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Datasheet for Three-fold Fan Prism (Two-Strut Girdle)


Copyright © 2009 by Bob Burkhardt

        Member Descriptions
        [name, end point names, weight (if in objective function),
        second power of length (if a constraint), member category,
        Obj/Con/Exc (put in objective function, use as a constraint or
        exclude from computations), flags]
        For assembly purposes, only the name and end point names are
        of interest.  The other information may be of interest after
        A Practical Guide to Tensegrity Design has been consulted.

# struts
<Member> strut1    p2' p1  -1.08483  sqr(2.5)   1 Obj CalcClear *
<Member> strut2    p4' p3  -1.0      sqr(2.5)   1 Obj CalcClear *
<Member> strut3    p6' p5  -1.40225  sqr(2.5)   1 Obj CalcClear *

# side tendon
<Member> side1     p3' p1'  3.0      sqr(0.5)   3 Con *
<Member> side1a    p3' p5'  3.0      sqr(0.5)   3 Con *
<Member> side2     p5  p5'  3.0      sqr(0.5)   3 Con *
<Member> side3     p5  p3   3.0      sqr(0.5)   3 Con *
<Member> side3a    p1  p3   3.0      sqr(0.5)   3 Con *

# bottom tendon
<Member> end1      p2  p1   1.0      sqr(0.5)   2 Con *

# top tendon
<Member> end2      p2' p1'  1.0      sqr(0.5)   4 Con *

        In-Situ Member Lengths
        These are the lengths of the members when they are in place
        and prestress is applied.  The strut lengths are from
        screw-eye center to screw-eye center, as are the tendon lengths.
        These values are in model units.

   strut1:      1.87018    strut2:      1.87018    strut3:      1.87019 
    side1:          0.5    side1a:          0.5     side2:          0.5 
    side3:          0.5    side3a:          0.5      end1:          0.5 
     end2:          0.5 

        Relative Member Prestress Force Magnitudes
        These values are useful for developing an assembly
        strategy for the structure.  The tighter tendons are much
        easier to tie in place early on, while the looser tendons
        can be left to the last.  This information is also used
        to adjust tendon lengths since the measured length of a tendon
        will be shorter for a highly-stressed tendon with the same
        in-situ length as a tendon which is not so stressed.

   strut1:     -2.02883    strut2:     -1.87018    strut3:     -2.62247 
    side1:      3.91592    side1a:      3.91591     side2:      4.16017 
    side3:      3.91591    side3a:      3.91592      end1:      2.28445 
     end2:      2.28445 

	Average tendon force magnitude: 3.48468

        Construction Lengths (in millimeters and halves)
        The construction length of a tendon is less than the in-situ
        length since when the tendon is measured off it isn't under
        any prestress force.  The construction length for the strut
        represents the length of the 5/16-inch-diameter wooden dowel.
        Braided nylon fishing line was used for the tendons.
        Prestress forces are assumed to affect tendon lengths and
        not strut lengths.

        Elongation of Tendon of Unit Cross Section
        Under Force of Average Magnitude (fraction)> 0.02
        Length Scale Factor> 209.5/1.87018
        Strut and Tendon Hub Adjustments - s;t> 4.75; 3.0
        (The 4.75 mm adjustment for the strut is the amount
         the screw-eye center extends from the dowel.  The 3.0 mm
	 adjustment for the tendon is half the outer diameter of the
         screw eye.)

   strut1: 200 0    strut2: 200 0    strut3: 200 0     side1:  49 0 
   side1a:  49 0     side2:  49 0     side3:  49 0    side3a:  49 0 
     end1:  49 1      end2:  49 1 

ray trace of three-fold fan prism
Three-fold Fan Prism (Two-Strut Girdle) with Point Labels

structure file:  tprism/x3girdle1b.rc
variable file:   tprism/x3girdle1b.dat
digit list:      src/mm.dls

CONTACT:

Bob Burkhardt
Tensegrity Solutions
Box 426164
Cambridge, MA 02142-0021
USA

e-mail: bobwb@juno.com

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