Achilles left foot, calf and knee.  The ankle joint  is identical to the knee joint: both are made from
identical Lovejoy universal joints.  Custom modifications include weight/size reduction and a nut welded
onto each end into which lower and upper components bolt into.  Since the knee joint only requires
one axis of rotation, one of the bolts is tightened maximally into the universal joint central hub, thus
constraining one axis of rotation.  This simple design will allow for a reversal in time when the u-joint
wears so that it's effectively it's own spare!  A fine design if I say so myself.  The design of Achilles
foot motor placement differes from Alf's: Alf had one servo above and one below the u-joint.  Achilles
has both above.   Putting both on the same side impacts servo independence: I prefer Alf's design, but
Achilles servos are so large that the other won't fit below the u-joint (well, I might try it one more time).
The keen observer will note the ball-joint of the side servo is aligned right through the axis of rotation
of the u-joint.  In Alf, both ball-joint attach points have this feature.  On Achilles, only one (side) has
this feature because the other servo isn't below the u-joint.  In addition to the use of Aluminum for
light weight, 220 weight-reducing holes were drilled in the foot and calf.

Copyright © 1999 Patrick M. Rael

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