Pete Woodworth mentioned these "Muscle Wires" [020617 MMDigest]
which are available in the UK from Maplin Electronics.  I thought
they might be useful in constructing a perforating machine
(instead of rows of bulky and expensive solenoids), or even
in a MIDI adapter for a player piano.  (Both subjects inspired
a lot of conversation a few weeks ago).

However, the problem with "Muscle Wires" is their limited speed
of operation.  Although they can be made to contract fairly quickly
by increasing the current through them, their return to original
length relies on cooling, and in the data I have seen it is quoted
as 1 second.  This severely limits the repetition rate achievable
in the applications mentioned above.

They are, nevertheless, an interesting device if you are into
other areas of mechanics (e.g., robots).

John Farmer
Worcestershire
UK