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freiform

Looking for rotator idea / design / approach

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Hi,

while having enough projects as it is, I thought about a computer controlled rotator for proper object framing. The electronics and software side should be relatively easy, using a small microcontroller, stepper driver and motor,  and a few odds and ends.

But how about the mechanics? Let's say I want to fit something between my small refractor (Lacerta 72/432) and a DSLR, I have M54 inside thread on the focuser and a standard T-2 (inside) or canon bayonet on the Camera. How would I go about that? Would it feasible to get a cheap manual rotator (i.e. [1])? It's relatively narrow, but maybe sufficient to fit a belt?  How about 3D printed parts? But I suppose the threads will be problematic and I do not know if PLA is the right material for the job.

There seem top be DIY focusers and mount controls in abundance, but rotators apparently are a relatively scarce species? 😁

Ideas and opinions are appreciated!

Sven

 

https://www.firstlightoptics.com/adapters/sky-watcher-camera-rotator-for-evostar-72ed-ds-pro.html

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Not sure if this is going to help, but I suspect that motorized rotator is not going to be easy thing to make - at least not by adapting simple mechanical one.

In order to have relatively smooth rotation, mechanical rotators have certain slack between parts and also screws to tighten it to prevent any accidental rotation (due to gravity or cable snag). These screws remove any further slack when tightened (no rotation possible without use of excessive force) - it is a bit like focuser lock screw which is not used with motor focusers as they are expected to hold focuser in place by holding torque.

Holding torque will hold rotator in place - prevent any accidental rotation same as with motor focusers, but in order for it to work and have no tilt - you need a design with some sort of ball bearings to allow for rotation - simple design like mechanical rotator will probably have tilt if you loosen up screws and leave them loose and rely on motor holding torque to stabilize rotator.

Here is idea of mechanical side of things, fairly "simple design" - and you can adapt it to both worm drive or belt:

image.png.44d2b9a0ddc017359256d138af589fae.png

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Posted (edited)

That is a nice design, but unfortunately beyond both, my tools and capabilities.

On the other hand, I would have to find two tubes with fitting threads, or maybe print tubes an adapt them some other way. I guess that the worm and gear can also be printed, with precision in rotation not being as important as with mount control. The bearings I found with a quick search seem too thick (outer - inner diameter), but I suppose there is something available somewhere, I just don't know the proper terminology. Maybe a slide bearing might also be feasible? 

 

/edit

found thin-section bearings that might do the job..

Edited by freiform
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I looked at this a while back. I concluded building it round a light weight roller bearing would be the way to go with stepped a belt drive similar to focusing a helical focuser on a lens.

Regards Andrew 

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I looked into this a few years ago using vintage SLR camera lenses for a widefield rig with ASI1600MM-Cool camera.  Because of the extreme accuracy required in the optical path, the camera, EFW and lens must be rotated as one unit including the remote focus system for the lens.  This turned out to be a large turret assembly.  I decided in the end to abandon remote rotation and just set up framing manually.  This is the thread.

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Have you considered a RC Servo? They are very easy (if you know how..) to control with a processor and are quire powerful in the larger sizes.

Sometime ago I made a rotator using just such a device. Pics attached

20190815_132021.jpg

20190815_132008.jpg

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Posted (edited)
18 hours ago, Gina said:

I looked into this a few years ago using vintage SLR camera lenses for a widefield rig with ASI1600MM-Cool camera.  Because of the extreme accuracy required in the optical path, the camera, EFW and lens must be rotated as one unit including the remote focus system for the lens.  This turned out to be a large turret assembly.  I decided in the end to abandon remote rotation and just set up framing manually.  This is the thread.

My refractor has one screw that fixes the focuser.  If I loosen this, I can rotate the focuser and everything attached to it. My point being, I never had to readjust besides maybe refocusing, so I don't see issues with the optical path. Am I missing something?  

 

18 hours ago, Tomatobro said:

Have you considered a RC Servo? They are very easy (if you know how..) to control with a processor and are quire powerful in the larger sizes.

Sometime ago I made a rotator using just such a device. Pics attached

Mhh, what are you rotating? I guess the motor itself is not the issue at this point 😁

4 hours ago, rpineau said:

You might want to take a look at this https://github.com/cytan299/field_derotator

 

 

2 hours ago, redtail said:

Those look interesting, especially the one on scopefocus. I am not quite sure on what it is actually rotating on, though. Do they already have a manual rotator in place, like [1]?

 

[1] https://teleskop-austria.at/CAA-1_Takahashi-TKA21200-Kamerarotator-fur-FS-60C-FC-76-Sky

 

 

/edit

For reference, it seems the actual term is AAC (Camera Angle Adjuster) rather than rotator.

Edited by freiform

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