Alt-BEAM Archive

Message #08798



To: beam@sgiblab.sgi.com
From: Nathaniel Martin nat@lumiere.net
Date: Mon, 3 Jan 2000 16:06:02 +0100
Subject: Biped Beam Bots



> I sent this message, but never saw it come back, so I'll try to send it
again:
>
>
> Has anyone ever built a biped (two leg) beam bot? I've seen many 4 and 6
> leg bots, but not any 2 leg beam robots.
>
> If no one has built one, maybe I'll try one in the future (after I build a
> 4 leg walker)
>
> Are there any reasons it would be impossible?
>
>
> -Nathaniel Martin
> nat@lumiere.net
>



8799 Mon, 03 Jan 2000 16:47:10 +0100 [alt-beam] Re: BI ped beam@sgiblab.sgi.com Evaristo Westplate 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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