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I'm simulating a shaft system in Simulink, where I have to find the displacement of a mass. I'm not sure how to model this in Simulink because of the shaft and pulley. I'm looking through the documentation and the closest thing I see to a shaft is the wheel and axle block. But the shafts are connected by a flexible shaft, which is similar to a spring. Any ideas?

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am304
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einfalles
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    Note that Simulink is primarily used to model mathematical systems, not physical systems. I assume you're using Simscape to do what you want. That said, consider modeling the system mathematically first - you might begin to understand why you don't need a "pulley" block; as for the spring, I assume the flexible shaft in your system is prone to *bending* and not axial forces, so the "spring" block won't help you. But let me know if I'm wrong. – Dang Khoa Dec 14 '11 at 17:57
  • Is this homework? I have used Simulink to solve this type of problem many times - as @strictlyrude27 says, you need to write out the math first. If you write the acceleration equations, then you can put it into Simulink using for instance s blocks, but you can solve the equations other ways as well. – sage Jan 02 '12 at 05:16

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This is a fairly trivial task when using SimScape, which is especially made to simulate physical systems. You'll find most of the blocks you need ready from the library.

I've used SimScape to create a model of a complete hybrid truck... In Simulink it can be done, but you'll need to build your own differential equations for the task. In your case, the flexible axle could be translated to another block with a spring/damper system inside.

If you haven't got access to SimScape, you may also consider to use .m (matlab) files to write your differential equations. This can then be used as a block in Simulink, varying (only) a few parameters over time.

Adriaan
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Take this step by step: 1. Draw a free body diagram, write out equations for all the forces as a function of displacement, velocity and acceleration of every element (including rotation obviously). For instance, you know that force on the box m will be *c*dy/dt* plus whatever the pulley experiences. 2. Sort out the rotation of the rod first. You know that *T=I*d(omega)/dt* if you get rid of the rest of the system. So, do something analogous to the car engine example of MatLab: Divide the input T by I to get the acceleration, integrate it to get velocity and one more time to get rotational displacement. 3. Keep adding bits one by one. First, you know that there will be a moment proportional to k*(theta_1-theta_2) acting. This will oppose the motion of rod 1 and act to create motion of rod 2. Add a new "branch" to your model to get theta_2 same way you got theta_1. 4. Go on including further elements...

Artur
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