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Re: DIY Spring Loaded Worms for the G11

 

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Hello Henk -

Thanks for your comments.? I'm of course familiar with your SLW modifications, and were part of the inspiration in trying this for myself.? Your use of the sideways spring to apply both the worm pressure as well as locating the worm block was especially clever.

Thank you for your suggestions on mitigating the periodic forces from the flex couplers.? I was looking into the belville washers for both the bottom bolts, as well as potentially to keep the worm from walking (bearing preload).? I may first try a regular compression spring and longer bolt under the sliding bolt.? I was also thinking about using some delrin or low friction plastic under the pivot, both for the small bit of compression, and the anti friction properties.

I do agree with you that the biggest room for improvement is how the worm bock is located by? the loose pivot bolt.? It's less than ideal.? The spring is a novel approach.? A set screw with a rounded nose may also be an option to push the worm block assembly to one side.? It's been something I've been pondering since the beginning, but haven't settled on a solution yet, at least not before seeing how the current m4 plastic washer works.? But its certainly my primary suspect from any large backlash.

I'm lucky that my static worms were pretty good.? I had somewhere around 8 to 10 arc sec peak to peak of native PE in the worm.? Not sure if swapping them would have improved things or not.? But guiding wise, it was relatively easy to get under 1 arc-sec RMS when? the conditions supported it.? In trying to dial the backlash out with the static worms, I also had some occasional binding, though only when running the worms quite tight.? Still, the backlash would vary depending on where you were on the worm ring.? I'm also hoping the SLW will help the mount handle just a tiny bit more wind without having to resort to excessive intentional weight imbalance.

Thanks again for your comments, and I'd love to hear your thoughts on my results or any other unexpected difficulties I may encounter.? Thanks again.
-Tony




On 5/21/2021 11:42 PM, Henk Aling wrote:

Hi Tony that looks great.? The basic idea is not that different from my humble construct below (for DEC)



Namely, both blocks are screwed fixed against the aluminum cover (and are aligned to prevent the 75 Hz vibration), both bottoms screws are loose and the one nearest the motor serves as the pivot.? I added 2 Belleville washers tightened lightly at the bottom one near the motor to keep the blocks flat against the plate and prevent wobble.? Note that the flex couplings are not quite symmetric around the axis because there is always some play and the setting screws pull them off center.? That in addition to the not perfectly centered motor axis yields significant periodic forces that try to wobble the block assembly.

That's the balancing part.? On top of that there is the additional friction because of the continuous spring pressure as compared to a fixed worm position with some play.? That will cause stronger up and down vibrations and may also push the worm away from the RA axis if the pressure is not right.? I've noticed that the Losmandy SLW have a setting screw, is that because of this perhaps?? So it's not really full time spring loaded, only at high points.? Altogether a lot of forces that need to be managed.

Here's the RA one,



The idea is that the pivot screw in its hole is pushed against the side away from the motor and stays there.? For RA, since the worm pulls itself away from the motor during tracking, this will hopefully be true.? But nevertheless we have two screws floating of which one is only loosely fixed in position.? Same with yours if I understand it right.? My spring system is more of the Flintstone kind than your professional looking tunable spring.? I regulate the force by the position of the screw around which it sits.? Further outside, more momentum.

So far it has worked very well for slewing.? This used to be my main problem (the ring gear is not round enough to work with a tight fixed setting and binds up), and it solved that.? As far as RMS is concerned, when I get less than 1" total RMS I'm happy (it happened once).? I have not had the chance to do much testing because I bought a lot of electronic gear that I am learning how to use so the focus has been elsewhere.

So far I'm still hopeful that this system will work.? If not, all I have to do is turn the bottom screws tight and I'm back to the old fixed system so it can't hurt to try.? Or just use the spring loaded configuration for slewing and the fixed on for tracking.?

Good luck and keep us posted on how it works!

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