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(VRML Model)
Schematic for the Tensegrity Obelisk
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> strut13 pt1A pt3c 0.0 sqr(2.5) 1 Con CalcClear Inelastic *
<Member> strut24 pt2A pt4a 0.0 sqr(2.5) 1 Con CalcClear Inelastic *
<Member> strut35 pt3A pt5c 0.0 sqr(2.5) 1 Con CalcClear Inelastic *
<Member> strut46 pt4A pt6a 0.0 sqr(2.5) 1 Con CalcClear Inelastic *
<Member> baset pt1A pt1B 0.0 sqr(1.5) 2 Exc *
<Member> apext pt6a pt6b 0.0 sqr(1.0) 2 Con *
<Member> guy1 pt1A pt3b 0.2 0.0 3 Obj *
<Member> guy2 pt2A pt4b 0.2 0.0 3 Obj *
<Member> guy3 pt3A pt5b 0.2 0.0 3 Obj *
<Member> guy4 pt4A pt6b 0.2 0.0 3 Obj *
<Member> TL12 pt1A pt2B 0.9 0.0 4 Obj *
<Member> TS23 pt2A pt3b 2/3 0.0 4 Obj *
<Member> TL23 pt2A pt3A 0.9 0.0 4 Exc *
<Member> tS23 pt2A pt3a 2/3 0.0 4 Obj *
<Member> TS34 pt3A pt4a 2/3 0.0 4 Obj *
<Member> TL34 pt3A pt4B 0.9 0.0 4 Exc *
<Member> tS34 pt3A pt4b 2/3 0.0 4 Obj *
<Member> tL34 pt3a pt4a 0.9 0.0 4 Exc *
<Member> TS45 pt4A pt5b 2/3 0.0 4 Obj *
<Member> tS45 pt4A pt5a 2/3 0.0 4 Obj *
<Member> tL45 pt4c pt5a 0.9 0.0 4 Exc *
<Member> tL56 pt5a pt6a 0.9 0.0 4 Obj *
<Member> tT33 pt3a pt3A 2/3 0.0 4 Obj *
<Member> tT44 pt4a pt4A 2/3 0.0 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
hub center to hub center, as are the tendon lengths.
These values are in model units.
strut13: 2.5 strut24: 2.5 strut35: 2.5
strut46: 2.5 baset: 2 apext: 1
guy1: 1.61188 guy2: 2.14435 guy3: 2.33364
guy4: 2.22517 TL12: 1.00969 TS23: 1.56806
TL23: 1.6292 tS23: 0.929175 TS34: 0.999215
TL34: 1.46278 tS34: 0.822359 tL34: 1.80241
TS45: 1.168 tS45: 1.32031 tL45: 1.79639
tL56: 1.23052 tT33: 0.818674 tT44: 0.666956
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.
strut13: -1.56288 strut24: -1.0168 strut35: -0.938242
strut46: -1.65821 apext: 0.25984 guy1: 0.322376
guy2: 0.42887 guy3: 0.466727 guy4: 0.445034
TL12: 0.908718 TS23: 1.04537 tS23: 0.61945
TS34: 0.666144 tS34: 0.54824 TS45: 0.778668
tS45: 0.880209 tL56: 1.10747 tT33: 0.545782
tT44: 0.444637
Average tendon force magnitude: 0.631169
Construction Lengths (in inches, 16ths and 32nds)
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 hub. The struts were cut from
1-inch by 1-inch hardwood garden stakes. The tendon material
was single strands of twisted #18 nylon twine. Its behavior
under stress is highly non-linear, so a look-up table
was used to compute strains. Prestress forces were assumed
to affect tendon lengths and not strut lengths.
Average Tendon Force Magnitude (chart units)> 20
Length Scale Factor> 48/2.5
Strut and Tendon Hub Adjustments> 0 0.5
(adjust the tendon lengths by subtracting a half inch from
both ends)
strut13: 48 0 0 strut24: 48 0 0 strut35: 48 0 0 strut46: 48 0 0
apext: 17 6 0 guy1: 28 5 0 guy2: 37 7 1 guy3: 40 11 1
guy4: 38 14 0 TL12: 16 7 1 TS23: 25 12 1 tS23: 15 7 0
TS34: 16 9 1 tS34: 13 10 1 TS45: 19 6 0 tS45: 21 13 1
tL56: 19 15 1 tT33: 13 9 1 tT44: 11 0 0
Base chord length = (2/2.5)*48" = 38.4" = 38 6 1
Material Quantities
This provides an estimate of how much material will
be needed to assemble the structure, in this case
inches of garden stake and inches of nylon twine.
The lengths must be adjusted to take into account the
fact that the strut extends past the hub and some length
of tendon is required to tie it to the strut.
The Quantity value given for each Type does not take
into account the Cross Section value. The total
Quantity given across from Tndns does.
Length Scale Factor> 48/2.5
Strut and Tendon Adjustments> 0 (-6)
Cross
Type Section Quantity Count
0 1 0 0
1 1 576 12
2 1 89.3237 3
3 1 582.046 12
4 1 874.588 30
Struts 576 12
Tendons 1545.96 45
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Schematic for the Tensegrity Obelisk
structure file: obelisk/stage2.rc
variable file: obelisk/stage2.dat
stress-strain chart file: v04oct_d/wellingtn.ssc
digit list file: src/standard.dls
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CONTACT:
Bob Burkhardt
Tensegrity Solutions
Box 426164
Cambridge, MA 02142-0021
USA
e-mail: bobwb@juno.com