3D printed star tracker

[kbrown]

30 minutes ago, vlaiv said:

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.

In case you didn't already know, the stepper driver can make a massive difference on the noise the motor makes. I've been using the Trinamic TMC2209 since I learned about them (same as in my Prusa i3 Mk3). They are more expensive than basic drivers and also require more learning if you want to take advantage of the more advanced features of it but if smoothness is the goal, it's worth it.

[pipnina]

3 hours ago, kbrown said:

In case you didn't already know, the stepper driver can make a massive difference on the noise the motor makes. I've been using the Trinamic TMC2209 since I learned about them (same as in my Prusa i3 Mk3). They are more expensive than basic drivers and also require more learning if you want to take advantage of the more advanced features of it but if smoothness is the goal, it's worth it.

This indeed. My stock Ender3 printer makes an awful racket. Sounds like some sort of robot orchestra when it's printing.

My boyfriend bought a second hand Ender3, with some mods including the mobo replaced with the Ender3 S1, which has upgraded stepper controllers.

It. Is. Silent. No noise besides that of things sliding over eachother and the fans.

As for the noise the gears make at higher RPM, this could be tolerance or backlash as gears should in theory sound relatively smooth when applying continuous force in one direction. But when switching direction even metal machined gears sound cataclysmic (unmodded skywatcher EQ mounts with the brass motor-to-worm train sounds like someone tried to put a car into reverse while going 70 down the motorway, as many of us have first-hand experience...)

 

Also Vlaiv, I'm very keen to see how you test the smoothness with a laser, I have envisioned using an optical mouse sensor myself as they can detect exceptionally small movements as well.

[vlaiv]

4 hours ago, kbrown said:

In case you didn't already know, the stepper driver can make a massive difference on the noise the motor makes. I've been using the Trinamic TMC2209 since I learned about them (same as in my Prusa i3 Mk3). They are more expensive than basic drivers and also require more learning if you want to take advantage of the more advanced features of it but if smoothness is the goal, it's worth it.

I know, but I wanted a budget variant. I also have silent stepper drivers on my ender 3 v2.

[vlaiv]

1 hour ago, pipnina said:

Also Vlaiv, I'm very keen to see how you test the smoothness with a laser, I have envisioned using an optical mouse sensor myself as they can detect exceptionally small movements as well.

Idea is very simple - It won't be able to do large section of movement, but rather small one - say 3-4 minutes of tracking. That is plenty enough to get general sense of smoothness of the motion.

You can trade resolution for angular section by the way.

One places laser on the output shaft. Laser is placed horizontally and aimed at the white wall. In case white wall is not accessible, or is not smooth enough - a piece of white paper / cardboard can do the trick as well.

Camera and lens are used to record laser point position and covert that into pixels (centroid on laser point is performed at regular intervals and recorded).

With something like ASI1600 - I'll have about 3800px horizontal resolution - then it is only matter of doing some basic math - like distance of laser to paper and camera paper distance / focal length.

Say that we use 1 meter of white wall and place laser 30 meters away.

That will give us ~6875 arc seconds of working space (so at 15.041"/s - that is 457 seconds of tracking or ~7.6 minutes), and at 3800px - we have something like 2"/px of base resolution. With centroid being sub pixel accurate - we'll probably have tracking on less than 1" precision - which is more than enough for star tracker.

(in case of A4 piece of paper - everything is scaled to 1/3 - so 10 meters away vs 30cm of size of paper - and shorter FL lens should be used - or camera placed closer to cover the paper).

 

[kbrown]

4 minutes ago, vlaiv said:

Idea is very simple - It won't be able to do large section of movement, but rather small one - say 3-4 minutes of tracking. That is plenty enough to get general sense of smoothness of the motion.

You can trade resolution for angular section by the way.

One places laser on the output shaft. Laser is placed horizontally and aimed at the white wall. In case white wall is not accessible, or is not smooth enough - a piece of white paper / cardboard can do the trick as well.

Camera and lens are used to record laser point position and covert that into pixels (centroid on laser point is performed at regular intervals and recorded).

With something like ASI1600 - I'll have about 3800px horizontal resolution - then it is only matter of doing some basic math - like distance of laser to paper and camera paper distance / focal length.

Say that we use 1 meter of white wall and place laser 30 meters away.

That will give us ~6875 arc seconds of working space (so at 15.041"/s - that is 457 seconds of tracking or ~7.6 minutes), and at 3800px - we have something like 2"/px of base resolution. With centroid being sub pixel accurate - we'll probably have tracking on less than 1" precision - which is more than enough for star tracker.

(in case of A4 piece of paper - everything is scaled to 1/3 - so 10 meters away vs 30cm of size of paper - and shorter FL lens should be used - or camera placed closer to cover the paper).

 

Suppose you should take into account lens distortion with this method. Software like Lightroom or Darktable can undistort the footage against known database of lenses. Failing that you should do that manually with a calibration grid.

[pipnina]

2 minutes ago, kbrown said:

Suppose you should take into account lens distortion with this method. Software like Lightroom or Darktable can undistort the footage against known database of lenses. Failing that you should do that manually with a calibration grid.

A lot of camera lenses are distortion-free already thankfully. If anyone wanting to try this already has a DSLR and an 18-55mm kit lens, it is likely to be pretty distortion free wih no post processing.

Can't say the same for the typical 55-200 kit lens option however. (as I understand, most of these kit lenses are basically rebrands even if they have Nikon or Canon stickers on them)

[vlaiv]

4 minutes ago, kbrown said:

Suppose you should take into account lens distortion with this method. Software like Lightroom or Darktable can undistort the footage against known database of lenses. Failing that you should do that manually with a calibration grid.

I don't think it will be necessary. It will certainly impact results over large time period - but I'm not looking at that - I'll be looking at deviation from standard speed in minute or half a minute intervals. Besides lens distortion there is also issue of tilt - both camera and laser - paper should be perpendicular to both and if it's not there might be linear speed gradient - but again, that is not something I'm worried about - I want to see jitter / noise in tracking performance rather than smooth changing curve beyond 1 minute.

 

[kbrown]

1 minute ago, pipnina said:

A lot of camera lenses are distortion-free already thankfully. If anyone wanting to try this already has a DSLR and an 18-55mm kit lens, it is likely to be pretty distortion free wih no post processing.

Can't say the same for the typical 55-200 kit lens option however. (as I understand, most of these kit lenses are basically rebrands even if they have Nikon or Canon stickers on them)

I have some L-series (i.e. pro) Canon lenses and they still distort a bit. It's only noticeable when you toggle the undistort option on and off in the software though. So visually it doesn't usually really matter...

[vlaiv]

Here are a few videos with sound of the thing in action:

Full slew speed at 2 degrees/s:

(this is close to limit of resolution offered by micropython that I'm using for simplicity - it is pulse every 30 micro seconds with 6400 steps per revolution - or 200x32 for micro stepping - motor is running at about 300RPM)

 

Next is x10 slower stepping speed - so around 30RPM on input shaft - with almost no noticeable motion on the output shaft. Noise is much more tolerable in this case:

 

Third one is equivalent of tracking speed - or sidereal. Input shaft is running at that speed - and output shaft is 1/5 of sidereal (because there is planned x5 belt stage as well).

No noise is coming from gears - its all from stepper motor ticking away ...

 

I guess that adding some lube will improve things, so that is next step  (and redesign of the thing - trying to make it thinner).

[vlaiv]

Few pics of internals that I promised:

base ring attached to stepper with 6002 bearing and sun gear (sun has 15 teeth, base annulus has 81 - both are module 1).

Next comes planet system: planet gears with carrier - they have 608 bearings inside and are supported by 6002 at top and bottom. Top and bottom gear in each planet have 33 teeth, and bottom is module 1 while top is 0.94... something something (can't remember it like that as fraction it is 48/51):

Planetary set installed:

Then comes output annulus with attached output shaft. It has 84 teeth at module 48/51:

It is supported by two 6002 on each side - one resting against top planetary carrier and other against gearbox housing.

Here it is installed:

There is gap between top and bottom annulus - which is where "split ring" in the name of the system comes from.

In the end - there is gearbox housing - which is nothing special, just a seating supporting the last bearing (giving rigidity and center to whole assembly) and means to bolt it to base of housing.

You can now see where the bulk of assembly comes from:

1. 81 teeth x 1mm module - means at least 90 mm of diameter of the whole thing (81 gear diameter + 3-4mm of outer shell on each side).

2. around 30mm of planetary system - 20mm gears + 2x5mm carriers (4mm thick + 1mm spacing), then 3x 6009 bearing which is 9mm thick - that together is already almost 60mm in height - add few times 3-4 mm of housing and support stuff ....

Now, I could design even higher reduction ratio in smaller diameter if I make output and input ring differ by 1 tooth - but that also require additional care when printing planetary gears as top and bottom gears will be offset and there will be overhang tooth from top gear to deal with in printing - which I wanted to avoid for this version.

Also - with less teeth in planets - I'll also need smaller bearings to support them in planetary system - at the moment planets are 33mm - which fits nicely on 608 bearings that are 22mm in diameter. If I want to go for say ~23-24 tooth per planet - that would require bearings with 15mm outer diameter - something I plan to source from Ali express at some point.

Wider support bearings would also contribute to rigidity. Bearings that I'm using are quite cheap and are not as so good - so there is a bit of "play" in them. This leads to things not staying on axis but rather bending a bit. Wider support bearings would reduce this bending for same amount of play in bearing.

[pipnina]

17 minutes ago, vlaiv said:

Few pics of internals that I promised:

 

base ring attached to stepper with 6002 bearing and sun gear (sun has 15 teeth, base annulus has 81 - both are module 1).

Next comes planet system: planet gears with carrier - they have 608 bearings inside and are supported by 6002 at top and bottom. Top and bottom gear in each planet have 33 teeth, and bottom is module 1 while top is 0.94... something something (can't remember it like that as fraction it is 48/51):

 

Planetary set installed:

 

Then comes output annulus with attached output shaft. It has 84 teeth at module 48/51:

 

It is supported by two 6002 on each side - one resting against top planetary carrier and other against gearbox housing.

Here it is installed:

 

There is gap between top and bottom annulus - which is where "split ring" in the name of the system comes from.

In the end - there is gearbox housing - which is nothing special, just a seating supporting the last bearing (giving rigidity and center to whole assembly) and means to bolt it to base of housing.

 

You can now see where the bulk of assembly comes from:

1. 81 teeth x 1mm module - means at least 90 mm of diameter of the whole thing (81 gear diameter + 3-4mm of outer shell on each side).

2. around 30mm of planetary system - 20mm gears + 2x5mm carriers (4mm thick + 1mm spacing), then 3x 6009 bearing which is 9mm thick - that together is already almost 60mm in height - add few times 3-4 mm of housing and support stuff ....

Now, I could design even higher reduction ratio in smaller diameter if I make output and input ring differ by 1 tooth - but that also require additional care when printing planetary gears as top and bottom gears will be offset and there will be overhang tooth from top gear to deal with in printing - which I wanted to avoid for this version.

Also - with less teeth in planets - I'll also need smaller bearings to support them in planetary system - at the moment planets are 33mm - which fits nicely on 608 bearings that are 22mm in diameter. If I want to go for say ~23-24 tooth per planet - that would require bearings with 15mm outer diameter - something I plan to source from Ali express at some point.

Wider support bearings would also contribute to rigidity. Bearings that I'm using are quite cheap and are not as so good - so there is a bit of "play" in them. This leads to things not staying on axis but rather bending a bit. Wider support bearings would reduce this bending for same amount of play in bearing.

The only thing I can think of immediately that could stop the cement grinder noise is switching to helical gears. These are good because they have multiple teeth engaged at once and "ease" into each mesh, unlike straight cut gears like used here and in the SW EQ mounts.

I believe the main disadvantage of helical gears comes from efficiency and limitations on maximum torque, but in most applications (car gearboxes for example) the benefits in terms of noise and smoothness outweigh the negatives.

Other factors certainly at play here but this gearbox makes very little noise for example with the helical shape

Might be worth an experiment with two gears side-by-side instead of redesigning the whole planetary gearbox at first.

[vlaiv]

2 minutes ago, pipnina said:

The only thing I can think of immediately that could stop the cement grinder noise is switching to helical gears.

Yes, I used herringbone gears before - and I really like them, but here it is a no go (or maybe it could be done but assembly would be very difficult) - because planetary system must slide into outer gear on assembly - something not possible with that configuration.

Regular helical gears would produce additional force in axial direction, so not sure if that would hamper performance.

One thing that worries me about helical gears is sliding action direction. With straight gears all the sliding happens along layer lines of 3d print - which is good sliding direction. As soon as we change the angle - there is additional component of sliding action that happens in "vertical" direction - which is notoriously poor for sliding (layer lines act as teeth on a file and grind against other teeth - so it's as smooth as running two files one against the other and expecting smooth motion ).

Here is couple of things that I think improvement can be found in:

1. using lubrication

2. using 0.2mm diameter nozzle to improve accuracy of small features like gear teeth

3. Checking out what happened here:

This is FreeCad wire frame view of sun gear and planets:

In particular - if we zoom in on any section - we get very nice fit:

This is without any printing compensation - just pure geometry. But check this out:

same thing with annulus gear - see interference fit for some reason (I know there are more lines in this drawing that it should be for seeing the issue, but I'll point out trouble areas):

Although that is very small portion of the tooth and 3D print precision will interfere anyway - I'd be much happier if it was not happening at that level - geometry should align properly at that stage.

This is FreeCad Gear workbench - regular involute external gear matching involute spur gear - and teeth don't match properly. Upper teeth in this last image is aligned 100% and somehow profile of it is "thicker" than groove on annulus gear. 

4. accepting some amount of backlash in order to make meshing smoother

In the end - I must keep in mind. This is supposed to be simple and cheap star tracker. It won't be guided, it won't be slewed around the sky at high speeds. It should meet following things:

1. easy to build

2. cheap

3. good enough for smart phone or DSLR + lens - in essence it is 21st century replacement for barn door tracker

Given amount of work I had to put in so far - I think it is failing at being easy to build - at least compared to something like barn door tracker.

 

[pipnina]

1 hour ago, vlaiv said:

Yes, I used herringbone gears before - and I really like them, but here it is a no go (or maybe it could be done but assembly would be very difficult) - because planetary system must slide into outer gear on assembly - something not possible with that configuration.

Regular helical gears would produce additional force in axial direction, so not sure if that would hamper performance.

One thing that worries me about helical gears is sliding action direction. With straight gears all the sliding happens along layer lines of 3d print - which is good sliding direction. As soon as we change the angle - there is additional component of sliding action that happens in "vertical" direction - which is notoriously poor for sliding (layer lines act as teeth on a file and grind against other teeth - so it's as smooth as running two files one against the other and expecting smooth motion ).

Here is couple of things that I think improvement can be found in:

1. using lubrication

2. using 0.2mm diameter nozzle to improve accuracy of small features like gear teeth

3. Checking out what happened here:

This is FreeCad wire frame view of sun gear and planets:

-SNIP-

 

Ah yes, assembly would be a bit tricky. The only way I can think of to make that buildable is to split a herringbone gear into two halves, then using a bolt going top-down to secure them. This way each half of the gear can be twisted into place I think...

Regardless as you say, a bit too complicated.

As for single-helix gears, I think they should still work fine as any axial force is going to be very small compared to the rotational forces we desire. Consider that the HEQ5 only produces a torque of around 2.4 newton meters at the driven end... I can far exceed that with a torque screwdriver and my wrist, and this is a big mount for up to 10kg payloads + counterweight and ideally operating at arcsecond accuracy or better.

As for the vertical sweeping motion, maybe i am missing something but I think actually the gear does not shift vertically during a gear mesh, the horizontal plane doesn't move and it just creates a barber shop pole illusion. The layer lines should be safe I think.

For the freecad screenshots, I think you are in perspective view, if you switch it to orthographic I think it will be easier to see the tolerance between gears!

[vlaiv]

9 hours ago, pipnina said:

As for the vertical sweeping motion, maybe i am missing something but I think actually the gear does not shift vertically during a gear mesh, the horizontal plane doesn't move and it just creates a barber shop pole illusion. The layer lines should be safe I think.

You are quite right - I thought about it and there is sliding - but not in vertical direction.

9 hours ago, pipnina said:

For the freecad screenshots, I think you are in perspective view, if you switch it to orthographic I think it will be easier to see the tolerance between gears!

I will certainly try this.

9 hours ago, pipnina said:

Ah yes, assembly would be a bit tricky. The only way I can think of to make that buildable is to split a herringbone gear into two halves, then using a bolt going top-down to secure them. This way each half of the gear can be twisted into place I think...

Yes, either that - splitting them into two halves by horizontal cut or splitting them into two half rings vertically, but in either case we need to bolt them down together after assembling.

[vlaiv]

On a separate note - all this thinking about how to optimize this arrangement - lead to me inventing a new gearbox type

At least I think it is novel - I haven't seen it before.

It is a cross between planetary gear and cycloidal disk type gear. It consists out of - outer annulus gear, then one large planet that is just a few teeth smaller than outer gear. This large planet sits on excentric circle on driving shaft and has several hole in it where pins from output shaft go.

It does not have large reduction ratio but it is slim and can be stacked to get required larger reduction ratios.

I'll make a model of it later to test it out and I'll post results.

[vlaiv]

Here is new reduction gearbox design

or rather - this is design of a simple toy prototype that needs to confirm that the thing is working.

At least - it's slim:

Operation is simple - for every rotation of input shaft - inner gear does one "shuffle" and moves only a few teeth along outer gear (actual number is difference in number of gears - in this example outer is 80 and inner is 75).

It is exactly operating like cycloidal gear set - except it is using standard spur gear. I think that it might be better when 3d printed than standard cycloidal disk, because this design allows for herringbone teeth without too much issues.

[vlaiv]

Meanwhile ...

(as I'm printing parts for above technology demonstrator)

It turns out that I was in proper view in FreeCad and that in fact - gears as I created them - don't mesh properly.

When one is making two external spur gears - then, pressure angle and module must match - but when matching external and internal gear - pressure angle changes (and perhaps even module a bit).

I've found this extensive resource that I must work thru in order to fully understand math behind all of this:

https://www.sdp-si.com/resources/elements-of-metric-gear-technology/index.php#Section1

 

[vlaiv]

Here is a recording of new gearing system:

Its not very smooth due to lack of any bearings, but it actually operates/rotates "smoothly" - or no hiccups due to design issues.

It is really the same thing as cycloidal disk/gear thing - but using involute gears.

[vlaiv]

I've come to conclusion that I'm over thinking / over designing the whole thing.

As is - this star tracker is supposed to have something like 179.2 * 5 = 896 : 1 reduction ratio or about 0.22"/step resolution. That is probably way to much for simple printed star tracker.

EQ5 / HEQ5 / EQ6 class mounts have that sort of resolution - while AzGTI has 0.625"/step and works very well as small portable EQ mount that can even hold small scopes.

Here is what are my current thoughts on the matter:

1. Drop resolution to something like 1-2"/step instead of going for sub one arc second per step. With x32 microstepping this equates to total reduction ratios of say 1:100 - 1:200 range (1"/step is 202.5:1 reduction exactly with x32 microstepping).

Not sure what would be the best way to do it. It turns out that such arrangement is within reach of simple belted system. Three stages of 1 : 5 will give 1 : 125 and 1 : 6 will give 1 : 216. That does not require complex gearing at all.

If I'm to go with any sort of 3d printed gear box - then I'm not sure how to spatially arrange things. I'd like output shaft to be rather rigid and supported by two larger bearings. Then it stands to reason that it will be driven by a belt. I can then either stack gearbox on top of the stepper - like I started - which seems too bulky, or I can add another transmission (belt or gear) between stepper and gearbox - with probably another reduction stage. But what is the point in that - that will give me again 3 stages (two belted and one compound / gearbox) - with too much reduction - and I can simply go with 3 simple belted stages.

On the other hand - I really do want to explore the performance of above gearbox (or even greater reduction one) and minimize it further (I have few ideas how to do that and I've found local source of thin bearings so I don't need to wait long time for aliexpress shipments) - but that can be separate project.

Your thoughts / ideas on how to proceed with this are welcome of course.

[Thalestris24]

Hi Vlaiv

Just doing a quick catchup on your development  Was wondering why you were limiting your design above  to 32 microsteps when 128 microsteps are possible and with a 0.9deg/turn motor? I'm sure there must be a good reason! Is it to do with holding current or precision? (I'm no expert on microstepping!)

Louise

[vlaiv]

9 minutes ago, Thalestris24 said:

Hi Vlaiv

Just doing a quick catchup on your development  Was wondering why you were limiting your design above  to 32 microsteps when 128 microsteps are possible and with a 0.9deg/turn motor? I'm sure there must be a good reason! Is it to do with holding current or precision? (I'm no expert on microstepping!)

Louise

Mostly to do with keeping the cost down and with simplicity.

There are two cheap / readily available drivers for stepper motors - A4988 and DRV8825.

Out of these two - DRV8825 supports 32 micro steps - A4988 supports only 16. On top of that DRV8825 is quite a bit less noisy in operation (not silent but not as noisy either).

I've also chosen stepper motor that is the cheapest of the bunch. There are nice smaller units (like Nema 8 ) - but they are often more expensive. Hence 1.8 degrees per step and not 0.9.

In final build, people will certainly be able to choose their components as most are drop in replacement - but I wanted to see what is the minimum budget that I could get by with.

 

[Thalestris24]

21 minutes ago, vlaiv said:

Mostly to do with keeping the cost down and with simplicity.

There are two cheap / readily available drivers for stepper motors - A4988 and DRV8825.

Out of these two - DRV8825 supports 32 micro steps - A4988 supports only 16. On top of that DRV8825 is quite a bit less noisy in operation (not silent but not as noisy either).

I've also chosen stepper motor that is the cheapest of the bunch. There are nice smaller units (like Nema 8 ) - but they are often more expensive. Hence 1.8 degrees per step and not 0.9.

In final build, people will certainly be able to choose their components as most are drop in replacement - but I wanted to see what is the minimum budget that I could get by with.

 

Oh ok. Though 0.9 deg steppers aren't especially (more) expensive, at least not here in the UK NEMA17 Stepper Motors - Ooznest | Kits, Parts & Supplies

You can get 128 step controllers for not a huge amount e.g. New DC 12-50V 4A Stepper Motor Driver 128 Microstep 2-phase Controller | eBay or 

DM542 Stepper Motor Driver Controller DC 24-50V Nema 23 / 17 CNC 4.2a DM 542 NEW | eBay

It may be worth it as that's where all the magic is!

Anyway, good luck with the project  

Louise

 

[vlaiv]

10 minutes ago, Thalestris24 said:

You can get 128 step controllers for not a huge amount e.g. New DC 12-50V 4A Stepper Motor Driver 128 Microstep 2-phase Controller | eBay or 

DM542 Stepper Motor Driver Controller DC 24-50V Nema 23 / 17 CNC 4.2a DM 542 NEW | eBay

That is way more expensive and powerful than it needs to be.

DRV8828 can be purchased for as low as 1-2 euro a piece.

If one wants 128 or even 256 micro steps then something like TMC2208/2209 is just a bit more expensive - ~4 euro a piece.

https://www.ebay.co.uk/itm/275420178213?hash=item4020526725:g:kYAAAOSw63Ni9ggA&amdata=enc%3AAQAHAAAAwN5a%2FWvx2BoXK9nD1CsIBwct65P6VAgZjY98Jn9lnotGFDdDLTAlBVbriWCM%2B2Ex4U3PxT2O7o6wxaNbW5gby2rQIMLH%2BpUE7ttf52hj%2B9BNovnDB0fnWBnGpUZFDI%2BZO3AZjKu5XDum%2BN95LDvoVvUll0xQqQK%2B0F63X2ErC41%2FO3YLdKkQvw3dJuPAXujnnwwZeL7znoBIF%2BaTF1n5wQfOJpsB2g5Cdu9fXVeXC98M5u3OmTeBWwns%2BPDZ3ZU8QQ%3D%3D|tkp%3ABk9SR77x797aYQ

One can also save about 5 euro by using 1.8 degree over 0.9 degree stepper.

If I'm going to aim to get it done within 50 euro budget - every little saving counts.

 

[Thalestris24]

46 minutes ago, vlaiv said:

That is way more expensive and powerful than it needs to be.

DRV8828 can be purchased for as low as 1-2 euro a piece.

If one wants 128 or even 256 micro steps then something like TMC2208/2209 is just a bit more expensive - ~4 euro a piece.

https://www.ebay.co.uk/itm/275420178213?hash=item4020526725:g:kYAAAOSw63Ni9ggA&amdata=enc%3AAQAHAAAAwN5a%2FWvx2BoXK9nD1CsIBwct65P6VAgZjY98Jn9lnotGFDdDLTAlBVbriWCM%2B2Ex4U3PxT2O7o6wxaNbW5gby2rQIMLH%2BpUE7ttf52hj%2B9BNovnDB0fnWBnGpUZFDI%2BZO3AZjKu5XDum%2BN95LDvoVvUll0xQqQK%2B0F63X2ErC41%2FO3YLdKkQvw3dJuPAXujnnwwZeL7znoBIF%2BaTF1n5wQfOJpsB2g5Cdu9fXVeXC98M5u3OmTeBWwns%2BPDZ3ZU8QQ%3D%3D|tkp%3ABk9SR77x797aYQ

One can also save about 5 euro by using 1.8 degree over 0.9 degree stepper.

If I'm going to aim to get it done within 50 euro budget - every little saving counts.

 

Oh ok. 50 Euro seems a bit low - especially if you cost your own time spent on it! Not to mention current levels of inflation... It's all relative, I suppose  

Louise

[vlaiv]

12 minutes ago, Thalestris24 said:

Oh ok. 50 Euro seems a bit low - especially if you cost your own time spent on it! Not to mention current levels of inflation... It's all relative, I suppose  

Louise

Well - I don't really count my time or amount of money I spent developing it.

Since I plan to release specs to general public - it's more "the budget" needed to complete the project or BOM if you like.

I'm really developing this so that anyone who has 3d printer or access to one - can build themselves working star tracker that they can use for DSLR+lens or smart phone astrophotography.

Sort of 21st century barn door tracker kind of thing, but instead of going to "dad's workshop" to whip up some sort of contraption out of wood and scrap metal - one would do few clicks online to get needed goods and then its 3d printing and soldering time