Mini truss tube telescope project for planets...

[thercman (Greg)]

Hey Guys!

So here is what I am planning to do. A 6 or 8 inch F8 primary. Leaning towards the 6" for an ideal camping scope. The design will be a minimalist design. One cage ring to hold the secondary with a wire spider. (still pondering how I am going to do that) Arrow shafts for the trusses and carbonfiber plate mirror cell/box... The focuser is a simple 1.25" helical design. Has anyone built one similar to this or seen it done? I have seen some travel scopes built but not like this. Do you guys think 6 trusses will be addiquate or will the standard 8 be best? Due to the long focal length a ring half way up the trusses is required since arrow shafts only come in 32" lengths. I was also thinking they could be screwed together, similar to tent poles... I am worried that using this method they may flex.

Also for planetary viewing I am trying to get the longest focal length I can correct? I know I will loose field of view.

Thanks in advance for the help!

[thercman (Greg)]

Well I found this picture of a design that was pretty much what I was thinking about. It has a crayford helical focuser from KineOptics, a wire spider and uses 6 trusses and a minimal mirror box.... I was like, BINGO! I was surprised to find it. I am more or less going to shrink this down. http://www.xmission.com/~alanne/DS3/DS3Main.html

Just wanted to say thanks to Alan Scott for displaying his build online for others to get ideas from.

[thercman (Greg)]

Here is a drawing of how the arrow shafts will be connected to create the length needed to reach the cage ring. Very simple design of just creating a spacer and adding it to a piece of all-thread and securing it with loctite. Each shaft will be aprox. 20" long. I need to build one up to see how much flex there is. Hopefully none. If there is some I may have to considering adding a ring to the center of the trusses. This will add an extra assmebly point and a bit more construction time. I had thought about using larger carbonfiber trusses but that will require the creation of inserts or mounting clamps of some sort unlike the premade arrowshaft parts.... Let me know what you guys think.

[thercman (Greg)]

Okay guys one more drawing for you! This seems to be a very standard way to mount truss poles to a cage ring. I also have another idea using a ball and socket joint similar to the Moonlite mounts. I'll draw that one up later. If you guys have any ideas, please toss them my way!

[thercman (Greg)]

Ball joint style..... So I just altered the drawing a bit to give you guys an image of the ball and socket joint. Basically just like it sounds and the side will be drilled and tapped so a handled screw will be able to apply pressure to the ball. At work I use paint for my designs and on my Mac I have a paintbrush program but it is not as nice as paint so pardon the unfinished drawing..... I really need to invest in CAD software.

[ZeroID (Brent)]

The Arrow shafts you are planning to use, what sort are they ? Pure Carbon Fibre or were they CF over alum tube or ???
I had toyed around with a similar idea some while ago but found that the pure CF shafts were way too flexible. The CF over microwall Alum were quite stiff by comparison. The project got shelved and I built a big Dob instead.

[thercman (Greg)]

Hi ZeroID,

Well I was considering the carbon over aluminum, but also the Easton X7 Eclipse target arrows. I use those to shoot indoor target and the are twice the diameter of a standard arrow which make them stiff. If I do go with an arrow shaft design then a 2 piece design with a center ring will probably be the best option for two reasons. First, the increased rigidity and second having shorter shafts improving transportation.

With that said there are also companies that make larger carbon tubes. I am also looking into these .5" OD tubes. They are 48" long and $14.70US ea. http://www.dragonplate.com/ecart/categories.asp?cID=102