tonyowens_uk
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Posts posted by tonyowens_uk
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Yes its a DLP structured light scanner not a laser one. Blue light filtered to reduce IR noise effects emanating from ambient solar lighting and with pretty mature software from a Russian developer using thermally-stable steel artefacts for calibration. A genuine metrological scanner not a toy. Its still significant work to run a scanning job but we found the fixture gave us big productivity benefits where small batches of supposedly identical parts are to be inspected.
Nothing odd about your motor mount IMHO. The adaptations I had to make when designing for 3D FDM and SLA printing involved abandoning concerns about material use/thick sections and focusing more on feature access, incorporation of living hinges and flexures, deprecation of threaded fasteners, and the usual FDM printability concerns (overhang angle, scaffolding, surface texture, access for finish machining). Initially I felt like a dog with two tails but now I just want to embed and extend the process to facilitate making rapid investment castings in nonferrous alloys. I'd like to connect with anyone who has done this at a professional level BTW.
Last year we invested in one of these:
from Mass Portal but we are still waiting for a delivery date.
Tony
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Such things are better in Ireland?
We get 21.1 where I live (alt. 65 m latitude 53N on the East coast 30 miles S of Dublin) i.e. Bortle 4..
The deeper Wicklow Mountains get down to 21.7 at 350m elevation with fair vehicular access (Aghavannagh area) but more oiks driving around at night
Finally down in Kerry there is the Cahirdaniel area of the Dark Sky Reserve (on the Ring of Kerry) where 21.97 (Bortle 2) at 50m elevation is available when the weather cooperates - which is rare.
Tony
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Hopefully the technical anecdote below isn't off topic.
I think there is enormous potential for rejuvenating telescope making using the better 3D FDM materials coming onto the market not to mention low cost bureau-printed SLS parts in NY 12. See below some 'gash CAD' of the guts of a special high resolution 3D scanner we built last year (for dimensional inspection of precision mouldings). Inspired obviously by a Hubble Optics Dob prototype structure I bought some years ago and which had sat in my workshop reproachfully for several years! The red bits were 3D printed parts.
As part of this I decided to put the turntable on a goniometric tilting table. To make the thing backlash-free and cheap I designed a preloaded dovetail slide into the table and had the parts FDM printed in PETG. The pictures and notes say it all.
That was the plan! The reality was around 1mm of flatness deviation and 0.5mm of tilt error on the top mounting surface of the assembled table. The dovetail slide surfaces needed to be 'scraped' a bit too to get an acceptable fit.
Milling the mounting surface flat. I found the solid 'skin' on the plate too thin to provide a machining allowance. Should have specced it to be thicker. Live and learn. The flexures really helped kill lash in the dovetail and get the parts to conform well. A bit of Kilopoise and knurled clamp screws and the result was good - much better than I'd expected.
The real payoff I discovered was the combination of prototyping speed and the intrinsic lightness and stiffness of heavy section parts modeled on traditional metal castings. This gives a high natural frequency and the structural damping of filled polymers. Very interesting for other kinds of instrument building e.g. telescopes!
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It's a well researched subject Carl, with some modern twists:
1. The criterion of mounting adequacy is lowest natural frequency of the OTA with the axis clutches (if any) closed. Aim for better than 15 Hz. and better than 25 Hz if high resolution planetary imaging is a science objective.
2. start with the axis modules and make them identical. Refined worm drive or traction or direct drive torque motor transmissions - take your pick. Each has pro's and cons and there is no clear winner
3. Get rid of bending moments in your structural design i.e all unloaded metal. Minimise use of counterweights. Decide at the outset whether this is to be portable, transportable or fixed installation as the design approaches differ for each.
4. Use stressed skin structures as far as possible - they are light and stiff. Don't ignore 3D printed massive parts as a way to do this on the cheap. Replace mechanical fasteners with bonded construction. Incorporate structural damping.
5. Ignore conventional thinking in mount design and look hard at the LBT on Mt Graham USA.
6. Get the controls equipment off of the mount and put it in a nearby humidity-controlled controls enclosure (except for motors and encoders obviously). Use quality high flex robot cable and IP67 multi-pole connectors.
7. If you go 'whole hog' you need a cost effective >= 24 bit absolute encoder on each axis. The only one I know of is Dave Rowe's as used by 10Micron which is brilliant and proprietary. If there are others out there I'd like to know....
8. You need mount modelling, for decent GOTO's and tracking accuracy, ideally a flavour of Tpoint.
Have fun! This kind of work is directly applicable to robot and machine tool design so worth a bit of effort if you are an early career design engineer!
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As you are based in Norn Iron, provided you are not too far from Armagh you could check in with events at the Planetarium there. http://www.armaghplanet.com/blog/category/about-us/armagh-planetarium
I was a little older back in the 70's when my own parents brought me there. There were people (Pat Corvan and several others) there who cared what impression it made on the mind of a 9 year old and removed the intimidation factor. I visited on and off on observing nights to use the 16" scope there for viewing planets, courtesy of my own and other understanding parents who drove me and a friend there and back the 17 miles from my home in the then-impoverished South of Ireland.
Your daughter might appreciate the star shows and some of the displayed hardware in the exhibition area. Whether the 16" is still in use I don't know.
Tony Owens
3D Printers
in DIY Astronomer
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That's very interesting material!
I did not mean to diss the use of screws just to draw attention to the ease of using clip fits and one-piece alternatives to the usual multi-part assemblies. Bonding-in threaded brass inserts works well where thread wear is an issue. But I note that on one of my unfinished printed designs, for a tip-tilt guidescope mount designed to go onto a Losmandy D rail, I've used a 1mm pitch M8 polished precision threaded stainless screw straight into a slightly undersize 3D printed and reamed hole to do one of the adjustments. Creep and a little heat does the rest. The print will be CF-reinforced PC or similar.