Subject:
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Tilt and Walking
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Newsgroups:
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lugnet.robotics
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Date:
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Wed, 24 Nov 1999 02:59:17 GMT
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Viewed:
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562 times
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Let's take walking first.
Things fall over when there is an unbalanced moment (also called a torque)
applied to them. If the moment (force times distance) is balanced, for example
by pressure from their feet, they can stand upright.
When things start to fall over, they move more rapidly when the unbalance is
greatest and also when their mass moment of inertia is lowest. This concept,
mass moment of inertia, is important, because that's what resists the
acceleration imposed by the unbalanced torque. In a translating world, rather
than a rotating world, we'd use the formula F=ma, where F is force, m is the
mass and a is the acceleration. The analogous rotating formula is T=Ia, where
T is the torque, the unbalanced moment, I is the mass moment of inertia, and a
is the angular acceleration.
Still with me?
Remember that the larger I is, the slower things will topple over. Basically
the mass moment of inertia, I, is the mass of an object times the SQUARE of
its distance from the overall center of gravity. So a walker which is tall and
broad and massive, can stand to change from foot to foot without toppling
over, if the foot motion is fast enough. That's why it's hard to knock down a
big man.
One of the reasons that people stand upright is that tends to maximise their
pitch and yaw mass moment of inertia.
This means that maybe a two-legged walker doesn't need weight-shifting. All
they have to do is move from one foot to the other before they fall too far.
Whew! Done with that one.
Remember tilt? This one's easier. How about using the mercury tube in cheap
switches and thermostats as a tilt sensor?
Why would anyone want a tilt sensor if their walker has enough mass moment of
inertia? To know when it's time to put the other leg down!
Or for running their dump truck. Or changing program tasks when thy are going
uphill or downhill. Or....
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Message has 1 Reply:
 | | Re: Tilt and Walking
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| (...) example (...) I was thinking about walkers too, and I came up with an idea... If the toes had a wheel, the walker could basically drag the toe as the foot moved forward, and therefore never have to shift the weight from one leg to the other. (...) (25 years ago, 24-Nov-99, to lugnet.robotics)
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