My mower uses a threaded shaft and nut for the steering.
The nut is mounted in a gymbal cage so it can swivel
freely, otherwise things jam up.
Position is not sensed; there are left and right limit
switches, so it stops at a known position. I tried to
make a center stop switch, but it was too much
trouble. It would have been nice to command the
center position and know it was travelling straight.
I have recently upgraded my ultrasonic 17 kHz
transponded so it works with much more power
and no more frequency shift. I expect to be
able to measure position with maybe one foot
error max. I receive the signal at 20 meters
distance with a 4:1 signal to noise ration.