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Modified Orthogonal Girdled Six-fold Prism Datasheet

©2004 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> strut1a    p2' p1   0.0
         sqr(cos(acos(-sqrt(3)/3) - pi/2) + sqrt(3)*cos(acos(-1/3) - pi/2))
         1 Con CalcClear Inelastic *
<Member> strut1b    p3' p2   0.0
         sqr(cos(acos(-sqrt(3)/3) - pi/2) + sqrt(3)*cos(acos(-1/3) - pi/2))
         1 Con CalcClear Inelastic *
<Member> strut2a    p4' p5' -1.0      0.0      1 Obj CalcClear Inelastic *
<Member> strut2b    p5  p6  -1.0      0.0      1 Obj CalcClear Inelastic *

# side tendons
<Member> side1a     p4' p2'  1.0      sqr(1.0) 3 Con *
<Member> side2a     p4  p4'  1.0      sqr(1.0) 3 Con *
<Member> side3a     p1  p4   1.0      sqr(1.0) 3 Con *
<Member> side1b     p5' p3'  1.0      sqr(1.0) 3 Con *
<Member> side2b     p5  p5'  1.0      sqr(1.0) 3 Con *
<Member> side3b     p2  p5   1.0      sqr(1.0) 3 Con *

# bottom tendons
<Member> end1a      p2  p1   1.0      sqr(1.0) 2 Con *
<Member> end1b      p3  p2   1.0      sqr(1.0) 2 Con *
<Member> end1c      p3  p1   0.1      3.0      7 Con *

# top tendons
<Member> end2a      p2' p1'  1.0      sqr(1.0) 4 Con *
<Member> end2b      p3' p2'  1.0      sqr(1.0) 4 Con *
<Member> end2c      p3' p1'  0.1      3.0      7 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.

  strut1a:      2.44949   strut1b:      2.44949   strut2a:            2
  strut2b:            2    side1a:            1    side2a:            1
   side3a:            1    side1b:            1    side2b:            1
   side3b:            1     end1a:            1     end1b:            1
    end1c:      1.73205     end2a:            1     end2b:            1
    end2c:      1.73205

        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.  The
        roundness of these numbers is extraordinary.

  strut1a:     -1.63299   strut1b:     -1.63299   strut2a:           -2
  strut2b:           -2    side1a:            2    side2a:            2
   side3a:            2    side1b:            2    side2b:            2
   side3b:            2     end1a:     0.666667     end1b:      1.33333
    end1c:            0     end2a:     0.666667     end2b:      1.33333
    end2c:            0

        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> 292/2.44949
        Strut and Tendon Hub Adjustments - s;t> 5.0 3.5
        (The 5.0 mm adjustment for the strut is the amount
         the screw-eye center extends from the dowel.  The 3.5 mm
	 adjustment for the tendon is half the outer diameter of the
         screw eye.)

  strut1a: 282 0   strut1b: 282 0   strut2a: 228 1   strut2b: 228 1
   side1a: 109 0    side2a: 109 0    side3a: 109 0    side1b: 109 0
   side2b: 109 0    side3b: 109 0     end1a: 111 0     end1b: 110 0
    end1c: 199 1     end2a: 111 0     end2b: 110 0     end2c: 199 1

ray trace of modified tensegrity truncated cuboctahedron
Orthogonal Girdled Six-fold Prism with Point Labels
(NB: The end1c and end2c tendons are not present in the diagram
but are essential for the stability of the sculpture.)
(VRML Model)

structure file:  tprism/x6girdle6.rc
variable file:   tprism/x6girdle6.dat
digit list:      ../src/mm.dls


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


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