About electric piano player solenoids.  It is very difficult to softly
play a piano by solenoid action.  Solenoids require a minimum amount of
power to start their acceleration, but then the velocity and power
increases as the plunger enters the solenoid coil.  A system must be
devised to apply sufficient electricity to start the solenoid, then
reduce the current before the solenoid obtains high velocity.

A pneumatic system inherently can be started with low vacuum and actually
looses power as the pneumatic reaches closed position, thus is much
easier to control.

Bob Lemon
Lemon's Player Piano Service
Sacramento, CA

 [ Editors note:
 [
 [ Wayne Stahnke solved this knotty problem with a permanent magnet
 [ mounted to the solenoid shaft.  As the magnet moves through a
 [ stationary coil a feedback voltage is developed in proportion to the
 [ speed of the shaft.  Thus the solenoid is a component of a "linear
 [ velocity motor", and the Boesendorfer SE system actually sends
 [ hammer-velocity commands to each of the 97 linear motors.
 [
 [ It can play *very* reliably as it plays *very* softly!  And if you
 [ wish to slowly raise the damper without striking the string, the SE
 [ will do that, too!
 [
 [ -- Robbie