Truss tube design

[molland67]

Hi,
I'm thinking of using my 10" f/5 mirror in a truss tube telescope to allow me to pack it down a bit when not in use (I need to keep it away from the kids at this point in time). There are plenty of truss tube / ultralight designs out there but what is being compromised by going down the truss tube path rather than making a solid cardboard tube type dob?
Regards,
Andrew.

[Lee]

I'm not sure anything is being compromised - as long as you make the truss design very stiff so it doesn't flex, which would seem to be the solid tubes advantage. I think you will need to collimate regularly with most trusses too.....

[iceman]

Steve (janoskiss) recently turned a solid tube into a truss, for exactly the same reason.

Do a search and you'll find his pictures and advice. Or send him a PM! :)

[astro_south]

Absolutely nothing.

OK, there are some things you should consider, but they are very minor:

1) Will need to check collimation everytime you set it up (checking collimation should be a matter of course for all newt owners anyway - tube or truss especially as it is easy to do). My truss consistently goes back together the same way, and 90% of the time it just requires a quarter to half turn on a push-pull bolt or nut. This can be done while the scope is coolong

2) the mirror will be more exposed to the elements and things dropped into the mirror box if you don't opt for a shroud (I have never bothered with one and rarely get dewing problems on my primary - the secondary mirror can suffer a bit of dew but I have yet to install some dew removal options).

A 10" f5 system is going to be easy to make rigid enough, so I doubt flex will be a problem


There are a few bonuses to the truss design....

1)primary mirror is able to cool quicker as it is more open to the elements

2)it can be transported easily enough after pack up and as you mention, can be stored away better

3)no significant problems with tube currents

4)IMHO is the coolest / sexiest looking scope design around (much nicer than the hot water systems....ohh I'm going to burn for that one ;) :D )

[ving]

and when you make it make sure you keep us in touch with what you are doing :)
we want step by step pics :D

[cristian abarca]

Hi Andrew I converted 10 inch F7.3 into a truss here are a few pictures http://www.iceinspace.com.au/forum/showthread.php?t=9779 . For me collimating every time I set up is the only down side, but you become so used to it that it only takes a couple of minutes. I use a shroud only when I view from home. The Dobsonian Telescope by David Kriege and Richard Berry is an excellent guide for building a truss telescope.

Regards Cristian

[Satchmo]

Make life easy for yourself :) :

http://www.focuser.com/cgi-bin/dman.cgi?page=category&plugin=dstore.cgi&category=4

Mark

[Orion]

Mark,
I've seen these before and am very interested. They certainly would save a lot of time and they don't look half bad either.
Being a ball and socket joint how do you determine the position of the mirror cage? Wouldn't the mirror cage be off to one side?:shrug: Maybe not.

[AstroJunk]

These fix to the upper tube assembly only, the rocker box still has traditional rigid clamps. When the whole thing is tightened up, then it should be pretty soild, and perfectly aligned!

It does look a neat solution. The only problem I can see is the risk of unscrewing the bolts too far in the dark and letting one drop on the primary:eek:

Not very likely though, and you should keep it covered when setting up/stripping down anyway.

I use obsession clamps http://www.obsessiontelescopes.com/ATM_parts/index.html which are ok, but a little fiddly.

Peter Read at SDM now uses an alternative (and seemingly very good design) that can be seen on this photo: http://www.sdmtelescopes.com.au/images/SDM005/SDM5_7.jpg

[Orion]

I use the same ones that Peter does, makes setting up easier.

You can use the Moonlight connectors on the mirror box also.

[Satchmo]

Orion, the answer is that he position of the cage takes care of itself so long as your poles are all exactly th esame length.Well a truss is a truss, and this is no different.. When you pop all the balls into their sockets the balls self align to the right angle and it becomes perfectly rigid. I've seen half a dozen scopes Aussie scopes using these now and they work brilliantly. It makes installing the truss on a new scope a half hour job at best. No calculation of angles required. Just mount the blocks and fit your tubes.

When you are setting up at night, you put plenty of tension on the lower balls to hold the truss tubes approximately in the right position, with upper pairs of ball touching and just drop the cage right on and do up the clamps.

Mark

[Satchmo]

These SDM upper clamps are from Astrosytems:

http://www.astrosystems.biz/utlltl.htm

Unfortunately they break the ideal rule that the truss rods be tied directly together as possible to the cage.. If you haven't done up the clamp real tight you can see that leaning on one pole will cause the other to swing around the clamp axis, multiply that X 4 truss connection pairs and the situation is bad for collimation. However do up the clamps nice and tight and you can get away with it.

Mark

[netwolf]

How about a simple truss tube design to reduce the weight of the OTA for use on a Equatorial mount. I saw a guy on Astromart under ATM parts advertising a Truss change over kit for people with sonotube dobs. Emailed him and its about 500USD without the aluminum tubes which he advises to get locally.

By the way how does one go about finding a good Wood worker in Australia, I came accross a forum once. Where someone had requested for a dob chair to be made for them and found someone to do it. I will dig out the link. I need someone like this who can make something up from drawings. I want to get a dob base made up similar to Rob's, to make it easier to motorize.

Regards
Fahim

[molland67]

Thanks for the feedback everybody.
The Moonlite ball and socket blocks look good.
Regards,
Andrew.

[cristian abarca]

Hi Fahim there are places that will cut whatever you want if you have it drawn on an autocad program, (I think that's what the programme is called), then all you do is assemble it. I know a few places in Melbourne. Some do it for as little as $100 plus timber. They are usually cabinet makers , staircase manufacturers or similar companies with the right machinery. I got a dob mount cut in this way and a member of our astronomy club got his 20 inch truss dob done.

Regards Cristian

[Omaroo]

Yep - In Sydney you can go to JJ Cabinets in Narellan. They have a AU$1M+ machine called a Morbidelli that is a huge CNC wood authoring machine. Brilliant bit of gear. Not sure of his prices though.

[AstroJunk]

I think that any flexure in the poles must be converted into a negligible rotation about the clamp - but having never played with one like this I can't be certain.

One thing is for sure, it must be harder to run power up the poles to the UTA given that wood isn't the best conductor in the world!

[molland67]

Please have a look at the attached drawing. I would like some feedback regarding the idea I have had to magnetically connect truss tubes (while playing with my kids Magnetix set). Apologies to anyone else who has also had this idea...

The truss tube would be made of anything light and stiff. The balls could be bonded into the tube ends. The toroids would be bonded to the upper and lower bits. The ball could be either a steel ball bearing or a spherical magnet. The toroid could be either a magnet or a steel ring. Obviously a steel ball would partner with a toroidal magnet and a spherical magnet would partner with a steel ring.

Whadayareckon?

[Orion]

This is the way I did it. I ran the wires through the poles. I simply connect the power on once the mirror cage is secured to the poles.

[Orion]

I would not trust magnets to hold my telescope together!

[Lee]

Me either......