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17-07-2011, 07:56 PM
Managed to find some time in the workshop over the weekend and progress 'Skeletope II' to a point where there is something to see.
With all credit to Rolf's awesome build for the ideas.
So in sequence, you start with the plywood and the router.
And you make some rings and bits (messy !!)
And you put them together to make a Mirror Cell
And a Central cage for all the trusses to come together, This still needs some further bracing to take DOB Bearings. It will be a dual mount scope,
And a UTA and slip ring for what I hope will be a rotating focusser system so I can still use it visually on the EQ6
Lined up in shortened form just for demonstration purposes.
In my messy workshop stretched out and clamped for measurments.
All the wood now has a good coat of Indothane varnish.
We're off to Australia for 5 days next weekend but when we get back I will also start building the observatory shed.
18-07-2011, 08:59 AM
Mate, I'll be keenly following your progress. I've been reading your ports in other threads on the development of Skelotope II - cool stuff! Exciting to see it come to reality.
18-07-2011, 12:49 PM
Cheers Alex, I've also made up a laminated base plate for the EQ6 to mount to the sewer pipe pier. 45 mm thick with about 19 layers, glued and screwed. Just need some large diameter screwed rod and lots of nuts/washers to attach it as a levelling plate. Even found an adjustable foot from a copier with the correct thread for the EQ6 base. Throw nothing away is my motto !!
And I've had a bit of a brainstorm about the rotating UTA/focusser idea after getting a mental block for a day or two. Sometimes you just have to stop thinking and let it come by itself.
It's all coming together.
18-07-2011, 01:31 PM
That looks great Brent, and very familiar! :D Seems like you've also got the tools for the job. When cutting the rings I was toying around with a hacksaw and a piece of string - but it worked in the end.
And it'll be interesting to see your rotating upper cage. Looking forward to see what you came up with.
18-07-2011, 08:40 PM
Hi Rolf, should look vaguely familiar. They say imitation is the greatest form of flattery so take a bow. I don't think I would have been brave enough to try the build if I hadn't seen yours and read the explanation of it's design parameters. I just hope I can do it justice.
I bought the router specifically for the job, only $100 at Bunnings and it's heaps of fun. Best friend is a Drill Press but I've got a small lathe, jigsaw, bench saw, Dremel and various sanders to assist. Definite 'man cave' stuff. If I get serious there is even a chain saw to attack trees that get in the way of the view ... :scared2:
Off to Aust a next weekend for 5 days. Might even get a chance to drop into Bintel in Sydney while my wife does her conference. :thumbsup: so I won't get onto the rotator system for a couple of weeks but I'm happy I have an elegant solution. It has to look the part as well as function correctly. Might even take a look at your machine head secondary mirror system later.
01-08-2011, 09:54 AM
Ok, so all those rings and things had to come together eventually. Spent a busy few hours cutting, crushing, drilling and assembling aluminium tubes and stuff.
Also my Sewer Pipe Pier first assembly of the wooden adjustment plate.
And I broke my workshop vice crushing the tube ends flat. More $$$
01-08-2011, 10:11 AM
Nice job Brent, I especially love the pier.
I live in a rented house I was wondering what I could do to overcome this issue.
01-08-2011, 11:17 AM
Hi Malcolm. The pier is a work in prgress. I'll buy 1 meter of M12 threaded rod, drill a concrete anchor into the slab and then screw the rod in and pull it all down from the bottom of the two plates. Three small feet at the bottom will allow me to drop any cables down the centre ( holes already drilled in the lower plate ) and keep things tidy. No concrete or internal fill needed hopefully but it's an option.
For anyone interested the current wieght of the OTA is 4.6 kilos but a wee bit more can be removed although I have some extras to add as well. It is surprisingly rigid and aligned, a tribute to the value of accurate jigging and measuring for parts.
01-08-2011, 11:48 AM
That looks excellent Brent, very well done. And the weight seems similar to mine. I got 7.85 kg without the primary mirror but including bits like secondary and its supports, the focuser and finder scope brackets. So you'll probably approach a similar weight as you add the bits and pieces.
Have you finished your design for the rotating upper cage yet?
01-08-2011, 11:50 AM
Thanks for that Brent, I will need to go back to the drawing board and consider weighting it down somehow as I can't drill into anything where I live.
I suppose concreting one end of the pipe and running a bolt from the bottom to hold the top plate is better than a tripod.
01-08-2011, 09:22 PM
Rolf > It's in my head, a very simple system but I have yet to work out the fine details of loading to keep it locked down to the slip ring. I don't anticipate it being spun like a wheel every night, just available when it gets real awkward. If it is not workable I will just screw it down permanently.
Malcolm > This piece of pipe is so heavy it can almost stand on it's own. I tried it with a simple AZ pipe mount a few months back and just filled it with gravel. It did not move. Held a lot of gravel too ! Walls are just over 32 mm thick and it widens at the base to about 320 mm. Main column is 280 mm diameter.
01-08-2011, 10:54 PM
Thanks Brent, looks like a viable solution. Cheers
08-08-2011, 08:49 AM
Spent a quiet couple of hours on Sunday in the workshop. Replaced all the temporary nuts/bolts with correct sizes and turned them head out so they looked nicer. Added more alum to the cage assembly and made up the plate to attach to dovetail bar. Now I can fit bearings for a new Dob base as well.
Still haven't built the rotator system for the upper cage assy but test fitted the spider from Skeletope I and checked basic alignment for focusser and main optical axis. Still looking good.
Just about ready to attack it with the matt black spray paint to kill any refective surfaces. Then some light baffles around the mirror and upper cage and fit the dovetail bar for a first full assembly, collimation and test on the EQ6.
And I bought a replacement vice ....
Then I get started on SkySlab Observatory .. :thumbsup:
15-08-2011, 10:19 AM
And another few hours spent in the workshop on Sunday. Made up the rotating fucusser cage, pretty simple system, we'll see how it works soon enough.
Stripped the frame and painted it all matt black, ditto for the mirror cell.
Now I just need some light baffling for the mirror and focusser cage opposite the Crayford and drop it onto a Vixen bar to see how it goes.
Don't know when THAT is likely to happen though, we've got possible snow predicted from a big polar blast for the next few days. It is absolutely freezing here !!
I'll put up some more pix tonight if it is not too cold downstairs in the workshop.
15-08-2011, 06:05 PM
And here are the pix. Full OTA assembled, then the focusser cage with it's retainers for the slip ring, works quite well in it's crude format. Just grab and slide.
Then looking down the black photon bucket hole. The three shiny strips are the mirror support bars on their centre rubber mounts.
OTA side shot, cell from the back, few nuts missing there. The cell from the side showing the mirror supports on ther rubber mounts. Finally the central cage which holds it all together.
And we DID get snow !!! Flakes falling at work, almost totally unheard of in Auckland. Currently the sky is cold and clear, no, cold and cloudy, no, cold and clear, now it's raining !! .... you get the picture.
15-08-2011, 08:09 PM
It's looking very solid and good Brent :) The rotating cage looks like a nice and simple solution.
Brrrrrrrr, it's seriously cold tonight. I also saw snow falling during the day today. Currently 2.3 degrees here in Waitakere Ranges, at around 200m. I wonder what it'll reach in the early morning, must come close to 0... definitely something of a record around here!
15-08-2011, 08:19 PM
Brent, this is turning into one seriously magnificent instrument! The workmanship that you've been putting into it is fabulous. Dead-set fabulous.
Keep it up!
16-08-2011, 06:23 AM
Morning Rolf, Alex,
3 Degree and ice on my windscreen this morning. They were touting there would be snow last night up your way Rolf. Used a lot of firewood last night keeping the house warm.
I've used some very simple engineering solutions Alex. Crushed tubes rather than fancy expensive connections, heaps of small nuts and bolts and rivets. Bunnings is my best friend at present ( or I am theirs more likely !!) It's more a matter of being accurate with your workmanship so it all fits without stressing joints. So far so good. Remember, Rolf's instrument is the model and epitome of magnificence, mine is but a cheap copy. Helps that I am a bit of a 'McGyvor' engineer from way back.
I think I really need to lug the EQ6 downstairs to the workshop now, do a fit up. It's been sitting in the lounge with the 114 Newt & the 80mm Achro as I've been getting familiar with guidecams and the GPUSB system.
Balance is slightly top heavy at present as expected with no mirror loaded and I'll do a weight check tonight but I am expecting about 7-8 kg in it's current form. Temperature permitting of course !!
I'll add some height to my DOB swivel base and get some bearings to fit to the cage. That will make it useable pretty quickly till 'SkySlab' is built. I have plenty of small computer type fans to sort any temperature issues. Light shrouding is my next big challenge.
Picked up a GSO 2" 32mm Kellner from the Scope bits sale at the Observatory on Sunday. It's at the very top edge of the 10" useabilty but I wanted a 2" to see what difference it would make to viewing and the price was ok for an experiment. I was trying to find a cheap 6" mirror to design a airline friendly travel scope around but no luck. Grabbed a couple of Filters as well, yellow, blue for some planetary viewing.
28-08-2011, 03:47 PM
Got a few more hours in the workshop today and look what I have now.
She is up on the EQ6, had to space the OTA off the bar as the cage interfered with the bar clamp knobs.
Then I got some white card and fabricated the Upper Cage baffle and the 'Light Bucket' for the mirror cell. I have bought black card as well to line the inside and it will get a matt black spray job to really finish it off and seal the surface.
I then slung the mirror cell fan on a nylon spider.
Then I ran out of time. :sadeyes:
Next will be diag, focusser and I stll need to make the primary mirror edge supports. I also want to make a new cradle for my DOB base. I want to be able to use this in a DOB configuration and it will be so much easier to do first light collimation and tests.
I'm going to have to slow down my astro projects a bit. Caused a bit of grief at home with the time I have spent on it recently so the Ob project will probably be put on the back burner for a few months anyway. Trying to do too much too fast.
But I got a bit of a go with my DSLR on the EQ6 on Friday night till about 1 am Sat morning. Haven't had a chance to go through them yet but got quite good alignment in and first glance is showing nice round stars for 20 sec exposures.
28-08-2011, 06:40 PM
That's looking gorgeous :)
I've always thought that a truss scope on an equatorial mount is a pretty sight, and this is certainly no exception! Congratulations on such as great build Brent.
I'll be intested in how stable you find it to be, the ability to hold focus and collimation etc. It looks rock solid and judging from my own experience you should be in for a treat.
BTW on the morning of the 16th we got down to 1.2 degrees here, that must be a record for this particular area. Even I as a native Dane thought it was rather cold :D We also saw snow flurries during the day, but it didn't settle though. Funny to experience that in Auckland :eyepop:
28-08-2011, 08:08 PM
Thanks Rolf, it's also bloody big!!
It seems surprisingly rigid even spaced off the bar, quite stable and still quite light. Bit forward heavy at present without the mirror but I have a 300 mm bar so will be able to slide it to get some adjustment.
I only have a single weight for the mount, the other disappeared in the post during delivery but so far it's seems quite happy with the single weight not quite at full extension.
I did some swing tests to see how much clearance I would have inside the planned Ob on the sewer pipe pier and looks like the park position would have to be an east west horizontal and it will still have a good horizon angle for most of the sky I have available to me. Even on the tripod it would reach about 300mm higher than the roofline for zenith views..
Looks like I will need a small stepladder for visual unless I use it in Dob mode.
29-08-2011, 08:48 PM
That's really impressive work. look forward to seeing the finished scope.
but had two quick questions.
have you thought about using a broader mid section between the upper and lower truss segments for the EQ6 dovetail to reduce axial flexure?
not sure how to explain it, but just as an example, for a normal reflector OTA, the tube rings are around 30cm apart for a length of around 80 to 100cm. as you reduce the gap between tube rings, axial flexure becomes more pronounced.
here, the length of the member from primary mirror to secondary looks well over 120cm as a rough guess but the cross section in the middle that's held by the dovetail looks like its around 15cm.
just wondering how you overcame axial flexure especially once its loaded with the primary mirror, secondary, focuser and other elements.
I recall you mentioned this design ensures that sag is equal at upper and lower halves, but how about axial stiffness when loaded?
how quickly are oscillations dampened?
secondly, your rotating upper cage concept is really good, but how does it affect balance of the scope say if you have a dslr or heavy eyepiece attached and you rotate it. do you have variable counter weights at the opposite end? does the upper cage ride on roller bearings?
30-08-2011, 06:45 AM
Hi Sam, (or Alistair ?).
The 'bottom' section of the central cage is a sandwich of 17mm ply, 2 x 5 mm spacer strips, 2 x 25mm hollow square alum and then 2 x right angle brackets( ~ 130mm ) all bolted together and is very rigid as is the rest of the OTA. Also the whole assembly is extremely light for it's size and so far the oscillation factor is less than a second when I give it a tap. I imagine there will be some flexure as it changes over but most imaging would be done in a single pass so once it is loaded in any direction it will to a large extent hold that position. Also once it gets the rest of the hardware I will do some balance tests and adjustments to minimise any tendency to overload the drives or mount points. The 300 mm mount bar will let me slide the whole OTA rather than add weight. Rolf has a very good explanation of the dynamics of the design.
Hadn't thought of weight with the rotating cage yet but good point especially when the DSLR gets attached. I want to minmise any extra weight addition so we will see how it goes and figure it out as necessary. My object now is to get it to first light and then refine any problems that show up.
No roller bearings, just a very smooth plastic surface between the two ply rings and a careful build to ensure it is all flat and smooth. Simplicity is my mddle name. I anticipate that most nights it will be fixed for the duration of the session.
I have to reiterate though just how surprisingly light and rigid the whole thing is. I'd almost be brave enough to stand it on end and stand on top of it. So far it has been a fascinating exercise in design and construction.
11-09-2011, 03:01 PM
Friday and Saturday, first two days of the Rugby World Cup were absolutely brilliant, sunshine, warm, gentle breeze. Then we must have said something and upset the Australians so for Sunday they sent us all the above.. !!
But every cloud has a silver lining and being unable to work outside due to adverse conditions I got some serious workshop time in.
So Skeletope I is no more, say hello to Skeletope II in it's DOB configuration. Completed the UTA with light sheilding, focusser and spider from SK I, built the light sheild for the mirror cell. Added the dob bearings to the Centre cage. Then rather than build all new components for the mirror cell I decided enough was enough and stripped SK I for it's hardware and fitted to the new cell base. Replaced all the industrial strength velcro I use to attach the mirror, put it all together and lowered it into place.
Discovered several things while pulling SK I to bits. It's amazing how much dust and spiders get inside a scope and where they go. And SK I wasn't as well constructed as I thought it was, there was a lot of wobble in those 4 aluminium rods supporting the UTA.
So guess I can't really blame you guys over the ditch for all the rain, I brought it upon myself really. Sorreeeee :shrug:
Oh, .... you want some pix then ? OK, here you go.
And btw this thing is light !! OTA as shown is 11.3 kilo. The new strut braced DOB base is about 4 kg compared to about 15 or more for my old construction. The OTA is currently very mirror heavy but there is more to be added at the UTA end, RACI, Camera, Guiding etc eventually.
Now I better go and modify my sig ...
18-09-2011, 08:58 AM
Not quite first light but managed to shoot it out the garage door between showers and line up on the houses etc about 4 km away. Couldn't get focus because as usual I am always a bit generous in my calculations and the focal point was about halfway down inside the focusser. Out with the hacksaw and chopped off 50 mm from each of the bottom truss tubes. Let me tidy up some not so pretty work anyway and now got focus about 20 mm of travel above the the bottom stop. Centred the spider, did a visual down the OTA to the mirror and aligned that and bingo, I could count the stars on a flag across the valley.
Chopping a couple of inches off the bottom has improved the balance point nicely but now I need another Counter balance weight for sure. Did a test rotation on the UTA assembly to see how alignment held and not bad at first glance but more testing to be done there.
Wiring fan, secondary heater and building the power control system is next while the clouds hang around.
I'll do a first light in the DOB base as soon as they give me a break.
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