Alt-BEAM Archive
Message #11858
To: beam@sgiblab.sgi.com
From: "Jim Taylor" ace27@icdc.com
Date: Wed, 15 Mar 2000 16:29:50 +1100
Subject: Re: driving muscle wire
> ugh muscle wire......how I loved thee......I too tried to biuld a super
> small walker using nitinol, some SMT parts, some really small lithium
> batterys, and some really thin music wire. I tried a 4 legger, a 6
legger,
> and a tilden worm. The 4 legger showed the most promise, and still does
> looking back at my work. However Nitinol is very tricky stuff. You mind
> as well be directly shorting the batterys. Not only do they draw alot of
> current, but it doesn't transfer very well into torque. It seems (even
with
> BORIS, and STIQUITO) no matter how small your driver, and control board
is,
> you need alot of battery storage. Unless you like 4 minute strolls :)
>
> Don't want to discourge you though.....My mini 4 motor walker walks fine
on
> a tether. However I don't think he will do any walking autonomously
>
>
> >
> >
> > > To drive a muscle wire you do not even need half of an h-bridge. The
> > > second transisotr is used to provide a path for current flow. All you
> > > would need is an NPN transistor with the muscle wire connected between
> Vcc
> > > and the collector, the emitter connected to ground and the base
> connected
> > > to the input through a resistor. You will want the base resistor small
> > > enough to drive the transistor into saturation and will probably need
a
> > > resistor in series with the muscle wire to control current flow.
> > > I do not remember off the top of my head, but I think the 50 micron
> wire
> > > nominally needs a 100mA current. I do not remember the resistance
(ohms
> > > per unit length) off the top of my head. There are a couple sites out
> > > there with properties on muscle wires (www.dynalloy.com does I am
sure).
> I
> > > would definitely reccomend checking them out because they give other
> > > helpful hints on using the wires, especially about attaching them.
> > > I did a concept project a while back using muscle wires for an
> > > autonomous robot design class. From my experience, which is anything
but
> > > all inclusive, I found that the technology is fun and promising but
> still
> > > needs some work. You only get about a 5% deformation and the power
> > > required is still on the high side. I finally settled on a design that
> > > used four muscle wires for movement of legs down and back (2 frames of
3
> > > legs) and the reverse stroke was handled by a spring system to save on
> > > power. I was using microprocessor control at the time, never got
around
> to
> > > trying it with BEAM control. If I find time one of these days, I may
go
> > > back and finish that... I would be interested to hear what your
> experience
> > > with the wire is like. Best of luck.
> > >
> > > John Gonser
> > >
> > >
> > > On Tue, 14 Mar 2000, David Perry wrote:
> > >
> > > > Okay - haven't asked a question for a while....
> > > > Okay i'm making a robot, quite advanced, very, very tiny, purely
> because
> > i
> > > > had the idea for it and couldn't get it out of my head all day and
> it'll
> > > > drive me mad if i don't build it.
> > > > The question is - what is the best way to drive muscle wire? You
would
> > only
> > > > use half a hbridge, (no need for switching wires) but i'm thinking
> thats
> > > > a little too large. Perhaps a 7hc245 would suffice. I need to drive
6
> > > > pieces of 050 LT, any advice would be appreciated.Oh and why am i
> using
> > > > muscle wire? - well i can't find 6x 4mm dia. gearmotors for under
$31
> > > > :-)
> > > >
> > > > thanks,
> > > >
> > > > David
> > >
> >
> >
>
>
> James Taylor
> "Edgar The Hate Bug"
> URL: http://fly.to/springmeadows
> ICQ 14888587
>
>
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