8" f/4 travel truss dob - arrgh not good enough! - Page 2

janoskiss (Steve H) · #21 19-06-2006, 10:27 PM

First light tonight was a disappointment. I stiffened the frame and the baseplate, but the thing still vibrates like crazy. It's okay for low powers but at 100x or more it is very painful. It took me back to my old wobbly Dirk Smith EQ mounted 4.5" Newt. I don't really know where to from here.

gaa_ian (Ian) · #22 19-06-2006, 10:29 PM

Ah, the pain of doing R&D !
What about a fold up plywood dob base ?

janoskiss (Steve H) · #23 19-06-2006, 10:47 PM

Quote:

Originally Posted by gaa_ian

Ah, the pain of doing R&D !
What about a fold up plywood dob base ?

I started making one, but the plywood I chose was too thin. But even if it wasn't I'm not sure the pull-apart design would be good enough either... And next w/e is new moon. I'd rather be observing than building more bloody dob mounts.

janoskiss (Steve H) · #24 19-06-2006, 10:49 PM

I might drop in at Bintel and try out vibration suppression pads under the feet (1/4" bolt heads).

janoskiss (Steve H) · #25 20-06-2006, 01:56 PM

Just back from Bintel. Tried out the meade "vibration isolation pads" - no good. Roger had some good tips. Trouble is they all require a lot more work..

Miaplacidus (Brian) · #26 20-06-2006, 02:07 PM

Come on, Steve, you can do it. (You probably don't realize it, but there's a sweep going to see who gets their gear up and running first, you or Ken.)

Cheers and Beers,

Brian.

ving (David) · #27 20-06-2006, 02:30 PM

it seems to me that you are trying to build it too light?

Merlin66 (Ken) · #28 20-06-2006, 04:03 PM

I once had a lightweight 6" f8, where the tube would vibrate like crazy. The solution was to run a cable from the front of the tube down to the base, under a roller, up to another roller held under a tension spring, one wrap around, down to the third roller then up to the mirror cell of the tube. Acted like a triangular stiffner which still allowed freedom of movement. Very simple ; very effective.

astro_nutt · #29 21-06-2006, 11:01 AM

I'm just wondering, have you tried a torsion test on optical tube and the mount/base?
Try placing the optical frame only it standing upright on a concrete floor and attach a laser..then place a mirror on the ceiling so the laser bounces off and reflects on the floor..With the laser on, try and adjust the focuser..etc and see how much play there is...then support the tube by the hubs using some drink crates or whatever and test again..next is the mount by itself..giving it a firm rap at various places...then the whole lot together..this is a way to find out where the most likely cause of movement.
I hope I don't sound too critical...but your scope looks cool and has great potential!!
I know it will work out for you!!

janoskiss (Steve H) · #30 21-06-2006, 11:11 AM

Thanks for the comments and suggestions. I have checked out the vibration of the various components separately. The OTA is good and sturdy. The base is okay now too. It's the A-frame sides that flex too much. Going to go back to the plywood route. I feel like I'm in a prequel to the sequel to a bad movie.

Roger Davis · #31 23-06-2006, 08:51 AM

Ahh Alian Gremlins! The Number of the Beast, you could call it 666 or Be'alzevuv (the original spelling!).
I think your problem was in the way in which the A frame was held together. Relying on aluminium grab instead of nuts ain't the best. You'd be better off redoing them with large pop rivets, that way you could put in three or four p-r's to reinforce the frame. Looked like an aluminium version of Burr Castle, but without the speculum mirror!

janoskiss (Steve H) · #32 03-07-2006, 01:29 AM

Here is the new model: http://www.iceinspace.com.au/forum/s...ad.php?t=11358
No first light yet. But there was a zeroth light before I strengthened the side walls by adding the lighter coloured outside panels you see in the pics, and it was already quite usable, viewing Jupiter at 200x. I also repositioned the sliders on the groundboard so I think this one will do fine.

ballaratdragons (Ken) · #33 12-07-2006, 10:04 PM

Quote:

Originally Posted by Miaplacidus

Come on, Steve, you can do it. (You probably don't realize it, but there's a sweep going to see who gets their gear up and running first, you or Ken.)

Cheers and Beers,

Brian.

I think Steve won. I only finished mine today.

Well, it was finished about a week ago but rain has prevented me from actually going outside and mounting mine until today.