Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Merope - engineering a low compromise compact 16" dob

  • Please log in to reply
231 replies to this topic

#1 Oberon

Oberon

    Mercury-Atlas

  • -----
  • topic starter
  • Posts: 2908
  • Joined: 24 Feb 2013
  • Loc: Hunter Valley NSW Australia

Posted 05 February 2015 - 09:25 AM

Since publishing an overview of my new 16" Dob "Merope" on the pinned "Post your home made scope" thread, I've had many PM's asking for more construction details. So this thread is my reply to you all. Feel free to join in sharing your own ideas and pictures. 

 

gallery_217007_4913_1576.jpg

 

First some background.

 

Merope arose from a decision to build a portable 16" f/4.5 binoscope "Sterope" constructed with marine plywood. As arrival of my mirrors would be staggered by a year, and my order for marine plywood was stuck somewhere overseas (unbelievably it was specially imported from Europe), I decided to first build an interim "quick and dirty" telescope using a cheaper construction grade ply to test and experiment with techniques and engineering ideas I was thinking of using on the bino-scope, and hopefully get it finished by Christmas to enjoy with my kids.

 

Of course, it didn't get finished by Christmas, and Merope soon went from being "quick and dirty" to being a no compromise exercise in engineering and finish. Well...there is no such thing as no compromise, so I've described it a low compromise. And naturally I had my own constraints. Below is a quick over view of the "musts" and "desirables" and "constraints" as I recall them, I'm sure many of them are common to us all...
 

Design Drivers (in no particular order):-
 

1. Must be portable. Must unpack and fit in boot of an ordinary sedan for long distance trips.

 

2. Must utilise wheels and be easy to move around home with minimal or no lifting.

 

3. Must be easily hoisted onto back of a utility truck for quick local trips without dismantling.

 

4. Must be stiff. Parts must not wobble, flop, twist, bounce or flex. Must maintain good collimation.

 

5. Must tolerate a wide range of eyepieces up to TVNag'31+PC without rebalancing.

 

6. Must be buttery smooth to operate

 

7. Must look good and be practical. Form should follow function. Engineering should be elegant.

 

8. Must be solid and robust, not flimsy or fragile

 

9. Must be a pleasure to use

 

Desirables:

 

a. should have setting circles for faint objects

 

b. should protect mirror from insects and spiders while not in use and stored in garage or verandah

 

c. optics should normally stay in the telescope and be mechanically protected to reduce risk of damage

 

d. should be inherently flexible, easily modified and capable of new attachments and later additions

 

e. trusses should fold flat and stay together as a single assembly

 

f. eyepieces should be accessible from the ground - mirror should be set as low as possible

 

g. should avoid anything electrical - no wires or soldered joints, no motors, switches or encoders. A fan may be an exception.

 

h. should be reasonably lightweight and capable of being handled by one person

 

i. should not use tools and/or loose parts for setting up, should utilise hand operated latches and fixtures

 

k. should not require extensions for eyepieces, focuser should have enough travel for occasional camera and eyepieces

 

Constraints:-

 

i. I only have tools for working timber, and cutting aluminium, steel and plastic. Any turning, milling or welding would have to be paid for.

 

ii. I have no experience or equipment for resin based composite materials (carbon fiber, fiberglass etc)

 

 

Most of the above first applied to my binoscope plans and were carried over to Merope. However after completing Merope I realised I had another essential requirement;

 

10. MUST be able to be wheeled into the house and fit through an ordinary door (and the pool fence gate).

 

Although at 700mm wide Merope met this condition nicely, there was no way my larger binoscope design would, so I've had to abandon my early Bino-Scope designs that influenced Merope and start again...but that's another story.


Edited by Oberon, 05 February 2015 - 09:32 AM.

  • BarabinoSr, okiestarman56, brave_ulysses and 12 others like this

#2 siriusandthepup

siriusandthepup

    Apollo

  • *****
  • Posts: 1049
  • Joined: 14 Feb 2006
  • Loc: Central Texas, USA

Posted 05 February 2015 - 09:57 AM

:gotpopcorn:

 

Looking forward to this!



#3 Pierre Lemay

Pierre Lemay

    Apollo

  • *****
  • Posts: 1347
  • Joined: 30 Jan 2008
  • Loc: Montréal, Canada

Posted 05 February 2015 - 10:02 AM

Oberon, I asked this question in the "post your home made scope" pos:t what are the weights of the different components of the telescope and the weight of the operational instrument (including eyepieces, finderscopes, counterweights, etc.).   Thanks.



#4 GShaffer

GShaffer

    Knight of Ni

  • *****
  • Moderators
  • Posts: 6397
  • Joined: 28 Feb 2009
  • Loc: Bogart, Ga USA

Posted 05 February 2015 - 10:49 AM

It has been quite some time since I have seen a telescope that intrigued me as much as this one.  Looking forward to this thread.......

 

One thing I noted was how much weight you had to add to the back of the cell for balancing....... I suspect upon reflection building the cell out of steel rather than aluminum would not have been an issue, even to the point of building the cell structure out of steel bar stock instead of tubing.....would you agree?


  • bbbriggs likes this

#5 Oberon

Oberon

    Mercury-Atlas

  • -----
  • topic starter
  • Posts: 2908
  • Joined: 24 Feb 2013
  • Loc: Hunter Valley NSW Australia

Posted 05 February 2015 - 05:24 PM

Hi GS, yes, the balance weights. They arose from shrinking the 1000mm diameter of my original design for a binoscope base to 760mm for Merope; the altitude bearings being the same diameter were also shrunk to scale shifting the center of rotation lower, too low to achieve balance without adding weights. I knew that was a risk, but decided to live with it for the sake of my primary design requirement for everything to flat pack neatly into the boot of my car, and perhaps replace the UTA in the future with CF as another project.

 

In any case the cell is welded from 40mm square stainless steel tube, not aluminum. I scrounged the stainless from scrap, so it cost me nothing. It looks good and is extremely strong and rigid, is as heavy as I am comfortable with, but was not kind to drill bits and hole saws. The 3 x identical short lengths of the tube were cut with a mitre cutoff saw bought for the purpose; I drilled it and set it all in a jig. I also cut 3 x identical short sections of scrap 6 x 50 x 75mm flat.  A mate who owed me a favour then welded it up for free...which is why on closer inspection the welding is a bit on the ordinary side.

 

In any case its an extremely simple and effective design that has several good engineering benefits:-

1. it provides equal support for all 3 points, ensuring any possible flexure does not tilt the mirror

2. it spreads the load across 3 equally spaced points permitting effective direct connection to the trusses, and ensuring by design that no flexure is possible between the cell and the trusses.

3. a triangle spanning a circle means the spans supporting load are the shortest possible length, again minimising another potential source of flexure

4. It can be easily scaled to other sizes or utilise other materials; steel , aluminum, carbon fiber, whatever.

5. The first whiffle tree is supported within the tubes, preventing any twisting stresses on either the tubes or the pins (bolts) used to support them.

6. each component is identical in every way to its mate, each part is exactly replicated, making design and construction very easy

 

And because collimation is achieved with the trusses, there is no requirement for collimation screws, eliminating another potential source of flexure.

 

Unfortunately I didn't take any photo's prior to assembly and only have concept plans without dimensions marked. I'll talk about the 18 point mirror support in a separate post.

gallery_217007_4913_30170.jpg

 

gallery_217007_4913_182200.jpg

 

 

 

gallery_217007_4913_62056.jpg

 

gallery_217007_4913_6313.jpg

 

 

 

gallery_217007_4913_24986.jpg


Edited by Oberon, 05 February 2015 - 06:08 PM.

  • starman345 likes this

#6 Oberon

Oberon

    Mercury-Atlas

  • -----
  • topic starter
  • Posts: 2908
  • Joined: 24 Feb 2013
  • Loc: Hunter Valley NSW Australia

Posted 05 February 2015 - 05:43 PM

Oberon, I asked this question in the "post your home made scope" pos:t what are the weights of the different components of the telescope and the weight of the operational instrument (including eyepieces, finderscopes, counterweights, etc.).   Thanks.

 Hi Peirre, question noted, I have a lot of details in spreadsheets for planning but need to make some reality checks first with actual build. Will come back to this.



#7 Oberon

Oberon

    Mercury-Atlas

  • -----
  • topic starter
  • Posts: 2908
  • Joined: 24 Feb 2013
  • Loc: Hunter Valley NSW Australia

Posted 06 February 2015 - 01:14 AM

Choice of Materials

my preferred choice of material to work with is timber and specifically plywood. After building a case for my solar filter collection by cutting a range of suitable holes in several layers of ply with large hole-saws and a router and then laminating them all together I realised that this method of laminating and routing had great potential for creating very strong, stiff and beautifully finished accurate flat structures with no joints, very suitable for mirror cells, solid azimuth rings and the like, and help maintain collimation so critical in a binoscope.

gallery_217007_4746_57406.jpg

 

So after working out my requirements I placed an order with a lumber yard along with other materials like Laminex or Formica. Months later still with no ply and no Laminex the merchant was cleaning up and came across several sheets of "Lamipanel" which is a heavy duty phenolic product design for sheeting bathroom walls with a Laminex like surface. It was a discontinued colour and finish and he thought I might be interested at the right price...aka for free, just take it away. Wow...4 large sheets at almost $1000 worth I was more than delighted. It has proved to be an excellent material for telescope building with some unique features many ATMs will find invaluable.

1. same expansion co-efficient as timber, pyrex and carbon fiber

 

2. incredibly stiff when laminated as a composite panel, a cheap CF substitute for some applications

 

3. ideal finish for flat bearing surfaces (glides beautifully on teflon)

 

4. light and stiff, may be used as lightweight substitute for aluminum plate

 

5. strong enough for some applications in its own right

6. cuts cleanly with a router even when floating free and unsupported

Below are some examples...

gallery_217007_4913_20417.jpg

 

Bottom plate of azimuth ring, plus bearing surface (the thin ring on the side), plus laminated ground-plate in background.

gallery_217007_4913_2985.jpg

 

Laminated with plywood with stained edges for primary mirror support

 

gallery_217007_4913_37220.jpg

 

Laminated again with plywood and stained for secondary mirror support. Silicon was used to glue the mirror to the Lamipanel and because all materials have the same expansion coefficient no stress is placed on the joint or the secondary itself through differential expansion.

gallery_217007_4913_13075.jpg

 

Examples of lamination prior to staining and finishing. The Lamipanel is 2.7mm and the ply is 4mm thick. Try as hard as you like, you will not bend or twist this little stick. You can drill and tap plates like these for machine screws even with fine threads.

gallery_217007_4913_50709.jpg

 

Laminated again, this time to 12mm ply. Complete overkill for this mirror lid, you could drive a car over it.

 

gallery_217007_4913_62744.jpg

 

Laminated here to underneath of ground plate. Designed for use as shower wall its highly scratch resistant and impervious to moisture and wet grass.

 

gallery_217007_4913_6313.jpg

 

Plus it looks great!


Edited by Oberon, 06 February 2015 - 03:30 PM.

  • sopticals, starman345, astrobeast1 and 1 other like this

#8 GShaffer

GShaffer

    Knight of Ni

  • *****
  • Moderators
  • Posts: 6397
  • Joined: 28 Feb 2009
  • Loc: Bogart, Ga USA

Posted 06 February 2015 - 10:22 AM

What country are you located in Oberon?  Pretty sure its not north america given you reference stuff in mm and lamipanel doesn't seem to be a term used here....... Pretty sure it is the same thing we call tile board here though......


  • brucesdad13 likes this

#9 Oberon

Oberon

    Mercury-Atlas

  • -----
  • topic starter
  • Posts: 2908
  • Joined: 24 Feb 2013
  • Loc: Hunter Valley NSW Australia

Posted 06 February 2015 - 03:11 PM

Oz. Definitely not North America!

 

Tileboard and Lamipanel (now renamed as "Aquapanel") are quite different products. Tileboard appears very much inferior to Aquapanel and would not have the properties I have described. Laminex Aquapanel (or Lamipanel) is a hard tough melamine coated phenolic resin board that is impervious to moisture. I found this description of Tileboard...

 

http://homeguides.sf...lash-28373.html

"Tileboard is a type of medium-density fiberboard, MDF, which is pressed board with a hard melamine top layer. The melamine is pressed to the surface of the MDF to create sections that resemble tile. Although the surface of tileboard is water resistant, the back and sides adsorb water easily. The edges of the tileboard are inserted into plastic trim pieces to protect the non-absorbent surfaces."

 

...and that it must be glued to a solid dry cement sheet.

In contrast...

 

"Laminex® Aquapanel® has a moisture resistant backing, and a balanced construction ensures board flatness. It has excellent impact strength, which is more than adequate for normal applications, enabling supporting framework to be spaced at 450mm centers."

 

and..

 

"Aquapanel sheets are 2.7mm thick compact laminate. Phenolic resin saturated kraft papers are bonded under heat and pressure to create a high moisture and impact resistant material.
The surface is smooth, providing a tough, durable, non porous surface that easily resists marks, stains, steam or moisture. The sheets can be used in dry, wet or hygiene areas."

 

Also not to be confused with Knauf Aquapanel which is a very different product again.

From what I can tell, the North American near equivalent would be "Resistop"

 

http://www.duratop-e...p-phenolic.html

 

and a similar "green" product is "PaperStone"

http://www.paperston...rmation-faq.php



#10 Oberon

Oberon

    Mercury-Atlas

  • -----
  • topic starter
  • Posts: 2908
  • Joined: 24 Feb 2013
  • Loc: Hunter Valley NSW Australia

Posted 06 February 2015 - 03:34 PM

Annoyingly Laminex have dropped the non-glossy surface that works so well with teflon from their Aquapanel range. So unless you are lucky enough to find some old stock like I did, Oz ATM's won't be able to buy it for use as bearing material which is a shame.



#11 jonathanCR

jonathanCR

    Messenger

  • -----
  • Posts: 474
  • Joined: 02 Jul 2007
  • Loc: Costa Rica

Posted 06 February 2015 - 04:53 PM

what a masterpiece!!!!!



#12 GShaffer

GShaffer

    Knight of Ni

  • *****
  • Moderators
  • Posts: 6397
  • Joined: 28 Feb 2009
  • Loc: Bogart, Ga USA

Posted 06 February 2015 - 05:02 PM

what a masterpiece!!!!!

what a masterpiece!!!!!


I get a warm fuzzy feeling every time I look at a pic of Oberon's scope or maybe its a "woodie" lol.....already putting notes down for converting my overbuilt 12.5" into something similar.
  • brucesdad13 likes this

#13 Oberon

Oberon

    Mercury-Atlas

  • -----
  • topic starter
  • Posts: 2908
  • Joined: 24 Feb 2013
  • Loc: Hunter Valley NSW Australia

Posted 06 February 2015 - 07:50 PM

Key Design Concepts

Caveat

The design package I use is Adobe Illustrator, which isn't ideal at all, but its what I'm been familiar with for a long time. There is no facility for experimenting with shapes in 3D space to find what works and what collides so all my design work is done in 2D and staring intently at the screen and rotating bits for hours trying to imagine the effects. I'm sure I could learn SketchUp or something like that, but the learning curve would get in the way of my thinking processes. Having arrived at a concept that works I measure what I need for fabrication and print it out for myself, occasionally making minor changes in the workshop if necessary.

gallery_217007_4913_97409.jpg

 

Side profile showing laminations; lamipanel is green, ply is the weird yellowy orange. The key feature is that the altitude bearings sit down within the azimuth bearing, not on top like most telescopes. The Azimuth bearing itself sits within the ground plate - although that is really a feature of an earlier idea to make it flatter still. (Note: I had hoped to get away with a 2.7 mm Lamipanel ground plate that only held the feet in tension; despite testing the idea successfully on my 8" it didn't work here so something was out with my geometry. In any case I didn't have time to play and so now I have a 23mm thick and very stiff laminated groundboard but may revisit the idea again later).

The benefits of this concept are:-

 

1. the eyepiece ends up lower to the ground reducing the need for steps (F/L is 1800mm)

2. the groundboard and azimuth bearing are wide and low, very stable

3. the telescope packs down very flat and so fits in the boot of my car (see below)

4. there are no joints or screws to weaken the structure, everything is very solid and stable

 

gallery_217007_4913_20016.jpg

 

gallery_217007_4913_87064.jpg

 

An alternative considered was a stiff ground-plate ring and a floppy azimuth section defined by the ring. I've seen several telescopes built that way, such as Mel Bartels. But the disadvantage of that design is that the altitude bearings do not fit so snugly within the ring as the ring is fixed and does not rotate, and thus it cannot bring the mirror and eyepiece as low to the ground as the method described above.


  • starman345 and brucesdad13 like this

#14 Oberon

Oberon

    Mercury-Atlas

  • -----
  • topic starter
  • Posts: 2908
  • Joined: 24 Feb 2013
  • Loc: Hunter Valley NSW Australia

Posted 07 February 2015 - 07:37 AM

The Ground Plate

 

gallery_217007_4913_135434.jpg

 

Cut base, laminate one side and then route out to lighten. In hindsight I could have taken out more material than this without compromising its strength and stiffness. Removing material with holesaws would have worked just as well.

 

gallery_217007_4913_75875.jpg

 

Top side laminated, feet cut to correct curve, feet bonded and hard up against Lamipanel.

 

gallery_217007_4913_11475.jpg

 

Cut a 650mm disc for a guide (not shown), lay on top and use 1/2" trim router to follow shapes

 

gallery_217007_4913_56796.jpg

 

View of underneath. Seamless.

 

gallery_217007_4913_62744.jpg

 

I picked up some colourbond aluminium/acrylic composite panel from a $10 offcuts and scraps bin. Gloss black on one side, gloss white on the other, it makes a beautiful finish. A small piece is glued into place and later trimmed with the router.

 

gallery_217007_4913_54692.jpg

 

Tap out the 3/4" nut to clear glue from threads, and the cut thread into timber. The timber thread serves to stabilise the screw; I had planned to make some levered lock nuts but it hasn't been necessary.

 

gallery_217007_4913_16226.jpg

 

Semi finished groundboard hung up for stain and varnish on edges.

 

gallery_217007_4913_13137.jpg

 

 

Fit teflon bearing. I whimsically cut pieces with a large hole saw to continue the circle theme (and because its easier) forgetting how expensive this stuff is.

 

gallery_217007_4913_43304.jpg

 

Fit leveling screws cut from threaded rod, with joiners epoxied and shackles fitted for handles and lifting.

 

gallery_217007_4913_48414.jpg

 

Fit wheel hardware. We'll talk about wheels separately.

 

Notes: The base is a little over-engineered - more solid than it needs to be (I'd rather err on conservative side), and more complex because of an abandoned earlier decision that placed the teflon bearing higher than the ground plate, half way up the side of the azimuth bearing.

if I was doing it again I would consider a thinner ply, say 1/2" or 12mm rather than 18mm, although this would make fitting the wheels more difficult. Alternatively I would consider just using a plain flat sheet with protrusions for the leveling screws (ie not bother with the crescents), and shape it a little different to better provide for the pulleys, and so avoid having to manufacture and fit a heavy bracket.

 

As it is it weighs 10.1 kg complete with the wheel hardware, which is easy enough to lift.


Edited by Oberon, 07 February 2015 - 07:52 AM.

  • starman345, brucesdad13 and Andrew_G like this

#15 starman345

starman345

    Wait, I'm Thinking

  • *****
  • Posts: 9478
  • Joined: 06 Jul 2010
  • Loc: New Brunswick, Canada

Posted 07 February 2015 - 01:34 PM

You knew there would be questions right? :grin:

 

1) Are the upper truss connectors  the same size heim joints as the lower ones? Can you show a picture?

2) Do you use a shroud? if so, do you find the three trusses are able to keep it out of the light path?

3) Are the wooden  discs that sit on the rockers held in place only by the weight of the primary mirror or are they restrained in some way?

4) The trusses are removed from the cell by removing the knurled cap on top of the green block?

5) Do the heim joints simply thread into a threaded end cap in the truss tubes? Made of plastic? Or other? I notice what looks like a rivet at the end of each truss pole close to the end cap, is that how they are secured to the truss pole?

6) How are the altitude bearings connected to the mirror cell-box-enclosure? And what do they ride on? I can see that it looks like you used the same laminate material on them as is in your upper cage, but what do they ride on, is there teflon hidden in there somewhere?

7) Am I correct in thinking RH thread joints on one end of trusses and LH on the other end to make your collimation method work?

 

Edit:

Ok, I found your gallery and its many pictures, now I have answers to 1,4 and 6.


Edited by starman345, 08 February 2015 - 07:49 AM.

  • GShaffer likes this

#16 Oberon

Oberon

    Mercury-Atlas

  • -----
  • topic starter
  • Posts: 2908
  • Joined: 24 Feb 2013
  • Loc: Hunter Valley NSW Australia

Posted 08 February 2015 - 10:56 PM

The Trusses #1 - components

as we now know, the most elegant and joy-to-use feature of the Merope design are the trusses. Simply twist them for collimation. Neither the mirror cell nor secondary support need to be adjustable as the mirrors are very easily and quickly aligned by twisting the trusses. Essentially we have created a manually operated Stewart Platform, which have 6 degrees of freedom. This solution greatly simplifies and improves mirror support and collimation.

In principle all we would need to do is attach the Heim joints to the sides of the UTA and LTA exactly the same as commonly done with many other Dobs and everything would work beautifully as described. Very simple.

 

But I wanted to do better. Nothing is ever so simple.

 

1. because I had no prior experience with Heim joints and because they aren't especially cheap I wanted to be absolutely sure that any slop in the ball joints would not result in bi-stability or flexure before I committed myself to purchase. I needed a way to eliminate any slop in the ball joint.

 

2. the trusses should fold up and hold together as one assembly, and always go back the same way they came off.

 

3. because of the way the telescope packs flat with the bearings wrapped tightly around the mirror cell, any clips or fixtures associated with the trusses must be flush, they must not protrude above, below or outside the wooden rings of the UTA or LTA.

 

4. all loads in tension and compression must act directly through the axis of the truss tubes, and must not induce any torsion or bending of the tubes.

 

Happily the design below meets all of these challenges. Below is a screen dump showing the essential bits, and I have attached a pdf file of the full drawing.

gallery_217007_4913_110343.jpg
 

Below are some close-ups of the components...

 

gallery_217007_4913_2333.jpg

 

gallery_217007_4913_71284.jpg

 

gallery_217007_4913_11864.jpg

 

gallery_217007_4913_55693.jpg

 

The rivets were an afterthought. After cleaning thoroughly with methylated spirits I super-glued the Delrin inserts into the truss tubes but came close to catastrophic failure when a joint under tension came apart from the mirror cell. The rivets were installed to prevent such failures but this is one area I might think long and hard about how to improve next time. I'd like to see the insert secured more robustly to the tube, as a failed glue joint may permit some flexure under load. Not that I've noticed, but perhaps epoxy would be better. Delrin isn't the sort of plastic that likes glue adhesives.

 

Suggestions welcome.

 

gallery_217007_4913_12844.jpg

 

gallery_217007_4913_96603.jpg

Attached Files


Edited by Oberon, 09 February 2015 - 12:30 AM.

  • Sean Cunneen and starman345 like this

#17 Oberon

Oberon

    Mercury-Atlas

  • -----
  • topic starter
  • Posts: 2908
  • Joined: 24 Feb 2013
  • Loc: Hunter Valley NSW Australia

Posted 08 February 2015 - 11:14 PM

You knew there would be questions right? :grin:

 

1) Are the upper truss connectors  the same size heim joints as the lower ones? Can you show a picture?

2) Do you use a shroud? if so, do you find the three trusses are able to keep it out of the light path?

3) Are the wooden  discs that sit on the rockers held in place only by the weight of the primary mirror or are they restrained in some way?

4) The trusses are removed from the cell by removing the knurled cap on top of the green block?

5) Do the heim joints simply thread into a threaded end cap in the truss tubes? Made of plastic? Or other? I notice what looks like a rivet at the end of each truss pole close to the end cap, is that how they are secured to the truss pole?

6) How are the altitude bearings connected to the mirror cell-box-enclosure? And what do they ride on? I can see that it looks like you used the same laminate material on them as is in your upper cage, but what do they ride on, is there teflon hidden in there somewhere?

7) Am I correct in thinking RH thread joints on one end of trusses and LH on the other end to make your collimation method work?

 

Edit:

Ok, I found your gallery and its many pictures, now I have answers to 1,4 and 6.

 

2) yes I use a shroud when children are around. It stretches over the UTA lower ring and sticks to the velcro on the mirror cell. The material is stretchy and between the rings and the trusses it is kept out of the light path, although you must check and probably tweak and pull it about a little to get it just right and prevent looseness.

3. no additional restraint. It was a matter of suck it and see. They slip neatly into place and might fall off if I tipped it upside down and shook it, but otherwise they show no tendency to fall off or be a nuisance. More photos later.

 

5) coming...

 

7) done



#18 Oberon

Oberon

    Mercury-Atlas

  • -----
  • topic starter
  • Posts: 2908
  • Joined: 24 Feb 2013
  • Loc: Hunter Valley NSW Australia

Posted 08 February 2015 - 11:56 PM

The Trusses #2: fixtures

Another early requirement was that the trusses be removed without the use of tools. That meant I took a long time before settling on the above design; try as I might I could not find an over-center latch arrangement that didn't require something to sit proud on a surface that need to be flush. Eventually I was forced to make my own screws by fitting screws with handles. I used more tube and Moonlite Delrin inserts for the handles as below. These soon proved too short - my hand would collide with the trusses - and so I rebuilt them a little longer.

gallery_217007_4913_25306.jpg

 

After a while I got tired of slowly twisting screws by hand and reverted to using a battery powered driver. Of course I had to sacrifice a set of Allen keys bought for the purpose, but this method is much better. I've shown the above purely because some people will insist doing everything up by hand (no tools) is important. Not for me, I'm happy to carry a battery driver with me in the car. Fast and tight. But it can be done and works OK.

gallery_217007_4913_61059.jpg

 

gallery_217007_4913_65407.jpg

 

Because the UTA uses lighter smaller screws I need to swap driver bits. As this is inconvenient I will re-engineer this one day and fit a hand operated over-center clip, possibly a bike seat clamp, as the stresses are less and the constraints more relaxed on the UTA than the mirror cell LTA.

gallery_217007_4913_51419.jpg

 

This closeup shows the following features for connecting the truss block to the cell:-

 

1. a V slot is routed into the cell surface for locating the Heim joints and to prevent yaw.

 

2. magnets are inserted into the V slot to hold the joints in place prior to fixing with screws. I've only got two hands, manipulating a truss needs three.

 

3. the countersunk M10 screw ties the timber ring to the stainless steel mirror support underneath.

 

4. the trusses connect as close as possible to #3 to eliminate flexure (note the 8mm hole directly in front of M10 screw)

 

5. the countersunk hole on right is for an M8 screw fixing the cell to the altitude bearing

 

6. the curved protrusion of the surface lamination over the mirror is a mirror clip to prevent the mirror falling out when tipped upside down. More on that later.



#19 GShaffer

GShaffer

    Knight of Ni

  • *****
  • Moderators
  • Posts: 6397
  • Joined: 28 Feb 2009
  • Loc: Bogart, Ga USA

Posted 10 February 2015 - 02:43 AM

Nother question.....Still thinking on the cell design and additional weights you had to add....

Do you know how many lbs (or kg) of weight you had to add on?
  • starman345 likes this

#20 starman345

starman345

    Wait, I'm Thinking

  • *****
  • Posts: 9478
  • Joined: 06 Jul 2010
  • Loc: New Brunswick, Canada

Posted 10 February 2015 - 08:21 AM

Nother question.....Still thinking on the cell design and additional weights you had to add....

Do you know how many lbs (or kg) of weight you had to add on?

I'd be interested to hear what Oberon thinks about this. Just thinking out loud, I haven't done a design but it appears to me significant weight can be shaved from the upper cage, the cage rings appear to be 2" wide and 1/2" thick, could probably get by with 1 1/2" wide and maybe even 3/8" ply, also use lighter, maybe M6 heim joints on the upper truss ends as Oberon mentioned might be a possibility. Altitude bearings enlarged a few inches in diameter and the scope might not need any counterweight at all. I'm curious how heavy those guitar tuners are......



#21 Sean Cunneen

Sean Cunneen

    Let Me Think

  • *****
  • Moderators
  • Posts: 3823
  • Joined: 01 Aug 2007
  • Loc: Flossmoor Il.

Posted 10 February 2015 - 08:47 AM

Your stewart platform idea is brilliant! Fantastic job!


  • Oberon and brucesdad13 like this

#22 Oberon

Oberon

    Mercury-Atlas

  • -----
  • topic starter
  • Posts: 2908
  • Joined: 24 Feb 2013
  • Loc: Hunter Valley NSW Australia

Posted 10 February 2015 - 09:02 AM

Weights and Balance

OK...jumping ahead then...my one regret with my design is that I didn't stick to the 1000mm diameter altitude bearing of my initial BinoScope design, but shrunk the bearing to match the reduced size of the azimuth bearing.

Here are some weight and balance calculations as presently configured...

gallery_217007_4913_134932.png

 

So as you see from the pie, the telescope is balanced with a 31mm Nagler with a little bit to spare, to say, cope with a Parracor as well.


  • BarabinoSr likes this

#23 Oberon

Oberon

    Mercury-Atlas

  • -----
  • topic starter
  • Posts: 2908
  • Joined: 24 Feb 2013
  • Loc: Hunter Valley NSW Australia

Posted 10 February 2015 - 09:25 AM

 

Nother question.....Still thinking on the cell design and additional weights you had to add....

Do you know how many lbs (or kg) of weight you had to add on?

I'd be interested to hear what Oberon thinks about this. Just thinking out loud, I haven't done a design but it appears to me significant weight can be shaved from the upper cage, the cage rings appear to be 2" wide and 1/2" thick, could probably get by with 1 1/2" wide and maybe even 3/8" ply, also use lighter, maybe M6 heim joints on the upper truss ends as Oberon mentioned might be a possibility. Altitude bearings enlarged a few inches in diameter and the scope might not need any counterweight at all. I'm curious how heavy those guitar tuners are......

 

 

The UTA is made from 9mm ply; its a bit too thin really, I'm not likely to go below 12 without a CF lamination in future. There isn't much to cut out of the UTA in timber except to cut circles out of the side plates and save 100g, 150g at most.

gallery_217007_4913_22867.jpg

There is room to lighten the secondary support. As you can see I've already drilled it to bits, but balsa or carbon would be better.

I'd like to get rid of the steel M8 Heim joints on top. But the problem with M6 is that the male is shorter; maybe a bit short and the female with a threaded rod just as heavy as the M8 male. So I'd like to use these plastic units from Germany, but only on the UTA, and stick to M8.

 

igubal_gelenkkopf_1.jpg

 

If I was feeling rich I might use carbon tubes to replace the aluminium trusses.

Titanium screws? All those SS screws add up...

gallery_217007_4746_88360.jpg

 

The guitar heads aren't lightweight either, but they are well worth in my view. It is possible to get lighter guitar machine heads that the ones I selected, but I'm happy.

I'll come back tomorrow with some precise weights for little bits like machine heads.


 


Edited by Oberon, 10 February 2015 - 09:27 AM.


#24 Oberon

Oberon

    Mercury-Atlas

  • -----
  • topic starter
  • Posts: 2908
  • Joined: 24 Feb 2013
  • Loc: Hunter Valley NSW Australia

Posted 10 February 2015 - 09:44 AM

For GShaffer...

 

UTA

Mass

 

grams

Mirror 16”

11200

Cell (below mirror)

4100

Cell timber ring

1400

Weight 1

4000

Weight 2

4000

Weight 3

3300

Total

28000



#25 Alex Parker

Alex Parker

    Ranger 4

  • *****
  • Posts: 363
  • Joined: 20 Oct 2013
  • Loc: Boston MA

Posted 10 February 2015 - 09:55 AM

 

 

Nother question.....Still thinking on the cell design and additional weights you had to add....

Do you know how many lbs (or kg) of weight you had to add on?

I'd be interested to hear what Oberon thinks about this. Just thinking out loud, I haven't done a design but it appears to me significant weight can be shaved from the upper cage, the cage rings appear to be 2" wide and 1/2" thick, could probably get by with 1 1/2" wide and maybe even 3/8" ply, also use lighter, maybe M6 heim joints on the upper truss ends as Oberon mentioned might be a possibility. Altitude bearings enlarged a few inches in diameter and the scope might not need any counterweight at all. I'm curious how heavy those guitar tuners are......

 

 

 

 

If I was feeling rich I might use carbon tubes to replace the aluminium trusses.

Titanium screws? All those SS screws add up...

 

 

This is starting to remind me of my bike racer days.  Every time you figure out how to save a gram, the next gram costs you 1.5X as much...


  • I forge iron likes this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics