Pulley with two hanging masses

Hello all,

I have been trying to simulate the classic physics problem: a pulley with two hanging masses. I am not sure which part did I messed up, but even though I set the weight for the two masses significantly different, the slipping does not occur, and the body just swings left and right, but not one up one down as expected.

I have uploaded my simulink document below. I should also state that I am using gravity in the -Y direction.

Any help would be greatly appreciated!

[Pin-Hao Cheng]

Alright nevermind, just realized you should have revolute joint connected to give it 1-DOF to rotate.

However when attaching revolute joint, I have an error of degenerative mass on the follower side. I overcome this error by attaching a solid after the joint. I will upload my Simscape files here for anyone that's interested in recreating the similar problem in the future.

[Eren Sarioglu]

I had the same problem, thanks a lot for the feedback !

[Pin-Hao Cheng]

Hey Eren, glad I could help! Totally get that feeling when you found someone else is having the same problems with you! :)

Answer 1

[Pin-Hao Cheng]

See comment and attachment above.

Answer 2

[IGNACIO]

Hello,

I've tried the model above, just changed the masses initial position so they are vertically aligned with the pulley ends (see attachment). The behavior is strange:

• Initial positions are fine, the centers of the masses are aligned with the pulley ends:
• 
• When starting simulation, the masses start to separate from each other, their frames not aligned with the cords, then they oscillate until a final position where one cord length is zero, an error condition is met, and the simulation is finished:
• I tried to restrict the movement of the hanging masses by inserting joints (prismatic, etc.) between the belt cable ends and the hanging masses, but in this case I always get some kind of error (singularity, etc.).

Can you please guide me to a solution where the hanging masses can only move vertically, as expected?