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Ovision worm gear assembly does it have a spring washer...may be mssing on mine

 

Hello


In October of this year I bought a used Losmandy G11 with an ovision worm gear.

I am unable to get the performance out of the gear at the RA axis.


I'm getting phd rms numbers of .9 arcsec and 1.0 arsec


After trying many things including 1 to 2mm of end play in the worm by adjusting

the end cap this? did not help. I adjusted both end points of the worm by using

a feeler guage to get even spacing from worm body to mount body. .020 in.


Gear Box to worm gear alignment is fine.


I swapped out motors and gearboxes from dec to ra and ra to dec

No difference.


I then swapped worms. an older dec worm by Losmandy (stainless Steel) to the ra axis and ovison to dec

axis. I now get Ra rns of .59 and Dec of .4 rms


At one time I cleaned all gears and bearings. I took off the end cap of the ovsion worm.

. Is? there supposed to be a spring washer or spring at the end of the OPW at the endcap?

Is there a schematic or drawing showing size if there is supposed to be one.


Thanks for any help and Happy Holidays


Greg
 

Hi Greg,

I think that your Ovision's worm gear endplay is not getting set correctly and there is no preload on the worm bearings. I don't have an Ovision worm because the original 2-piece worm blocks loaded with ABEC-7 bearings and Losmandy HP worms were getting sub arcsecond PE numbers after adding Bellevue washers and careful adjustment of the drivetrain and when guided well under 0.5 arcsecond PE from PHD2.?

Have you looked at Michael Herman's article on the G11 drivetrain? If not download it from Yahoo and read it and apply these ideas to your Ovision and you should be GTG. Be sure to clean and relube using SuperLube for long life with minimal separation, gummin up and low viscosity even below freezing. Use SPARINGLY, clean up your clutch discs and be sure to reassemble with the wavey spring washers under the clutch knobs NOT directly on the thrust bearing races. Also do not get hung up on minimal backlash, without a temperature compensated worm gear you will only be making trouble for yourself when the air temps get low enough to shrink the back lash to zero causing stalls.?

Cheers/Chip
 

Thanks Chip

?I took apart the Ovision worm and it does have a spring washer installed
?cleaned and lubed the assembly.

I used an eye loop to look at the worm. There are a few pits in the brass
on the top surface in a few places. I don't think that will cause any issues

Will re-swap Ra? and Dec assemblies.
I have read MIchaels white paper. Considering new bearings and spring washers
On both Ra and Dec although Ovison bearings seem fine upon inspection

While running PHD I noticed I have to keep Agressivenes to 60
and min motion to .25 hysterysus to .35 otherwise Ra is to active.
This is with Dec worm at Ra

I had also tore down both ra and dec and relubed and cleaned up cluth surfaces
Dec had some lube underneath pads. Didn't seem to help Ra performance after
clean and relube of Ra

Greg
 

Hi,

Nice to read of your observations and maintenance work.

I suggest that you try to separate what PHD2 is telling you, from how the mount is actually performing.? It would be easy to misinterpret the PHD2 messages.

So I suggest you do the following to diagnose the mount.? The diagnostic will also point to where the worm system problem is, if there is a problem at all.

The diagnostic is the PE measurement itself.? For that, you can use the free program PECprep.exe, which you can download from the EQMOD group.? When you run that program, you first select the mount type as G11.? It has all the right mount parameters built in.

You will also need to select as the input file a clean PHD2 log file.? To get that, find where where on your? PC that your PHD2 log files are normally stored.? Usually they have a simple date code, and they are text files.??

You set up your mount and put your autoguider camera at prime focus of your imaging scope.? Do not use a guide scope...you must eliminate any mechanical coupling issues.??

Point at the intersection of? celestial Meridian and Equator.? Do a very careful drift alignment...the PHD2 has a drift align tool that works well.? You want the guide star to stay in the autoguide camera field for 30 minutes.??

Return to the meridian and equator position and choose a star to ttack.? Allow PHD2 to autoguide to assure it knows N,S,E,W.? Then stop autoguiding and erase or rename the current PHD2 logfile.? You then tell PHD2 to Turn Off guide signals, and start "autoguiding" again.? NowE clean logfile will just have records of the star fluctuations from RA worm motion...the raw PE.? Let that run for about 4 worm periods...which are 239 sec (4 minutes) each.? So maybe let the tracking go for 20 to 30 minutes.

Then rename that PHD2 file with something describing the scope, thd camera, and the date, like G11_SCT_SSAG_Dec_24_2017.txt

Use that in the PECPREP program to analyse the PE.? ?It will tell you the periods that make up the worm PE...each gear and bearing and the worm fundamental, and harmonics, will be shown.? You should hope to get the overall "RMS PE" about 1 arcsec.? If you are near that,? it is about the design limit of the mount.? I show an example near the end of that PDF about improving the G11 PE.??

Anyway...that's my suggestion.

Once you have the mount understood, you can start to set up PHD2 for proper autoguiding.? For that, I find the PHD2 Wizard very helpful.??

All the best,
Michael?






On Dec 24, 2017 11:49 AM, "gvblk4@... [Losmandy_users]" <Losmandy_users@...> wrote:
?

Thanks Chip

?I took apart the Ovision worm and it does have a spring washer installed
?cleaned and lubed the assembly.

I used an eye loop to look at the worm. There are a few pits in the brass
on the top surface in a few places. I don't think that will cause any issues

Will re-swap Ra? and Dec assemblies.
I have read MIchaels white paper. Considering new bearings and spring washers
On both Ra and Dec although Ovison bearings seem fine upon inspection

While running PHD I noticed I have to keep Agressivenes to 60
and min motion to .25 hysterysus to .35 otherwise Ra is to active.
This is with Dec worm at Ra

I had also tore down both ra and dec and relubed and cleaned up cluth surfaces
Dec had some lube underneath pads. Didn't seem to help Ra performance after
clean and relube of Ra

Greg
 

Hi Michael,

You know I always forget that people, even people I KNOW are new or new to their Losmandy mount, don't know all of the required bits many experienced people don't mentioning. Thanks for reminding us that you have to start at the beginning to get to the end we are hoping the help people to find.?

So how is it going in the mile high city??

Chip



??
 

Hi Chip,

You are great in 1,000 ways... why its such a nice friendship.?

It's nice and frosty here...snow everywhere.? The high can be 15F one day and the low... negative numbers.? The next day the high can be 40F (people in shorts and tee shirts too).? But snow is always just a day away.? I don't know how anyone does astronomy here... but some folks do. The housing prices are insanely low, but the heating bills must be high to balance out the economy.? Gas prices are about $2.40/gal.? Not in California any more Dorothy!? But there is no beach here so Susan will not consider moving here.

Having fun with Hunter who's at 2.5 a real mensch already.? ? Beth took him to see Nutcracker ballet and he's memorized all the music already.??

We went to see Greatest Showman at the movies and it was a fun movie.? Easy story and the music and presentation reminded me both of LaLa Land and of Hamilton.??

Flying back home on Jan 2... to warmth... though still chilly.? SanJose had a 3.5 quake the other day... still nothing in the 5 or above range... we are way overdue for something to happen.

Have a great New Year!

Michael




On Dec 27, 2017 3:42 PM, "chiplouie@... [Losmandy_users]" <Losmandy_users@yahoogroups.com> wrote:
?

Hi Michael,


You know I always forget that people, even people I KNOW are new or new to their Losmandy mount, don't know all of the required bits many experienced people don't mentioning. Thanks for reminding us that you have to start at the beginning to get to the end we are hoping the help people to find.?

So how is it going in the mile high city??

Chip



??

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