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Experimental 3D printed equatorial wedge for older SW SynScan mounts


Mognet
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As I'm being a bit tightfisted economical with my money at the moment, I thought I'd experiment with adapting my old style SkyWatcher SynScan alt-az mount by designing and printing a wedge to enable me to experiment a bit more with astrophotography. I'm not expecting it to be hugely accurate, just vaguely. But if I can get it to follow the same patch of sky to get 30 second exposures with my longer camera lens and without trails then I'll be happy. I seriously doubt it's strong enough to take the weight of a scope though.

I haven't tried it out yet as I'm waiting on a clear sky, but I have mounted a camera and rotated it using the controls. There is some slippage in the mount in a couple of places which isn't unexpected as the balance is off, and there is some flex in it as it's only printed in PLA with 30% cubic infill

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I'm not publishing the plans yet as it's still a prototype. I know already there are some small changes that need to be made. The teeth on the original mount don't mesh with the holes in the print so might cause further slippage, and I need to tidy up a few other dimensions

 

Hoping that this is actually a practical idea instead of one of my usual bonkers ones!

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Looks great 👍 similar concept to the nexstar 4 / 5 mount but yours has better execution with a thread to adjust the angle

Couple of minor suggestions if they help, I'd be tempted to offset the top plate from the bottom plate to help the center of gravity be over the top of the tripod, below to give you an idea

Easy-build Adjustable Equatorial Wedge for ETX

If you could also somehow incorporate a polar scope I think you'd be onto a winner 👍

As for the mount itself slipping, they are fairly simple beasts, quite easy to strip and regrease and the slippage is likely down the the amount of tension on the bolt for the axis, there's a bit of a sweet spot, not too tight, not too loose, I have the celestron version, but there is very little difference

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14 hours ago, chemistorge said:

No use to me, but excellent design.

Thanks. My designs vary between crazy and good, and I think this one could be one of the good ones

2 hours ago, doublevodka said:

Looks great 👍 similar concept to the nexstar 4 / 5 mount but yours has better execution with a thread to adjust the angle

I've not seen one of those before, but it is quite similar

2 hours ago, doublevodka said:

As for the mount itself slipping, they are fairly simple beasts, quite easy to strip and regrease and the slippage is likely down the the amount of tension on the bolt for the axis, there's a bit of a sweet spot, not too tight, not too loose, I have the celestron version, but there is very little difference

I noticed that when servicing the mount a few years ago. I was never quite sure I put the right tension on the azimuth nut when I put it back together. It's possible that I may not have set it tight enough

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Last night was the first decent clear night here in ages so I took some time to experiment with the wedge. And it does work. Took some thinking about and a little swearing

The SynScan alt-az software isn't designed to be used like this so initial attempts at using star alignment had to be ditched. Either it wouldn't align, or it would give alignment stars I couldn't see, or it would cause trailing. It seems the way to do it is to set the location to 90 degrees north (or south if you're in that hemisphere) and then skip the star alignment. Target alignment can then be done by guesswork and trial photos.

The camera stayed pretty much with the chosen star field for the twelve minute period I was shooting in. These are 200x200 pixel crops from the top left corner of the first and last images. For a first test and for my purposes it's acceptable

Example.png.4b1629d9cc86e61c6add6e4348ae4329.png

This is the result from last night once I'd figured most things out. It's shot on a Nikon D3100 with a Nikkor 35mm 1.8G lens, 22 subs of 30 seconds each, F4, ISO1600, no darks or flats, processed roughly in Sequator and GIMP

20210812-1-seq.thumb.jpg.240291a8a8f0855658665fb6ee7a125d.jpg

I would have taken more subs, but the camera battery ran out of power after those 22. Which led me on to a problem I was expecting. My print sizing isn't quite correct so the holes in the wedge don't engage with the teeth in the mount and it seems that friction alone cannot be relied on to keep the wedge in place so when I went to change the battery the whole thing rotated. I definitely need to modify that part of the design, and I think I'll just make up an adaptor for my existing one as that piece was a ten hour print

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  • 2 months later...

Hoping the skies stay clear tonight so I can test version 2

I adjusted some of the dimensions and took out the nice curves that fitted the base as they were a bit of a pain to place properly and their positions weren't calculated. The result isn't quite as pretty but it will still work. This version was printed and set up about a month ago and there doesn't seem to be any warping of the PLA so far, unlike the previous version. There is a wobble in the adaptor which seems to be due to play in the adjustment screw and mounts. I might also need to boost the thickness of some parts too

497699025_WedgeforSWAlt-Az.thumb.png.3226627e439c13b7ae8aeb4c8b1a9344.png

20211015_190913.thumb.jpg.cc95f49149a8b700731e95c695aa619c.jpg

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This is a really nice piece of engineering. I am just starting the 3d printing  and cad journey and to be honest I didn't really think it was capable of stuff like this. something for me to aim towards

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11 hours ago, dmki said:

This is a really nice piece of engineering. I am just starting the 3d printing  and cad journey and to be honest I didn't really think it was capable of stuff like this. something for me to aim towards

Thanks. 3D printing is quite capable of things like this, and more too. Several members here use 3D printing for lots of things, including clocks, telescopes and rockets for display

The biggest of the telescopes. Chriske has made several different types

Rocket for display, also by Chriske

And one of Gina's clocks

 

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On 13/08/2021 at 12:32, Mognet said:

... The SynScan alt-az software isn't designed to be used like this so initial attempts at using star alignment had to be ditched. Either it wouldn't align, or it would give alignment stars I couldn't see, or it would cause trailing ...

Would loading the firmware for an eq mount give you the star alignment option? In effect, your mount now acts more like an eq than an alt-az.  I know Celestron hand controllers can be programmed with either firmware so I suspect Skywatcher hand controllers can too.

Excellent idea by the way!

Edited by Stargazer33
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21 minutes ago, Stargazer33 said:

Would loading the firmware for an eq mount give you the star alignment option? In effect, your mount now acts more like an eq than an alt-az.  I know Celestron hand controllers can be programmed with either firmware so I suspect Skywatcher hand controllers can too.

Excellent idea by the way!

Thanks

I don't think that's an option for this mount. Certainly nothing obvious from looking at their site and I didn't see anything in the handset menu for it

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4 hours ago, Chriske said:

Hey,

Nice 3D-print project. Could you explain a bit more how this tracker works.
I can't figure out how you track stars with this device(it's probably me, I know, sorry...😳)

Hi,

That's ok. It basically converts the alt-az mount into an equatorial mount, so what is normally the vertical axis (the azimuth axis) becomes the equatorial axis

Alignment is crude. The camera is set parallel to the equatorial axis using the markers that were already on the mount, and then the mount is roughly aligned with Polaris. After that the handset controls are used to point the camera at the appropriate patch of sky, and the mount rotation should match that of the stars

 

3 hours ago, PeterW said:

I’d have designed it for a fixed angle to avoid flex and possible failure, but seems like yours is delivering the goods!   
good job!

Peter

Thanks. I did consider creating a fixed angle version, which would have been fine for my use, but I wanted to share it with the community too so opted for the adaptable version. The hinge seems to take most of the weight, so I think it's fairly safe. I wouldn't trust it with anything more than the weight of my camera and 70-300 lens, i.e. less than a kilo

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ok, now I'v got it..!  I thought the upper grey and black part were also printed...silly me...😁
Suggestion, change the threaded rod with something more stable, as Peter also explained. I'd print a wedge to fill in that gap + a little possible polar tuning. Or is there really need for that long threaded rod..?

That rod btw: nice print, very nice print indeed...!

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3 hours ago, Chriske said:

ok, now I'v got it..!  I thought the upper grey and black part were also printed...silly me...

That's ok. Perhaps I should have used this photo originally. It shows the whole thing with the camera too

20210812_002308.thumb.jpg.b2cf0ebbfb1c040df179c04e3f7cee5c.jpg

3 hours ago, Chriske said:

Suggestion, change the threaded rod with something more stable, as Peter also explained. I'd print a wedge to fill in that gap + a little possible polar tuning. Or is there really need for that long threaded rod..?

That rod could be a problem. I don't think it needs to be that long either, and at larger angles the mount may not be able to cope with the shifted weight. I'll see if I can come up with something stronger and more stable that can still be adjustable

 

3 hours ago, Chriske said:

That rod btw: nice print, very nice print indeed...!

Thanks. I used OpenSCad for the design, and the thread uses this bit of code. It creates a 2D shape of the cross section of the thread and the extrudes and rotates it

module adjustment_thread(height, threadTolerance = 0) {
    threadDepth = screwThreadDepth - threadTolerance;
    innerRadius = rScrewThread - screwThreadDepth - threadTolerance;
    
    function ra(x, z) = [x * sin(360 * z), x * cos(360 * z)];
    input = [
        for (lp = [0:0.05:1]) ra(innerRadius + (threadDepth * lp), lp / 4),
        for (lp = [0:0.05:1]) ra(innerRadius + threadDepth, 0.25 + lp / 4),
        for (lp = [0:0.05:1]) ra(innerRadius + (threadDepth * (1 - lp)), 0.5 + lp / 4),
        for (lp = [0:0.05:1]) ra(innerRadius + 0, 0.75 + lp / 4)
    ];
	
    translate([0, -adjustmentBlockPlateLength, offsetToTop - bodyThickness / 2]) rotate([0, 180, 0])
        linear_extrude(height = height, twist = -(height/(screwThreadDepth*4)*360)) 
                polygon(points = input);
}

 

Edited by Mognet
Use the right code for the thread
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19 minutes ago, Mognet said:
module adjustment_thread(height, threadTolerance = 0) {
    threadDepth = screwThreadDepth - threadTolerance;
    innerRadius = rScrewThread - screwThreadDepth - threadTolerance;
    
    function ra(x, z) = [x * sin(360 * z), x * cos(360 * z)];
    input = [
        for (lp = [0:0.05:1]) ra(innerRadius + (threadDepth * lp), lp / 4),
        for (lp = [0:0.05:1]) ra(innerRadius + threadDepth, 0.25 + lp / 4),
        for (lp = [0:0.05:1]) ra(innerRadius + (threadDepth * (1 - lp)), 0.5 + lp / 4),
        for (lp = [0:0.05:1]) ra(innerRadius + 0, 0.75 + lp / 4)
    ];
	
    translate([0, -adjustmentBlockPlateLength, offsetToTop - bodyThickness / 2]) rotate([0, 180, 0])
        linear_extrude(height = height, twist = -(height/(screwThreadDepth*4)*360)) 
                polygon(points = input);
}

 

Not my cup of tea....😳😳😳😳

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12 minutes ago, Chriske said:

Not my cup of tea....😳😳😳😳

Visual design tools are much easier to use. I chose OpenSCad over FreeCAD for this project as I didn't have the patience to get threads working

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13 minutes ago, PeterW said:

For many simple things OpenSCAD is much quicker

Agreed.  I started with OpenSCAD and found simple stuff was a doddle.  Once I started trying to create more complex designs I moved to FreeCAD and found it very powerful, but the learning curve is undeniably steep.  Perhaps it's not so bad if you have other experience of using these sorts of tools.

I'm almost all GEMs these days so it's not a project I have a use for, but it's certainly very neat and worth the effort given the widefield image posted.  I may be imagining patterns where there are none, but I'd say it's approximately centred on the North America Nebula and the Pelican?

The threading on the camera clamp in the last photo looks very tidy.  I must conclude that the printer is quite nicely set up.

James

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OpenSCad is good but slow, and designs can take some thinking about. FreeCad I find frequently frustrating. Fusion 360 is brilliant, but takes ages to load on my laptop. Updates are worse as they can take 30+ minutes

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7 hours ago, Gasman said:

Have you tried DesignSpark Mechanical at all? It's a freebie cad app for Windows and very intuitive. If I can learn Cad with it anyone can 😏.

Steve

Downloaded it last night and had a quick play. Just watched a batch of tutorial videos and it looks quite good. Only thing that seems to be missing compared to FreeCad and Fusion 360 is constraints in sketching. I initially found them frustrating, but they are also useful at times Also has constraints, which are not on by default but need to be enabled in settings

Edited by Mognet
Found the constraints
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