Alt-BEAM Archive

Message #08802



To: beam@sgiblab.sgi.com
From: Daniel Grace lifebytes_98@yahoo.com
Date: Mon, 3 Jan 2000 10:57:20 -0800 (PST)
Subject: [alt-beam] Re: Y3K


> i wont say no more about it.
> (dont wanna start an argument: mac vs win)
Not mac vs win, mac vs pc. There are more OSs than
Windoze.

~Daniel

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8803 Mon, 3 Jan 2000 15:54:34 -0600 RE: BI ped beam@sgiblab.sgi.com owner-beam@sgiblab.sgi.com [mailto:owner-beam@sgiblab.sgi.com]On
Hi,

>Yes, please send a link to the picture!

I will look for the picture and setup a web page for it.

>Just curious... could you explain the pressure sensors a bit more?

Each foot has four pressure sensors. One in the "toe", one on the "heel"
and the two others on both sides (sensors are spread like a cross).
The toe and heel sensors are linked so that they form a voltage divider.
When both sensors receive the same amount of pressure then the output
voltage will be roughly 0.5*Vdd. Same goes for the other two sensors. This
setup will work regardless how heavy the robot will be (taking into account
the maximum range of the pressure sensors). When the robots leans forward
then the front sensor receives more pressure while the back sensor sees a
drop in pressure.

This setup was tested first with an ankle joint and a foot turned upside
down. We placed a bottle on the foot and the controller kept the bottle
upright. Very cool when the leg (with ankle and foot attached) is moved
around and the bottle stays upright. The pressure sensors work very well
and small changes in weight distribution can be detected very accurately.
Ofcours this setup will only work if the upper body of the robot can't move
otherwise you will need something like a gyroscope in the upper body to
respond to moves of arms or something else. The robot we build used mostly
the ankles to stay upright. Once you start moving it becomes a different
story.

Hope this helps. As soon as I have the photo up I will post the link.

See'ya


Evaristo

Gizmo homepage: http://www.crosswinds.net/~evaristo

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