Alt-BEAM Archive
Message #11790
To: beam mailing list beam@sgiblab.sgi.com
From: John Gonser mail@nadn.navy.mil
Date: Tue, 14 Mar 2000 15:51:12 +0000 (US/Eastern)
Subject: [alt-beam] 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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