necessary torque for holding open a book

One way would be to make a retractable detent acting perpendicularly
to the direction of force.  Retract the detent while turning the page,
then extend the detent to hold the book open after the page is
turned.  Kinda like a crossbow works.  It takes alot of force to pull
back the string and hold it, but once the trigger mechanism (the
detent) catches it, it doesn't require any force to hold it back.

BRW

     There's nothing wrong with running a motor into stall, if you
have the feedback to do it properly.  It's a standard force
control problem.  If you want to hold something in place with a
small force, you can program a motor controller to do that.
This is much easier to do electrically than mechanically.

                John Nagle

BRW wrote:

Those are some helpful suggestions.  I thought of another idea that
perhaps might work as well.  I was wondering if I attached a small
weighted ball to the arm/horn of a servo would that weight cause the
arm to fall against the page and hold it down when power is switched
off?  I have never used a servo motor before, and it seems like I read
somewhere that a servo has to be in a certain position to be at a
state of rest.  Is that correct?  Would it be a better idea to use a
DC motor for that purpose?

Those are some helpful suggestions.  I thought of another idea that
perhaps might work as well.  I was wondering if I attached a small
weighted ball to the arm/horn of a servo would that weight cause the
arm to fall against the page and hold it down when power is switched
off?  I have never used a servo motor before, and it seems like I read
somewhere that a servo has to be in a certain position to be at a
state of rest.  Is that correct?  Would it be a better idea to use a
DC motor for that purpose?

Those are some helpful suggestions.  I thought of another idea that
perhaps might work as well.  I was wondering if I attached a small
weighted ball to the arm/horn of a servo would that weight cause the
arm to fall against the page and hold it down when power is switched
off?  I have never used a servo motor before, and it seems like I read
somewhere that a servo has to be in a certain position to be at a
state of rest.  Is that correct?  Would it be a better idea to use a
DC motor for that purpose?

Those are some helpful suggestions.  I thought of another idea that
perhaps might work as well.  I was wondering if I attached a small
weighted ball to the arm/horn of a servo would that weight cause the
arm to fall against the page and hold it down when power is switched
off?  I have never used a servo motor before, and it seems like I read
somewhere that a servo has to be in a certain position to be at a
state of rest.  Is that correct?  Would it be a better idea to use a
DC motor for that purpose?

Sorry for all these extra messages.  They wouldn't appear for a long
time after I posted them.