HEQ5 Pro Bearing and Clutch Adjustments

[The Thing]

Can anyone tell me if, when the clutches are released and the axes are 'free', when the motors are run, should the scope move? Mine does.

New full set of SKF bearings. The scope is mounted and the axes are balanced for imaging i.e. slightly off and the thrust bearings set to give a tiny amount of endfloat. I am thinking that there is some drag between the brass gear thingies and the aluminium outer bits. I have removed all grease except for a smear where the clutch operates.

TIA
Duncan

[MarkS]

Mine doesn't.  But I don't think it is anything to worry about -as long as the scope moves pretty freely when its manually turned.

[The Thing]

Since the first post I have had the brass thingies out and wiped the smear of grease off, also wiped inside the aluminium housings. This has improved things a bit.

[mickw]

If the motors are driving the scope, the clutches are not really disengaged.

Seems like there is some drag in there somewhere, if that's right, this will likely get worse as the weather gets colder.


Wipe more grease off 

[The Thing]

An update.

First thing I forgot to do when I started imaging was to reset my EQMOD AutoPEC data - so I was trying to guide with out of sync and no longer relevant values! Be warned. Also check that the Gain setting for PEC playback is set to 1x, mine seemed to have jumped to Zero. Bug? It has been alright since. It may have been the upgrade to 1.27k...

The new PEC curve generated for 5 worm cycles was a different shape, smoother, less rounded, more peaky.
Here are the before and after.


BTW This image is in the Gallery -Home > Instruments and Data Files > Observing Kit album, I hope people can see it!

[The Thing]

Here is a screenshot of PHD2 showing the guiding I got after the bearing replacement, it's a definite improvement of about 2 arcseconds on average, which is about 2 pixels on the 1000D CCD. Also there was good seeing that night.

This is with HEQ5 Pro, Meade LX90 8" UHTC, Baader Alan Gee II Telecompressor (f/l 1250), Brightstar OAG, QHY5.

The error graph used to exhibit a jagged line with regular +/- excursions of the same amplitude. This I interpreted as 'stiction' in the bearing causing the mount to jump round rather than rotate smoothly. Hence the bearing replacement...

[MarkS]

So you're saying the RMS error in RA is still around 1 arcsec but the error graph has a slightly different characteristic?

My PEC gain always seems to default to zero - which is very annoying!  It caught me out yet again last night.  I wasted the only hour of clear sky last night in running a PEC test with the gain accidentally left at zero!

[The Thing]

Yes, Robert saw my guiding graph at your observatory warming and his comment was "that's not right" (pre bearings). It was a sawtooth RA plot, now it more reflects random seeing effects.

[MarkS]

By the way, which bearings did you replace?  The RA worm bearings or the main RA axis bearings or both?

[The Thing]

By the way, which bearings did you replace?  The RA worm bearings or the main RA axis bearings or both?

The lot, worms, RA and DEC.
The worm bearings were very lumpy and the worm wouldn't freely rotate. The DEC axis was the best but still sticky. The RA axis felt like it had glue in the bearings at certain points. That made getting balance right uncertain as the axes had to be way out of balance to get any movement. It all affected the smoothness of the guiding or lack of it.

I also undid the puck carrier at the end of the DEC shaft and re-centred it as it wasn't right, it sort of clicked back into position!

[The Thing]

Hi All.

I've applied a Belting Online belt drive kit to my HEQ5 and have been testing it out. It has a 4:1 ratio which is what Mark is trying to achieve for his EQ6.

It's made a huge improvement. Here is the PHD2 screen shpwing how it guided last Tuesday night. Compare it to the previous one lower down. Kit: HEQ5 Pro with EQMOD (no handset), LX90 8" UHTC, Baader Alan Gee II Telecompressor, Brightstar OAG, QHY5L-II Mono guide camera (was a QHY5 before).

[RobertM]

That looks a really interesting and not prohibitably expensive mod.  You might even find the actual improvement better than you can see from the graph as you're in the seeing 'noise' range.  As an example I've had guiding to 0.2 arcsec but the other night it was nearly 1 which about the range you're seeing there.

Does the belt mod allow the cover to go back on ?

Robert

[MarkS]

You've beaten me to it!  Well done.

Half arcsec guiding at 0.5sec guidecam exposure is a very impressive result.  I generally get 0.4-0.6 arcsec at 1.0sec exposure with my 47:12 ratio.  Are you using PEC as well?

I have received my 48:12 pulleys and hope to do my conversion this weekend or next.  Then PEC will work properly because all the gear ratios line up and this should allow me to use much longer guidecam exposures, making it easier to find decent guidestars and also allowing better performance in bad seeing because the guidecam exposure can then integrate over the seeing fluctuations instead of chasing the seeing.

Mark

[Rocket Pooch]

Sorry why does PEC help Guiding?

[The Thing]

The mod should allow the cover to go on but if the small pulleys are set low enough the grub screws foul the mounting plate. So no. I have bodged a bit of a gasket for the time being while I decide if I am going to make the holes in the mounting plate the motor spindles come up through round to stop this happening (they are oval).

The screen dump was taken while recording PEC using the AutoPEC function in EQMOD. Interesting shaped graph resulting.I was asleep when the PEC kicked in after 5 worm cycles were recorded I have a load of nice defined subs of the Crescent waiting to be processed.

Good question Mr Pooch. If things are tickety boo and Polar Alignment is good then using PEC corrects for PEC error by varying RA tracking speed and then the guiding has very little to do if the allowed stellar excursions are set to be less than the seeing, so few corrections are sent to the mount. That's my understanding of it.