[ Ref. Tempo Compensation Methods in 191021 MMD & subsequent ]

I have thought about this matter on and off for some time (years!),
with not much of a conclusion as to how to describe the maths of
generating a constant torque the way it is usually done in a pianola.

The calculations and explanation offered is true but for that case
where the motor turns at a constant speed.  In the wind motor, it is
driven through a pressure compensated control box with a variable
aperture.  The form of drive control is effectively a 'Constant Torque'
rather than a 'Constant Speed'.

The details of the Ampico B motor, being electric, is almost certainly
designed as a constant torque motor.  Just how Ampico did this, I don't
know.  I have never seen one.  Whether it was due to a specific coil
winding design or some kind of constant current control, maybe
knowledgeable readers might be able to add something.

Music rolls are cut at a constant speed and must be played back at
a constant speed also.

Paul Rumpf

Melbourne, Australia

 [ The Ampico B take-up spool motor is, indeed, a series-connected
 [ motor in which the shaft torque at low speed is proportional to the
 [ current.  But the motor speed is closely regulated by a "high gain"
 [ centrifugal governor that adjusts the average motor current to
 [ maintain constant revolutions per minute of the take-up spool axle,
 [ the speed unaffected by torque demand.  See the illustrations at
 [ https://www.mmdigest.com/Gallery/Tech/Ampico/spoolmotor.htm 
 [ -- Robbie