Datasheet for Tensegrity Tetrahedron (2nd version)

Copyright © 2005 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> s1    c1   p1   -1.00   sqr(170)   1 Con CalcClear *
<Member> s2    c1   p2   -1.00   sqr(170)   1 Con CalcClear *
<Member> s3    c2   p3   -1.00   sqr(170)   1 Con CalcClear *
<Member> s4    c2   p4   -1.00   sqr(170)   1 Con CalcClear *

# tendons
<Member> t1-2  p1   p2    1.00   sqr(216.903670735357)   3 Con *
<Member> t1-3  p1   p3    1.00   sqr(216.903670735357)   2 Con *
<Member> t1-4  p1   p4    1.00   sqr(216.903670735357)   2 Con *
<Member> t2-3  p2   p3    1.00   sqr(216.903670735357)   2 Con *
<Member> t2-4  p2   p4    1.00   sqr(216.903670735357)   2 Con *
<Member> t3-4  p3   p4    1.00   sqr(216.903670735357)   3 Con *
<Member> tc    c1   c2    1.00   sqr(108.451835367679)   4 Obj *

        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.
        The values are in model units.

       s1:                   170        s2:                   170
       s3:                   170        s4:                   170
     t1-2:      216.903670735357      t1-3:      216.903670735357
     t1-4:      216.903670735357      t2-3:      216.903670735357
     t2-4:      216.903670735357      t3-4:      216.903670735357
       tc:      108.451835367679

        Relative Member 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.

       s1:     -70.4163056034263        s2:     -70.4163056034263
       s3:     -70.4163056034265        s4:     -70.4163056034261
     t1-2:      6.57870696324024      t1-3:      38.3435141103065
     t1-4:      38.3435141103062      t2-3:      38.3435141103065
     t2-4:      38.3435141103063      t3-4:      6.57870696324026
       tc:      108.451835367679

        Average tendon force magnitude: 39.2833293907693

        Construction Lengths (in mm 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 a member
        represents the distance between the locations where it
        departs from the hubs.  The struts are cut from
        5/16-inch diameter hardwood dowel.  The tendons are made
        of single strands of braided nylon fishing line except
        for member tc where two strands are used.
        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)> .02
        Length Scale Factor> 1
        Strut and Tendon Hub Adjustments - s;t> 7 3.5
        (subtract 2*(7 mm) off strut lengths to get dowel lengths;
         subtract 2*(3.5 mm) off tendon lengths to get hub-adjusted
         in-situ tendon lengths)

       s1: 156 0        s2: 156 0        s3: 156 0        s4: 156 0
     t1-2: 209 0      t1-3: 206 0      t1-4: 206 0      t2-3: 206 0
     t2-4: 206 0      t3-4: 209 0        tc:  98 1

pedagogic view of tensegrity tetrahedron
Tensegrity Tetrahedron Point Labels

     structure file:  tetra/tetra4.rc
      variable file:  tetra/tetra4.dat
cross-section table:  tetra/tetra4.cst


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


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