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Is the eq platform as wonderful as the Dobsonian mount?

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#26 osbourne one-nil

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Posted 27 November 2020 - 02:40 PM

This is my understanding:

Thanks Jon - that's great. Between you and YouTube, I get it now!

 

I'm surprised they're not more common. 



#27 junomike

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Posted 27 November 2020 - 02:54 PM

That probably depends on the platform.  With the Tom O. platform, you just grab the handle and pull.  It takes maybe 5 seconds.  Then you have to reacquire the target but the actual resetting is super easy.  

 

attachicon.gifJstar on EQ Platform reset handle.jpg

 

I am not sure how one resets other platforms, the Tom O. platforms use steel against brass for the northern axis which is where the drive is and roller/ball bearings on the southern axis.  

 

Jon

Jon, That's true, I've seen some that have motors to re-set and some have handles.  Some go for 60 min, others 90min.

 

One negative  (IMO) that I don't see mentioned and didn't know until recently is that the Platform replaces the bottom board of the base which prohibits the easy use/Mod of Setting circles. 

If this is no longer correct, please correct.



#28 Jon Isaacs

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Posted 27 November 2020 - 02:55 PM

Do eq platforms need much smaller motors and batteries than go-to?

If they cost $400+, I wonder why more scope makes are not building them. Maybe the buyer base is unaware of the benefits? The main drawback I see is the extra height if the scope was otherwise already the perfect height. I also wonder how well they handle vibrations.

 

I think it's basically because of their limited latitude range and the fact that all the do is track.  They're not cheap.. The good ones.. And with GOTO available, it's a small market.

 

As for alt az, because that is what a dob does and is simpler. The eq platform was never intended to sleep in RA and declinations. It just tracks. ... Ah... I mean manual slewing and motor tracking. Best of all worlds. Did you mean that an eq platform can slew? I doubt it, not would I want that.

 

 

For astrophotography, it's necessary if you want to guide. Did you read the link when astrophotography with the 25 inch Obsession was discussed? I also mentioned my Platform is a dual axis, that means it can slew two axes.

 

It's not necessary to use it, i normally just operate it like a normal Dob. For visual, it's only useful at high magnifications.. but unlike Chucky, I found I prefer manual tracking so currently my Platform is on long term loan.

 

If I ever get into EAA, that's where it could be handy. 

 

Jon


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#29 tommm

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Posted 27 November 2020 - 03:06 PM

waytogo.gif

 

I have a basic understanding of how they work, I don't think I could design one without doing some research.  And sometimes I have had to look at a picture to make sure I know which end points north, smile.gif

 

This is my understanding:

 

Imagine you had a large cone whose central axis was pointing at the polar axis and riding on bearings.  If you were sitting on the cone, if it rotated at sideral rate (23hours 46 minutes), then the sky would not move, it would track as an equatorial mount.

 

If you now cut that cone off so it has flat surface, that flat surface also tracks.  

 

That's my understanding of how an equatorial platform works. 

 

Jon

That's the general idea:

 

eq platform, geometry.JPG

 

You can see that the north sector of the platform can be a cylinder (imagine cutting out the bottom part of the front face of the cone) and the back sector can be cylindrical, or a pivot like a bolt (Poncet type) placed on the axis of the cone. You can also place the north sectors vertical, but then to keep the bottom face of each sector flat rather than twisted (so it can ride against a fixed bearing), they must be angled, and the surface is not cylindrical.

 

So there are 3 general approaches, Poncet, de'Autume (or VNS), and cylindrical bearing:

 

eq platform, 3 basic types.JPG

 

 

The Osypowsky platforms are VNS, Vertical North Sector type. This is the more difficult type to make since it requires cutting an elliptical curve on the north sectors.  Many folks do this using a jig to rotate the rough cut sectors mounted on the platform against a fixed belt sander or similar as shown below (note the "fin" attached to the platform top to angle it at your latitude).

 

eq platform, sanding sectors.JPG

 

Eugene Baraff derived all the equations to design a VNS type platform back in mid 2000, and gave a graph of the curve to cut the north sectors.

 

Some (including me) thought that this type was preferred due the sectors being vertical so not as prone to moving under the heavy load of a large scope.  I no longer think that. I would now build a cylindrical bearing type, because it is much easier to accurately cut out a cylindrical north bearing using a router and circle cutting jig, and flexing is not an issue if built with the north sector braced.  There is also no scrubbing of the bearings on the north sector of a cylindrical sector platform. On a VNS type the north sectors slide across the bearing surface as the platform rotates, i.e. the bearings don't roll along a line parallel to the sector edges, they follow a curve on the face of the sectors. You can easily demonstrate that by holding a pencil in fixed position against the sector surface as you rotate the platform. I don't know of any real downside to the scrubbing though. It wasn't an issue for me.

 

Example of cylindrical north sector platform (this one used a tangent drive):

 

eq platorm, cylindrical sector, tangent drive.JPG

 

The platform I made also included a pseudo dec drive as shown below on the underside of the platform.  The south pad (the one furthest back in the second photo below) sits on a 3/4" diameter rod that has a slot cut in the other end, and a ball bearing mounted in the slot. This rides against the aluminum disk that is rotated by the motor. The disk is eccentric on the shaft, so as it rotates it moves the 3/4" rod up/down over about 1/2" range iirc. I made electronics and hand pad with buttons for slow/fast slewing in RA and pseudo dec.

 

eq platform, pseudo dec drive.JPG

 

eq platform, photo.JPG

 

There was a quite active Yahoo group on platforms in early-mid 2000 where Gene posted his calculations and I posted calculations for required motor torque for north sector and pseudo dec drive. I no longer use a platform since I rebuilt my scope and included Alt/Az drives using OnStep in the rocker box:

 

Alt and Az drive components.JPG

 

The platform made a huge difference in convenience for me, both at star parties (long lines of viewers as someone mentioned) and at being able to relax while I looked at star charts and other things knowing the object would stay in the fov.  Just roughly pointing the platform toward Polaris usually was good enough to keep things in the fov for 20 minutes or so.  Much better alignment is required for AP of course.  The photos are from a Powerpoint presentation I gave on platforms in 2005.


Edited by tommm, 27 November 2020 - 03:07 PM.

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#30 Second Time Around

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Posted 27 November 2020 - 04:49 PM

One negative  (IMO) that I don't see mentioned and didn't know until recently is that the Platform replaces the bottom board of the base which prohibits the easy use/Mod of Setting circles. 

If this is no longer correct, please correct.

Not necessarily.

 

I can place either of my Dobs on my Sumerian platform.  To do so Michael at Sumerian suggested putting non-slip pads to hold the aluminium feet of my 8 and 10 inch OOUK Dobs.  Although I've done this and it seems to work, I'm not 100% confident that someone as accident prone as me won't have a mishap.

 

After lockdown ends I'm going to have the top board of the platform replaced with a design like the Asterion Ecliptica  Light.  These are made in Ukraine and are a similar price to the Sumerian (just under 400 EUR).  As you can see from the picture of the Ecliptica Light there are 3 retaining grooves on the top board.  In these I'm going to put non-slip pads.  Unfortunately I can't retain the top board of the Sumerian as it's been shaped and cut away to reduce the weight (see bottom  pic below).  In fact the Sumerian weighs just 2kgs/4.4lbs compared to 5kgs/11lbs for the Ecliptica Light.  The Sumerian is rated for a payload of up to 40kgs, the Ecliptica Light 30kgs.  Asterion also make a heavier duty model called the Pro that has a payload of 50kgs.

 

Bear in mind these payloads are for Dobs as they have a low centre of gravity.   For other set ups the payload would be lower. 

 

One of the pics below of the Ecliptica Light shows it with a tripod on.  I'm going to try this with my 72mm f/6 refractor on a Berleback Report 112 Astro tripod, and also with a Pentax K dSLR on my Leofoto 364C carbon fibre tripod.  I may need to figure out some form of locking arrangement for these though.

 

Any ideas for such a locking arrangement, or indeed any other modifications gratefully received!

 

Ecliptica Light   

 

Ecliptica Light.jpg

 

ecl-ecliptica-tracking-platform.jpg

 

 

Sumerian

 

Sumerian dobson-platform.jpg

 

Apologies for all the editing but our internet connection is playing up this evening.


Edited by Second Time Around, 28 November 2020 - 04:31 AM.

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#31 Chucky

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Posted 27 November 2020 - 05:35 PM

(( For visual, it's only useful at high magnifications.. but unlike Chucky, I found I prefer manual tracking so currently my Platform is on long term loan. ))

I like both manual and platform tracking. This applies to all powers. For me it just depends on the situation. When I show newbie friends the platform really really helps. And tracking helps when I observe with my club buddies at our dark sky site as we all tend to go between scopes to share views. Awful nice to know the object doesn't move. But manual many times has its place too. My scopes move well. So I guess for me I'm covered either way. Not a bad problem to have. It's truly a personal thing.

Edited by Chucky, 27 November 2020 - 05:49 PM.


#32 Chucky

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Posted 27 November 2020 - 05:58 PM

(( Do eq platforms need much smaller motors and batteries than go-to? ))

Really amazing that my platform can track a 75 lb scope with a tiny 9 volt battery for several full night's observing..... or even more.
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#33 sanbai

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Posted 27 November 2020 - 10:56 PM


 

Not necessarily.

 

I can place either of my Dobs on my Sumerian platform. 

....

 

Ecliptica Light   

 

Sumerian

 

All very interesting information!

Not to safe the money, but I'm actually thinking that my father in law may have fun building a platform. He has a small shop at home to build stuff as hobby.

 

How easy is to play together with a generic platform and a Nexus DSC?


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#34 jessebear

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Posted 27 November 2020 - 11:58 PM

I always thought they would become more common as well, given the increased interest in things like EAA and AP in general. Probably much easier to just go the AVX/small refractor route though.

 

I built an 8" F5 dob with OnStep over the summer and I've enjoyed using it, but I wanted to see what an EQ platform would be like for my (manual) 10" dob. With some good advice from here, the Arduino forums, and the OnStep folks, I've finished designing one using aluminum extrusion and 3D printed parts. I need to cut the aluminum yet, but the parts are printing. It's a Gee-type Poncet platform, though I'm thinking I could have gone the VNS route as well with a bit more math. While it's designed for my latitude down to the ten thousandth of a degree, I know neither my printer nor fab skills are anywhere close to turning that precise of a design into as precise of a reality. Should still be fun though.

 

uESzm0T.png

 

 

It sits a little over 4.5" off the ground and should be good for just over 73 minutes of tracking. I'll be using limit switches so that it automatically resets itself at the end of a run, though I need to work out what would be a 'safe' return speed. It may just be more prudent to have it automatically stop at the end of a run and wait for input to reset.


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#35 Jon Isaacs

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Posted 28 November 2020 - 04:43 AM

Jon, That's true, I've seen some that have motors to re-set and some have handles.  Some go for 60 min, others 90min.

 

One negative  (IMO) that I don't see mentioned and didn't know until recently is that the Platform replaces the bottom board of the base which prohibits the easy use/Mod of Setting circles. 

If this is no longer correct, please correct.

 

The Platform can replace the ground board but it doesn't have to...  

 

I do not use setting circles but I believe that it would be possible to use setting circles with encoders using the platform as a ground board.  It might require a bit of effort the first time but much less than setting up GOTO on a scope.

 

Jon


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#36 Second Time Around

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Posted 29 November 2020 - 12:42 PM

All very interesting information!

Not to safe the money, but I'm actually thinking that my father in law may have fun building a platform. He has a small shop at home to build stuff as hobby.

 

How easy is to play together with a generic platform and a Nexus DSC?

Very easy with my OOUK Dob as it's made from aluminium and doesn't have a bottom board as such.  I'll leave it to others to answer on other more conventional makes.



#37 Tom Stock

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Posted 01 December 2020 - 09:24 PM

I'm certain you've seen these videos, but just in case you haven't:

 

https://www.youtube....YCbeeGjI&t=240s

https://www.youtube....uF9bfbiW4&t=55s

 

I'm in the process of moving from an SCT on a GEM, to a push-to dob on an equatorial platform.

 

Really excited about it actually.


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#38 stargazer193857

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Posted 01 December 2020 - 10:06 PM

I'm certain you've seen these videos, but just in case you haven't:

https://www.youtube....YCbeeGjI&t=240s
https://www.youtube....uF9bfbiW4&t=55s

I'm in the process of moving from an SCT on a GEM, to a push-to dob on an equatorial platform.

Really excited about it actually.

I approve of your choice.

And thank you for the videos.

Edited by stargazer193857, 01 December 2020 - 10:10 PM.


#39 GeneT

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Posted 06 December 2020 - 07:52 PM

There's a thread about imaging with a 25 inch F/5 Obsession on a Tom O. Dual Axis platform. 

 

https://www.cloudyni...m/#entry8530321

 

I have a dual axis Tom O Platform. It's very solid, tracks accurately and retains the essential Dobsonian nature, it's a Dob that tracks.

 

But I found I preferred manual tracking... old habits die hard.

 

Jon

I have owned two dual axis Tom O Platforms. They are superb! However, several years ago I quit using them on my 12.5 inch, F5 Portaball. Find, look, nudge, find. . . .I am able to view fine even at 300X or higher. Most of the time, however, I am viewing between 100X and 200X. 


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#40 Jon Isaacs

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Posted 06 December 2020 - 08:13 PM

I have owned two dual axis Tom O Platforms. They are superb! However, several years ago I quit using them on my 12.5 inch, F5 Portaball. Find, look, nudge, find. . . .I am able to view fine even at 300X or higher. Most of the time, however, I am viewing between 100X and 200X. 

:waytogo:

 

I manage some rather high magnifications hand tracking.  I think longer focal length Dobs are easier because the lever is longer, you move the scope a smaller angle.  

 

I manage about 800 x with my 10 inch.. It's not easy but it's doable. But if I lose the object, I have drop back down 300-400x to find it.

 

The highest magnification i tracked was with my 22 inch. It was more of an athletic tracking event, not really observing, I just wanted to see it I could do it.. 3.5 mm Nagler + 2x Barlow + Paracorr. That was all I had, 1610x.. 

 

Jon


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#41 Chucky

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Posted 06 December 2020 - 08:23 PM

(( Find, look, nudge, find. . . .I am able to view fine even at 300X or higher. ))

Platforms really come into their own when you aren't in a rush. Want to share views or just wish to slow down and exchange filters, different eyepieces, read about the object, grab a drink, step away to talk to others, take in nature.

 

Awful relaxing to know the object is still dead centered in the sweet spot of your optic.  No need to waste time and effort to relocate. 


Edited by Chucky, 06 December 2020 - 08:45 PM.

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#42 stargazer193857

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Posted 06 December 2020 - 08:35 PM

So with properly made alt az pads, the platform is not needed just for high power observation. But it is very useful for relaxed viewing and shared viewing, sketching and such. Then for astrophotography, the bearing needs to match the site, especially for longer exposures.

The main downside I see is the extra height, if someone had already chosen focal length for optimal height. Those who thought theirs was too short will of course appreciate the platform. Those who already bought an adjustable chair won't care.

Edited by stargazer193857, 06 December 2020 - 08:38 PM.


#43 Chucky

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Posted 06 December 2020 - 08:40 PM

((  But it is very useful for relaxed viewing and shared viewing, sketching and such.  ))

 

This is an accurate assessment. 


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#44 Jon Isaacs

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Posted 06 December 2020 - 08:41 PM

(( Find, look, nudge, find. . . .I am able to view fine even at 300X or higher. ))

Platforms really come into their own when you aren't in a rush. Want to share views or just wish to slow down and exchange filters, different eyepieces, read about the object, grab a drink, step away to talk to others, take in nature.

 

Awful relaxing to know the object is still dead centered. 

 

If I used my 12.5 inch more, I'd probably have not lent my Platform out. But with the 16 inch, it adds just enough height that it's too tall for a good part of the sky without short ladder with something to hold on to.

 

But I just like tracking by hand.. given the choice between tracking by hand and tracking with a drive, I prefer tracking by hand.. 

 

Jon


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#45 Chucky

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Posted 06 December 2020 - 08:49 PM

((  But I just like tracking by hand.  )) 

 

I many many times do too Jon.  But there are times when I get an improved experience with tracking.  Sure is nice to have the ability to go either way depending.



#46 Jon Isaacs

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Posted 06 December 2020 - 08:57 PM

((  But I just like tracking by hand.  )) 

 

I many many times do too Jon.  But there are times when I get an improved experience with tracking.  Sure is nice to have the ability to go either way depending.

 

About the only time I wish I had motorized tracking is splitting doubles. But my best doubles scope has a sling primary and is too tall with the platform..

 

Jon



#47 Chucky

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Posted 06 December 2020 - 09:15 PM

(( About the only time I wish I had motorized tracking is splitting doubles. But my best doubles scope has a sling primary and is too tall with the platform.. ))

Yes doubles like platforms for sure. And slings and too talls tend to not. Situation dependent.  Type of observing and scope in these cases. 


Edited by Chucky, 06 December 2020 - 09:21 PM.

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#48 stargazer193857

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Posted 06 December 2020 - 10:55 PM

(( About the only time I wish I had motorized tracking is splitting doubles. But my best doubles scope has a sling primary and is too tall with the platform.. ))

Yes doubles like platforms for sure. And slings and too talls tend to not. Situation dependent. Type of observing and scope in these cases.


At first I did not catch why a sling is bad. Now I got it.

#49 GeneT

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Posted 08 December 2020 - 01:09 AM

waytogo.gif

 

I manage about 800 x with my 10 inch.. It's not easy but it's doable. But if I lose the object, I have drop back down 300-400x to find it. (Same here.)

 

The highest magnification i tracked was with my 22 inch. It was more of an athletic tracking event, not really observing, I just wanted to see it I could do it.. 3.5 mm Nagler + 2x Barlow + Paracorr. That was all I had, 1610x. (Wow!)

 

Jon


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#50 azcubs76

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Posted 13 December 2020 - 03:49 PM

I always thought they would become more common as well, given the increased interest in things like EAA and AP in general. Probably much easier to just go the AVX/small refractor route though.

 

I built an 8" F5 dob with OnStep over the summer and I've enjoyed using it, but I wanted to see what an EQ platform would be like for my (manual) 10" dob. With some good advice from here, the Arduino forums, and the OnStep folks, I've finished designing one using aluminum extrusion and 3D printed parts. I need to cut the aluminum yet, but the parts are printing. It's a Gee-type Poncet platform, though I'm thinking I could have gone the VNS route as well with a bit more math. While it's designed for my latitude down to the ten thousandth of a degree, I know neither my printer nor fab skills are anywhere close to turning that precise of a design into as precise of a reality. Should still be fun though.

 

uESzm0T.png

 

 

It sits a little over 4.5" off the ground and should be good for just over 73 minutes of tracking. I'll be using limit switches so that it automatically resets itself at the end of a run, though I need to work out what would be a 'safe' return speed. It may just be more prudent to have it automatically stop at the end of a run and wait for input to reset.

I would love to see your design if you're willing to share anything. I recently got a 3D printer and am thinking about doing the same thing. I'm an electrical engineer and am good with the electronics part of it if you want to collaborate.

 

I don't mind the manual tracking on my 8" Dob even at 300x but it's almost impossible to share views with family and friends as it's out of the view in moments. I did recently get an APM/Lunt 4.7mm 110º EP which makes a huge difference. I can easily build an EQ platform for less than that one EP though. 
 


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