Could be tell me were you purchased your bellow couplers and what modifications you had to make?

Also where did you purchase your wavy washers and what sizes?

Love your results

Thanks, Brent? ??

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Oh man!? Too funny...? I read your reply too quickly, and I thought you signed your email "Love, Brent".? I'm flattered, but I don't think our friendship is quite there yet! :)? Had a good laugh about it when I realized my mistake.

I got both items at Aliexpress.?


I bought both M6x12x.3 and M5x10x.3.? Currently running the larger ones.? I'm considering stacking these with flat washers to get a little more "spring".


I purchased the 5x6.35 version to fit my 5mm shaft to the 1/4" worm.

The couplings are just slightly too long to fit without any modifications.? Firstly, I had to put a serious bevel on both sides of the coupling.? I did this with the drill press and a file.? This allows the coupling to just sneak into the recess of the worm block, as well as the slight recess where the bearing sits in the motor bracket.? The coupling still won't quite fit, so I also had to shim the motor bracket out slightly.?? You can see the bracket is not quite fully seated against the worm mounting plate.?? I just put a piece of wire in there to tighten up against, but you can really use anything you want.???

In the future, I will probably just drill through the 5/8" pocket where the bearing sits so it can be pushed inward towards the pulley, overhanging just a couple of mm.? This will allow? a larger recess for the coupling to fit in, and I should be able to tighten the bracket properly.? The bearing can be "floating" since it will effectively be kept in place sandwiched between the coupling and the pulley.? I'll put a couple of 1/4" washers on the shaft to keep the pulley from rubbing the outer race of the bearing.

Or maybe this will finally be the push I need to design my own brackets.

I have seen this behaviour in DEC before. It happens more often that not when your scope is on one side of the meridian and pointing right at the zenith. It bounces N/S because it is "hanging down".
Couple of things you can check.

1_ Do you have lateral axial play in your DEC worm.
2_ Is your gearbox shaft to worm coupler secured without rotational play or flex.
3_ This is extreme but older G11 had a bronze bush only (no bearing) mating with the DEC spur gear. So if there is lateral play between that gear and the bush then that can contribute to lateral axial play. It's easy to check. Mesh the DEC worm to the max then tighten the clutch to the max. Move and rotate the DEC saddle plate by hand. If you feel any "click" it's likely something's giving other than the worm.

Anyway check that first and report back see how you go.

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I took the plunge and designed and printed my own tucked motor brackets.? They won't win any beauty pageants, but they're functional and super easy to print.?? For simplicity's sake, I went with an outboard belt drive system hanging off the side.? In the future it should be pretty easy to print up a housing to cover up the belt drive and keep it looking clean.? The inside of the bracket has ample clearance for the extra length of the bellows coupling.? There are two 5mm wide bearings in the housing, with 15mm space between the two, which should be sturdy enough to support the load on the shaft.? The main plate is 13mm thick.? The nema 17 mounting slots should allow for 20:60, 16:60 or even 12:60 gearing with a common 200mm belt.? You can certainly run other ratios with a shorter belt.?? I'm currently running 16:60.?? My stepper motor body is 48mm in length, and the back just clears the altitude knob.

The prototype bracket that's currently installed was printed at 20% infill, and it seems strong enough.? Just the same, I plan to eventually print them in PETG or ABS at 100% infill for strength and rigidity. I'd like to test this prototype under the stars first before I give it the final stamp of approval, but I don't see any obvious cause for worry.? It took five revisions before I finally got the shafts aligned perfectly, but I want to star test them before I'm 100% confident everything is aligned.? Turning by hand, these feel every bit as smooth as the old brackets, and my test slews are nice and smooth.?

Thanks,
-Tony

Marc,? I believe you have hit the nail on the head (so as to say). I believe the cause is item 1 and is caused by lateral axial play in the DEC worm gear with the scope pointing close to the zenith.
Thanks,

For your reply,? Brent

GuitsBoy, would you share the STL file when you are satisfied with it.
I have been working on a modified version of Rockmover's design. But this looks simpler.
I want to add a spring idler pulley to add adjustable tension to the belt, to adjust as
the belt stretches' or the motor loosens slightly by the screws holding the motor in the 3d printed mount.??
Also do you have multiple bearing blocks to keep the large pulley aligned or do you just have one and the coupler
connection with bearing block of the losmandy mount?
Also if a cover can be designed then a PEC sensor can be attached to the main gear axle for PEC input to OnStep.

Thanks? ?Brent

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Hi Brent -

We're getting close, but I still want to star test and make sure it runs well.? I already discovered one oversight.? The big pulley was off center by 1mm, which means it could potentially rub against the inside of the cover.? I just aborted a 17 hour print half way? through once I realized.? I'm re-printing the latest revision now in PETG with 100% infill, and will use the new bracket and cover on the RA axis.?? For now, I'll use the off center bracket on the DEC axis with a big pulley I had previously turned down slightly to reduce the OD for use with the rockmover brackets.? The RA is the more important test, IMO.? Once I know it works, Ill send over the STL files so you can tweak however you want.

The brackets do use two bearings to support the big pulley shaft.? It does not rely on the coupling for stability.? The bearings are separated by 15mm, so the shaft is well supported and stabilized.

Personally, I don't think a tensioner is really necessary.? If the GT2 belt were to stretch to the point where a tensioner would take up slack, the teeth would no longer be a perfect mesh and would likely be contributing error.? But Ive used GT2 belts for a few years now and I've never noticed any stretch at all.? Seems like an unnecessary added complexity in my opinion, but I'm sure you could rig something up if you really want it.

Where would you want to put the PEC sensor??? Are you talking about putting it on the shaft?? Or integrating it into the big pulley?

Here's a few photos of my progress on the brackets:

Thanks,
-Tony

Thanks GuitsBoy,

I apologize, I did not read your first post detailed enough as I was too excited to see the simpler approach over rockmover.
When I read it again I realized it was stabilized. I agree that the idealer pulley probably is not needed. It was just hard to tension
the belt with rockmovers design.
As for the PEC, I believe that as long as the large pulley shaft (attached to the motor) extends out your cover
a PEC sensor (if you want I could send you the url) double backed to your cover and attached to the shaft. Then the correct?
ratio added to the config.sys for PEC.
Thanks for the additional images?

Brent

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Thanks Brent -

If the PEC sensor is directly reading the worm shaft itself, it would be on the large pulley which attaches to the worm itself, and not the motor.? If the PEC sensor can be divided by the appropriate ratio in the config (ie. 1:3.75) then you could have it on the smaller pulley which is connected to? the motor.? I would think having it on the motor would have greater accuracy, but you would have to find a motor with an extra long shaft.?? Putting it on the large pulley side would probably be easier, since you can simply buy a 5mm shaft in whatever length you desire.? Either way, it seems like you would just have to drill through the cover to pass the shaft through.? Sadly I'm a little unfamiliar with how it actually works in OnStep.? I don't run native PEC at all, and only occasionally use the Predictive PEC algo in PHD2.

As for tensioning the belt with this bracket, its very simply.? Just gently hold the motor to one side to tension, and snug the screws with the other hand.? I didnt find rockmover's brackets to be terribly difficult to tension, but since the cap screws are inside the bracket, it might be tougher to get the hex key in? there.? It's certainly tougher to initially put the screws in.

There's a slight chance the clouds might hold off for an hour or two after sunset, in which case I might be able to test the brackets tonight.? Otherwise, wednesday is? the next earliest reasonably clear sky here in NY.

Thanks,
-Tony

Tony (GuitsBoy),
Sorry I was wrong in my PEC description. The sensor is on the big pully with an extended shaft (. The other end directly connects to the worm.
I have used 2 designs where I changed the pulley for a 1/4" shaft (including bearings with 1/4" inside dia) and? used a stiff direct connect to the worm.
Or another design with a pulley with a 5mm shaft?(bearings for 5mm shaft) where I use a coupler to translate to the worm shaft.
The 1/4" design does not allow any flexibility so does not work with a spring load design.
Since I use a MaxPCB, I have to use a EthernetAddOn (OnStep Wiki) which has encoders inputs and PEC input which have to be 3.3v translated to 5v.s for the
PEC sensor and the encoders (AstroDevices G11 sensors).
Sorry all this is probably needless information. But I am seriously interested in you design from issues I have had trying to implement a DIY spring loaded design.

Attached is the rockmover modified gear reduction images with the PEC sensor. I had to lower the case over the large gear to prevent interference with the AstroDeices encoders on the G11 axes.

thanks again? Brent?

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Hi Brent -

The weather did not cooperate last night, so I was unable to star test the thing, but I did play around for a couple of hours in the daylight.? I'm pretty confident these things will work as they should.? I don't feel any added resistance or misalignment, at least on my mount.? It seems to fit pretty well.? If you encounter any slight misalignment, hopefully the fix is as simple as widening the holes just a touch, but for me, it seems a good fit.? If you do try these brackets, please let me know if the fitment was off at all.? And if you have any other suggestions, I'll try and incorporate them.???

I used M3x16 cap screws to mount the stepper motor.? To mount the bracket to the mount I used #6-32 x 1-1/2" cap screws, and to mount the cover use a single #6-32 x 1" cap screw.? The bearings were 625zz, and the shaft was 5mm x 50 to 60 mm long.? The 60T pulleys I used (44mm OD) just clear the housing cover by a fraction of a mm.?? You can turn the pulley down to gain clearance if you need it.

Any questions, let me know.?

Thanks,
-Tony

Thanks soo much,? I currently have ASA filament on the printer. I will try that with 100% infill.
I will let you know how it works and post pictures showing the setup when I get it working.
It looks really great!

Thanks again

Brent

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How do you find ASA is to print??? Do you have an enclosed printer??? The brackets on my mount are currently printed in PETG at 100%, but the added rigidity of ABS or ASA does sound welcome.?? I was going to try the ABS first, but figured it would take a couple of tries to counteract the shrinkage.? Is the ASA any easier in your opinion?? My printer is open, with a heated bed, so probably not ideal for either ABS or ASA.

Best of luck with your build,
-Tony

Tony,
I actually like PETG better. It seems to me a harder plastic and more rigid. But all I have right now is ASA.
I am not an expert on 3d printing but I have not seen shrinkage with ASA.
My printer is open bed also. But I have it in a enclosed room and use a space heater to raise the temperature.?
I have a large 3 sided box around the printer to try to prevent drafts. As such I have seen no issues with ASA.
I printed your DIY spring loaded components in ASA with no issues.

How was your print orientation? Was it as shown in the STL file with the worm side up and the gear side down on the base?

Thanks again I will let you know how it goes. I really appreciate your work.

Brent

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Thanks for the info.?? I guess I'll stick with PETG for now.? Previous PLA+ brackets did start to warp in the sun, but hopefully PETG will stay solid.

Yes, I did print the orientation you describe, so that the largest flat surface is against the print bed.? The only unsupported overhang is the 1mm bearing spacer lip.?? I got some stringing there, but easily cleaned them up with stepper drill bit and dremel when I sized for the bearings.? I had to do similar touching up with other brackets as well, as I'm sure you have.

Always happy to tinker and share.? I hope the brackets work out well for both of us.? Good luck with it.

Thanks,
-Tony

Yes, that was the

As another 3D printer enthusiast, I will chime in with my 2 cents. Nice design you have which can print as shown with no overhangs. Rather than tinkering with slicer settings to deal with shrinkage in holes, I have just taken to pressing them out by 0.1mm to 0.2mm in the original design where fit is critical.

Another strong filament option I use on my gear is "high-temperature PLA". I specifically have been using Veracity ProPLA from Filastruder. Prints like PLA but at a higher temp 230C / 60C, and tolerates exposure to sun and hot car as well as PETG.? Personally, I would avoid 100% infill. You get good strength with 50% infill or less and 4 or 5 layers on the base and walls. Dimensional consistency I have found to be better with partial infill.
--
Edward

SO I think (and this just my opinion/experience) when I printed the modified rockmover design with PETG, it did not appear to warp.
It might because the thickness of the walls. But when I used PETG to print thinner case walls for my electronics after a period of
time they did warp unless it was held together by a cover. It might be the moisture/heat that causes it to wrap. I have not tried ASA for cases yet
but mainly thick designs.?
I am just a novice at this :-)?

Thanks Brent

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Thanks for your suggestions, Edward.? Any idea what the glass transition temperature might be?? From your comments, I suspect somewhere around the same as PETG, maybe 85c or so?? My google searches turn up results for regular PLA.

My initial fitment test prints were done with PLA at 10% infill, and while I did notice the 100% PETG resulted in the screws being slightly snug against the holes, it still appears to locate the worm shaft well.? There is a small amount of free space in the pocket (.5 mm) where the worm mounting plate sits, so that dimension is not critical.? We really only need to center the big pulley shaft (actually just off-center) between the two mounting holes.? So if the distance between holes shrinks ever so slightly, the shaft should still be more or less centered.? Please let me know if my thinking is flawed here.

If I find myself re-printing the brackets again, I'll give 50% infill a try.? If it doesn't seem sufficient, perhaps I'll simply beef up the bracket design.? At the very least, 50% infill would be a better use of material, gram for gram.? I really don't know how much rigidity is required here for tracking accuracy.? The actual delivered torque on a well balanced scope is probably quite low.

Thanks again for your comments,
-Tony

Hi Brent -

I was able to test the new motor mounts last night, and they seem to have worked well.? We had a nearly full moon, and poor 2/5 seeing conditions, but nothing jumped out at me as an obvious problem.? The mount was happily guiding at .8 arc-sec rms at 23? above the south horizon.? Fairly challenging conditions to guide through, for certain, so I was quite happy with anything under an arc-sec.

I think I'll wait for you to test the brackets out as well, and if they work for you too, Ill make them available on Thingiverse, along with the spring loaded worm components.

Thanks,
-Tony