10” Equatorial Platform for Dummies

[Jim-Lad]

Hello John,

I love the simplicity of your instructions and it has given me the confidence to have a go at building as per your design. I've ordered some of the parts today but I am unsure what size (height, length) the aluminium segments should be as the printed size does not seem to match correctly with the top board when I print off the template (probably my printer settings) - If they are 200m in length then that's fine - I can work out the height, otherwise could you let me know what the recommended dimensions are?

Many thanks,  Jim

 

[westmarch]

22 hours ago, Jim-Lad said:

Hello John,

I love the simplicity of your instructions and it has given me the confidence to have a go at building as per your design. I've ordered some of the parts today but I am unsure what size (height, length) the aluminium segments should be as the printed size does not seem to match correctly with the top board when I print off the template (probably my printer settings) - If they are 200m in length then that's fine - I can work out the height, otherwise could you let me know what the recommended dimensions are?

Many thanks,  Jim

 

Hi Jim,

i’ve just gone out and measured my segments., the length is 170mm.  To be honest I just printed Reiner’s segments off and made sure that the right angled edge was lined up with the top of the board and the start of the 20 degree angle on the board. The length of the segment will change depending on your latitude.

Blind faith is a marvellous thing.  As they say in Yorkshire, “It’l be reet”.

John

Edited April 13, 2021 by westmarch
slang

[Jim-Lad]

Hi John,

Thanks, I'll make sure my template matches your measurement. 

Best regards, Jim 😎

 

[westmarch]

Hi Jim,

hope the attached  gives you confidence. 

B W

John

[Jim-Lad]

Hi John,

Oops - I forgot to hit the submit reply button! 

Many thanks, I'll make sure my template matches your measurements. 

BTW, for the South pivot point I'm going to try substituting an inverted mini-ball head from a camera tripod (£5 approx. on Ebay)  - once it's all up and running I'll post my efforts...

Best regards, Jim 😎

 

[westmarch]

On 18/04/2021 at 11:38, Jim-Lad said:

Hi John,

Oops - I forgot to hit the submit reply button! 

Many thanks, I'll make sure my template matches your measurements. 

BTW, for the South pivot point I'm going to try substituting an inverted mini-ball head from a camera tripod (£5 approx. on Ebay)  - once it's all up and running I'll post my efforts...

Best regards, Jim 😎

 

Go Jim!  We all learn from each other.

John

[FrankRyanJr]

John, your design and build is the exact inspiration I needed to get building my EQ platform. So to you ant the other contributors - THANK YOU!

I've a couple of questions before I get the jigsaw out if that's ok? (*update I think I've answered everything bar the motor question in the next post! 🙂 )

1- Your plans are for a 10"dob. If you've got a different size, for example mine is a 16" GSO with a circular base diameter of 800mm. How do you work out what the initial length and width measurements should be (in step 1 of your plans). 

2- In step 2 where you measure 122mm each way from the centre and then the angled line at 20° - does this measurement of 122mm matter? For my scope it looks like it'd have to be more so that the end of the angled line finishes just a little underneath the feet of the base board of the scope. 

3- The size of the aluminium arcs. I'm presuming these are left as is and printed off from Reiner’s  page to be cut exactly as they are. Again, I'm guessing the arc of the circle stays the same no matter how wide. Also the time it takes to roll from start to finish is constant (sidereal rate) so no 'scaling' needed there?

3- Motorhead! Will the EQ-1 have enough torque to drive my set up?

It'd be good to know but I lack the smarts to work it out. I remade the base of mine from plywood because the composite board all these dobs are made from is super heavy by comparison. (I saved 6Kg doing this). 

So now I'm running at 56kg fully set up (see pic). 

Lastly, how do you reset? Do you just turn the drive off and slide the platform back to the start? Is there any need for an alarm or indicator that the arc is at the end? I'm imagining screaching metal or the whole thing being driven off in the middle of the night!

Thanks again!!

Frank

 

Edited April 30, 2021 by FrankRyanJr

[FrankRyanJr]

So, I figured I'd scale up your plans exactly) onto the footprint and outline of my base and it's actually looking pretty good. By eye the footprints looked different but when you scale it precisely (and I overlayed your plan onto my plan in photoshop) I could align the 3 feet with mine showing what lengths to draw. 

The black outline in the pic below is just that and this is what I'm going to use as a cutting template for the top and base of the platform. 

[westmarch]

Hi Frank,

You are certainly boldly going where nobody, except @Moonshane has gone before.  The short answer to all your questions is that you are going way beyond anything that I would have attempted. Reiner effectively did the work for conventional 8” and 10” dobs.  Given that most of the weight of a dob is the mirror, yours is really heavy.  My advice would be try to PM  @Moonshane for advice. He has been checking in recently so may be able to help.

In answer (guesses really) to your questions:

1. The important point is to have the feet of the dob as close as possible to the outermost edge of your platform and that should be as close as possible to the perimeter of the circular dob base. You are trying here to create as wide a base as possible since when it tilts you do not want the centre of gravity of the dob to go outside the base or it will topple over. That is a very real risk with your setup. You could end up injured and under this is if it falls and at best it could be a very expensive exercise.

2. You are altering the effective length of the VNS ellipse so you will get some target drift.  For visual observing, it probably doesn’t make a lot of difference, particularly if you are using your dob as a light bucket for DSOs with a wide angle, low powered EP.

3.You need to up the size of the bearings and also the thickness of the aluminium arcs to provide better mechanical strength.  Hard to say if the motor can cope - common sense would say it will struggle.  The weight of your rig will certainly give rise to more inertia and friction .

4. Reset - you turn the drive off and slide the arcs back to the start point - it takes some physical effort with a 10” which is why designs for larger dobs have a clutch built in to release the motor and let the arcs run back on the bearings.  When the rig reaches the end of its travel, it hits the bolt stops on the aluminium arcs and starts sliding on the bearing.  You hear the judder but the weight of your rig may mean instead of sliding, it simply burns out the motor.

Sorry Frank if I sound like a wet blanket here but I really think you need better advice than I can give.

John

 

[FrankRyanJr]

Not at all and thanks for replying! Half the fun is figuring this stuff out and if @Moonshanehas any advice I'm all ears!! 

I've seen dobs larger than mine on eq platforms and for sure the whole rig I'm making will need to be beefed up to accommodate the weight and higher COG. I'm sure I can source stronger bearings / metal / suitable motor with clutch.  

[Atomic__Bear]

OMG!  THANK YOU!  This is exactly what I’ve been looking for. I’ve spent a few weeks gathering info about making one of these for my 8” Orion XT8 and this ticks every box. Solid, good looking, inexpensive and relatively easy to make. This will be my winter 2021 project!  I’ll check back in when I’m done to report on my success level. 👍

[Atomic__Bear]

John,

I got an Orion XT8i dob for my birthday a couple months ago (my first scope ever) and I'm super impressed.  The only thing it's lacking (for now) is an EQ Platform, so I started researching and found TONS of useful information in a LOT of different places!  I read through your guide (stellar DIY instructions, bro - good job!) and I'm leaning toward making a VNS platform like yours (or very similar).  I'm curious about the pivot "bearing" for the South side... All the other VNS style EQP's I've seen so far have a radiused / latitude-angled south bearing, except for Reiner Vogel's.  Do you still recommend using a pivot-type South Bearing, or looking back, would you change to a radiused / angled one?  I'm about to start gathering the parts and start fabrication, but I thought I'd ask first.  Again, awesome build, and I'm looking forward to this project more than I have on any other one in many years!  Cheers,  Chris in Vancouver Canada.  (49° N. Lat if that helps for your answer - I know from reading a bunch that the pivot mount likes to be used in further north latitudes, but I'm not sure if 49° is far enough)  Thanks and CLEAR SKIES!

[westmarch]

On 11/08/2021 at 04:51, Atomic__Bear said:

John,

I got an Orion XT8i dob for my birthday a couple months ago (my first scope ever) and I'm super impressed.  The only thing it's lacking (for now) is an EQ Platform, so I started researching and found TONS of useful information in a LOT of different places!  I read through your guide (stellar DIY instructions, bro - good job!) and I'm leaning toward making a VNS platform like yours (or very similar).  I'm curious about the pivot "bearing" for the South side... All the other VNS style EQP's I've seen so far have a radiused / latitude-angled south bearing, except for Reiner Vogel's.  Do you still recommend using a pivot-type South Bearing, or looking back, would you change to a radiused / angled one?  I'm about to start gathering the parts and start fabrication, but I thought I'd ask first.  Again, awesome build, and I'm looking forward to this project more than I have on any other one in many years!  Cheers,  Chris in Vancouver Canada.  (49° N. Lat if that helps for your answer - I know from reading a bunch that the pivot mount likes to be used in further north latitudes, but I'm not sure if 49° is far enough)  Thanks and CLEAR SKIES!

Hi Chris,

Reiner has put up VNS segments for 48 and 50 degree platforms without specifying an alternative arrangement for the South bearing. I would go with the master’s judgement. 😀

Good luck with the build.

John

[LondonNeil]

reviving an old thread with some questions If any of the platform users could give some comments based on longer use?  I'm particularly interested in how well the drive works, any problems with slip?  I'm researching a build for a 12" dob so am thinking about the extra weight.  I'm also interested to know if the hand filed segments lead to any noticeable error/wobble?  I've worked out a design in my head that would tackle both possible issues but makes it a more complex build...and KISS has a certain neatness!  Also long term experiences with the EQ1 motor would be interesting.  I think i may go with a PWM digital speed control and high torque low speed 12V motor, maybe with a worm gear reducing gearbox but again, KISS is tempting!

[FrankRyanJr]

With the  platform I built as inspired by the guys before me on this thread for my 16''  (project link below)  I could get away with one drive on the downward motion but I rely on both drives rotating at the same speed to track. I hand cut the arc's and filed to as close to the template as possible and for visual at high mag I get around 30 min of tracking with the object centered. I've tried imaging on the setup but I find the wobble is very frustrating and I've pretty much given up. I don't have the patience for it. I used to do planetary with an ETX125 (5'') Mak and that also used to drive me bonkers - chasing the planet around the chip get's old really fast! 

Honestly, with a 12'' dob I think one EQ drive will do fine and if you are super careful in making / cutting / levelling / orienting the base then you'll get very decent tracking. 
However, if you've the ability to make it with a stepper motor like a Nema one and control the speed via some kind of input then I'd heartily recommend it.  You'll just eliminate any doubts you have with what may be causing drift or tracking rate issues if you get them. 

Best of luck with the project! 

https://www.flickr.com/photos/franks_astrophotography/albums/72157719520338922

 

Edited September 29, 2021 by FrankRyanJr

[LondonNeil]

I fear I may be talking to myself but typing is like saying it out loud isn't it?  It helps me think it through anyway.

Still trying to settle on a design.  I've worked out I want.

A.  durable build.  i don't want motors to burn out, rollers or bearings to wear out and so on

B.  reliable,  i don't want slipping drive wheels or temprementality

C. i want accurate tracking...just because!

 

I'm a competent diyer with a decent skills and tools but not professional, nd not equipped with more than hand tools, this combines with A and B to mean we need a reasonably simple design but can do some stuff needing neat and accurate.

C....well thats the perfectionist and engineer in me.  i'm looking at all the designs on the web and seeing assumptions and lazy shortcuts.  many may make sod all difference....i'm to lazy to do the maths!  haha!  but i am intrigued to see if i can solve the puzzle with a simple design that is perfect mathematically, eas to build and works reliably.

 

so on to things i don't like.

VNS designs.  i don't like that the north bearings have to be basically carefully filed to shape, its not accurate.  i don't like that they don't say vertical as the table tracks and since they aren't a knife edge, you get more inaccuracy.  I don't like that the bearing contact point moves on the roller, even with the angled bearings, again it leads to tracking inaccuracy in rotation speed.  this last one can be overcome by curving and twisting the bearings...but you'll need good maths and a 3d printer so...no.

https://chrismadsen.org/2020/09/3d-printed-equatorial-platform/

the answer here is a CS design, easy to cut very accurately. ...if its own inherent drawbacks can be overcome. for example, this high quality looking design is a CS

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

 

friction drives, inherently unreliable and subject to wear, particularly tricky with a CS design for a higher latitude and heavy dob.

screwdrive should be more reliable than friction, but the rotational rate will not be uniform, the screwdrive drives the pin and a uniform rate but as its only tangential to the bearing at one point, and its angle to the driven point on the bearing varies, the rotational rate will vary

https://www.kirchdorferweb.com/astronomy/eqplatform.html

My next idea was to consider a gear drive, but such a large difference in size from small drive gear to driven gear would be far from ideal, basically just one tooth meshing at anytime, noisy and vibration and even if I could make the teeth on the bearing edge (3D printing possibly) in reality that's not going to happen.  Then I considered using a piece of chain wrapped round the platform CS bearing and acting as the large gear, meshing with a sprocket,  that is simple to make but the vibration would be worse, with the sprocket only meshing on one tooth.  Sprockets are designed to have the chain wrapped around them....Ah ha!  so wrap the chain!  I think I have a workable idea,...so bicycle chain wrapped along the CS bearing edge and attached at the end of the segment, set a drive sprocket over to one side and have the chain come unwrapped from the bearing (which it will do tangentially) over to the drive sprocket, around half of it, across the mount to an idler sprocket at the other side of the mount, wrap half way around that and then back to the CS bearing where it wraps around that and is attached at the far end of the segment.  Cracked it....I think.  this would give a totally linear pull on the chain as the sprocket is driven,and that would pull the CS bearing at a uniform , smooth and constant rotational rate.

I just need to decide....is this overkill ...probably, but is it actually that much harder than a friction drive?  probably not so....there may be a detailed build coming.  can't start until the Dob is in my hands and i can take measurements.  Oh yes, the Dob, a 12" Skywatcher f/5 classic tube.  not sure on the weight but must be about 40kg at a guess, hence why i don't want a simple friction drive!

 

comments welcome (polite ones haha!)

 

[LondonNeil]

Hi @FrankRyanJr !  I started typing my last response last night, and finished it tonight after your response.  Good to see I'm not talking to myself!  Your mount looks good.  Half hour centred you say, and presumably a little longer if you're fov is wide and you accept a bit of my drift.  Yes I've seen a few comments on vns designs they suggest that sort of range while CS designs seem to be getting twice that, I guess th lots of people are making their bearings a bit short.  Either they print Reiner's segments and these aren't more than about 8 degrees, or the rollers are short and the bearings are traversing their length over about 8 degrees?  Anyway whatever, CS designs seem to get about 15 degrees/1 hour

[Time Traveler]

Mr. Westmarch, thank you so much for your detailed instructions!!!

 

 

Edited December 5, 2021 by Time Traveler

[Time Traveler]

I used those little "L" shaped brackets to hold the motor in place.  It can just "float there" while turning. (not held down)   Also added a bubble level and a Peg to stop motor at end of run.  Longer bolt on arc stops motor in the other direction. Still waiting for clouds to go away!!!  Westmarch  FrankRyanJr

 

 

Edited December 11, 2021 by Time Traveler

[Time Traveler]

Changed the little peg to a micro switch to shut down motor, in I walk away for some reason during end of travel.

[westmarch]

15 hours ago, Time Traveler said:

Changed the little peg to a micro switch to shut down motor, in I walk away for some reason during end of travel.

Hi Terry,

Great piece of innovation.  I need to get round to fitting a clutch to disengage the motor and allow me to reset the platform by rolling it back on the rollers. Currently I have to get down on my knees and lift/slide it to the starting position and my back is not all it once was.

Maybe that is my winter project.

BW

John

[Time Traveler]

Yeah, good idea!  I was thinking of some kind of lever that would raise that portion of the platform.  Is there a picture on the web of the "clutch" idea?

 

[westmarch]

Most of the clutches I have seen are either electromechanical and expensive or overly complicated dual axis drives with some sort of gearing connecting the two drives.

I think a mini drill bit might do it.  The shaft of the drill bit would clamp in the EQ1 flexible collar and the end of the roller shaft would go into the drill bit. The drill bit could then be loosened to allow the roller shaft to run free within the bit.  The platform arcs would then run free over the rollers to reset their position.

This sort of drill chuck would do it:

https://www.manomano.co.uk/catalogue/p/6-to-8-mm-quick-release-chuck-screwdriver-impact-wrench-chuck-quick-release-drill-14-bit-adapter-hexagonal-shaft-chuck-j00501-38736194?model_id=38717673

John

Edited January 16, 2022 by westmarch
spelling

[A P B]

John,

Thanks so much for posting all this information! I ordered all the bits last night. Looking forward to being able to track things with my Zhumell 130 f5. 

I'm hoping to be able to cut the segments out on my laser cutter out of Perspex. Interesting to see if it works like aluminum or slips. Just have to figure out how to the draw segments for my 45 degree latitude. The maths are above my paygrade at the moment.

Adrian

[westmarch]

Hi Adrian,

Not sure about Perspex - suspect it may crack for a normal dob but it may work with a table top dob - good luck.  I should point out that the equatorial base dimensions are probably going to be a bit large for a table top scope, so you may have to adjust them.

The 46 degree template will be fine on Reiner Vogel’s instructions.  

http://www.reinervogel.net/Plattform/Vorlage Plattform 14 hoch.pdf

Most Dob users are using the scope as a light bucket so the low mag EPs have a decent field of view and cope nicely with a little target drift. 

John

Edited January 18, 2022 by westmarch