Alt-BEAM Archive
Message #11796
To: beam mailing list beam@sgiblab.sgi.com
From: John Gonser mail@nadn.navy.mil
Date: Tue, 14 Mar 2000 14:05:52 -0500
Subject: Re: driving muscle wire
> 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
>
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