Newsgroups: comp.robotics
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From: abrown@hpcvcec.cv.hp.com (Allen Brown)
Subject: Re: A sense of balance
Message-ID: <1993Feb18.015047.12250@hpcvca.cv.hp.com>
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Organization: Hewlett-Packard Company, Corvallis, Oregon USA
References: <Brian_Sullivan.156@ccs.carleton.ca>
Date: Thu, 18 Feb 1993 01:50:47 GMT
Lines: 34

Brian_Sullivan@ccs.carleton.ca writes:
: A thought on pendulums. As the robot moves, they tend to jiggle 
: about. Using a weight to dampen movement, will slow things down, but 
: pendulums love to swing. 

A weight will not dampen movement.

: A device used in ocean going ships to dampen wave movement might be 
: of interest. A large tank on deck is 1/2 filled with water. As the ship 
: rolls to the left the water moves left, when the next wave attempts to roll 
: the ship right, water in the tank continues left, dampening the roll, etc. 
: Works rather well.

This depends on resonance, or a mismatch in resonance.  It depends on
the wave action being at a narrow frequency.  The tank has a
resonance.  If the waves were to hit at the resonant frequency of the
tank this would actually increase the rolling of the ship.

: What if you were to fill a small ballon with about 1/2 oz of water and 
: attack it to the pendulum. Bet the same effect will keep the pendulum 
: pointer down, even over uneven surfaces. 

The pendulum is also a resonant structure.  What you have proposed
here is a rather complex (in terms of analysis) coupled resonant
system.  I suspect you will get chaotic behaviour.

A better way to damp resonant action is with a resistive element.  For
instance the shock absorber in your car is used to damp the resonance
of your suspension.  Forcing an element thru a viscous fluid makes a
resistive element.

This reminds me of Mechanics in college.  Nasty hard it was!
--
  Allen C. Brown  abrown@cv.hp.com or hplabs!hpcvca!abrown or "Hey you!"
