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Datasheet for Structure Based on Laminated Skew Prisms


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> strut13a pt1A pt3c -1.0 2.0      1 Con *
<Member> strut24a pt2A pt4a -1.0 5.0      1 Con *

<Member> end1a    pt1A pt1B  1.0 sqr(1.0) 2 Con *
<Member> end2a    pt4a pt4b  1.0 sqr(1.0) 2 Con *

<Member> guy1a    pt1A pt3b  1.0 sqr(1.0) 3 Obj *
<Member> guy2a    pt2C pt4b  1.0 sqr(1.0) 3 Obj *

<Member> eq1a     pt2A pt3a  1.0 sqr(1.0) 2 Con *
<Member> eq2a     pt2A pt3b  1.0 sqr(1.0) 2 Con *

<Member> strut13b pt1B pt3a -1.0 4.0      1 Con *
<Member> strut24b pt2B pt4b -1.0 4.0      1 Con *

<Member> end1b    pt1B pt1C  1.0 sqr(1.0) 2 Con *
<Member> end2b    pt4b pt4c  1.0 sqr(1.0) 2 Con *

<Member> guy1b    pt1B pt3c  1.0 sqr(1.0) 3 Obj *
<Member> guy2b    pt2A pt4c  1.0 sqr(1.0) 3 Obj *

<Member> eq1b     pt2B pt3b  1.0 sqr(1.0) 2 Con *
<Member> eq2b     pt2B pt3c  1.0 sqr(1.0) 2 Con *

<Member> strut13c pt1C pt3b -1.0 5.0      1 Con *
<Member> strut24c pt2C pt4c -1.0 2.0      1 Con *

<Member> end1c    pt1C pt1A  1.0 sqr(1.0) 2 Con *
<Member> end2c    pt4c pt4a  1.0 sqr(1.0) 2 Con *

<Member> guy1c    pt1C pt3a  1.0 sqr(1.0) 3 Obj *
<Member> guy2c    pt2B pt4a  1.0 sqr(1.0) 3 Obj *

<Member> eq1c     pt2C pt3c  1.0 sqr(1.0) 2 Con *
<Member> eq2c     pt2C pt3a  1.0 sqr(1.0) 2 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.

 strut13a:      1.41421  strut24a:      2.23607     end1a:            1
    end2a:            1     guy1a:      1.41421     guy2a:            1
     eq1a:            1      eq2a:            1  strut13b:            2
 strut24b:            2     end1b:            1     end2b:            1
    guy1b:            1     guy2b:      1.41421      eq1b:            1
     eq2b:            1  strut13c:      2.23607  strut24c:      1.41421
    end1c:            1     end2c:            1     guy1c:      1.41421
    guy2c:      1.41421      eq1c:            1      eq2c:            1

        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.

 strut13a:     -1.41421  strut24a:     -2.23607     end1a:            1
    end2a:            1     guy1a:      1.41421     guy2a:            1
     eq1a:            1      eq2a:            1  strut13b:           -2
 strut24b:           -2     end1b:            1     end2b:            1
    guy1b:            1     guy2b:      1.41421      eq1b:            1
     eq2b:            1  strut13c:     -2.23607  strut24c:     -1.41421
    end1c:            1     end2c:            1     guy1c:      1.41421
    guy2c:      1.41421      eq1c:            1      eq2c:            1

        Average tendon force magnitude: 1.09205

        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 3/16-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 simple
        metal pin stuck into the end of the strut, so no member-length
        adjustments were necessary.  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> 88/sqrt(2)
        Strut and Tendon Hub Adjustments - s;t> 0 0

 strut13a:  88 0  strut24a: 139 0     end1a:  61 0     end2a:  61 0
    guy1a:  86 0     guy2a:  61 0      eq1a:  61 0      eq2a:  61 0
 strut13b: 124 1  strut24b: 124 1     end1b:  61 0     end2b:  61 0
    guy1b:  61 0     guy2b:  86 0      eq1b:  61 0      eq2b:  61 0
 strut13c: 139 0  strut24c:  88 0     end1c:  61 0     end2c:  61 0
    guy1c:  86 0     guy2c:  86 0      eq1c:  61 0      eq2c:  61 0

        Material Quantities (in millimeters)
        Estimates of the total amount of material required to build
        the structure.  The adjustment in this case includes "waste":
        for the strut, the amount lost when sawing the strut from a
        length of dowel (1 mm from each end); for the tendons, the amount
        of extra needed to successfully tie the tendon (50 mm extra at
        each end).

        Elongation of Tendon of Unit Cross Section
        Under Force of Average Magnitude (fraction)> .02
        Length Scale Factor> 88/sqrt(2)
        Strut and Tendon Adjustments - s;t> -1, -50

                    Cross
         Type     Section    Quantity Count

            1           1     715.182     6
            2           1     1911.69    12
            3           1     1051.63     6
        Strts                 715.182     6
        Tndns                 2963.32    18


pedagogic view of structure based on laminated skew prisms
Structure Based on Laminated Skew Prisms with Point Labels

structure file:  mast/x3l2mast2b.rc
 variable file:  mast/x3l2mast2b.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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