Idea for 3D printed motorized Bahtinov flip mask

[bojan]

I think I will try to print this for my C11 on first occasion..

The original idea was to print 4 segments, but then I realized 3 or even only 2 will be enough to produce usable diffraction pattern.
The flip segments will be fixed on the steel rope ø1 mm (purple), which will act as a flexible shaft, moved by DC motor.
It is a pity MyFocuserPro currently does not support mask.. Maybe one day it will :-)

EDIT:
It just occurred to me the steel rope could be used as a heater..

[AlexN]

Thats cool!

Purely aesthetically, I think the 3 segment design is best - im sure optically 2 would do the job just fine!

What would be cool is an integrated bahtinov mask + flat panel + scope cap.

You could make the 3 circles of the bahtinov mask slightly smaller, and integrate them into one ring, and have the front cap with 3 sub-apertures in it... Rotate the mask rim to the full right limit = sealed cap, rotate to the full left limit = 3 sub-aperture bahtinov mask.

A secondary motor to flip the whole thing out of the way once focus is achieved.

Weight could be a concern, but then on a C11, all your weight is at the rear of the scope anyway, adding a bit to the front wont necessarily hurt...

[bojan]

Hi Alex,

Thank you for reminding me of this project, I almost forgot about it :P

Yours is very interesting idea, I will think about it.. it may be doable to integrate diffraction masks into lid as frame, with motor to flip "mask / no-mask".
As to scope cap, I was thinking about larger one to cover this contraption.. but my 3D printer is a bit small for this (175x175mm), so something big like that must be printed in segments and assembled (glued) later.. and this may compromise the accuracy a bit... probably not enough to preventing it working as lid anyway.

Flats I usually take on the sky before sunset.. so flat panel is lower priority for me at the moment :-)
Anyway.. I started printing it right now.. when finished, and if it fits OK, I will put stl files here.

[bojan]

Well, it works OK... especially with brighter stars (I expected that).
Unfortunately, my original measurements were in error, so the ring turned out too small (~6mm..).. so I will have to print the whole thing again.
I also found suitable motors (https://www.ebay.com.au/itm/385140211523?hash=item59ac253f43:g: zKQAAOSwYSNjNBpV&amdata=enc%3AAQAIAAAA4NP7BrrGrZJzA6 HsZol9GDN9fJIKf2lBjToCUhcUkd7Dait4f 3%2Fv%2B5rNWmJDqNk4ASPeeRiEWH39obc0 E8lnFr1QPcIsRYxpRPiBE%2F9KUY%2BkuhV mSK%2FJI4wsnn3b1rG%2FBrRcB1d%2Bh04U JBuqt%2FKPev1C4oqCeeREzgLlZlCrol8CG E47wWXFW3PwKIpW711pMYhJ0mb1BuMYvDAG Y2NLcU8Zkrm8LHn5uyEn3KL%2F3Virqftrr gvAVptP0z7ngJ2UrRYRuHR%2FiiBlFzsbx3 3zNosTggU%2F2FbmtCbUmPkhXWUN%7Ctkp% 3ABFBMut_PtKpj)...

[bojan]

Control circuit will be simple DPDT relay with additional diodes and limit switches (like on attached schematic), or USB relay board (https://au.banggood.com/8CH-Channel-12V-Computer-USB-Control-Switch-Free-Drive-Relay-Module-PC-Intelligent-Controller-p-1533752.html?cur_warehouse=CN&rmmds=search) (application works only with 32-bit windows, which is OK with me).

[bojan]

After some more experimenting, I changed the concept somewhat..
This mask has larger area (so diffraction spikes will be more prominent) and when not in use it fits under the original C11 lid.
During exposure, each half of the mask is folded around shaft inside dew cap.
I plan to add the end parts as well, to make the mask completely cover the aperture when used.. but a trouble adding those additional 8 slits and hinges may not be worth really..

[bojan]

Printing mechanicals.. Bracket for motor (with gearbox), mask hinge will be on the shaft ø2 mm, also visible on image.

I am still not entirely sure what the electricals will be like, motor needs only 1~1.2 V to rotate with acceptable speed, so there will be a need to regulate Supply voltage to that value.

Also, because of gearbox, the moment is pretty high, and I definitely don't want to crash the mask into C11 corrector plate.
So the limit switches will have to be very reliable and precisely adjusted.
I will do it with camshaft and ø1.5 mm pin, which will operate limit switches (hopefully realiably).

[AlexN]

That new design is looking really good mate. I love it...

I'm looking at 3d printers to start tackling some small projects I have planned.. similar sort of things to this, and brackets to hold equipment to my scope/mount.

Any recommendations on a decent starter/intermediate 3d printer?

[bojan]

Alex,

I don't know.. I built my own, more that 10 ago, and I still use it.
Have a look at ebay... Jaycar had a good one couple of years ago.
I think any will do, provided it has heated plate and filament motor next to printing head.. they are going for 400~500 AUD

[bojan]

This is what the assembly may look like after I print the flaps..
Also it may turn out a single motor will suffice..

[bojan]

Testing how critical parts fit into assembly...
So far so good.

[bojan]

While waiting for some parts to repair 3D printer, I tried to use test printouts done when it was working OK. I assembled them by gluing them together with acetone..
On the image, limit microswitches are visible. Diodes are below switches, inside the bracket cavity.
If that proves to be functionally OK, I may even decide to keep them as finished product :-)
However, I still need to print the BM flaps.. this has to wait for printer to work OK, hopefully soon (next week).

[bojan]

3D printed behaves again.

Test with partially printed flaps, to see how everything fits together (the white collar is only here so hinges are oriented properly and at right distance, it will not be mounted on C11.. (maybe it will))

[bojan]

How to prevent the mask falling on the corrector plate, and to force it to fold at the appropriate angle into bracket.

[bojan]

After wiring and a bit of adjustment of limit switches height, it works OK.
It takes ~2 sec to open/close the mask.
Power adapter is 3.3V.
At the moment. I am using 2x3 toggle switch to activate the mask (it provides alternate voltage polarity). Later, it will be done via USB relay board, from desktop computer (already used to control the mount)

Now I need to print the mask segments.

[AstroViking]

This is coming along really well, Bojan.

[bojan]

Yes.. slowly.. But surely :-)
The mask (as it is now) is ready for test on telescope (probably next weekend, if weather permits).

[bojan]

Test.. Video (zipped webm file) is attached.

[bojan]

Final version of electro-mechanical assembly.. movement is very repeatable, limit switches are individually adjustable but apparently there is no real need for that. Power comes from 2xAA or AAA batteries (3V) via DPDT switch (to control polarity).

Both assemblies will be mounted opposite of each other and tightened with 2xM3 screws (used for corrector front ring, they are long enough to accommodate additional 4mm).
The whole thing fits under the cover, however, I am not sure if cable can be mounted permanently (without drilling into scope ring), so perhaps I will have a connector.. and anyway for the each session I have to remove the cover and place the dew shield.. so additional effort to connect cable will not be a problem, it is done with telescope in park position.

The next step is to control the mask from computer via USB relay board and power adapter... one day :-).
Once all is properly tested, I will post stl files.

[bojan]

Assembled to C11, works..

I just need to sort wiring and connect that to PC in the observatory.. and no more climbing on ladders in the dark :-)

[AlexN]

Thats an awesome result mate! I love it!

[bojan]

Thank you Alex for kind comment.
I will place stl files here later, in case somebody wants to do their own printing.

[Leo.G]

That's looking very good Bojan!
I was going to ask about the added mass when looking at your images but I see they were close up images and it's a big tube, the small amount of weight is nothing to it.
Is there any way it can misalign and cause issues (make it hard to get focus) if it's misaligned?


The mention of climbing ladders in the dark, my son has always had hearing related balance issues and I'm just an old fool so the small step ladder I purchased to use with my Newt I added some red LED lights along the front of the bottom step and an 18650 battery holder under the step. If I take the Newt and ladder out it's as simple as slipping a single (or twin, I don't remember) 18650 battery in the little holder and I always know where the bottom step is in the dark. Simple but very effective solution, more so in my sloping back yard. My ladder isn't exactly a step ladder and has a decent bar on the back to hold, it's more like a platform ladder I guess (if there's such a thing). But it IS very easy to lose orientation in the dark and you mentioned you're 10 years older than I am and I know my overall balance and reaction times are not what they used to be.

[bojan]

Hi Leo,
Small misalignment is not the problem.. see attached image (taken last weekend), when both sides of diffraction pattern are symmetrical, focus is there.
And... I also have a balance problem (after nasty inner ear infection 10 years ago) and I am actively avoiding situations that could result in dis-orientation and fall.
So any gadget that enables me to do things in observatory remotely is good.. There will me lots more in the future.

[Leo.G]

That's working well then Bojan.


You've probably mentioned, what motors and gearing are you using and how is the torque?


Yes imbalance is no fun, my sons middle ear never formed (a condition also known as Large Vestibular Aqueduct Syndrome) so not only was he born deaf (recovered a small amount of hearing in one ear with grommets when he was 4, we had no idea because he taught himself to lip read as a a baby) and NO ONE believes he is deaf when they hear him speak.

[bojan]

Wiring mod for Relay PCB (https://www.aliexpress.com/item/1005006781536777.html?spm=a2g0o.pro ductlist.main.1.32d1QUDDQUDDXU&algo_pvid=052c55ae-049a-4f29-acd3-3511c1eaa0d8&algo_exp_id=052c55ae-049a-4f29-acd3-3511c1eaa0d8-0&pdp_npi=4%40dis%21AUD%2117.88%215.7 2%21%21%2182.52%2126.41%21%402101c7 2a17319055016056352e747a%2112000038 278707474%21sea%21AU%21866261649%21 X&curPageLogUid=W1bmfN8RIyMg&utparam-url=scene%3Asearch%7Cquery_from%3A) .. and motors used.

[bojan]

As to software.. it was not easy to find a right application.
It seems there are couple of versions.. some work, some don't.

The one I started to use I found here (https://info.kmtronic.com/usb-8-relay-software.html), it seems to work only on 32-bit machines (which is OK with me, my desktop in observatory is HP Compaq 32 W'7).
There is also source provided, so it is possible to tailor it to one's taste.
And, the remaining 6 relays could be used for other functions, like open-close the ROR, heater, filters... etc.

The other one (RightBoot) (https://www.rightbooth.com/relaycontroller.html) is not free (there is annoying eval mode before you pay) works on only W'10 (and up.. it doesn't work on W'7 64-bit).

[bojan]

Fitted on ADM bar with 3D-printed brackets..

[bojan]

Wired and functional, both local and remote (from desktop).

The functionality is similar to two corridor lights.. I can open mask locally (by using switch on battery compartment (3V, I will have down-regulator later), and then close it from desktop.. or other way around, as convenient.