The method 42, wherein the step of selecting comprises selecting {HEAD ~ drive units} in {TAIL ~ response} to an actuation of either one of the open limit actuator and the close limit actuator 
The method 42 , wherein the step of selecting comprises selecting { HEAD ~ drive units } in { TAIL ~ response } to an actuation of either one of the open limit actuator and the close limit actuator
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH