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Datasheet for X-Module Tetrahedron


Copyright © 2007 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.

<Member> end1     pt1A  pt1B   0.0  sqr(2.95572) 3 Con *

<Member> st13p    pt1A  pt3a   0.0  sqr(2.43699)  1 Con CalcClear *
<Member> st13q    pt1B  pt3b   0.0  sqr(2.43699)  1 Con CalcClear *

<Member> side1ap  pt1A  pt3b   1.0  0.0       3 Obj *
<Member> side1cp  pt1A  pt2B   1.0  0.0       3 Obj *

<Member> side1aq  pt1B  pt3a   1.0  0.0       3 Obj *
<Member> side1cq  pt1B  pt2A   1.0  0.0       3 Obj *

<Member> gird1ap  pt2A  pt3a   0.0  sqr(1.0)  2 Con *
<Member> gird1bp  pt2A  pt3b   0.0  sqr(1.0)  2 Con *

<Member> gird1aq  pt2B  pt3b   0.0  sqr(1.0)  2 Con *
<Member> gird1bq  pt2B  pt3a   0.0  sqr(1.0)  2 Con *

<Member> st24p    pt2A  pt4a   0.0  sqr(2.43699)  1 Con CalcClear *
<Member> st24q    pt2B  pt4b   0.0  sqr(2.43699)  1 Con CalcClear *

<Member> side2ap  pt2A  pt4b   1.0  0.0       3 Obj *
<Member> side2bp  pt4a  pt3a   1.0  0.0       3 Obj *

<Member> side2aq  pt2B  pt4a   1.0  0.0       3 Obj *
<Member> side2bq  pt4b  pt3b   1.0  0.0       3 Obj *

<Member> end2     pt4b  pt4a   0.0  sqr(2.95572) 3 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 pin insertion
        point to pin insertion point, as are the tendon lengths.
        The values are in model units.

     end1:      2.95572     st13p:      2.43699     st13q:      2.43699
  side1ap:      1.47679   side1cp:      1.66364   side1aq:      1.47679
  side1cq:      1.66364   gird1ap:            1   gird1bp:            1
  gird1aq:            1   gird1bq:            1     st24p:      2.43699
    st24q:      2.43699   side2ap:      1.47679   side2bp:      1.66364
  side2aq:      1.47679   side2bq:      1.66364      end2:      2.95572

        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.

     end1:      1.61982     st13p:     -4.27662     st13q:     -4.27662
  side1ap:      1.47679   side1cp:      1.66364   side1aq:      1.47679
  side1cq:      1.66364   gird1ap:      3.07959   gird1bp:      3.07959
  gird1aq:      3.07959   gird1bq:      3.07959     st24p:     -4.27662
    st24q:     -4.27662   side2ap:      1.47679   side2bp:      1.66364
  side2aq:      1.47679   side2bq:      1.66364      end2:      1.61982

        Average tendon force magnitude: 2.00855

        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 1/4-inch-diameter wooden dowel.
        The tendons were made of 12-lb.-test braided nylon fishing line.
        In this case, the attachment point at the hubs was a 5 mm o.d.
        (size 217½) screw eye in the end of the strut.  Prestress
        forces are assumed not to affect strut lengths.

        Elongation of Tendon of Unit Cross Section
        Under Force of Average Magnitude (fraction)> .02
        Length Scale Factor> 208/2.43699
        Strut and Tendon Hub Adjustments - s;t> 4, 2.5

     end1: 243 1     st13p: 200 0     st13q: 200 0   side1ap: 119 1
  side1cp: 135 0   side1aq: 119 1   side1cq: 135 0   gird1ap:  78 0
  gird1bp:  78 0   gird1aq:  78 0   gird1bq:  78 0     st24p: 200 0
    st24q: 200 0   side2ap: 119 1   side2bp: 135 0   side2aq: 119 1
  side2bq: 135 0      end2: 243 1

        Construction Lengths II (in millimeters and halves)
        The construction length for the strut now represents the length of
        a 3/16-inch-diameter wooden dowel.  The tendons continue to be
        made of 12-lb.-test braided nylon fishing line, but now
        the attachment point at the hubs is a small nail stuck into the
        end of the strut, so no member-length adjustments were necessary.

        Elongation of Tendon of Unit Cross Section
        Under Force of Average Magnitude (fraction)> .02
        Length Scale Factor> 150/2.43699
        Strut and Tendon Hub Adjustments - s;t> 0, 0

     end1: 179 0     st13p: 150 0     st13q: 150 0   side1ap:  89 1
  side1cp: 100 1   side1aq:  89 1   side1cq: 100 1   gird1ap:  59 1
  gird1bp:  59 1   gird1aq:  59 1   gird1bq:  59 1     st24p: 150 0
    st24q: 150 0   side2ap:  89 1   side2bp: 100 1   side2aq:  89 1
  side2bq: 100 1      end2: 179 0

pedagogic view of x-module tetrahedron
X-Module Tetrahedron with Point Labels

structure file:  chain/x2l2chain5.rc
 variable file:  chain/x2l2chain5.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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