Speaking of strange roll-tracking systems, I have a British 'Autoplayer'
player piano which is fitted with an extremely interesting and unusual
tracking mechanism.  I have never seen this kind of tracking device on
any other piano, and never seen it mentioned in any book on the subject
(although I've only got 2 books on player pianos!).  I wonder if any
other reader has come across this kind of system.

The system makes use of 2 moving holes in the tracker bar.  The holes
which sense the edges of the music are mounted on brass plates which
slide sideways in grooves at the back of the tracker bar.

There are 4 pneumatic motors to work the system: 2 to move the roll
across, and 2 to move the holes in the tracker bar; and there is a
pneumatic 'computer' to sort it all out.  The moveable holes are linked
together mechanically so that they always move in opposite directions to
one another, and always by the same amount.  This means that they are
always centrally positioned.

When the system is at rest, the sensing holes lie hidden behind the edges
of the music roll.  When the player starts up, both of the holes move
outwards until one of them just becomes uncovered.  The roll is then
pushed over to that side slightly until the hole becomes covered again.
The holes then move out a bit more, and the cycle repeats itself until
both of the holes are just uncovered.  Because the holes are always at
the same distance as each other from the centre of the tracker bar, the
roll is always centrally positioned.

The system works perfectly, and was clearly designed to look good as
well.  The mechanism is totally symmetrical and aesthetically laid out,
with the 2 smaller motors mounted upside down on the larger ones.  There
is an embossed brass plaque at the bottom with a list of patent numbers
on it, and the message: 'Clean screens under this cover occasionally'.

Needless to say, it is a joy to watch in operation.  In effect, the holes
are constantly moving in and out as they 'ride' on the edges of the roll.
Of course, this system can cope with very large variations of roll
widths, and it is a digital system as opposed to the usual analogue
systems.  By this I mean that the sensing holes are either fully open or
fully closed.  They are never half open, and therefore there is no
dependency on the usual delicate air-balance principle.

During reroll, the system is disabled, and the spool reverts to a central
position.  It is not spring loaded to one side.  I have never had any
trouble with roll damage during rewind.

I would be interested to know if anybody else has ever come across a
system like this before, or indeed whether anybody else has ever come
across an Autoplayer piano before.  This is the only Autoplayer piano
I've ever seen, although I do come across Autoplayer rolls from time to
time.  I did actually buy this piano because I was fascinated by the
automatic tracking system!

Melvyn Wright
http://members.aol.com/supermuzik/homepage.htm