Datasheet for Split-Level Prism
with Equal-Length Struts

Copyright © 2008 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.

# strut
<Member> struta    p3' p1  -1.0  sqr(2.0)  1 Con *
<Member> strutb    p4' p2  -1.0  sqr(2.0)  9 Con *

# interlayer tendon
<Member> xlta      p1' p1   1.0  sqr(2.0)  3 Obj *
<Member> xltb      p2' p2   2.0  1.0       3 Obj *

# end tendons
<Member> enda      p2  p1   1.0  1.0       2 Con *
<Member> endb      p3  p2   1.0  1.0       2 Con *
<Member> enda'     p3' p1'  1.0  sqr(1.50) 4 Con *
<Member> endb'     p4' p2'  1.0  sqr(0.75) 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.
        The values are in model units.

   struta:            2    strutb:            2      xlta:            1
     xltb:      1.58114      enda:            1      endb:            1
    enda':          1.5     endb':         0.75

        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.

   struta:           -2    strutb:           -4      xlta:            1
     xltb:      3.16228      enda:          1.5      endb:          1.5
    enda':            1     endb':            2

        Average tendon force magnitude: 1.69371

        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 3/8-inch-diameter wooden dowel.
        The tendons were made of 25-lb.-test braided nylon fishing line.
        In this case, the attachment point at the hubs was screw eye
        at the end of the strut.  The size of the eye varied slightly
        from eye to eye, so I didn't do any member-length adjustments
        here since my model isn't of sufficient complexity to take this
        situation into account.  I will adjust the lengths to take into
        account the screw eye diameters when I do the actual assembly.
        So the strut and tendon lengths given here are measured from
        screw-eye center to screw-eye center.  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> 241/2
        Strut and Tendon Hub Adjustments - s;t> 0 0
   struta: 241 0    strutb: 241 0      xlta: 119 0      xltb: 183 1
     enda: 118 1      endb: 118 1     enda': 178 1     endb':  88 1

pedagogic view of split-level prism with equal-length struts
Split-Level Prism with Equal-Length Struts with Point Labels

structure file:  tprism/x6prism6b.rc
 variable file:  tprism/x6prism6b.dat
    digit list:  src/mm.dls


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


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