how to use a variable-length cable
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Amir Jafarimoghaddam on 27 Nov 2020
I am trying to model a window washer robot hanging from a cable in simscape multibody. The cable length must be controllable to simulate the vertical maneuvers. Should I necessarily use a cable-pulley system to do so? I think there is a problem using cable-pulley, due to the fact that the pulleys can rotate just about the local reference frame z-axis, the belt-cable must enter and leave the pulley in the x-y plane of the pulley. So, during simulation, this alignment must be maintained by the rest of the mechanism. It may be a limitation preventing the robot from moving freely.
So far, I have been used a rod and two spherical joints in its both ends (one spherical joint to attach the rod to a base on the roof, and one spherical joint to attach the rod to the robot) to let the robot freely move and perform lateral motions. But the problem is that the rod length is fixed and vertical maneuvers cannot be done by the robot.
What should I do?
Juan Sagarduy on 27 Nov 2020
I think that you need a prismatic degree of freedom linking upper and lower parts in your rod. Each part with its own mass. So something like Sph J1 - m1_rod - PJ - m2_rod - sph J2.
Then the displacement in PJ can be set kinematically. Test this out with a simple mechanism, so that it you verify it is kinematically possible.
Good luck Juan