Jump to content


Photo

16" Ultralight Dob

  • Please log in to reply
29 replies to this topic

#26 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 22839
  • Joined: 23 Jun 2003
  • Loc: Los Angeles

Posted 11 October 2013 - 05:22 PM

Re: Mark's recommendation of Albert Highe's book, "Engineering, Design and Construction of Portable Newtonian Telescopes" :
+1 !

#27 acochran

acochran

    Viking 1

  • -----
  • Posts: 533
  • Joined: 19 Jun 2008
  • Loc: So. CA

Posted 11 October 2013 - 06:37 PM

Possibly research metal cable string type reinforcing of a truss system? I understand they can stiffen a truss or strut system. See the Dobstuff web site. See also the diameter of tubing that Dobstuff uses for different size scopes.
Andy

#28 Arjan

Arjan

    Mariner 2

  • -----
  • Posts: 212
  • Joined: 21 Jan 2009
  • Loc: Netherlands

Posted 12 October 2013 - 01:47 AM

Probably a matter of how much reality deviates from theory. Trusses should only be handling axial push and pull forces, so their endpoints could even be pivoting. Bending forces are absent, theoretically at least.

In my 10" Dob, I use 10mm U-profiles. The endpoints can rotate, so that the whole truss structure folds up for storage. I've never noticed any sag, but admittedly, never used a camera on it either...

#29 salies66

salies66

    Lift Off

  • -----
  • Posts: 5
  • Joined: 25 Aug 2013

Posted 12 October 2013 - 02:21 AM

hello http://www.astrosurf...ger/william.htm
ere is mine, made ​​with fully from the recovery, the structure only 8kg for a total weight of 20 kg, a new, more lightweight and compact version is a study, if it can give you ideas

#30 careysub

careysub

    Surveyor 1

  • *****
  • Posts: 1900
  • Joined: 18 Feb 2011
  • Loc: Rancho Cucamonga, CA

Posted 13 October 2013 - 01:30 PM

As Albert Highe makes clear any deviation from the ideal force alignments in a truss can increase actual deflection by a factor of two or three (or even more) - this includes the connection points not being exactly on the member centerline, and the truss attachments not pivoting and being at the wrong angle.

In addition it should be remembered that ideal trusses only carry in-plane loads attached to their ends. Any other load will generate bending forces on the members. This includes torsion (mentioned by Don) and the weight of the truss members themselves. They are, after all, just beams on their own and can sag from their own weight if very long and thin






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics