How to fix guiding error for my EQ5

[SteveBz]

Hi Guys,

I have the basic EQ5 sold by many companies.  I have the CG-5 Celestron version with SkyWatcher drives and enhanced handset to allow the ST4 cable from my QHY5 mono cam (the legacy one) to send corrections from PHD2 to the mount.

My guiding is very erratic, just look at the graph here:

When I bought the telescope and mount, it was frozen and I had to unfreeze it with a hot kettle and towel and then fine sand it with 1200 wet'n'dry before it would reassemble.  I suspect that it has been damaged both by my efforts but also by the previous owner. What to do other than change my mount?

If I have to change the mount later, so be it, but I want to eliminate other possibilities first.

Regards,

Steve.

 

[MarsG76]

Three possibilities come to mind, one is backlash, at least in RA since it looks like your DEC corrections are only in one direction.

Another is gear spacing. Perhaps after the freezing/thawing process the grease between the teeth needs to be re applied.

The third possibility is seeing/corrections related. Was your seeing particularly unstable, stars bouncing all over the place, and/OR, you corrections too aggressive. If you havent tried guiding on it during another night, try it and see if your quiding improves from 4.34" to 1" or less RMS.

[newbie alert]

What did you send down with wet and dry?

[SteveBz]

1 minute ago, newbie alert said:

What did you send down with wet and dry?

The internal gears because they didn't fit.  Both the Dec and RA mechanisms were frozen.

[SteveBz]

2 hours ago, MarsG76 said:

Three possibilities come to mind, one is backlash, at least in RA since it looks like your DEC corrections are only in one direction.

Another is gear spacing. Perhaps after the freezing/thawing process the grease between the teeth needs to be re applied.

The third possibility is seeing/corrections related. Was your seeing particularly unstable, stars bouncing all over the place, and/OR, you corrections too aggressive. If you havent tried guiding on it during another night, try it and see if your quiding improves from 4.34" to 1" or less RMS.

I don't think it's one or three.  If I track the tracking I get almost perfect repetition each time but with huge identical jumps (like the 15" one) always in the same place.  Personally, I think the gears are buggered (that's a technical term), but I wondered if I made it, say more aggressive, or set it at a higher correction speed eg x2, not x.5, if I could at least minimise it.

I'm feeling a bit strapped for cash at the moment and it's not really the time to go and buy an NEQ6 Pro, which is really what I want to do. 

Steve

[MarsG76]

34 minutes ago, SteveBz said:

I don't think it's one or three.  If I track the tracking I get almost perfect repetition each time but with huge identical jumps (like the 15" one) always in the same place.  Personally, I think the gears are buggered (that's a technical term), but I wondered if I made it, say more aggressive, or set it at a higher correction speed eg x2, not x.5, if I could at least minimise it.

I'm feeling a bit strapped for cash at the moment and it's not really the time to go and buy an NEQ6 Pro, which is really what I want to do. 

Steve

Increasing the Guide speed will most likely increase the problem by overshooting the corrections.

If your gears a shot, than perhaps replacing the gears/cogs will be a lot cheaper than a new mount...

check these peeps out: 

https://www.deepspaceproducts.com

[SteveBz]

43 minutes ago, MarsG76 said:

Increasing the Guide speed will most likely increase the problem by overshooting the corrections.

If your gears a shot, than perhaps replacing the gears/cogs will be a lot cheaper than a new mount...

check these peeps out: 

https://www.deepspaceproducts.com

Thanks,  I'll look into it.

Steve

[almcl]

If I've read the PHDLog viewer correctly, you're at six seconds between guide exposures?  If that's the case, what about reducing to two seconds, or whatever the guiding assistant recommends?

The other thought is that the big RA jump looks as though it might be an exact match for the worm period.  I know you've already had it apart, but it might be worth looking for some specific damage on the worm threads, or even a bit of foreign material? 

[SteveBz]

53 minutes ago, almcl said:

If I've read the PHDLog viewer correctly, you're at six seconds between guide exposures?  If that's the case, what about reducing to two seconds, or whatever the guiding assistant recommends?

The other thought is that the big RA jump looks as though it might be an exact match for the worm period.  I know you've already had it apart, but it might be worth looking for some specific damage on the worm threads, or even a bit of foreign material? 

Both correct.  I've dropped it as low as I can.  If I drop it too low, it looses the star and jumps even further.  On very very clear nights I can drop it a bit further and I do.

On your second point, the big jump IS exactly the worm period.  It's a good idea to take it apart again, there could easily be some grit in it.  I'll do it over the summer.

Thanks

Steve.