In addition, each drive roller has its own drive motor so it can be driven independently in {HEAD ~ either direction} about {TAIL ~ the common axis} 
about
In addition , each drive roller has its own drive motor so it can be driven independently in { HEAD ~ either direction } about { TAIL ~ the common axis }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL