Alt-BEAM Archive

Message #04410



To: "'beam@sgiblab.sgi.com'" beam@sgiblab.sgi.com
From: Wilf Rigter Wilf.Rigter@powertech.bc.ca
Date: Thu, 10 Jun 1999 12:53:45 -0700
Subject: [alt-beam] Re: thoughts from a day at the zoo



content-type: text/plain;

Hie sparkly,

The attached drawing shows the legs in the two positions at the end of
rotation in each direction as viewed from above. This should work but
perhaps more experienced builders can comment. Turning is accomplished by
changing the average stride vector away from the centerline of the body.
This could be done by changing feedback from end of stride detectors or
differentially change the tension of the leg centering springs. The three
turning examples show front motor, rear motor and two motor turning. The
legs are shown in their normal stride length but this can be affected if
springs are attached to the legs. Remember that the legs lift and the body
tips for normal walking gait and the front motor would lift one leg higher
than the other so I am not sure how turning affects the gait. Perhaps the
rear motor turning is the most efficient since there is little lift on the
rear legs. The other thought that came to mind is using nitinol wire for a
waist motor to change the vector between the front and rear legs..

regards

Wilf Rigter mailto:wilf.rigter@powertech.bc.ca
tel: (604)590-7493
fax: (604)590-3411


<>



> -----Original Message-----
> From: Dennison [SMTP:dennlill@buffnet.net]
> Sent: Sunday, May 09, 1999 1:43 PM
> To: beam@sgiblab.sgi.com
> Subject: Re: thoughts from a day at the zoo
>
>
> --
> >Anyways, I digress...
> >My little walker seems to be coming along fine (based on the "Compleate
> >Walker" Schematic found at Ian's site -{BEAM ONLINE}) i have moved from
> >the breadboard stage to succesfully soldering the circut to a little IC
> PCB
> >from radio shack. and the LEDs are blinking nicely... (actually gives a
> >newbie quite a sense of accomplishment,
> > (till a friend walks in and says "So what! it's jus
> > blinkin lights.. My X-Mas tree does THAT!")
>
> Oh, I had a severe case of that. My friend was like, "oh thats neat, but
> why
> don't you build something cool, like a RC car." I just groaned.
>
> >But I hope to someday move up to more advanced challenges and the novice
> >beamer strts to dream of things like 4 motor walkers and "heads" and
> >thingies like that...
>
> It's easyer than you think!
>
> >what has been buggin me is that I had never seen it succesfully explained
> >how you get a walker to "turn" when a sensor is triggered due to the fact
> >(i guess) that the mechanics and chaos theory are somehow related here.
> >Chiu has a three motor jobby that he explains simply has the reverser
> turn
> >the middle motor, and that seems to werk.. but I was wundering what
> else
> >you could do...
>
> Eh, well in the case of two motor walkers, turning isn't very easilly
> done.
> Infact it's rarely done, and of the two methods I know of, one of them is
> sort of like 'cheating' as it involves you swinging the front motor leg
> around and around. So it acts like a wheel. But if we wanted a wheel, why
> build it with legs?
> The other is just a matter of tweaking and tweaking the timeing and the
> frame and base on your particular robot untill it does what you want.
> Relatively hard to do, as it varies from bot to bot.
>
> >ok, now here is where the zoo comes in... i was pushin the stroller, and
> >we stopped to look at some Madagascar ringed Lemers or sumpthing, and the
> >side walk was at an incline, the stroller has to lock (one for each back
> >wheel) that you can activate by simply pushing down on a lever near the
> >wheel with your foot. (you've all seen em) after we saw the lemer go to
> >the bathroom, and scratch its butt, we decided it was time to go. I
> >realesed the brake (flippin lever up w/foot) on ONE wheel, and started to
> >push, the stroller went around in a circle as applied the force. Using
> the
> >remaining locked wheel as a pivot (a good one).
> >sooooo... i thought hmmmm... maybe thats it, say you had a four motor
> >walker with a "Head". the head turns toward the light (lets say you want
> >it phototropic, or "voric" or watever) and then locks on leg in place the
> >leg remains locked, (simply not turned on) till the body is in line with
> >the head and then all leg motors are operational again.
>
> Thats a neat idea, but I'm fairly sure it won't work. Jsut because in
> walking you tend to need all the legs involved to get anywhere. And with a
> four motor walker, you can make some pretty sexy turns as it is just by
> modifying the gait, so it wouldn't be nessesary.
>
>
> Dennison
>
>
> >There.. all that to say that small thing. I guess i'm sharing this cause
> i
> >have been up at night wundering just how do you get the thing to do
> that..
> >lemme know if this is simply a laughable solution and you guys have moved
> >on to much more efficent methods...
> >just my $.02
> >-Sparky
> >


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Attachment: TURN.GIF

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