Tip of the cord of a pulley system
Simscape / Multibody / Belts and Cables
The Belt-Cable End block represents the tip of a cord by which to anchor, drive, or load a pulley system. This tip serves as an interface between the belt-cable domain specific to pulleys and the frame domain general to all multibody components. A belt-cable port (E) identifies the cord whose tip this block defines and its relative placement within a pulley system. A frame port (R) identifies the local reference frame of the tip and its placement in the broader multibody model.
The cord is inextensible. Its effective length can change only if a source of a cord is provided—for example, in the form of a spool. If the second terminus of the cord is another tip, the length of the cord is fixed, and so must be the distance around the pulleys from one tip to the other. This distance is monitored during simulation, through calculations based on the placement and geometry of the pulleys. The two measures—the length and the distance—must always agree.
The cord is also always taut. From one of its tips to the nearest pulley, the cord must form a straight line, one tangent to the circumference of the pulley and parallel to its plane of rotation. The reference frame of the tip is placed on this line with its z-axis directed along it and away from the pulley. Constraints imposed on the tip by components outside of the pulley system must act without interfering with this alignment.
Note that the frame and belt-cable ports belong to different physical domains. As a rule, ports connect only to like ports—frame ports to other frame ports, belt-cable ports to other belt-cable ports. The belt-cable domain imposes also the special requirement that each network of belt-cable connection lines contain one (and no more than one) Belt-Cable Properties block. The necessary attributes of the pulley cord are specified through this block.
R — Local reference frame
Reference frame by which to connect the tip of the cord to the remainder of a multibody model.
E — Cord attachment point
Point at which to terminate the cord of a pulley system.