to do the same thing Sara so it might not be just you, perhaps they all do it ?

It doesn't seem to be affecting the quality of the images you've been producing recently

[astrofox]

I dont have a skywatcher mount but the description sounds like classic mechanical backlash with the delay at a max after a change in dirrection.

[Astro_Baby]

This one sounds like excessive backlash, its odd if the worm adjustment is ok but not impossible. The worms might be well sorted out with respect to the ring gear BUT its possible that either the motor is set too far off the spur gear, thats the bit where the motors final drive connects to the end of the worm OR the motor transfer gear (the itty bitty gears on the end of the motor itself) are wonky. Be careful if you mess with the transfer gears as making them too tight can lead to some setious gyp later on.

I cant tell you what the gaps should be in an ideal world but broadly speaking there should be a gap between the motor transfer gears and the spur gear about the thickness of a standard sheet of photocopy paper.

The high speed oscilaation thats being experienced is an odd one and I have no idea at all what would cause that.

[Astro_Baby]

Ps theres a menu option somewhere on the synscan that allows for modifying backlash.....i havoe no ecperience of using that as all the mounts I have tuned havent needed it.

[fwm891]

I had a similar prob on my eq6 after a belt mod and traced it to not doing up the thrust washers at the end of the ra and dec worms properly

[swag72]

Thanks for popping in Mel!! I have stripped down the DEC again, with a better idea now of how things work and what does what. I am hoping that it was the work gears and they are now adjusted so that the play on the DEC axis has almost gone (still a tiny bit there) and the gears don't bind. It was a fine line between them indeed. So maybe that will be problem solved, I'd like to think so, but I'm not that lucky!!!

[Astro_Baby]

The suggestion that it could be the worm end floats above is a good one too.....these should be in contact but not too tight. Too tight and they will cause binding and motor stalls, too loose and there will be play and or backlash.

Tuning these mounts is more of an art than a science and much messing about is the most normal outcome. Tuning my own HEQ5 took about a week AND it was subject to slipping a little each time. The mount needs bedding in and constant fiddling for a few days. Given your in spain I wonder if heat may be an issue as the metal could be getting very hot during the day and cooling a night unevenly. The brass gears will expand and contract at a very different rate to the steel worms, axis shafts, bearings and the mount casing itself.

I cant say as ai live in the uk and hot weather is a strange phenomenen which almost never happen

[swag72]

The update to this is that it was indeed the gears and worm adjustment and after about 3 hours we finally got it running without binding as well as eliminating virtually all movement in the DEC. It was a very fine line and very small adjustments got us there. So last night, guiding through EQMOD as the ST4 cable also broke during all of this, so compounded the guiding issues further, I am please to report that it all worked well. Settings tweaked in EQMOD and Maxim, and my 30 minute subs came out like a dream. HURRAH!!! Back in the saddle!! Thanks to everyone who put some thoughts and comments on the thread.

I think that we were also happier to fiddle with the mount as I finally found a place in Spain where I can get it serviced and fixed if needed. Not needed now, but good to know it's available.

If anyone out here in Spain ever needs their SW mount serviced at least I now know where it can be done. Always nice to know.

[Astro_Baby]

There ya go, told you so.....these mounts are great performers but a bit of tweaking can turn them into star performers......glad its all sorted out.

Having done this you wont ever need a mount servicing place. A full stripndown is easy enough if you ever need to do it.