The drum 1 is driven to rotate at a constant speed in {HEAD ~ the direction} indicated by the arrow by {TAIL ~ means} of a main motor 2 through a power transmission mechanism  
The drum 1 is driven to rotate at a constant speed in { HEAD ~ the direction } indicated by the arrow by { TAIL ~ means } of a main motor 2 through a power transmission mechanism
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH