3D printed star tracker

[Elp]

If you want inspiration for simple the Omegon LX is one of the simplest tracking mounts I've seen, all mechanical no belts, and it works quite well for widefield.

Edited August 9, 2022 by Elp

[vlaiv]

Just an update.

After about 15h of printing, I'm currently here:

right is proof of concept worm wheel for azimuth adjustment of equatorial wedge - left is actual assembly being, well, assembled

I seem to started suffering from moist filament, so need to sort out drying before I proceed (a lot of zits, blobs and increased stringing). Next is well - worm itself and rest of the housing including clutch for locking of azimuth motion.

Here is design so far:

I still haven't done rest of it - hopefully this week.

Bill of material so far: x2 608, x1 6006, x1 51108 - those are standard bearings (very cheap).

As far as I can see - I'll probably need x3 more 608 and couple of 6005 for wedge itself.

Some M4 and M5 nuts and bolts and M5 threaded rod (about 10cm of it so far).

I think that wedge will be usable on its own - for mounting SA or AZ-Gti. Not sure of carrying capacity though.

[Thalestris24]

Cool project, Vlaiv! Might metal gears be better and more rugged? I'd have thought the Star Adventurer, or similar, gears would be easily obtainable? (Though I admit I've no idea really.) Then you'd just need to make the housing/add a motor etc.?

Re: Filament absorbing moisture. If you get some large ziplock plastic bags (47 x 33 cm) you can store/dry filament by including a few handfuls of silica beads in a small porous/mesh bag. I find I can quickly and easily dry the beads for re-use in my microwave oven . 

How are you finding FreeCAD? My educational Fusion 360 is about to expire so I might switch to FreeCAD. I'm not sure what I might lose by using the hobbyist Fusion 360 instead - especially with things like threads and custom threads. I suspect it's not easy to create T2 threads in FreeCAD but I'll have a look.

Cheers

Louise

[pipnina]

5 minutes ago, Thalestris24 said:

Cool project, Vlaiv! Might metal gears be better and more rugged? I'd have thought the Star Adventurer, or similar, gears would be easily obtainable? (Though I admit I've no idea really.) Then you'd just need to make the housing/add a motor etc.?

Re: Filament absorbing moisture. If you get some large ziplock plastic bags (47 x 33 cm) you can store/dry filament by including a few handfuls of silica beads in a small porous/mesh bag. I find I can quickly and easily dry the beads for re-use in my microwave oven . 

How are you finding FreeCAD? My educational Fusion 360 is about to expire so I might switch to FreeCAD. I'm not sure what I might lose by using the hobbyist Fusion 360 instead - especially with things like threads and custom threads. I suspect it's not easy to create T2 threads in FreeCAD but I'll have a look.

Cheers

Louise

I couldn't find a spare part listing for the main worm-driven gear, but the motor-to-worm gear train replacement parts are about €35 and a worm gear replacement is €45 for EQ5 tier mounts! They are made of brass and low volume however so not surprising that they are expensive.

[vlaiv]

4 minutes ago, Thalestris24 said:

Cool project, Vlaiv! Might metal gears be better and more rugged? I'd have thought the Star Adventurer, or similar, gears would be easily obtainable? (Though I admit I've no idea really.) Then you'd just need to make the housing/add a motor etc.?

Re: Filament absorbing moisture. If you get some large ziplock plastic bags (47 x 33 cm) you can store/dry filament by including a few handfuls of silica beads in a small porous/mesh bag. I find I can quickly and easily dry the beads for re-use in my microwave oven . 

How are you finding FreeCAD? My educational Fusion 360 is about to expire so I might switch to FreeCAD. I'm not sure what I might lose by using the hobbyist Fusion 360 instead - especially with things like threads and custom threads. I suspect it's not easy to create T2 threads in FreeCAD but I'll have a look.

Cheers

Louise

Hi Louise

I sorted moisture with one of those Ikea samla cases with silica beads inside and little hygrometer to tell me relative humidity (it sits at 10% which I believe is minimum for device). There I store filament when not in use. I also used food dehydrator initially  without any modifications for few hours and it really helped to get things started in right direction.

In fact that set me off to whole new direction with my 3d printing / modding. I'm in the middle of Ikea lack enclosure build. I added banana pi for running Klipper firmware (made mistake of going with Banana pi M4 - which is not well supported as far as OSes go - so I ended up using Ubuntu 16.04 and upgrading it to 20.04 just to be able to install all that is needed for klipper + fluidd).

Right now I'm finishing electronics enclosure for Banana PI + step down voltage converter and will move on to print electronics enclosure for small MeanWell PSU that will power BPI, air filter fan and LED strip for lighting

above is banana pi enclosure with mounting system being ready to install on outside of enclosure

For that reason, star tracker project is a bit on a hold, but will continue soon.

Not sure I want to use any sort of metal gears if they are not very cheap and easily accessible everywhere. Aim of the project is to be able to print star tracker almost anywhere in the world (like no need to import things - only purchase locally in hardware store).

As far as FreeCad goes - I find it very useful, or rather - I leaned to use it properly after all this time and now I don't even think about it. Sure, there are always some new things to be learned - but it is quite powerful tool. Just few days ago I leaned how easy it is to create technical drawings from 3d designed objects:

Piece of cake really.

As far as threads go - I do my own threads and it is easy in FreeCad, but maybe a bit involved as you need to draw your own profile.

I simply draw profile of single tooth - for either nut or bolt and then do helix revolution of it - either additive if bolt or subtractive if nut. Metric threads are really easy to make - 60 triangle is base. I use this page whenever in doubt:

https://en.wikipedia.org/wiki/ISO_metric_screw_thread

I don't like tool that is offered for threads in FreeCad as it uses some sort of Bezier curves and threads end up not looking good.

[Thalestris24]

1 minute ago, pipnina said:

I couldn't find a spare part listing for the main worm-driven gear, but the motor-to-worm gear train replacement parts are about €35 and a worm gear replacement is €45 for EQ5 tier mounts! They are made of brass and low volume however so not surprising that they are expensive.

Oh ok, I was thinking more in terms of generic parts that could be made use of. As I've never looked, I accept you're probably right! At the same time I intuitively feel someone must have made a star tracker from scratch before somewhere.... There are some projects on Thingiverse but, yeah, all also seem to use printed gears. However, presumably the aim is to control the tracker at a sidereal rate so that could be controlled by an Arduino-type processor, stepper motor and the control pulses adjusted for whatever the worm/gear/stepper motor combo allows? I'm just thinking out loud - I've probably missed something obvious! I'm so out of touch with astro things these days! I do have a motorised rail which I use for a microscope and which allows microsteps in the micrometer range.

Louise 

[Thalestris24]

3 minutes ago, vlaiv said:

Hi Louise

I sorted moisture with one of those Ikea samla cases with silica beads inside and little hygrometer to tell me relative humidity (it sits at 10% which I believe is minimum for device). There I store filament when not in use. I also used food dehydrator initially  without any modifications for few hours and it really helped to get things started in right direction.

In fact that set me off to whole new direction with my 3d printing / modding. I'm in the middle of Ikea lack enclosure build. I added banana pi for running Klipper firmware (made mistake of going with Banana pi M4 - which is not well supported as far as OSes go - so I ended up using Ubuntu 16.04 and upgrading it to 20.04 just to be able to install all that is needed for klipper + fluidd).

Right now I'm finishing electronics enclosure for Banana PI + step down voltage converter and will move on to print electronics enclosure for small MeanWell PSU that will power BPI, air filter fan and LED strip for lighting

above is banana pi enclosure with mounting system being ready to install on outside of enclosure

For that reason, star tracker project is a bit on a hold, but will continue soon.

Not sure I want to use any sort of metal gears if they are not very cheap and easily accessible everywhere. Aim of the project is to be able to print star tracker almost anywhere in the world (like no need to import things - only purchase locally in hardware store).

As far as FreeCad goes - I find it very useful, or rather - I leaned to use it properly after all this time and now I don't even think about it. Sure, there are always some new things to be learned - but it is quite powerful tool. Just few days ago I leaned how easy it is to create technical drawings from 3d designed objects:

Piece of cake really.

As far as threads go - I do my own threads and it is easy in FreeCad, but maybe a bit involved as you need to draw your own profile.

I simply draw profile of single tooth - for either nut or bolt and then do helix revolution of it - either additive if bolt or subtractive if nut. Metric threads are really easy to make - 60 triangle is base. I use this page whenever in doubt:

https://en.wikipedia.org/wiki/ISO_metric_screw_thread

I don't like tool that is offered for threads in FreeCad as it uses some sort of Bezier curves and threads end up not looking good.

With ziplock plastic bags it's simple as you can see the beads and if they've darkened! In practice, small amounts of moisture in filament aren't critical. I have some black pla filament which I've had on the printer for quite a few months and it's still ok. I will put it in a bag for a few days soon though!  

Louise

 

[pipnina]

28 minutes ago, Thalestris24 said:

Oh ok, I was thinking more in terms of generic parts that could be made use of. As I've never looked, I accept you're probably right! At the same time I intuitively feel someone must have made a star tracker from scratch before somewhere.... There are some projects on Thingiverse but, yeah, all also seem to use printed gears. However, presumably the aim is to control the tracker at a sidereal rate so that could be controlled by an Arduino-type processor, stepper motor and the control pulses adjusted for whatever the worm/gear/stepper motor combo allows? I'm just thinking out loud - I've probably missed something obvious! I'm so out of touch with astro things these days! I do have a motorised rail which I use for a microscope and which allows microsteps in the micrometer range.

Louise 

Ah fair point.

I found some brass worm gear sets on ebay for pretty cheap. But they are only 1:60 ratio so they'd probably need to be "doubled up" in some way as big mounts have several hundred to 1 gear ratios.

https://www.ebay.co.uk/itm/203162743596

I guess 3D-printed large gear attached to the worm and a smaller 3D-printed gear on the motor, with a belt between them would be pretty cheap in component parts to boost the ratio up to 200:1 or so?

Belts are pretty cheap from the rowan set so maybe it could work? https://www.firstlightoptics.com/rowan-astronomy-mounts/rowan-astronomy-sky-watcher-heq5-pro-spare-belt.html

To be honest your idea makes a lot of sense.

[Thalestris24]

1 hour ago, pipnina said:

Ah fair point.

I found some brass worm gear sets on ebay for pretty cheap. But they are only 1:60 ratio so they'd probably need to be "doubled up" in some way as big mounts have several hundred to 1 gear ratios.

https://www.ebay.co.uk/itm/203162743596

I guess 3D-printed large gear attached to the worm and a smaller 3D-printed gear on the motor, with a belt between them would be pretty cheap in component parts to boost the ratio up to 200:1 or so?

Belts are pretty cheap from the rowan set so maybe it could work? https://www.firstlightoptics.com/rowan-astronomy-mounts/rowan-astronomy-sky-watcher-heq5-pro-spare-belt.html

To be honest your idea makes a lot of sense.

Yeah a Rowan belt setup is quite good - works great on my HEQ5 Pro  But I was thinking of something different which I'm now not sure if it could easily be done - it was just a thought that flitted across my mind. I'm probably overcomplicating things! I have one of these focus rails that I bought a few years ago. As you can see, they don't come cheap but probably much cheaper if you just buy individual generic components. The magic is in the usb controller and software which allows a high precision of control (microstepping). But... It's a linear rail and I'm not sure if it would easily translate into a worm gear type setup. You can get less precise, but very similar, parts as spares for 3D printers e.g. Lead Screw on Ebay. However, thinking about it, being linear they can't easily be used in the same way as a normal gear ratio rotating system - unfortunately.  They could maybe be used for a precision 'barn door' type setup. When I first started in astronomy, I did consider making a barn door thingy but decided an equatorial mount would be an awful lot better - once I could afford one! But then I didn't know about precision lead screws and stuff. There's always more than one way to crack a nut!

Louise

[vlaiv]

I've already settled on type of reduction for this star tracker.

It will be either split ring planetary gear type or cycloidal drive.

These can both be made very compact.

Worm gear above is meant only for fine/precise alt azimuth adjustment of polar wedge for star tracker.

Actual drives that will move the tracker will be one of these types:

https://www.youtube.com/watch?v=aTiBB2n-pNQ

or

https://www.youtube.com/watch?v=-VtbSvVxaFA

Reduction needed is order of 200:1

This can be easily calculated depending on needed arcsecond per micro step precision. I went with something like ~1"/micro step for star tracker (AZGti has 0.6"/micro step for example).

360 x 60 x 60 = 1296000 arc seconds in single revolution

200 steps per revolution for 1.8 degree stepper, and if we say use 32 micro stepping we get 6400 micro steps per revolution.

1296000/6400 = 202.5

So we need exactly 202.5:1 if we want to get 1"/micro step

200:1 is easily achieved in two step reduction - 1:10 x 1:20 for example, or even in single stage for split ring compound planetary gear thingy.

For full tracker (AzGTI type device) - I'd go with cycloidal drive + 1:7 belt as final stage to offset motor shaft from output shaft, so cycloidal drive would need to be something like 1:30 which is easily achieved.

[Thalestris24]

20 minutes ago, vlaiv said:

I've already settled on type of reduction for this star tracker.

It will be either split ring planetary gear type or cycloidal drive.

These can both be made very compact.

Worm gear above is meant only for fine/precise alt azimuth adjustment of polar wedge for star tracker.

Actual drives that will move the tracker will be one of these types:

https://www.youtube.com/watch?v=aTiBB2n-pNQ

or

https://www.youtube.com/watch?v=-VtbSvVxaFA

Reduction needed is order of 200:1

This can be easily calculated depending on needed arcsecond per micro step precision. I went with something like ~1"/micro step for star tracker (AZGti has 0.6"/micro step for example).

360 x 60 x 60 = 1296000 arc seconds in single revolution

200 steps per revolution for 1.8 degree stepper, and if we say use 32 micro stepping we get 6400 micro steps per revolution.

1296000/6400 = 202.5

So we need exactly 202.5:1 if we want to get 1"/micro step

200:1 is easily achieved in two step reduction - 1:10 x 1:20 for example, or even in single stage for split ring compound planetary gear thingy.

For full tracker (AzGTI type device) - I'd go with cycloidal drive + 1:7 belt as final stage to offset motor shaft from output shaft, so cycloidal drive would need to be something like 1:30 which is easily achieved.

I wish I could print so precisely! All the gear ratios and cycloidal drives are beyond me! Looking forward to seeing the finished article though!

Louise 

[kbrown]

3 hours ago, vlaiv said:

As far as threads go - I do my own threads and it is easy in FreeCad, but maybe a bit involved as you need to draw your own profile.

I simply draw profile of single tooth - for either nut or bolt and then do helix revolution of it - either additive if bolt or subtractive if nut. Metric threads are really easy to make - 60 triangle is base. I use this page whenever in doubt:

https://en.wikipedia.org/wiki/ISO_metric_screw_thread

I don't like tool that is offered for threads in FreeCad as it uses some sort of Bezier curves and threads end up not looking good.

A long time ago I wrote a FreeCAD macro to create metric threads. It's nothing fancy but it's worked okay for me so far with all sorts of sizes. I'd have to do a bit of cleaning up work on the macro but happy to share if you like?

[vlaiv]

26 minutes ago, kbrown said:

A long time ago I wrote a FreeCAD macro to create metric threads. It's nothing fancy but it's worked okay for me so far with all sorts of sizes. I'd have to do a bit of cleaning up work on the macro but happy to share if you like?

That would be interesting to see.

I haven't written any macros in FreeCad yet, but I think it can't be that hard if it uses python or similar.

[kbrown]

4 hours ago, vlaiv said:

That would be interesting to see.

I haven't written any macros in FreeCad yet, but I think it can't be that hard if it uses python or similar.

Yes it's Python. With the Python console open in FreeCAD you'll get an idea on what's going on under the hood when you use the program. I added a simple UI with PyQt to my macro as well. Anyway... I'll do some house cleaning on the macro and post here soon.

[kbrown]

Here we go. Just extract the contents of the zip file into your macro folder (in my case ~/.local/share/FreeCAD/Macro) and it should become available to FreeCAD under the menu Macro / Macros... When you launch it you should see an UI like this:

Internally the macro creates a sketch for the thread profile and a helix path object. The profile is then swept along the helix to create the thread. It will also create a cylinder and do a boolean union (fusion) of the swept geometry and the cylinder.

As a bit of a caveat it will do the same thing even if you choose "Internal" thread mode. The difference is how the tolerance value is handled. The resulting geometry is meant to be used as a cutter to another object (e.g. a nut or something). I should really have it to generate a proper internal thread instead of this intermediate thingy.

Nonetheless, hope it's useful...

thredster.zip

Edited September 20, 2022 by kbrown

[vlaiv]

9 hours ago, kbrown said:

I should really have it to generate a proper internal thread instead of this intermediate thingy.

Not sure if there is any difference.

You can either take cylinder and helix sweep and subtract both or you can subtract helix and then add helix sweep - difference is just the profile that is used.

[Thalestris24]

Looks like I'll be able to continue with the Fusion 360 after all  It says the personal license has a limitation of '10 documents' which seemed a bit restrictive. But when I asked, they clarified and explained it just means you can only have 10 designs open at a time. Since I mostly only work on one or two things at a time, that's not a problem. It's just coming up to 3 years since I first bought a 3D printer and started with the Education Fusion 360 License - both items just to make the Lowspec spectrometer! I've found having a 3D printer so useful for other things, especially as I'm a compulsive tinkerer!

Louise

[vlaiv]

36 minutes ago, Thalestris24 said:

I've found having a 3D printer so useful for other things, especially as I'm a compulsive tinkerer!

Oh, yes!

I'm actually struggling to keep the flood of ideas at bay, keeping sort of backlog of things I need to print

[Alien 13]

On 21/09/2022 at 18:32, vlaiv said:

Oh, yes!

I'm actually struggling to keep the flood of ideas at bay, keeping sort of backlog of things I need to print

Me too, it starts with a look at other hobbies that might be useful for parts like Cine follow focus systems, camera cage parts, RC cars and aircraft etc and before you know it you are down another "rabbit hole"😃

My big project is still under consideration but will involve robotics and harmonic type drives but fear the cost could be astronomical if I start... a small version of Boston Dynamics "Spot".

Alan

Edited September 24, 2022 by Alien 13

[Thalestris24]

Any news / progress on the star tracker, Vlaiv?

Louise

[vlaiv]

7 hours ago, Thalestris24 said:

Any news / progress on the star tracker, Vlaiv?

Louise

I'm afraid not.

I've taken on too much DIY projects (finishing enclosure for 3d printer and modding it) and on top of that we are finishing top floor of the house (floors, doors, electrical appliances) so I'm all over the place at the moment and most of side projects have been put on hold last few weeks.

Hopefully, I'll have more time by the end of November to get it going again.

[Thalestris24]

1 hour ago, vlaiv said:

I'm afraid not.

I've taken on too much DIY projects (finishing enclosure for 3d printer and modding it) and on top of that we are finishing top floor of the house (floors, doors, electrical appliances) so I'm all over the place at the moment and most of side projects have been put on hold last few weeks.

Hopefully, I'll have more time by the end of November to get it going again.

Ahh busy, busy, busy! No worries - take care and all the best!

Louise

[vlaiv]

Update:

I'm not sure if I'm going to pursue this any further.

It looks like I'm hitting the wall, both on budget and on my design skills - at least that is what it seems at the moment.

I designed and 3d printed 179.2:1 split ring compound planetary gearbox - and thing is huge.

Here is image of it next to RPI pico and drv8825, sitting on top of nema 17 stepper.

Yep - there is nema 17 stepper under all that plastic

If you don't believe - here is another image from different angle:

Now you can appreciate the size of the thing - combined with nema 17 motor - it is already as large as something like AzGTI - and that is only power train - no housing for the tracker itself.

Cost is also slowly building up. In that gearbox I have something like 7e worth of bearings, stepper is another 10e, electronics so far are about 10e as well - and that is just on breadboard - no custom PCB or anything like that. I'm still missing 12V to 5V reducer (another say 2e).

There might be up to 5e worth of plastic in above gearbox.

I'm probably going to need additional 10e of bearings for wedge and tracker case, and when I'm finished - I think that I'll miss the 50e mark by maybe 50% or even more - and the thing is going to be huge by the looks of it

Main problem is lack of stock thin bearings that have large bore diameter. I can source them locally - but they start from 10e a piece and run up to 30-40e or even more.

I might turn to AliExpress for these - but that is 1-2 months wait on goods - so its going to be slow process (I'm already waiting for few things - like green laser to test the smoothness of this drive and 3/8-16 "blind rivnuts" that I'll use for tripod attachment on the wedge).

If I manage to bring it down in size, and if it provides enough smoothness of tracking - I might consider bringing it to a finish, but even so - its not going to be "easy DIY" star tracker for the masses - it really does require skill to print and assemble it, and PCB is going to be additional challenge.

As is - it runs at x5 sidereal rate because I envisioned another 5:1 reduction via belt. If I redesign it - then I'll move motor from the bottom and onto a side of the gear box and 5:1 belt reduction will be "first stage" with output from the gearbox directly attached to base of the star tracker.

Thing runs and provides that 179.2:1 reduction and makes funny noises . On sidereal or close to sidereal rate - funny noises are down to stepper and at "slew speed" (2 degrees per second - although I don't think star tracker needs slew function) - gears start to be heard and it all sounds like concrete mixer . I still haven't applied any grease to it - must purchase white lithium + ptfe grease and try that.

[vlaiv]

Btw, I'll later post some images of internals, so you can see what it looks like (and why it's so huge - one might say "over engineered").

[CraigT82]

Well no one gets it totally right on the first go Vlaiv. MkII will be better!