3D printed star tracker

[CraigT82]

9 hours ago, vlaiv said:

Spur gear, for example - does not have simple profile:

This site really helped me get my head around involute gear teeth.

https://www.tec-science.com/mechanical-power-transmission/involute-gear/geometry-of-involute-gears/

I use Civil 3D and haven’t really found a satisfactory but quick way of drawing gears yet, so have to draw one tooth manually and polar array it. I found a few tutorials on YouTube where they seem to use random arcs to create the involutes but this site helped me to come up with my own way of drawing those curves with proper geometry. 

Edited July 30, 2022 by CraigT82

[EarthLife]

You can also do it in openscad (free parametric design program).

A ready made design file can be found here ..

https://github.com/openscad/MCAD/blob/master/involute_gears.scad

Load that into openscad and uncomment the first top bit where it says "Simple Test" to show how to use it. It takes a few seconds for the design to show up in the window but once it does just zoom out until you see the whole gear, then save it as an STL file (or whatever). Can then import it into your usual cad software and use as you like.

 

[EarthLife]

13 hours ago, vlaiv said:

I'm using FreeCAD.

I too have FreeCAD, but prefer to use the free Autodesk 123D Design program, it's GUI and ways of doing things are easier for me I find.

Autodesk no longer have it available for download but a quick internet search will produce some download links. If you start using 123D Design then make sure you disable the "Check for updates automatically" option (in preferences) otherwise it tends to sit there doing nothing at times whilst it tries it's hardest to download none existent updates.

[Elp]

I used to use Autodesk Fusion which is excellent but my trial which I kept renewing every year as a learner stopped working and I think I have to subscribe to it now. Someone mentioned it can still be used for free but I haven't got the option under my management console.

[newbie alert]

Vlaiv, are you familiar with Onstep?  A few guys on there have 3d print designs, one of which lately done a startracker with a budget of 100 dollers

[vlaiv]

2 minutes ago, newbie alert said:

Vlaiv, are you familiar with Onstep?  A few guys on there have 3d print designs, one of which lately done a startracker with a budget of 100 dollers

Heard of it, but I was not aware they also have star tracker.

Last time I checked it was for motorizing EQ mounts, right?

 

[newbie alert]

1 hour ago, vlaiv said:

Heard of it, but I was not aware they also have star tracker.

Last time I checked it was for motorizing EQ mounts, right?

 

Onstep is more the board components... But a few people have gone a stage further and designed and made their own mounts, I've seen friction drives and now a few 3d prints...Inc this one which is the startracker

https://onstep.groups.io/g/main/topic/91624985

[vlaiv]

18 minutes ago, newbie alert said:

Onstep is more the board components... But a few people have gone a stage further and designed and made their own mounts, I've seen friction drives and now a few 3d prints...Inc this one which is the startracker

https://onstep.groups.io/g/main/topic/91624985

That is a bit more complex and in some areas a bit different than I intended.

Mine would just track in RA, so it would not include counterweight.

Wedge part is a bit more elaborate though.

[saac]

Seems to be some confusion about Fusion 360. I can confirm that it is still available free for personal use. 

Jim

[EarthLife]

2 minutes ago, saac said:

Seems to be some confusion about Fusion 360. I can confirm that it is still available free for personal use. 

Jim

The trouble with fusion 360 is that it's partly 'cloud' based, which means you MUST allow to access the internet every now and then at least.

Autodesk is moving to this 'cloud' based method of operating, which means you're totally at their mercy. I used to use fusion 360 until they decided to stop me (along with many others) about a year ago or so for no reason at all. They've recently tried to get me to go back to using it (the paid subscription version) but I told them that I would never use ANY cloud based software again after learning of what they are really getting up to.

This emerging 'cloud' system is something everyone should be extremely cautious about, you'd be very wise indeed never to allow yourself to become dependant on ANY cloud base software. Giving the public free access draws people in, then once they believe you've become dependant upon it, they'll pounce. Watch yourselves !

[saac]

I really don't have any issue with the cloud server side of Fusion 360, it hasn't restricted anything that I have wanted to do over the past 4-5 years or so of use.   It is a an incredibly powerful suit with industry standard profiles and  a wide user base both commercial and private.  For me, the wealth of help available both on-line and published, together with inbuilt scripts such as (astro) screw threads, gears etc is a welcome time saver.  I guess we all have our favourite pieces of software, best thing to do is try each one out and find what works for you I guess; Fusion 360 it for me  

Jim 

Edited July 30, 2022 by saac

[EarthLife]

Yes it is a good piece of software, until that is they decide to remove your access (they don't warn you) !

Just make sure that every design you do in it you export to your own PC on it's own SSD/HDD in a format that can be imported into other CAD software. IF you don't do that, you'll loose all access to everything you've ever done when the time comes.

[Elp]

That's the issue I had, used it fine for 3 odd years updating the free license every year, then all of a sudden I could no longer use it free, I can't justify the subscription as I don't use it often enough. Think all this subscription nonsense started with Adobe and everyone followed suit, give me an offline version of PS (on another note I had a fully working mobile version which I paid for, they updated it for more modern OSs with less features (the old one was just like the desktop version with a mobile interface) and now the old one doesn't work).

[Alien 13]

I feel inadequate as I use Tinkercad but it does all I need and is super fast.. Idea to stl file in less than 10 mins most of the time.

Alan

[vlaiv]

Talk about bed adhesion

Test worm for azimuth movement of polar wedge is being printed

Yes, that thing is 90mm tall and only about 8mm thick with different sections being printed at 0.2mm and 0.12mm

[vlaiv]

Here is little update - prototype of polar alignment wedge azimuth assembly:

 

This is just to test out worm/worm gear geometry and assembly. Worm gear shaft will still use 608 bearings but worm itself will be resting on 51108 axial ball bearing and will be supported with 6006 radial ball bearing (both rather cheap).

Worm is running rather smooth without any grease applied to it.

There is some backlash as I added 0.1mm distance between nominal shaft positions. Maybe that won't be needed for final version, or maybe I should work on some sort of spring loaded auto backlash adjustment?

I'm not yet sure what sort of design to go for - for worm gear itself. As is - it is rather difficult to print and very good dimensional accuracy is needed. I also needed to beef up some sections of it to make it rigid enough  (5 perimeters and 55% infill) - last one broke in couple of places due to stress from over tightening the knobs.

I'm thinking of adding M5 threaded core (running all the length of worm and bearing shafts) and some nuts instead of current arrangement. 1 meter of M5 threaded rod is something like 0.5e in hardware store here - but from what I can see online - quite a bit more expensive elsewhere (for some reason). It would involve also sawing it to right size and using socket wrench to tighten up m5 nuts to hold knobs in place and push against ball bearings (just a bit of pressure to keep everything in place in above prototype.

Where should I draw the line? What sort of complexity will make this "advanced" rather than "easy" build level?

 

[saac]

Print quality looks good vlaiv, looks like you have the printing profile dialled in well.  Yes constraining your design to both the material and manufacturing method is essential else you will be overdesigning and potentially wasting time.  Have you looked at the trackers on thingiverse for inspiration? Not a massive selection, mostly basic, but one or two are novel. 

Jim 

Edited August 1, 2022 by saac

[vlaiv]

15 minutes ago, saac said:

Have you looked at the trackers on thingiverse for inspiration? Not a massive selection, mostly basic, but one or two are novel. 

Not really, at least not recently.

I had this idea for quite some time - to build one that will have cycloidal drive (after seeing some 3d printed ones in action), instead of popular options like worm, or belt / gear system, or even strain wave (which seems to be popular at the moment).

Math is straight forward - Say we want something like 1" per step resolution and we work with 32 micro steps.

One revolution will have 200 steps with 32 micro steps - that gives 200 x 32 = 6400 steps per revolution.

On the other hand we have 360 degrees x 60 arc minutes x 60 arc seconds = 1296000 arc seconds in one revolution.

1296000 / 6400 = 202.5

We need something like 200:1 reduction to be able to do that. Belt and pulley can be used as final reduction - something like 5:1 or 7:1, which leaves "primary" reduction at something like 40:1 or 30:1 - ideal for cycloidal drive. I think it will also be low backlash (not very important for star tracker, I know) - and should be smooth if printed correctly.

I have to say - that I'm surprised by how much I enjoy designing this stuff and yes, there is real risk of over "engineering" things (as if it can be called engineering - not really an engineer here).

 

[saac]

18 minutes ago, vlaiv said:

Not really, at least not recently.

I had this idea for quite some time - to build one that will have cycloidal drive (after seeing some 3d printed ones in action), instead of popular options like worm, or belt / gear system, or even strain wave (which seems to be popular at the moment).

Math is straight forward - Say we want something like 1" per step resolution and we work with 32 micro steps.

One revolution will have 200 steps with 32 micro steps - that gives 200 x 32 = 6400 steps per revolution.

On the other hand we have 360 degrees x 60 arc minutes x 60 arc seconds = 1296000 arc seconds in one revolution.

1296000 / 6400 = 202.5

We need something like 200:1 reduction to be able to do that. Belt and pulley can be used as final reduction - something like 5:1 or 7:1, which leaves "primary" reduction at something like 40:1 or 30:1 - ideal for cycloidal drive. I think it will also be low backlash (not very important for star tracker, I know) - and should be smooth if printed correctly.

I have to say - that I'm surprised by how much I enjoy designing this stuff and yes, there is real risk of over "engineering" things (as if it can be called engineering - not really an engineer here).

 

It is definitely enjoyable, something almost cathartic seeing your creation coming to existence (very slowly) before your eyes. And yes, that is it vlaiv, welcome to the brotherhood of engineering.  What remains to be seen is who you will rank alongside, James Watt or Bodget and Scarper    Given the attention to detail you normally bring to your work I'm going with the former   Watching with interest to see how your design evolves, good luck with it. 

Jim 

Edited August 1, 2022 by saac

[DaveL59]

On 30/07/2022 at 18:48, EarthLife said:

Yes it is a good piece of software, until that is they decide to remove your access (they don't warn you) !

Just make sure that every design you do in it you export to your own PC on it's own SSD/HDD in a format that can be imported into other CAD software. IF you don't do that, you'll loose all access to everything you've ever done when the time comes.

Also applies to OneDrive if they decide you breached their T&C's they'll just disable and then you find you can't get hold of them in the time before they wipe your data/files. So I've read, personally I never use anything cloud based that I pay for unless its done thru work directives. I'd rather run my own fileservers than trust whoever to maintain security, privacy and continuous service and pretty much all of them have failed at least one of those if not more.

[gazza]

What about this 3d printed startracker, full goto, and automatic polar alignment. Have just built one myself:

https://openastrotech.com/

Auto PA:

https://www.youtube.com/watch?v=BKDGDcrhc6Q

 

cheers

Gary

 

[vlaiv]

4 hours ago, gazza said:

What about this 3d printed startracker, full goto, and automatic polar alignment. Have just built one myself:

What is the total cost and how much time did you put in building it?

[gazza]

Hi,

cost was a bit over  $200 Australian dollars, from what I remember:

Most of the cost was in the MKSGenL v2.1 with drivers  $60

Stepper motors had them already

Camera mount $30

Bearings $60

Hardware Screws/nuts/bolts etc about $40

A kilo of filament (PLA)

Took about 2 weeks to print all the bits at about 8 hours a day, and about 6 hours to assemble.....

Hope this helps

Gary

[vlaiv]

9 minutes ago, gazza said:

cost was a bit over  $200 Australian dollars

I'm sort of aiming for something very basic - partly because it is much easier to start with / build, and also because it will be less expensive and accessible to more people. Other reason is - I'm simply doing something like this for the first time, I just got my 3d printer and I started using CAD software

I'm hoping to develop very simple "plug / play" kind of device. Just polar align, aim your camera / smart phone and hit single "go" button as far as tracking goes. No guiding / no slewing / no connection to computer and such in this iteration.

Hardware also needs to be cheap and easily accessible - few types of common bearings, screws and nuts and of course stepper + controller (probably RPI pico) + driver. Hope to keep total cost south of $40-$50USD.

On a separate note, I'm having second thoughts on cycloidal gear system and instead considering split gear compound planetary type system.

First one would still need belt and pulley for additional reduction, while second can easily hit 500:1 in single straight forward assembly (not that I'll that much for 1" / microstep). Gear system can also be fully 3d printed and there is no need for small metal pins. Only concern currently is tracking accuracy - but we will see how it behaves.

[gazza]

Good luck with your design, I'm following the thread, as simple is always good. I built this one so I could set it up and run it remotely. Something small and cheap to take on trips for widefield shots would be very welcome. Good luck!!

cheers

Gary