Modifying Spool Block to include variable radius

Consider the simplified mechanism where the spool has a variable radius (like the one from the image attached below), and the opposite end of the cable is attached to a spring-damper system. Modeling this with a 1D Simscape approach assuming the cable is always coplanar to the spring-damper is doable either with a CVT block or by implementing a custom 'wheel and axle' block but this approach ignores the cable tangency changes between the pulley and spool as the spool is rotated. The 1D approach wrongly assumes that the tangency point is always constant.

Changing the 1D block 'wheel and axle' to accept a variable radius as function of the spool rotation is relatively easy, however I haven't been able to identify how to change the multibody block for a spool. Is it possible? Are there any other modeling techniques available with simscape to capture the proper cable dynamics?

Answer 1

[Steve Miller]

The way your system is drawn, it doesn't seem like you should need a change in spool radius or wrap angle. However, it seems you have already figured out how to handle varying spool radius (Variable Ratio Transmission or modified Wheel and Axle block). Wrap angle is a fixed parameter in most blocks, though you could make it an input signal.

Simscape Multibody blocks in the Belts and Cables library will calculate the wrap angle for you, but varying radius is not supported directly. For full cable dynamics, you would need to model the cable as a chain of elements and use contact forces to model the contact between the cable and the pulley, and there you could vary the radius

--Steve.