Robert M. Gary wrote:
The turn coordinator is almost always a self contained electric unit.
The attitude indicator and DG are unsually powered by air produced by
an external "fan" (we call it a pump). It may blow or suck depending on
the plane but it makes no difference, the effect is air moving across
the instrument.

The advantage a turn coordinator has is that the gyro within doesn't
need to be free in space. It's axis barely changes, which means
it's much easier to direct drive with an electric motor. It only
needs to register a slight precession force.