[amsat-bb] what positioner interfaces exist?

I've been looking at how tracking hardware interfaces to positioner hardware. There seems to be multiple ways used to induce movement and multiple ways to sense/track position. some seem to require up, down, right, left (4 bit) control signals along with an analog voltage provided for position indication while others may just count pulses to track position and may use unipolar vs bipolar motors. I've also seen syncros and steppers used. What is being used and what is common for positioner interface requirements? What means are used to sense/track position and what signaling is needed by various systems to induce a change to that position?

Thanks,

Eric AF6EP