If a machine could be made that had 100% mechanical efficiency, it would be called an

It would OUTPUT exactly enough energy to pour back into its INPUT and
keep itself running.  It would be called an "Perpetual Motion" machine.

It would be completely useless, however, as anything but a curiosity
to be stared at.  If you ever tried to make it actually DO anything besides
keep itself running, it would run down and stop, because you had taken
energy out of it.

What you need in order to turn the world upside down is a machine that
has 101% mechanical efficiency ... enough energy coming out of it to
keep itself running AND have a little bit left over, that you can take and
do other things with.

Such a machine would need to create energy inside itself, which
everybody knows is not possible.