Project Cyclops, A Design... - Department of Earth and Planetary ...

There are 24 members in the base structure (not
including the piston).
For the geometry chosen, the lengths of the members
are as follows:
No. of Members Length (ft)
3 61.5
3 52.0
3 42.0
3 45.0
6 54.5
6 58.7
The structure configuration is well suited for mass
production. The basic element consists of three identical
truss elements, which can be factory assembled and
erected with a minimum of field welding.
Weight and Cost
A preliminary weight estimate of the structure may
be obtained without a detailed structural design effort
by requiring that all members have L/r ratio less than
200 (r = radius of gyration of the member). Rough
calculations indicate that 8 in SC 40 pipe will meet this
requirement and should be strong enough. Based on the
use of this pipe (28.56 lb/ft), a total weight of base
structure W is easily found. We obtain I¢ = 36,600 lb.
Allowing an additional 10% for fittings we obtain a base
weight on the order of 41,000 lb. Note that this weight
does not include bearings, wheel and track, or pistons.
At a material cost of $0.20/lb, we find that the basic
steelwork will cost $8,200 per base structure. It seems
likely (although no figures can be provided at this time)
that the assembled structure (again excluding piston,
bearing, and wheel and track) would cost $16,000 to
$24,000 if mass produced. No calculations were made
for a 100 meter dish. If the design is practical for this
larger size the material cost alone would be on the order
of $300,000.
Design
Considerations
If we require that the center of the dish at zenith be
located directly over the central bearing of the base
structure, we find that the maximum dish radius that
can be accommodated is Rma x --- 68 ft. The limiting
factor is backup structure interference with ground at
maximum angle from zenith.
The structure is statically determinate, carries its
loading by tension or compression in all members, and is
completely triangularized; no stability problems should
occur. Horizontal loads are carried by the central
bearing, while vertical loading is carried by the three
wheel supports. Drive for the azimuth positioning is
provided by powering the wheels. Became side loads are
carried by the central bearing, the wheel and track
tolerances in the horizontal plane are not critical. In
fact, it may not be necessary to provide more than a
reasonably level roadway since final pointing adjustments
in elevation can be made by the elevation piston if
compensating feedback is provided.
A better estimate of the cost cannot be obtained until
strength calculations are complete for the design Ioadings.
Such strength calculations will yield requirements
on piston, bearing, and wheel and track assemblies; only
after this is completed can a cost estimate of these
members be obtained.
PI TO
\\
\
30* TYP I -'
TWIN
PIPES
p_/i'_', IIA DETAIL A
SUPPORT //' '\\// _, h
PISTON / /' I W _\\
CASING ? -'_ ,, 1
BEARING
Figure F-2. Mass produced Az-El mount.
ACTIVE ELEMENT BASE STRUCTURE
The active element base structure design is an attempt
to incorporate the mechanical positioning devices and
the structural support into a single unit. It comprises
three main pistons and two stabilizing pistons (see Fig.
F-3). The dish is supported at three points. The piston
connected to point a_ moves only vertically, whereas the
pistons connected to a2 and a3 rotate in ball joints at
both ends. The pistons P4 and Ps provide only tension
and are needed only for stability. Tracking and declination
angles are achieved by adjusting the relative lengths
of all three pistons (P_, P2, P3), with the constraint that
the extension of piston P1 should be kept to a minimum
since this piston carries all horizontal loads. A simple
rack, connected to the upper ball of the piston and
parallel to the piston, drives an encoder, which provides
the position feedback required for pointing. Since
deformations in the structure below do not influence the
I
200