Redback wrote Digital servos for hobbyists still use a simple potentiometer for the feedback to an A/D-converter.
For professional digital servos (order of magnitudes more expensive than our hobby servos) one does away with the potentiometer and instead use an encoder that generates a series of digital pulses as the servo arm is moved. The pulse train is decoded in order to determine the position and speed of the servo arm. This is a more robust, but significantly more expensive, method.

champion wrote: Digital servos are not necessarily faster than digital ones. Look up the manufacturers specifications.
As for efficiency, what is the efficency of a servo? If it is defined as the amount of mechanical work the servo can do relative to the amount of electrical energy one does need to put in, again digital servos are not necessarily better. Instead the type of servo motor and gear train has a bigger influence.

So one may ask, in what way are digital servos superior to analog ones?
I mentioned some factors in my previous post. IMHO opinion the biggest advantage digital servos have over analog ones are that they usually have less deadband and more holding power. This is of significance for aircraft where the expected forces on moving surfaces are big and where very accurate control is needed, e.g. pylon, IMAC and pattern.
IMHO, digital servos are not needed for most medium-sized sport and scale aircraft. It is better to spend the difference in price on a control system that is up to scratch, i.e. low friction, rigid and with no slop.

However, I am convinced that the price difference between digital and analog servos will continue to decrease and in a couple of years time analog servos will no longer be manufactured.

/Red B.