Losmandy_users@groups.io

Re: 811G lack of DEC dampening options!

#82098

Hey there Loren,
That does help me understand a bit more; thank you.

My only additional question: Have you tried adjusting the worm block position to fit snugly on either side of the worm gear yet? or are you using the mount unadjusted as you received it??

I will have to say I need to defer a bit to other visual users, perhaps they will have more insight. As an imager I use a TVC value of zero and compensate for backlash in PHD2. When I do center visually at centering speed (for example for model building) I don't really experience what you describe as excessive springiness and my worm blocks have been snugged up well. ?I've included the TVC definition below from .

Note that the TVC value is the number of steps that the controller will compensate for backlash. Your setting of 5 (2.8 arc seconds) may (?) be too small for any noticeable difference as the setting can go all the way up to 255 steps. I might suggest adjusting the worm block position to reduce mechanical back and forth travel of the worm within the blocks so that TVC needs to work less. After that, without knowing what TVC settings you have tried, might I suggest you try larger TVC adjustment intervals? Maybe 0, then 125, then 0, then 75, then 0, then 35, etc. in order to see what gross overcorrections do to the mechanical motion??

Wish I could give you a definitive answer.
Ryan

?TVC?(Time Variable Compensation) This menu item helps compensate for the response delay caused by gear backlash when changing direction in Dec. The TVC can eliminate the hysteresis that causes this to happen. You can select a value between 0 and 255, which is the number of steps made at high speed whenever the Dec. direction is changed. You should choose a "TVC Value" that results in a short or no delay when changing the guiding direction in Dec. If you see a short jump, you have to decrease the value.

So, the number is the number represents motor steps taken at high speed when reversing DEC direction. For a G11, one step is approximately 0.56 arc seconds, so value of 50 means rotate the motor by about 28 arc seconds to take up backlash. Maximum value of 255 provides for about 143 arc seconds of backlash.

Re: 811G lack of DEC dampening options!

#82097

Ryan
The term "springy oscillation" describes what I see when mainly centering the scope for visual use i.e. repetitive image movement with a period of maybe less than 1/2 second.

I've observed really minor play in both RA and DEC blocks (with tight clutches), it doesn't appear to be caused by loose hardware at either worm per-se, this was tested with the CW and OTA mounted. I've adjusted Gemini's TVC factor with no improvement (currently set to value 5). I need to do more experimenting to isolate the effect I'm trying to describe, it's possible that the oscillations are occurring on both axes, maybe due to a mechanical coupling on the 30" steel pier that the mount is bolted to.

I'll try to upload a video showing centering movement using RA and DEC commands.

Loren

Re: 811G lack of DEC dampening options!

#82096

Hey Loren
I’m looking for further clarification if the term “springy oscillations”?

For perspective, it is difficult to troubleshoot a system with verbal descriptions that don’t match a recognized vernacular as it can introduce misinterpretation and result in misguided advice.?

The way that the spring-loaded worm works is that the worm is allowed to pivot in the worm block both toward and away from the ring gear. The spring is there to apply a constant force, pressing the worm gear into the ring gear to ensure even contact regardless of thermal expansion and minute eccentricities in the symmetry of the worm gear and the ring gear. The design of a non-spring loaded worm gear is simpler but also generally much more dependent on being properly set in the assembly process and the hit-or-miss quality you see in reviews is one result. It can work great if you get a decent sample, and you don’t want to fiddle with anything, and you don’t mind a “ship it back to the manufacturer to adjust it” approach. Many people are in this camp, and there is nothing wrong with that. We pay good money for this stuff and it is reasonable to just expect it to work ?

Losmandy mounts are designed with a different approach. They are built to last a lifetime, they are sturdy with user replaceable parts and they are designed with things like the spring-loaded worm block that reduce the performance impacts from inherently variable limits on the perfection of machined metal. This creates a mount which, while not “perfect,” can allow the user to minimize many of these variables to a great extent and achieve a mean level of performance with all other copies of the mount. There is, however, a bit of a learning curve involved.

Due to the perpendicular vector of the springs thrust against the worm/ring interface there is no situation in a properly adjusted worm block where the spring would rebound along the axis of rotation.?

Correct me if I’m wrong but what I believe you are experiencing is DEC backlash, which is normal to an extent in these mounts but also mitigated to a great extent through proper adjustment. If that is the case, you are in good company as I would bet good money that everyone on this board has dealt with it at some time.?

With the counterweights and OTA removed and the DEC clutch tightened, is there currently any back-and-forth play in the DEC axis and do you see any parts of the worm block shifting laterally while the DEC axis shifts back and forth?

Can you upload a short video that captures these variables?
1) amount of DEC movement?
2) closeup of worm block while trying to see if there is any play in the DEC axis?

That will give us more information to assist.?

Hope we can help and welcome to the group.?
Ryan

Re: 811G lack of DEC dampening options!

[email protected]

#82095

I bought a G11G last spring and thought the idea of a spring-loaded worm gear was great, as it was, my EQ6-R Pro didn't have this. I hadn't got to the point where I would see any apparent improvement as I have still yet to do any serious astrophotography. Since then, I bought an EQ8-R Pro which also doesn't have a spring-loaded worm gear. I love the completely stiff axis of those 2 EQ mounts. I am now at the point where I can evaluate the adjustable spring's worth. I find making the spring adjustment a bit fiddly and hit or miss. The wobble in the RA axis is quite noticeable which sends me down a rabbit hole of adjusting. I now realize that it is supposed to wobble a bit. I have wondered how accurate tracking can be because of this wobble. At least now I have both kinds of mounts to eventually let me know what is good or not.

811G lack of DEC dampening options!

#82094

I'm a new 811G owner, as of November 2023. I received the mount from Losmandy with all of the newest features: spring-loaded worm, tucked motors, Gemini 2 updates, hand-tuned by Scott. At the moment I have a heavy 130mm TOA refractor mounted with about 29 pounds of CW (11+11+ 7).

So, I am familiar with non-spring loaded worms so the observed degree of "springy" oscillations during slews or centering is really annoying. Based on my search of this problem on the user group, I was able to reduce the effect to a minimum on RA, by tedious east-loading of the counterweights. Also, I reduced centering speed to less than 10 steps, which does help. But the DEC axis has no dampening feature (namely, counterweights) that can be adjusted. So I'm currently tolerating the large oscillations on DEC. I've tried different saddle positions of the OTA, thinking an offset might reduce the effect... as of now, nothing really seems to minimize the effect.

What are my options?

I considered replacing the DEC worm spring with a stiffer spring, I am not sure that would actually dampen centering oscillations very much. I could add a? dampener counterweight but that requires a good bit of experimenting and it maybe very sensitive to OTA balance conditions. Is there some simple worm adjustment that could reduce this effect?

Loren