Alt-BEAM Archive
Message #05906
To: beam@sgiblab.sgi.com
From: Bruce Robinson Bruce_Robinson@bc.sympatico.ca
Date: Sat, 28 Aug 1999 10:28:00 +0800
Subject: Re: Walker leg centralizing info
> Jason - wrote:
> >
> > Hi all, recently the thing that made me dislike
> > or bored of building bots is the fact that how
> > to centralize a leg in a two motor walker....i
> > heard stuff like mechanical stops and springs
> > and etc. i am all tired of that and it can make
> > the ot reall uncool and messy....
>
> I'm surprised no one jumped on this one. So from me you get a long,
> technical discussion.
>
> The legs on a walker form part of a system. As they oscillate, you want
> them to remain centred about one spot. So the goal of the system is to
> keep moving the legs back toward the centre whenever they move away from
> it. However, you don't want the system to respond TOO quickly, or the
> legs will never move.
>
> What this means in practical terms is this. You need something that will
> measure where the legs are relative to the centre, and exert an
> appropriate force to direct them back to the centre whenever they drift
> away.
>
> Springs do this very nicely when you arrange them proplerly. Electronics
> can do it too, but you need to sense the position of the legs. I devised
> a purely mechanical device that determines when the legs are moving too
> far in one direction, and changes the bias on the microcore to prevent
> it -- but if you though SPRINGS were ugly, you definitely will not like
> this design (and it's very complicated).
>
> The one thing that is very elegant is gravity. If you can arrange the
> geometry of your motors and legs so that they will be centred when the
> body is lowest (relative to the feet), then you may find your legs
> staying centred. If you look carefully at some of Tilden's walkers,
> you'll notice that the motors are often mounted so the shafts are NOT
> perpendicular to the ground. This means that there will always be some
> kind of restoring force caused by gravity.
>
> The bottom line is, whatever method you use, there has to be some kind
> of feedback that tries to restore the legs to centre: springs, gravity,
> electronics. Gotta have something.
>
> Regards,
> Bruce
Home