I recently had an idea (probably ages old) for the transmission of data on a
continual basis using analog voltages, and would like to get some criticisms
on it before I get too deep into trying to make it work.  The basic idea is
to use frequency-dependent filters to determine the amplitude of some analog
signal at a given frequency.  Perhaps the best way to explain the idea is
with an example:

Example:  Take a robot with 40 separate actuator "muscles".  For now just
consider the actuation control and disregard the feedback mechanisms. To
establish real-time control of 40 actuators on a digital link would not be
impossible, but would perhaps restrict expandability, etc.  So we assign
each "muscle" a control frequency based around a signal amplitude.  Muscle 1
gets 20khz, 10vpp centered on 0v.  To move it from neutral, the amplitude of
the 20khz signal drops to say 5vpp or rises to 15vpp.  The actuators are
tuned to listen on a specific frequency, which is then smoothed to a
relatively DC voltage.  All 40 actuators are installed as said, at perhaps
22khz, 24khz, ... and so on (no calcs yet, but assume there is enough
bandwidth), each with an independent filter to see what component of its
tuned control frequency is present.  So now to control all 40 actuators at
once it would (only?) be necessary to sum 40 separate control signals into
one analog signal, and inject that to the backbone where each actuator will
single out its respective command.

The apparent advantage of this method (to me) would be the increased amount
of data transfer on a single wire, with the primary disadvantage being
somewhat imprecise control all around.

The way I would envision it working is having a powerful processor to
generate the analog stream, and multiple PICS spread around the network to
read the filtered frequency and do the actuator control, then perhaps
eventually "capturing" analog streams to memory for replaying, for example,
a walking routine for a humanoid robot.

Is there any major problem I'm overlooking in a network like this?  It seems
pretty sound to me, but I'd really like to get some expert opinions, or
maybe advice from someone experienced with a similar network.  If it looks
feasible I very well may be turning it into an "open hardware" project for
robotic control, but I'd hate to take it that far and have a miserable
failure!

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