{HEAD ~ Two electrical cables} of {TAIL ~ an articulated robot arm} are in the form of helical cords which lengthen and shorten respectively during the rotation of the arm 
of
{ HEAD ~ Two electrical cables } of { TAIL ~ an articulated robot arm } are in the form of helical cords which lengthen and shorten respectively during the rotation of the arm
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH