double - do double duty; serve two purposes or have two functions; "She doubles as his wife and secretary" roll - begin operating or running; "The cameras were rolling"; "The presses are already rolling" run - be operating, running or functioning; "The car is still running--turn it of...
These names are from the URDF in the ROS package for quadruped robots. The hip_joint is located at the top of the leg and is responsible for the left/right rotation function, which is important when walking and during balance adjustment. The upper1_joint follows the hip_joint and has the...