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Sirius/HEQ5 Pro Guiding Problem

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#1 hoa101

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Posted 03 April 2013 - 09:15 PM

I am looking for a little help with my guiding issues. My setup is the Orion SSAG and mini-guidescope.

The guiding is very good for the most part, but on a fixed interval I get a big jump in RA. The peak is maybe 3-4 times the magnitude of usual jitters in the RA curve and reaches the first dotted line on my graph's y-axis.

Does anyone know what may be causing this? I suspect something with the worm gear... I'm hoping somebody has insight into what might be going on.

Thanks for the help.

#2 jrcrilly

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Posted 03 April 2013 - 09:18 PM

on a fixed interval I get a big jump in RA.


What is the interval? That should reveal the source. The magnitude would be useful as well.

#3 hoa101

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Posted 04 April 2013 - 07:23 AM

I'll try to get data the next clear night. Maybe Friday

#4 EFT

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Posted 04 April 2013 - 10:30 AM

The interval will tell you whether it is coming from the worm or the spur and transfer gears. It's possible that you just have a piece of stuff (e.g., casting debris, grit, metal shaving, etc.) stuck in one of the gear trains that gives you the big jump when you go over it.

#5 hoa101

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Posted 04 April 2013 - 11:43 AM

That is actually what my buddy said too. Since it's under warranty I would send it back (again) instead of trying to fix it I think. Not having much luck with my gear so far.

I'll post the data hopefully on Saturday.

#6 hoa101

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Posted 06 April 2013 - 09:50 AM

The interval will tell you whether it is coming from the worm or the spur and transfer gears. It's possible that you just have a piece of stuff (e.g., casting debris, grit, metal shaving, etc.) stuck in one of the gear trains that gives you the big jump when you go over it.


Here is the data, as promised. Seeing was ~4" and there was 5-9mph wind, so take that into account here.

SSAG with 50mm guide scope at 4 second exposures. Any more than that and the DEC axis started to chase ghosts.

Posted Image

I average the big periodic peaks in RA and came up with a "time" of approximately 97 between peaks. Does that correspond to real time or just guide intervals?

Unfortunately I do not have data from a night with good seeing. The peaks are much more pronounced with low exposure times, probably because the guider "chases" the bump in the RA gears. Here is a mockup of about what it looks like.

Posted Image

What gear has a period in the neighborhood of 100 seconds (intervals??)? And, is it easy to fix or should I talk to Orion about further warranty work?

Thanks for the help!

Edit: Clarification

#7 hoa101

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Posted 06 April 2013 - 04:29 PM

Okay, I did a little investigating. The period of my problem is exactly the period of this small gear here when in sidereal tracking speed.

I'm a little confused as to what that means though. Isn't that the one that goes directly to the motor? Worrisome...

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#8 EFT

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Posted 06 April 2013 - 05:13 PM

It could still mean that something is stuck in the teeth or that the gear is damaged. Take a toothbrush and use it to clean out the teeth of the gears a bit. These don't need a lot of grease in the first place. That might take care of the problem. If it doesn't and the mount is still under warranty, then I would consider sending it in since there is no good way to replace that gear unless they want to send you a new motor.

#9 hoa101

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Posted 06 April 2013 - 05:41 PM

Yeah I was thinking the same. The magnitude is completely unacceptable for a mount of this price range. I get a displacement of one-pixel or more when seeing is good with a 160mm focal length guide scope.

Thanks for the help, I'll let you know how it goes.

#10 astro_baby

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Posted 07 April 2013 - 03:40 AM

Clean out the teeth from all of those gears pictured. i would do it slowly with a q tip. That way you can check if you find any offending bits of grot. It could be grot on the biggest of them gears as well causing the motor to semi stall.

To give you an idea of how small a bit of grot you might be looking for I have had the same mount grind to a halt because of a piece of grot inside that gearvtrain. The piece of grot was about the size of a single iron filing so small only the glint of light coming off it revealed it....but it was enough to jam the gears.

Those gears also look a bit underlubed. I would put a smear of grease on those when your cleaned up. Use TF2 but Superlube is good. Something quite tacky...nions differ on lubes but ai use TF2 which is a Lithium Teflon composite.

#11 hoa101

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Posted 07 April 2013 - 01:24 PM

I "flossed" the offending cog with shop cloth (the blue synthetic throw-away towels, not sure what you call them in the UK). I have many rolls of it for cleaning the cogs on my road bike.

Anyway, I seem to have discovered a tiny, tiny piece of metal in there. I mean TINY... maybe smaller than the head of a pin. I only noticed because of the sunlight glinting off of it. I am hoping that this was the problem, because I really do not want to mail the head back to California!

I will probably clean the transfer cogs as well, but not the worm cog. I do not want to disassemble the head. Superlube is on order - should arrive Tues/Wed. I have some Polyurea-based grease that is also designed for cold temp and waterproof... but Superlube is cheap enough, so I'll just use that to be sure.

Now I just need to wait for clear skies.

#12 astro_baby

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Posted 08 April 2013 - 01:56 AM

That tiny bit may well have caused it. Mine was on the worm transfer gear and was so tiny I disnt believe it was the cause of a complete mount stall but in fact it was.

I will keep fingers crossed for you.

#13 hoa101

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Posted 10 April 2013 - 08:49 AM

Unfortunately the problem is not solved, which pretty much narrows it down to the RA motor and/or the gear. The clicking noise I get when slewing at high speed in RA makes me suspicious as well.

I took PE data without guiding, and the problem is very evident there as well. Every ~95 seconds I get a 4-8 arc-sec jump in RA tracking, which makes imaging basically impossible with anything but very short focal lengths.






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