Jump to content


Photo

RA Slop Tolerance?

  • Please log in to reply
14 replies to this topic

#1 MHamburg

MHamburg

    Apollo

  • *****
  • Posts: 1029
  • Joined: 21 Jun 2006
  • Loc: Brooklyn, NY/Berkshires, MA

Posted 24 November 2012 - 04:58 PM

Just finished an Ed Thomas hypertune and am left with a bit of slop in the RA axis. Adjusted this as best as I could with the mount balanced (weighted slightly to the east) and fully loaded (Edge 11 HD), but could not get all the wiggle out. Motor sounds fine at slew rate 9, But I haven't gotten a chance to test it out under the stars yet. How obsessive should I be? What is tolerable?

Michael

#2 orlyandico

orlyandico

    Fly Me to the Moon

  • *****
  • Posts: 5355
  • Joined: 10 Aug 2009
  • Loc: Singapore

Posted 24 November 2012 - 05:21 PM

I have no idea. What's the mount?

The best measure would be to look at the RMS error when guiding. Too much slop or too tight a worm engagement would affect the RMS guiding error.

On my CGEM using a 200mm finder, the best I can get is about 0.18 pixels RMS. This amounts to a bit less than 2" of error. Yes it's not too great...

#3 RTLR 12

RTLR 12

    Aurora

  • *****
  • Posts: 4516
  • Joined: 04 Dec 2008
  • Loc: The Great Pacific NorthWest

Posted 24 November 2012 - 09:26 PM

Did you adjust the worm gear shaft end play?

Stan

#4 MHamburg

MHamburg

    Apollo

  • *****
  • Posts: 1029
  • Joined: 21 Jun 2006
  • Loc: Brooklyn, NY/Berkshires, MA

Posted 25 November 2012 - 01:38 PM

Sorry to omit it is a CGEM. Yes I believe I eliminated the worm gear shaft end play (but now I am doubting myself.) I would like to avoid tearing down the mount again.
Michael

#5 RTLR 12

RTLR 12

    Aurora

  • *****
  • Posts: 4516
  • Joined: 04 Dec 2008
  • Loc: The Great Pacific NorthWest

Posted 25 November 2012 - 05:47 PM

There is no tear down required to check or adjust the end play. Just pull the cap off the end of the axis shaft so you can see the end of the shaft and wiggle the RA axis back and forth. Look for movement at the end of the shaft. If there is movement you need to adjust the slotted bearing retaining nut until the play is gone.

Stan

#6 MHamburg

MHamburg

    Apollo

  • *****
  • Posts: 1029
  • Joined: 21 Jun 2006
  • Loc: Brooklyn, NY/Berkshires, MA

Posted 26 November 2012 - 09:43 AM

Stan, once again many thanks for your advice!
Mich :bow:ael

#7 EFT

EFT

    Vendor - Deep Space Products

  • *****
  • Vendors
  • Posts: 2544
  • Joined: 07 May 2007
  • Loc: Phoenix, AZ

Posted 27 November 2012 - 10:27 AM

Once you get the worm mesh as tight as the mount will allow (i.e., just slightly backed off from binding), then whatever slop is left really can't be reduced any further. The amount of slop can vary considerably from mount to mount with some mounts being quite tight while others are loose. The slop is simply backlash between the worm and ring gear and is not necessarily a bad thing. RA slop can be easily accounted for by a slight off-balance of the axis to keep the gears consistently loaded to one side.

#8 TxStars

TxStars

    Apollo

  • *****
  • Posts: 1328
  • Joined: 01 Oct 2005
  • Loc: Lost In Space

Posted 28 November 2012 - 12:43 AM

Depending on the maximum room there is between the retainer and worm you may be able to add a thrust bearing which can reduce binding:
http://www.vxb.com/p.../Thrust/Kit8670

#9 EFT

EFT

    Vendor - Deep Space Products

  • *****
  • Vendors
  • Posts: 2544
  • Joined: 07 May 2007
  • Loc: Phoenix, AZ

Posted 28 November 2012 - 12:54 AM

Depending on the maximum room there is between the retainer and worm you may be able to add a thrust bearing which can reduce binding:
http://www.vxb.com/p.../Thrust/Kit8670


While there might be room on one side of the worm, there is no room on the other side since the standard bearings sit right against the cap with no spare room. It would be nice if the system were designed with enough space on each side for a thrust bearing. It is precisely because of this that the bearings are almost always installed too tightly in the first place which damages the bearings and adds to PE.

#10 MHamburg

MHamburg

    Apollo

  • *****
  • Posts: 1029
  • Joined: 21 Jun 2006
  • Loc: Brooklyn, NY/Berkshires, MA

Posted 28 November 2012 - 10:04 AM

Thanks for the info, Ed and TxStars. I am waiting for clear skies here in the East so I can actually adjust and calibrate the mount.
Ed- I really learned a lot from the Hypertune DVDs.
Michael

#11 TxStars

TxStars

    Apollo

  • *****
  • Posts: 1328
  • Joined: 01 Oct 2005
  • Loc: Lost In Space

Posted 28 November 2012 - 10:34 AM

In that case the standard bearings could be replaced by tapered roller bearings and then they could be set "Snug" and cure the problem.

#12 EFT

EFT

    Vendor - Deep Space Products

  • *****
  • Vendors
  • Posts: 2544
  • Joined: 07 May 2007
  • Loc: Phoenix, AZ

Posted 28 November 2012 - 11:56 AM

In that case the standard bearings could be replaced by tapered roller bearings and then they could be set "Snug" and cure the problem.


For the most part it is still a space problem. While tapered bearings in this size are no impossible to find (they are used in some medical equipment), they are uncommon and expensive. I'm not sure if there would be sufficient benefit to switch to them. Standard bearings are OK in this application as long as they are not over tightened. Taper bearings would have the same problem to some extent in that, if they were installed with too much preload, they would still not work well. However, they night not be as easily damaged since they are designed for the axial load. Another possibility might be angular contact bearing, but again you get into more specialized bearings when you go that way.

#13 TxStars

TxStars

    Apollo

  • *****
  • Posts: 1328
  • Joined: 01 Oct 2005
  • Loc: Lost In Space

Posted 28 November 2012 - 05:27 PM

Well a single ball on center at each end of the worm to reduce play would be cheap and be easily replaced.

#14 EFT

EFT

    Vendor - Deep Space Products

  • *****
  • Vendors
  • Posts: 2544
  • Joined: 07 May 2007
  • Loc: Phoenix, AZ

Posted 01 December 2012 - 11:12 AM

I have found a source for angular contact bearings of the correct size and am ordering a couple sets to try them out and see if I think there is sufficient advantage to switch to them for this application.

#15 MHamburg

MHamburg

    Apollo

  • *****
  • Posts: 1029
  • Joined: 21 Jun 2006
  • Loc: Brooklyn, NY/Berkshires, MA

Posted 01 December 2012 - 01:39 PM

Please keep us posted, Ed.
Michael






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics