Clever looking equatorial platform- but does it work?

[markse68]

Hi, I stumbled across a new equatorial platform for dobs called the Triangulum- it’s a very interesting concept where by tilting the circular tracks the maker says it can be adjusted for different latitudes from 30-60 degrees. I’m really struggling to get my head round the geometry of this- what do you think- should it work? Traditionally an eq platform is made with cross sectional circular segments of a cone. They are tilted because the cone is laid on its side and the circular planes are perpendicular to the axis of the cone which is now your polar axis. But if you then tilt the circular sections more or less, do they still function as a virtual cone? 🤔 If you cut a cone on a plane that isn’t perpendicular to it’s axis then you get an ellipse not a circle. I’m confused- will this work or will it just be an approximation?

Mark

[markse68]

I think I worked it out- as well as changing the angles of the circular sections you must also have to change the distance between them to make them fit the new cone- if you look at the lower tray to the left in the picture there are what looks like indents or markings for sliding the smaller circular section along the extruded aluminium beam.  Mark

[AlexK]

Nice find Mark!

Yeah, at least the rear sector is also fully movable along the meridian for sure. See two rows of holes in the bottom plate? They are for the ball bearings caret shifting, probably per degree of the target latitude. So it can be reassembled for a different latitude using that mechanism first, then adjusting the tilt everywhere. The front one need to be only tilted to match the new virtual vertex position of the cone defined by the second radius.

I can also see a clever declination adjustment system with the end stop trigger as well.

Do you have a direct link? Or that's a prototype?

Edited November 19, 2020 by AlexK

[markse68]

7 hours ago, AlexK said:

I can also see a clever declination adjustment system with the end stop trigger as well.

Hi Alex, clever isn’t it! yes indeed- full motorised positioning too. It’s a bit of a beast weighing in at 30kg- more than my complete scope- but it’s made for big dobs up to 100kg! I’m in two minds about all that extra complication but if you travel a lot with your scope then it’d be useful. Only needing to make one variation of the product for any customer location is good for them too, though it adds extra cost for the customer that may not be justifiable if you don’t travel far with your scope! 

7 hours ago, AlexK said:

Do you have a direct link? Or that's a prototype?

I think they’re still working on ironing out niggles but sounds like it’s close to production release. I couldn’t find a web page- only a fb page: 

https://www.facebook.com/groups/764497804293915/?ref=share

Mark

Edited November 19, 2020 by markse68

[Peter Drew]

My interest level in equatorial platforms keeps coming to the surface.  When the original Poncet design appeared I ended up making one to try and get my head round as to how they worked.  This idea has gradually been modified almost out of recognition by DIY experts and a few manufacturers although the end result principle is much the same, moving an alt-azimuth mounted telescope in an equatorial manner.  I'm thinking of revisiting the original design as it is both simple to make and could be engineered to carry considerable weight.  If I remember correctly, the main shortcoming of the Poncet was that the drive mechanism was tangential to the drive direction so not of a constant speed.  This lead to all manner of modifications to help address this.  The original design had the top moving surface confined by a plane angled to suit the latitude, it ran on bearings attached to either the running or fixed surface, apart from some form of drive system, that's all that was needed.  My current thoughts have been in the direction of driving one of the bearings which should rotate the driven surface without loss of accuracy once the radius of operation and motor speed have been determined.  The simplicity should lend itself to rugged construction and significant load bearing.   🤔

[AlexK]

For UK high latitudes you have to follow certain designs. The one above will be hard to reproduce as the gravity vector have to be split between two directions, thus direct driving you are considering might be inefficient without additional measures (like gearing sectors, fine coating of mating driving surfaces, expensive bearings, or that classic tangential threaded rod). I would instead leverage the 3-points of contact designs with the South single point pivot bearing raised high for the ultimate platform stability and sliding horizontally sectors, which will allow the direct driving by the horizontally rested motor shaft.

However, with the modern electronics advancements the cost of a nonlinear motor controller with BT/WiFi connection to the head unit (for that hand controller) is around $5 for the most capable microcontroller allowing even the voice control e.g. the ESP32). So no need to compromise or over-complicate the mechanical side, especially for a large heavy instrument which inertia might be devastating if the platform slips by an accident. I've been personally poking the idea of leveraging a linear actuator for my platform which provides the zero-slipping guarantee.

OTOH, the cost of 3D printing is also so negligible lately that I would rather design a fully 3D printed, fully teeth-geared system with replaceable parts for any latitude mounted as needed when traveling (e.g. I have 3 primary observing locations in California, approx 6 degrees of latitude apart max. So, having just two inserts I can cover the entire California if I don't like tilting the platform for that much (which might be dictated only by certain flaws of the construction not taking care of wide enough CoG position variations, which is easy to address during your custom-tailored design phase). As you have already mentioned this (subject of the OP) platform is a commercial endeavor targeting the production costs slashing. A DIY platform for your specific telescope (or range of telescopes) could be made to perform MUCH better exactly due to the simplicity of a single latitude design.

Edited November 19, 2020 by AlexK

[markse68]

23 hours ago, Peter Drew said:

My interest level in equatorial platforms keeps coming to the surface.

Cool- looking forward to seeing the results Peter  

Im starting to seriously contemplate building one too- it would be very useful for sketching 👍

16 hours ago, AlexK said:

A DIY platform for your specific telescope (or range of telescopes) could be made to perform MUCH better exactly due to the simplicity of a single latitude design.

Simple is good 👍 Id not be after ap accuracy but just not having to nudge the scope continuously for a while would be a big plus

Mark

[markse68]

On 19/11/2020 at 12:49, Peter Drew said:

  If I remember correctly, the main shortcoming of the Poncet was that the drive mechanism was tangential to the drive direction so not of a constant speed. 

Hi Peter, I googled but obvs not well enough- do you have any further info on this? I’d have thought a tangential drive is what you want for constant velocity? Or was it a tangent arm that was only tangential at one position?

Mark 

edit- you mean this kind of thing? Yes i can see that wouldn’t give constant velocity of rotation unless the motor speed was varied

 

Edited November 21, 2020 by markse68

[AlexK]

On 21/11/2020 at 11:04, markse68 said:

That's the South side single point pivot I've been talking about for higher latitudes.

The tangential rod driving mechanism is unnecessarily junky here though, as it's following the classic Poncet "finger" idea, which is considered a flaw due to the too long platform reset time (besides, the classic Poncet platform is actually an imaging device, so it has a very little appeal for visual work).

[markse68]

2 minutes ago, AlexK said:

(besides, the classic Poncet platform is actually an imaging device, so it has a very little appeal for visual work).

What's the difference Alex? I mean between imaging and visual?

Regarding the raised South pivot bearing, does that have an advantage over having another arc for the South- that would also raise polar axis for higher cog?

I didn't realise that was the objection to the leadscrew drive- though it makes sense. I thought it was because it didn't give accurate velocity across the full motion?

Mark

[AlexK]

35 minutes ago, markse68 said:

What's the difference Alex? I mean between imaging and visual?

Regarding the raised South pivot bearing, does that have an advantage over having another arc for the South- that would also raise polar axis for higher cog?

I didn't realise that was the objection to the leadscrew drive- though it makes sense. I thought it was because it didn't give accurate velocity across the full motion?

Mark

The difference is that imaging tasks doesn't need platform resetting often as it intended for long exposures of the same object. While visually you may reconsider your target quickly after starting observing it. So to avoid the tracking stopped in the middle of the session you want to reset the platform each time you starting the new target finding/observation just to be sure. So the platform reset better be be easy and quick. Poncet "finger" usually have to be "rewound" back to the start with the motor, which is often geared at its peak performance, so can't be simply speeded up much to achieve that rotating backwards (unless you have a gears switch, or a finger clip, which are both too complicated thus prone to systematic tracking errors and less reliable overall).

Another arc means you have 4 points of free resting for the platform. Which is always inferior to 3 points as it is hard to make all 4 on a single plane/surface at all times mechanically (we are talking simple plywood garage DIY project of course). A wooden platform can sag under uneven load and simply with time and weather elements. So it may start rocking around some unpredictable "axes maze" or overload one of the bearings often. In addition, for the high latitude you have a stronger side sliding force on the top platform, which will push into side rollers also unevenly. So your platform will tend to wobble between 8 (!) points of possible contact having 2 sectors. That's why rollers are often made soft, to at least remove all gaps. The high above the CoG South bearing will take that side load perfectly and allow to use just 2 rollers on the north sector without any side-support necessary, so you can go with the most simple, most efficient, stable, and most reliable horizontal motor shaft driving position. Besides, if you draw the cone for a higher than 45 degrees latitude you will notice, that the South end sector tends shrinking to zero anyway 

As I have mentioned earlier, the recent advances in the modern electronics make the complex driving speed variation a piece of cake even for DC motors, not to mention steppers very popular lately due to silent driver chips available. If in the past all you could do is changing the speed, now you can change the entire math model of that speed changing flow based simply on the internal timer (started on the motor start from the end stop). Thus taking into account any flaws of your DIY construction.

[markse68]

Thanks for that Alex- makes a lot of sense. I’ve started building a platform in my head so this is all very valuable input

Mark

[AlexK]

The most crucial part of the platform planning is figuring your telescope CoG geometry. That should be taking into account all of the possible configurations (e.g. the heavy smartphone in the DIY Starsense Explorer cradle and its counterweight attached). Which will often limit what you can use in your design given the optimal size of the platform. As too large a platform will interfere with your dancing around the eyepiece in the dark in X/Y/Z dimensions, while a too small one might limit your guiding time or have compromised stability at the ends of the tracking range.

[Odyssey]

Hi everybody! TEPP can be viewed and ordered on this website:  http://triangulumastro.com/
I'm the official tester, it works! Exposures of up to 300 sec can be made with a 100kg telescope guided.

MEADE LightBridge 16 "

Triangulum Equatorial Photographic Platform

SW F / 4 Coma Corrector, Asi294McPro, -20 Celsius, Astronomik L2 filter

60mm guider, Asi120mmMini, Asiair,

71x120sec

a total of 2 hours 22 minutes expo

DSS, Fitswork, Psp

Edited April 21, 2021 by Odyssey

[AlexK]

The image looks great, thank you for sharing! (a bit weird your LB16 with 4 vanes gives 8 spikes stars, just some photoshoping art I guess?).
Though the website seems to be dead to judge anything about the product.

[Odyssey]

I'm glad you like it!

The website address was wrong, I fixed it!

The four spider mounts cause four spikes.

The EQ platform causes the 8 spikes. This moves the telescope equatorially for 110 minutes and forms 4 spikes.

The system then resets and Dobson sees a slightly rotated image at the same target. Hold this again for 110 minutes.

I photographed two series so it became a 2x4 spike. If I make three series, it will be a 3x4 spike!

 

Image 1: M1 Meade LB16  20x180sec (1 series)

Image 2: M51 SW Stargate 20  69x60sec (1 series)

Image 3: NGC2403 SW Stargate 20  74x60sec (2 series)

There are also a number of videos available on my YouTube channel about taking pictures.

https://www.youtube.com/channel/UC60fDZLjUTkrPP_M7bdopDQ

 

 

Edited April 21, 2021 by Odyssey

[LondonNeil]

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p2700_Geoptik-Equatorial-Platform-for-Dobsonian-Telescopes---variable-Polar-height.html

another 'triangulum'

Very useful thread, I'm trying to get my head around these platforms.  I found another thread first and posted some questions and ideas I'd had

 

I thought I preferred CS designs as they can be made to track more accurately without the need to play with electronically controlling the drive to maintain uniform radial rotational speed, but I would like a 3 point support.  Okay that can be done....either don't fret about hitting the CoG (hmmm, not that wise) or use a raised south bearing single pivot.  What i don't get though, is how does a VNS design manage a 3 point design? Does it manage to achieve a 3 point design and still hit the CoG? can anyone explain?

having read that the errors from a VNS are merely +/-1% I may just do a VNS if the single point south bearing does still allow for the CoG to be hit (without a loooooong base), can it?

 

[LondonNeil]

My internet research has found the split ring Equatorial mount design, it looks interesting.  Anybody know the advantages and disadvantages?

[LondonNeil]

BTW, Ed Jones on youtube shows a great way to 'grind' a CS so the load to the bearing is vertical.  

[Odyssey]

M106 galaxy

Meade LB16" Classic Dobson

TEPP

60/240mm Guiderscope, Asi120MM mini,

ZWO Asi294McPro, -20 C deg,

147x60sec,

20x Dark

20x Flat

two runtimes,

Anti spike Mask,

DSS, Fitswork, Psp

2022.01.08 01:30UT-04:30UT Europe, Hungary

[philon]

On 30/09/2021 at 23:47, LondonNeil said:

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p2700_Geoptik-Equatorial-Platform-for-Dobsonian-Telescopes---variable-Polar-height.html

another 'triangulum'

No, the pointed out Geoptik AERTHA is NO Triangulum!!! The thread is about the Triangulum, which is a DUAL-AXIS  EQ-Platform. We should not compare apples with oranges here.  I would have bought the TEPP, if it was not so heavy (30 kg!). Unfortunately, the buyer stopped selling it for now and also his domain.


The Geoptik AERTHA has almost nothing in common except the flexible altitude design with the Triangulum. I owned one and tested it thoroughly with my 16-inch Dobson. I but selled it because of various reasons:

1. No Declination axis at all and no ST4 Port (due to no high level drive unit)
2. Instead, a very simple Ardunino-based manually speed correction. This 1$ "drive-unit" went into smoke, when I accidentally slipped the platform and thereby inducting current through the motor. This could nowadays easily be prevented with a little circuit under the stepper driver. Support helped due to guarantee, but it was really avooidable.
3. No good quality of the whole Electronics (see 2., cables went loose, cheep construction and not reliable for the long run)
4. NO ENDSTOP at all for the RA axis !!!
5. Not precise and very slippery belt drive construction (I always had trouble and in the end put a 3D printed array on the part). It uses a very cheap planetary gear with a lot of backslash. 
6. Not usable for higher altitudes (I live in southern Germany around 49 degrees north). The two base rings only had a distance of around 20 cm, so the whole construction went nuts, the instrument wobbled around 2-4 mm (!!!) in altitude. I had to manually fix the South Pole with special construction (see https://www.astrotreff.de/forum/index.php?thread/267791-massive-eq-platform-geoptik-aertha-polhöhe-verstellbar-30-60-800-fp/) Then the platform was then usable at least for my geographic location.
7. Very high center of gravity (no good stability)
8. Altitude knobs can not be used without tools and not from above, which is very impractical in the field.
9. The platform is very heavy

Unfortunately, I can not recommend the AERTHA platform for higher altitudes than 40 degrees at all – it will be not stable enough for a dobsonian.
Would I buy it again: no. Sorry to say.

I now own a very simple, used EQ-platform from Dieter Martini made of wood – at least with an end stop. It is very strong, very light  (1,5 KG) and simple. I am planing to build a dual axis platform by myself in the future, if not a newer, lighter and more affordable TEPP-like EQ will come into place.


Cheers Axel

Edited August 6, 2023 by philon