The other two articulated joints of blade 2 follow circular orbits around axle 4, since these are kept at {HEAD ~ a constant distance} from {TAIL ~ axle} 4, which is equal to the length of a blade arm 3 
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The other two articulated joints of blade 2 follow circular orbits around axle 4 , since these are kept at { HEAD ~ a constant distance } from { TAIL ~ axle } 4 , which is equal to the length of a blade arm 3
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD 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