Home made equatorial mount

[wongataa]

This year  have been building an equatorial mount.  It is based on the OpenAstroMount.  It is now at a state where I am happy with it.  I do have a couple of small changes I will make at some point but they won't affect how it looks.

I have had good results when using it so far.  I have only attached my Canon camera to it so far but I will be trying a lager telescope to see if it can cope with that.  There has been a learning curve in working out how to set up the control software coming from a star tracker where you have no control after setting it running.

It has motorised altitude and azimuth axes so the polar alignment is fully carried out with a computer.

 

Now I just need more clear skies to use it!

[Mandy D]

That looks engineered! What is the expected payload capacity?

[CraigT82]

What a unique mount, Looks like it is driven via long belts around the two large round plates?  What is the need for the tall ‘rats cage’ pillar? That looks like it might be a weak spot.

[Chriske]

AWESOME...!!!😳😳

[Peter Drew]

Very nice, interesting design and use of materials.   

[wongataa]

46 minutes ago, Mandy D said:

That looks engineered! What is the expected payload capacity?

I'm not sure what the payload capacity is.  I will have to try something heavy and see what happens.

[wongataa]

39 minutes ago, CraigT82 said:

What a unique mount, Looks like it is driven via long belts around the two large round plates?  What is the need for the tall ‘rats cage’ pillar? That looks like it might be a weak spot.

The RA and Dec axes are driven by belts around the large wheels.  The wheels are to help get the gearing at a sensible ratio.  The pillar is just to raise it up more.  When it was attached directly to the tripod it was a bit low for where is use it in my back garden.  It needed to be higher to see over some trees and roofs better.  It is a very sturdy pillar though.

[vlaiv]

This is really interesting.

3 minutes ago, wongataa said:

The RA and Dec axes are driven by belts around the large wheels. 

I actually have concern about this bit.

Small error on last stage can be significant in terms of absolute error.

When belt is placed at first reduction stage - then any error it produces is small in magnitude (but much faster - which puts strain on guide system). Belt at last stage can have significant amount of error. If meshing is not very precise there could be fraction of a degree of peak to peak error (which is much larger than say half an arc minute often found in even cheap mounts).

[wongataa]

3 minutes ago, vlaiv said:

This is really interesting.

I actually have concern about this bit.

Small error on last stage can be significant in terms of absolute error.

When belt is placed at first reduction stage - then any error it produces is small in magnitude (but much faster - which puts strain on guide system). Belt at last stage can have significant amount of error. If meshing is not very precise there could be fraction of a degree of peak to peak error (which is much larger than say half an arc minute often found in even cheap mounts).

Well so far there have been issues during use so hopefully it works OK.

[vlaiv]

4 minutes ago, wongataa said:

Well so far there have been issues during use so hopefully it works OK.

I just checked website for OpenAstroMount and I see that it is friction belt not timing belt - which is good as far as any meshing error goes - no meshing, no error. I do wonder how much friction there is, will belt slip at some point?

In any case, given that it is open source project and that it is in part 3d printed - if any issues arise in use - some modifications can be done to mitigate the issue.

I've seen PHD2 guide RMS of 0.5-0.7" quoted and that must be from tests, which would indicate that the mount works as intended.

[markse68]

That looks very cool- nice build! Is the altitude angle also motorised?

Mark

[Rusted]

Pretty, but I wouldn't start from there.
I predict a jelly on steroids when loaded with a telescope.

It has lots of parallel tubing held only at the ends.
There is no triangulation anywhere.
Except the PA by accident. Where there was no choice.

There is no boxing anywhere to provide accumulated plate stiffness in all planes.
There is no strength from 3D thickness in solid castings.
All the computerised adjustments are potential flexure points.

Firmly skin the open tubing assemblies in aluminium or CF plate.
Gain from the well known "stressed skin" effect.
Then you might be able to hang a telescope from it.
Though I still rather doubt it myself.

If I really, really had to use a printer I would be designing thick castings.
Using very large diameter axes and thick, large junction plates using only sliding bearings.
The Dobsonian taught us that the largest amateur telescopes can be mounted on plywood.
Your design committee could easily do the same.
If they stopped using spindly, off-the-shelf components.

Good luck!

Chris

Miserable old git with 60 years of DIY telescope mounting experience.

Here is my polar axis opened up for photography. That side is usually closed with another 10mm plate.
Using all-plane highly compressed, box sections using multiple studs [threaded rods] in the absence of castings.
10mm aluminium plate. Compressed in all planes by large diameter studding. [Threaded rods up to 16mm Ø]
50mm stainless steel axes/shafts. Oversized, self-aligning, flange bearings.
180mm Ø thick disk using multiple studs at the Declination 'T' junction.

All this could more easily be achieved with a 3D printer using thick section castings.
And basic engineering principles from the Victorian era.
And, you probably won't even need a chain hoist to lift it. 

[wongataa]

9 hours ago, markse68 said:

That looks very cool- nice build! Is the altitude angle also motorised?

Mark

Yes it is.

[Alan White]

Nice to see folks doing proper Astronomy and building things.
Tinkering and building is part of the fun after all.

[markse68]

4 hours ago, wongataa said:

Yes it is.

should have read your op more carefully- sorry

Edited October 24, 2022 by markse68

[wongataa]

7 hours ago, Rusted said:

Pretty, but I wouldn't start from there.
I predict a jelly on steroids when loaded with a telescope.

Quite possibly it will.  I don't know until I get around to trying it!

Part of the fun has been doing it myself even if it isn't the best for certain use cases.  Ideally I would have used more metal parts but I don't have machine tools to make metal parts.  If I do come across issues then I will look at improving the design.  If skin panels would be an improvement they would be easy to add.  For my primary use case of a camera and lens it is perfectly suitable.

It is my first time using 3D printed parts and that has been a learning experience as well working out the best way to implement them and how the various printing parameters affect the final parts.

BTW there is no design committee.  Someone posted their deign for a home-made mount that isn't particularly expensive hence off the self parts and 3D printing.  I just took that design and modified it a bit.

Note that you can't call 3D prints castings.  They aren't cast parts.  I think you just mean thick section prints.

 

 

[Rusted]

1 hour ago, wongataa said:

Quite possibly it will.  I don't know until I get around to trying it!

Part of the fun has been doing it myself even if it isn't the best for certain use cases.  Ideally I would have used more metal parts but I don't have machine tools to make metal parts.  If I do come across issues then I will look at improving the design.  If skin panels would be an improvement they would be easy to add.  For my primary use case of a camera and lens it is perfectly suitable.

It is my first time using 3D printed parts and that has been a learning experience as well working out the best way to implement them and how the various printing parameters affect the final parts.

BTW there is no design committee.  Someone posted their deign for a home-made mount that isn't particularly expensive hence off the self parts and 3D printing.  I just took that design and modified it a bit.Note that you can't call 3D prints castings.  They aren't cast parts.  I think you just mean thick section prints.

 

A very reasonable response considering my [hopefully constructive] criticism.

If you have a drill then you make holes in plates to clamp over the present construction.
No doubt the slots in the "techno-bars" allow standardized T-headed bolts.
Carbon fibre plate is available online.

Thick section printing is much like casting in layers.
Pouring metal one ladle at a time.
As long as we agree on the basic idea that's all that matters.

The printing material is relatively weak and flexible.
At least it is compared to cast iron and aluminium.
Use carbon fibre reinforced plastics?
Print a whole new mounting in very thick sections to simulate castings and reduce flexure.
I suppose that might be costly an time consuming? 

[John Wick]

From a purely engineering perspective i have to say i admire the work. I come from a engineering design background and have to say its aesthetically pleasing to look at, i cant vouch for its functionality, those with more astro knowledge will have comments for that, but from my perspective, very nice.

[malc-c]

On 23/10/2022 at 17:42, vlaiv said:

This is really interesting.

I actually have concern about this bit.

Small error on last stage can be significant in terms of absolute error.

When belt is placed at first reduction stage - then any error it produces is small in magnitude (but much faster - which puts strain on guide system). Belt at last stage can have significant amount of error. If meshing is not very precise there could be fraction of a degree of peak to peak error (which is much larger than say half an arc minute often found in even cheap mounts).

I must admit the instructions are a work of art with very clear and animated drawings.  The actual drive is geared, its not direct from the motor.  

Quote

Both RA and DEC are driven entirely by belts, resulting in extremely low backlash. On both axis there is a two-stage belted gearbox with a reduction of 9:1 which, in combination with the large RA and DEC wheels, gives a total reduction of 316:1 and 234:1 for RA and DEC respectively.

 

Personally I like the design.  By the time all the profile sections are screwed together the structure seems sturdy enough.  Seeing this is an open source project I'm sure the design would have changed to include extra bracing or plating as suggest in post above it it was deemed necessary.

 

 

There are quite a few commercial mounts costing £2500 upwards that look less sturdy.  But adding some nice CF plate to enclose the frames making it less open frame would look nice, and could add more stiffness if required

[CraigT82]

Just need and OpenAstro tripod and pillar extension to go with it