There were many attempts to update the motors without paying anything, but the fundamental problems were lowering the speed & increasing the encoder resolution.

The new one is going to require a major expense in motors.  The original motors were 75:1 for the lower 2 & 50:1 for the outer one.  Even the smallest servos would be real big, heavy, & fragile.  A corkscrew drive would be big.   Servos wouldn't have better encoders.  The whole thing was built around the mighty N-20.

There was a simulation of 300:1 motors which showed promise.  It's believed it can never go too slow.  The 75:1 motors had problems holding their position in certain orientations.  It's not known how fast the motors can stop.  The motion would be more precise because the encoders are higher resolution.

The motors are attached via a common platform so they could be upgraded without printing a new nozzle.  But with the new encoders, the platforms need to go closer to the gears.

The total shopping list ends up being new motors, new H bridges, & a kg of PLA for $75 or a lot of money for an air vent.