Equatorial Platform - New Build

[wobblewing]

On 12/01/2021 at 18:34, AlexK said:

N/P!

On a side note, an EQ platform will interfere with core Dobsonian principles no doubt, as a dob is not intended to work on a significant slope (that's why a trivial EQ wedge you have sketched above would not work well with it if at all, you need an EQ platform). So, many folks has figured that for the visual tracking it is better to have two of the pads on the N-S line and on the West side of the platform (the third is tangent to that line on the East) as eventually they will get more load as the EQP tracks over the meridian.

Thanks for feedback, I'm continuing the platform with N&S segments and worm drive connected to the platform using printed ball joints (just for fun 😄 ).. only doing a little bit at a time, so it'll take a little while.  Have found you can print quite reasonable ball joints, albeit never as tightly toleranced as proper metal ones.  One thing about this approach is that the commanding of the stepper motor is not going to be linear across the whole path of the platform, although I'm not sure it in reality is going to be significant - need to work out the maths.

Edited January 14, 2021 by wobblewing

[AlexK]

10 hours ago, wobblewing said:

Thanks for feedback, I'm continuing the platform with N&S segments and worm drive connected to the platform using printed ball joints (just for fun 😄 ).. only doing a little bit at a time, so it'll take a little while.  Have found you can print quite reasonable ball joints, albeit never as tightly toleranced as proper metal ones.  One thing about this approach is that the commanding of the stepper motor is not going to be linear across the whole path of the platform, although I'm not sure it in reality is going to be significant - need to work out the maths.

I guess, you've missed the point of the worm drive. What you are describing looks like the classic Poncet platform drive, which indeed needs some flex connection like a driving finger or a disk/ball joint and nonlinear drive speed along the HA (hourly angle) range. What I've meant is building the real worm drive underneath:

...with the worm made from the trivial steel threaded rod (3D printer rods are not ideal for that actually as the cog will need thin tooth profile). And a 3DP sector of a huge cog between two passive sectors perfectly orthogonal to the polar axis, so the motor tracking speed is totally linear. I'll try to find the design I had in mind, but in a nutshell: the rod with the motor are installed on the long C-shape bracket engaged with the worm by a spring. You can rock the caret down with a pedal to disconnect the worm when need to reset the platform.

Sure thing, with the modern electronics advancements a microcomputer-driven Poncet implementation is on par in complexity with the 3D printed worm cog, so it's up to you. But from my guts feeling the real worm drive should be much more reliable mechanically and have less of the guesswork (e.g. how you will sense the current Poncet position to define the driving speed? The original platform expects you resetting the platform to the end stop each time and then just tracing the time ellapsed).

Sorry, Neil, it looks like we have eventually hijacked your thread. Though in exchange it has gained more visibility on the forum no doubt!  
 

Edited January 14, 2021 by AlexK

[Rusted]

I gave my Poncet platform a cone and [narrow] friction wheel speed adjustment for the threaded drive rod.

That was before computers had shrunk from sports hall dimensions and pinhole astrophotography was still all the rage.

[wobblewing]

Sorry Neil,  Will start another thread 🙂  Didn't expect it spark up as much conversation!

[wobblewing]

I have created this thread for follow-up, so as not to pollute Neil's thread further (although appreciate this ship may have already sailed!):

 

 

Edited January 15, 2021 by wobblewing

[Stub Mandrel]

On 12/01/2021 at 17:39, wobblewing said:

Yes, but did you work out the geometries?  I don't think it'll work if you follow the axis of rotation at 52degrees, the Dob will fall off the platform!  Unless I've completely missed your point 🙂

Here's a drawing to explain my reasoning.  Based upon my Dob with CofG about 24cms and 52.2deg latitude.  It'll fall off the platform.

 

 

The platform is more or less horizontal.

I have no worries about thread drift! It all seems relevant to me.

[wobblewing]

6 minutes ago, Stub Mandrel said:

The platform is more or less horizontal.

I have no worries about thread drift! It all seems relevant to me.

Don't worry, I'd completely miss-interpreted what you said 🙂  Ignore that!

[Chriske]

AlexK,

Do you have permission to post this image.
And if so why not post the creator of this mount's name...?

Edited January 16, 2021 by Chriske

[Stub Mandrel]

1 hour ago, Chriske said:

Do you have permission to post this image.
And if so why not post the creator of this mount's name...?

It's an embedded link, rather than a cut and paste, which, rightly or wrongly,  appears to be generally accepted practice.

Although an acknowledgement is polite, the URL of the image does show the source and its appearance here should encourage search engines to locate your website.

It's legal in the EU and (presumably still legal in the UK) and explicitly does not infringe copyright:

https://www.copytrack.com/embedding-images-legal-theft/

Quote

Embedding

Embedding, also referred to as inline linking, framing, and, typically when applied without permission, hotlinking, allows you to make content visible on multiple webpages via the original location. By means of a link to the original website of an image, but also text or video, can be shown on another website without affecting copyright.

The embedded content acts as an inserted window to the website where the content is hosted: the content appears to be part of a third party’s webpage, but is in fact retrieved and loaded via the original website where it is hosted. In 2014 the Court of Justice of the European Union has ruled that the embedding of protected content without permission constitutes no copyright infringement^*.

^* Rulings of the Court of Justice of the European Union:
Nils Svensson and Others v Retriever Sverige AB
BestWater International GmbH v Michael Mebes, Stefan Potsch

 

Edited January 16, 2021 by Stub Mandrel

[Chriske]

To be clear :

The name of that file has been changed.
The drawing is mine.
The mount as is, is my idea.
I made a couple of these mount, I call these mounts Boxmount.
Published an article in Sky&Telescope in 1983(if I remember well).
A variant of that mount I did use again to mount my Bino-Kutter I made last year(posted here on SGL).
Posted that boxmount on CN years ago.
And yes it would be most polite to mention the source/original poster where ever it has been posted before.

[Stub Mandrel]

5 hours ago, Chriske said:

To be clear :

The name of that file has been changed.
The drawing is mine.
The mount as is, is my idea.
I made a couple of these mount, I call these mounts Boxmount.
Published an article in Sky&Telescope in 1983(if I remember well).
A variant of that mount I did use again to mount my Bino-Kutter I made last year(posted here on SGL).
Posted that boxmount on CN years ago.
And yes it would be most polite to mention the source/original poster where ever it has been posted before.

As Alex.K is in the USA and the image is on a Belgian website, it's unlikely he was the person who appropriated it.

The site it's hosted at is: http://telescopemaking.be/

Changing the number in the filename suggests that site has appropriated many of your files.

Which links to http://users.telenet.be/telescoopbouw/Welkidex.htm and http://users.telenet.be/telescoopbouw/Welkidex-e.htm

This misled me into thinking it was your website (I thought you were something to do with the Urania Project).

You might want to do a 'whois' search on telescopemaking.be, but I suspect you may struggle to find who has appropriated your images. According to google it can't find any examples of it, so it must be on unindexed pages.

Assuming Alex is nothing to do with that website, he may have found it embedded elsewhere, and it may be a long and complex search to unravel the truth.

You can contact the registrant via this website, although their personal details are hidden:

https://www.dnsbelgium.be/en/whois/info/telescopemaking.be/details

Edited January 16, 2021 by Stub Mandrel

[Chriske]

All these links, they’re all mine.
But absolutely out of date.

[AlexK]

Wow! I have simply pasted the Image URL from Google images search, when by an accident saw that platform image among other findings, as I recall liking the idea some year back and wanted to demonstrate the barn door principle difference from a poncet. But I'm not sure where exactly I saw it for the first time (most likely on the CN forum indeed). And that was not that exact CAD drawing. I saw it made in crude wood with the additional pneumatic lift arm assist system. So, if it was yours, all the due credits going to you, Chriske! Please, let me know how I should attribute the image in my post above, remove or replace it with a more suitable one. I'll edit the post right away if I still can.

Neil, thank you so much for looking into that closely! I'm a total dummy in EU/UK law differences vs US in regards of such incidents.

 

[Chriske]

The idea btw is not mine. I read about it in 'Astronomy' magazine(late '70, if I'm not mistaken).
Prof Greame White(Univ. Australia) suggested that a mount like that 'Boxmount' could solve many problems. He actually never built one himself. In that article were he wrote about his idea, he added a drawing. Noting more then a few lines, not even a real drawing in fact. I immediately started building 'my' version of 'his' Boxmount and wrote a letter + a few pictures of that built and sent it to Mr White. The man had asked in that same article to sent him the result and possibly pictures of his idea, 'to see whether his idea could be build and would do the job' if someone should build that mount.
The man was very pleased with my letter and told me to send that same message to Sky&Telescope.
After that first built lots of amateurs did copy that build and even improved it. Some amateurs did built a 'nested' boxmount.
Anyway, I still use boxmounts for larger telescopes. The Boxmounts I build nowadays are about 15 to 20 cm high, depending on the version.
And yes I always install a pneumatic lift arm assist system to compensate for the weight of the dob it'll support.

Leave as is Alex, no need to edit that post.
So in the end, credit should go to Mr White also. He's the one with that 'silly' idea to mount a telescope on top of a wooden box with a hinge, to track the stars...😂

[AlexK]

Thank you, Chriske, for the interesting story behind that design. I thought that's just the ordinary Barn Door tracker, which is known from 1975: https://en.wikipedia.org/wiki/Barn_door_tracker (I built one being a kid in 1979 to track the Moon with my DIY electrophotometer during a winter eclipse. The idea to use it for Telescope tracking never crossed my mind until recently (~2010), as prior to my beloved z12 I had motorized GEMs exclusively all the way to a 150mm Newt.

By the way, do you have a thread on this forum about your more recent Boxmount advancements? Or I should just search the CN?

Edited January 17, 2021 by AlexK

[Chriske]

This is my latest 'boxmount' it differs a lot compared to my original design. It action is very smooth btw.
Needles to say, the tripod is very sturdy..:-))

For those who are not familiar with the boxmount ; lots of drawings and pictures on this page.
There are lots of (white)printed parts involved btw

[Chriske]

But I think it"s time to leave this thread. Although it is a eq. platform, it has nothing to do with the original post.
Sorry Neil...🥴

[Stub Mandrel]

11 hours ago, Chriske said:

But I think it"s time to leave this thread. Although it is a eq. platform, it has nothing to do with the original post.
Sorry Neil...🥴

Not at all Chris, your mount adds to the body of knowledge and is nicely executed although the 'rustic' tripod made me do a double take!

[Chriske]

13 minutes ago, Stub Mandrel said:

.... the 'rustic' tripod made me do a double take!

These are a few leftover from a very old apple tree. It had to go, pity.

[Astrobits]

Your Boxmount is a most interesting design, Chriske. I am currently planning to make an equatorial platform and will investigate this option for my 16" scope. However, with the rotation axis in the centre of the platform I think that the scope will need a very low COG to be safe at +/- 15 degrees of tilt ( 2 hours) unless it is firmly attached to the platform.

Nigel

[Chriske]

Although I made a smaller boxmount with which I've taken pictures of the nightsky, I never used my larger Boxmounts to do astrophotography. I think it would be feasable using a precise threaded rod.

For the smaller one I used a threaded rod I did cut it myself on a lathe. for my large Boxmounts I simply buy threaded rods. That's because I never take pictures with that large one. The thick threaded rods are 'rolled', not cut. These rolled rods do not allow smooth tracking, far to many irregularities in the threads itself. But perfect to track stars for visual observing. Tracking stars with these threaded rods there's a 'wobble' in the motion, but only a veeeeeery small wobble, most of the time hardly visible. What could be done to improve tracking precision is cleaning up the surface of the rolled threaded rod with a die. It makes a big difference.
Precise tracking to do astrophtography is only possible when the upper part of the platform is near the horizontal position and for a short time. Remember it is in fact nothing more then a barndoor tracker, only 'a bit' larger.
The hinge I use is a heavy duty one. To compensate for the weight of the scope + upper part of the platform I always use a pneumatic lift unit. It's nothing more then a pump out of a rear-door of a car(not mine..,-)). You need to test were it has to be installed. You can fine tune this system until the scope 'only weigh just a few grams'. To compensate for different temp outside I place a very small weight on top of the platform. When it gets colder I relocate that (very small)weight more to the west of the platform. Works perfect. That adjustment is only needed to compensate for Summer/winter.
The largest Boxmount I ever made is 1m² and is patiently waiting to carry a large binocular I'm busy building(2x20") is on hold now, due to build of 150mm (lens)bino.

To fully understand how it works, you need to look at the pictures of my Kutter-Bino.
And btw Nigel, the rotation axis of a boxmount is not at the centre of the mount. That axis is mounted at the far-west or the far-east side of the mount. Tracking with that rod is done at the opposite side of the hinge.  See here.
I prefer to mount the hinge at the east side and the threaded rod at the west, so the telescope is 'falling down' during tracking. You can reverse the two, so you would be pushing the telescope upward. But I prefer the first one. Don't know why but it 'feels' more natural imo.
In the pictures of the Kutter-Bino I made the paltform round. That's the only one. All other are square platforms, because it far easier to attach the driving parts.

[AlexK]

7 hours ago, Chriske said:

I prefer to mount the hinge at the east side and the threaded rod at the west, so the telescope is 'falling down' during tracking. You can reverse the two, so you would be pushing the telescope upward. But I prefer the first one. Don't know why but it 'feels' more natural imo.

And that prob. explains why your mount so tall compared to the classic barn door, which is essentially just two plates doing "a closed door slowly opening to the West"

By the way, the Astrobits' confusion about the platform closeup above is due to the Azimuth Polar Alignment center axis is projecting to the hinge base piece behind it, creating an illusion it's a single module.

Edited January 18, 2021 by AlexK

[Chriske]

Correction : my mounts closes as I explained higher up.
The hinge is at the east side of the mount, the threaded rod at the west side. So I need to close the box to track the stars.

[Astrobits]

22 hours ago, Chriske said:

And btw Nigel, the rotation axis of a boxmount is not at the centre of the mount. That axis is mounted at the far-west or the far-east side of the mount. Tracking with that rod is done at the opposite side of the hinge.
I

 

Ahh! O.K. It's just that your image seemed to show a pivot point in the centre of the disc and is explained as line of sight effect by AlexK. Thanks for the clarifications.

Nigel

 

[wobblewing]

Well... Here's mine.. I finally finished it!  I ended up having to pay £2.30 for a stepper motor driver PCB.  Other than that, it's from the parts bin and made from an old shelf.

All 3d printed included the ball joints.  Driven by a stepper motor and worm gear pushing/pulling the platform (way more torque than needed, but this can be turned down on the driver PCB)... BBC micro:bit coded in Python... Powered by a 2S or 3S Lipo.

It actually works really well and I've got the accuracy spot on!

Edited February 22, 2021 by wobblewing