Alt-BEAM Archive
Message #05904
To: beam@sgiblab.sgi.com
From: Jason - evenflow88@hotmail.com
Date: Sat, 28 Aug 1999 10:35:39 +0800
Subject: Re: Walker leg centralizing info
>
>
>
> >From: Bruce Robinson
> >Reply-To: beam@sgiblab.sgi.com
> >To: beam@sgiblab.sgi.com
> >Subject: Re: Walker leg centralizing info
> >Date: Fri, 27 Aug 1999 12:55:33 -0700
> >
> >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
>
> well...not that i say spring is ugly but it is kinda hard for me to find
it
> here....and it is quite expensive too..i tried some small springs bbut it
> didnt work at all.....so do any of u guys know any electronics that could
> solve this problem like the encoder wheel that tilden mentioned.....and
> another thing is bruce what do u mean by 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.
>
> thanks a lot
>
> jason
>
> ______________________________________________________
>
5905 Sat, 28 Aug 1999 10:25:50 +0800 proximity sensors beam list Ivan patrick Codd <15392988@Queens-Belfast.AC.UK>
> hi again!
>
> does anyone know of any small low power reflective proximity
> sensors with a range of about a few centimetres, maybe four or
> five.
> any sensors i have looked at have extremely small ranges,
> usually less than 1 cm. are there sensors available with longer
> ranges?
>
> thanks again.
> Ivan Codd.
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