Tensile Whippletrees and Double-Driving
Differentials (AWECS Methods) 
The Whippletree is a classic mechanism of cascaded beam
"scales" seen in diverse places, from draft animal harnessing to Calder
Mobiles. Its a way of equalizing forces by balancing tension. In
traction kites one often sees pulley-bridling in this mode, with no
spars needed, and the control-bar itself is a Whippletree element. Tri-tethers can
be rigged into 3D whippletrees for isotropic kite arrays.
These methods are dynamically similar to mechanical
differentials used in AWECS transmissions.
A major use in AWE is converting pumping action to rotation. Long-stroke
reeling reverses reel rotation and has no inherent equalizing for
constant output. Short-stroke pumping, on the other hand, is better suited
for constant rotation.
Short-stroke pumping converts into constant rotary motion
by many methods. The simplest is a single free-wheel ratchet or sprag with
an elastic return, but there is some elastic loss and considerable
jerkiness requiring flywheel mass to smooth. Recently, two
"double-drive" mechanisms were
described, the Nordic Track exercise machine,
with double sprags on
a de Prony Brake*
shaft, and the Double Driver screwdriver currently being promoted as a
Christmas gift (who knew AWE tinkering was so popular?). We had
discovered a two-bike freewheel configuration a few years ago as well.
We now find in the common differential gear found in vehicle axles a
COTS mechanism to do this job at high duty from small to megascale.
*The de Prony Brake is the cheapest and most accurate way
to measure shaft power for AWECS testing.
CoolIP ~Dave Santos 21Nov2011 AWE4847 Comment and development of this topic will be occurring here.
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