Alt-BEAM Archive

Message #05907



To: beam@sgiblab.sgi.com
From: "Jason -" evenflow88@hotmail.com
Date: Sat, 28 Aug 1999 05:00:18 GMT
Subject: [alt-beam] Walker leg centralizing info @mindstorm




Hie , all the thing this list has ever offered on how to centralize a
walker's leg is springs and mechanical stops...so why not use a better
approach of designing a circuit that will do the job like mark did..i think
dave knew this as i saw in his scoutwalker 1.1 kit there are no end stops
....so i think dave knows it but just wouldnt want to let us know not that i
am scolding him but i am just expressing all the feelings of newbie that
wants to know more but those old timers kept all the secrets away/...another
thing i dont understand is what do u mean by perpendicular thinghy in
walkers leg....even in bram's tutorial it is mounted the same way but he
still uses a mechanical stop...and using springs is hard as newbie dont know
where to put them on...and mark uses electronics to centralize his walker's
leg ...thats what he said to me when i mailed him.....

p/s:i saw that in lego mindstorm people could put up a walking robot with a
microprocessor less than 3oo bucks...i wondeer why dave wants to mark up the
price of his walker kits so high..people wouldnt buy them but instead they
will go into the lego mindstormm..just a thought

jason

______________________________________________________



5908 Sat, 28 Aug 1999 00:59:31 -0500 [alt-beam] Re: Walker leg centralizing info @mindstorm beam@sgiblab.sgi.com Richard Piotter Dave sells kits. Premanufactured boards, mass quantities. It ain't
cheap. He also has to make a living. You don't NEED to buy his kit. As
for electronics leg centering... You could use potentiometers to bias
the Nvs. That's electronicly simple, but mechanicly a pain. Stop
switches are possible too, but they can get clunky however. Springs are
simple. You simply place them between the legs and the body so the legs
are centered. Nothing dificult about that at all. I mean, it's not that
hard to figure out. Sometimes, it's more convenient to tie a spring
between legs rather than the body. I used a solid spring from ACE
Hardware between each leg on Bronco. It has give, but not a lot. Maybe
you can see it in the pictures at my web page. get an idea. All it is is
coat hanger wire and a $0.60 spring. Not expensive, not dificult, and it
works great!!! It has enough give for biasing the legs one way or
another. It actualy will walk toward the low spots on the floor it's so
sensitive to the ground angle, but it walks a very straight line on an
even surface.

Jason - wrote:
>
> Hie , all the thing this list has ever offered on how to centralize a
> walker's leg is springs and mechanical stops...so why not use a better
> approach of designing a circuit that will do the job like mark did..i think
> dave knew this as i saw in his scoutwalker 1.1 kit there are no end stops
> ....so i think dave knows it but just wouldnt want to let us know not that i
> am scolding him but i am just expressing all the feelings of newbie that
> wants to know more but those old timers kept all the secrets away/...another
> thing i dont understand is what do u mean by perpendicular thinghy in
> walkers leg....even in bram's tutorial it is mounted the same way but he
> still uses a mechanical stop...and using springs is hard as newbie dont know
> where to put them on...and mark uses electronics to centralize his walker's
> leg ...thats what he said to me when i mailed him.....
>
> p/s:i saw that in lego mindstorm people could put up a walking robot with a
> microprocessor less than 3oo bucks...i wondeer why dave wants to mark up the
> price of his walker kits so high..people wouldnt buy them but instead they
> will go into the lego mindstormm..just a thought
>
> jason
>
> ______________________________________________________
>


5909 Sat, 28 Aug 1999 01:23:54 -0400 [alt-beam] Re: Walker leg centralizing info beam@sgiblab.sgi.com SG Don't EVER underestimate the power of that spring.
a world of headaches was solved when i added the centrilizing spring to my
walker.
as far as unattractive, the mega building supply warehouse in your area
has many chrome(ish) looking springs from various sizes to choose from.
even down to the size that make sharp looking tactile sensors.
(speaking from exp here)
in my humble and newbie opinion:
if the leg mechanics and shape are a HUGE part of
the walker or bot (...whats the M for in "beaM" again?)
the spring (or springs) are not at all contradicting to
the overall philosophy and spirit of your bot construction.

note:
as far as where to put it (i fergit who mentioned that) if you are using
servos, and you bend the very center of your leg assembly to make room for
the mounting screw, that little bend forms a
---^--- or ____/\____ (my attempt at ascii)
if bent inward towards bot, (requires some forthought when initially
bending your leg wire)that notch makes a perfect place to hook a spring.
You can connect front and back legs together with one spring notch to
notch, though some advise against this.
Hope this helps someone, it werks for me.
-Sparky


At 10:28 AM 8/28/99 +0800, you wrote:
>you could use springs, then conceal them with something. presto!
>-----------------------------------------------------------------------
>Daniel Chia:
>danndom@mbox5.singnet.com.sg
>Robotics Web Page(unfinished):
>http://home.crosswinds.net/~danstryder/
>"It takes 99% sweat and 1% ingeniuty to have success" - Thomas Edison
>---------------------------------------------------------------------
>----- Original Message -----
>From: Bruce Robinson
>To:
>Sent: Saturday, August 28, 1999 3:55 AM
>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
>
>

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