AS Product Design Project idea

[Peter Reader]

Ah fantastic! I think I could make an adjustable secondary holder -instead of an adjustable spider. Will let you know if any other problems arise and keep you posted on build/design.

Thank you all!

Pete

[Astrokev]

After all the recent discussion, I really look forward to seeing pics of the finished build. I'm expecting an amazing piece of engineering. No pressure!

[Peter Reader]

Will be going to North Devon Astro meeting this Wednesday to talk it over with some engineers who have experience in this kind of thing. I'll post the final engineering drawing soon enough.

Thanks for the support, will keep you all updated!

[Peter Reader]

UPDATE:

I'm at the "design ideas" stage of the course and have come up with the following sketches of possible designs (sorry some are not rotated correctly):

Constructive criticism and comments welcome!

Thanks

Pete

[Astrokev]

Hi Peter

Good to see your designs coming together. Some good concepts there.

#3 is similar to my 6" tube construction I made some years back. I must dig it out of the attic and post a picture. For what it's worth - for this design, you may struggle to keep the centre of gravity close to the primary mirror end. Like yourself, I wanted to do this to make "depth" of the mount box (or the length of the mount fork arms, depending on what you decide to do) as short as possible. In practice this proved difficult, but not impossible. The trick is to use the thinnest, lightest materials for the box at the focusser end, and much heavier and thicker materials at the primary end. For the tube connectors, aluminium tubes from a DIY store proved OK for my 6".

Not sure I fully understand your last design. What are the hinges for?

Look forward to seeing your final design!

Kev

[Peter Reader]

Ok thanks for the heads up on the balancing issue!

The last design is designed to fold in half. You have to imagine the section containing the secondary mirror rotating about the hinges and onto the top of the tube section containing the primary mirror. It will then be held in it's portable position by a simple two part hooking mechanism.

I am pretty sure I like the second mount (as I could make it polar aligned and hence trackable -in theory), but not sure which tube to go for yet. My project is based around portability and flat packing.

Thanks for the feedback

Pete

[Peter Reader]

Just to bring you guys up to date on the project, I've completed a tube design on Solidworks 2010 CAD Software:

Mount model coming soon

[Peter Reader]

Here is the finished product model:

Will keep you posted on the build!

Pete

[Astrokev]

Hi Peter

Couple of things to think about -

With a hinged OTA, careful thought will be needed to ensure that the optics retain collimation after each set-up.

The OTA will put a lot of strain on the fork arms. The design of these may need to be modified to increase their strength and general robustness, so as to reduce flexure. Also the join between the fork ands the main polar bearing will need to be pretty beefy.

Looking good. Look forward to seeing the next stage!

Kev

[Peter Reader]

I'll take that into account, thanks. I plan to use steel for the c shaped fork so it shouldn't flex too much to matter.

I'm stuck on ideas for the friction bearing for the "altitude" (declination?) axis... any thoughts? It needs to be detachable so I thought of maybe using a wing nut...

Thanks for the help so far, build pictures to come.

Pete

[Astrokev]

I made a wooden fork mounted scope years ago (6"). For this I got a couple of circular bearings from a friend (they were actually wheel bearings of an old Triumph Spitfire) and had another friend with a lathe turn down some steel pipe to fit in the bearings. The pipes were welded to flat plates to make flanges which were screwed to the OTA. The bearings simply slid into U-shaped wooden "cups" which were fixed to the end of the fork arms. It was easy to mount/dismount as needed.

For friction control, I made a plastic collar which slid over the end of one of the dec pipes. To this collar I mounted a tangent arm, the end of which located onto a fixed pin at the bottom of the fork arm. The plastic collar was split, with a bolt/wing-nut to tighten or loosen the collar onto the dec pipe. (In actual fact, the locating pin for the tangent arm was mounted on a screw drive and motor I ripped out of an old machine being discarded from my workplace. This ran off a battery, and enabled me to have a dec drive to center objects. Not needed, but a bit of fun to make!).

Hope this is reasonably clear (easier to make than describe!). May give you some ideas.

Kevin

[Peter Reader]

Update: Just completed the eyepiece holding half of the OTA.

I'm using 4mm laser ply wood. You can see the panels slot together at the edges at right angles and are reinforced with internal pine lengths.

The focuser was designed for a circular OTA so I had to heat and bend a piece of plastic to the correct shape to achieve a snug fit.

Will post pictures of the second half of the OTA and the completed OTA.

Comments/criticisms/warnings are most welcome.

I still haven't settled on a way of securing the two OTA sections so that it stays rigid once in use. Any ideas welcome (no matter how crazy).

Thanks everyone

Pete

[Peter Reader]

Here's both parts of the tube:

[ponytale]

how about 4 ply wood flanges 2 on one part and 2 on the other so it the two parts will only assemble in the correct alignment, perhaps with tapered v shaped interlocking pieces ? as per sketch attached when together use those lever over latches you see on most tool boxes and the like which will pull it tight together,

interlock.doc

[Peter Reader]

I think I see what you mean! It's great idea! It would also distribute the weight force on the hinge that will be put on (when scope is on it's side). Thanks!

[yesyes]

Hey, this is coming along nicely !! The real thing looks so much better than the drawings.. ;-)

Are you going to paint it black inside? You're going to get reflections from those Nyloc nuts...

[Peter Reader]

The plan is to either: cover the screws with rubber, spray paint the whole OTA black or use different coloured nuts...

I had to use these nuts as our school didn't have any others in stock -should be able to reduce the reflections before the deadline by any of the methods above.... hopefully...

Thanks for the heads up!

[Peter Reader]

Build update:

Have combine both halves of the OTA with long hinges. Everything seems to line up ok (I'm shocked).

Have brought some latches to secure the OTA in folded position that will be put on tomorrow.

[Peter Reader]

UPDATE: OTA completed:

Wing nut friction bearings:

R.A axis bearing:

The fork was then painted with black primer paint for an undercoat:

Mount pictures coming soon...

[Peter Reader]

UPDATE: Product practically finished! Just needs a coat of paint and will be done!

[callump]

Pete, i think this looks really great.

Hope you get some good views through it.

Keep posting on the progress...

Callum

[Astrokev]

Great job there Pete. Your OTA looks really good. I worry a bit about the robustness of the RA axis mount and the fork arms though. How much flexure are you getting?

Kevin

[Peter Reader]

Very little actually. It bounces slightly when I turn it quickly but otherwise it's reasonably smooth to move around and holds it position nicely (so must have got the balance pretty near). All in all very pleased with this. Will post final set up when it's painted and operational.

[Astrokev]

Look forward to seeing that. Well done again.

[Peter Reader]

Tested it out during the day today and managed to see some birds in a far away tree. The image is quite "cloudy"/"misty"... I've cleaned both mirrors and they are aligned fine... any ideas?