A motor drives {HEAD ~ a brush} to sequentially connect {TAIL ~ the terminals} to the slip ring to energize the terminals in sequence 
to sequentially connect
A motor drives { HEAD ~ a brush } to sequentially connect { TAIL ~ the terminals } to the slip ring to energize the terminals in sequence
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH