Free body diagram problem

  • Thread starter ghobbs
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  • #1
ghobbs
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Hi

I have a problem in understanding the attached free body diagram problem.

I have a shaft that is pivoted at the top. Below the pivot is a magnetic bearing with a radial stiffness of 2600N/mm. I've modeled this as a springs in parallel. Below the bearing is a motor with a radial stiffness of 1200N/mm.

The problem is that I don't know how to model the motor. I've previously thought of it as springs in parallel, but that's not correct. The motor is in equilibrium when on axis, but as soon as it moves off axis it is radially attracted. It's almost like it's a spring with a negative force.

I'm trying to produce a free body diagram for this system. When I apply a force F at the bottom of the shaft I want to know the reaction forces and deflections at the pivot, bearing and motor.

Any thoughts? Thanks.
 

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Answers and Replies

  • #2
Dr.D
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Is this a vertical shaft motor with only one bearing?

Your figure does not show very much. Please add a bit of detail, both in the figure and in words.
 
  • #3
ghobbs
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There is a lower bearing, but at this stage it's not assembled. I'm not sure what detail I've missed out. I guess the idea of a free body diagram is to keep it simple.

The pivot at the top is fixed, so the shaft is only able to pivot about the pivot. There is a magnetic bearing which I've modeled as springs in parallel. There is a motor which I'm not sure how to model. The shaft can be regarded as infinitely stiff.

Please let me know what detail I've missed out.

Any thoughts anyone? Thanks.
 

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