Teleoperation Computer - Converts the user-suplied control input
(e.g. joystick) into a desired velocity vector which is supplied to
the trajectory generator.

Trajectory generator - Takes the desired velocity vector and maps this
into a combined pitch-roll oscillation, whose purpose is to
alternatively load and unload the legs.  The resulting output is a
desired 6 element vector (delta-x, delta-y, delta-z, delta-roll,
delta-pitch, delta-yaw) which is then fed to the body attitude
controller.

Body attitude controller - Attempts to satisfy the desired 6-element
position vector via one uncontolled force (gravity acting through the
c.g. and four controllable force vectors (the feet).  The additonal
criteria of stability is imposed by requiring that the c.g. either
remain in a stable triangle or have a velocity vector which is going
into a stable triangle.

Detector Stepper - Parses the four force requests out to the
individual leg controllers.  If the force in a given leg is non-zero,
then the leg is instructed to operate in force-control mode.  If the
requested force is zero, then the leg is switched to position-control
mode and moved forward in preparation for reloading during the next
step.

Leg controllers - Simple closed-loop controllers which function in
either force-control or position-control mode.

Safety/reliability issues - We have been discussing safety issues
throughout the design and implementaion of the controller.  Issues
such as sensor failure, hydrolic failures and emergency stops have all
been discussed, and safety measures will be implemented in the
software using a Layered Control approach (derived from Behavior-Based
Artificial Intelligence).  This approach allows us to implement
successive safety measures without the need to redesign the basic
control system.

Circle vs. Gantry testing - The circular track testing system will
allow us to examine the issues assocociated with control system timing
and integeration, as well as the overall system response and dynamic
capabilities.  In the event that more static leg testing is required,
we can clamp the leg support arm in place, effectively making the
system into a "gantry" again.


