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EM_98721993-Newcomer
3-Newcomer
April 20, 2023
Solved

How to calculate reactions on eccentric shaft supports

  • April 20, 2023
  • 3 replies
  • 2417 views

Hello everybody,

I was trying to calculate reactions on the supports of a shaft.

In particular, the shaft has an eccentricity on one side, and is supported by two bearings. Moreover, the motion of the shaft is imposed by a drive motor linked by a spur gear connection,

Using Creo Mechanism I tried to model the supports with a bearing connection and a gimbal connection, in order to have 0 Redundancies. 

I attach a simplified version of the model I would like to analyze.

In this particular case of eccentric shaft, the reactions calculated by Creo are completely different from the values I would expect.

If I try to suppress the eccentricity of the shaft, instead, the reactions become correct.

It seems that, for some reason, Creo doesn't succeed in calculate eccentric shaft reactions on a shaft constrained in this particular way.

Is there anybody that can explain me this behaviour or even better, can help me find a way to correctly calculate these reactions?  

Thank you

Eleonora

 

 

 

Best answer by ChrisKaswer

One way that will absolutely work every time is to support each bearing position by a "General" constraint. This offers you the ability to individually select the DoFs you wish to constrain and will calculate reactions in all constrained directions for each joint. Even if you "think" you've over-constrained the model, it will work. It also allows the ability to apply stiffness and damping in any of the 6 DoFs as well. I've used this approach to model an ICE crankshaft with exact results for reactions at every main bearing and crankpin joint. This is the best (I believe only) approach to use when you have more than 2 bearing supports along a shaft.

 

Cheers

3 replies

S
SweetPeasHub17-Peridot
17-Peridot
April 20, 2023

Can you zip the Creo files for the simplified model and attach? 

V
VR_971331812-Amethyst
12-Amethyst
May 18, 2023

First, clever idea to use 2 gimbal. If you have chosen use Pin, then the Measures of Moment for the Connection Reaction would be needed too.

Did you monitor your Connection Reaction by 2 radial axes (X and Y for example) instead of Magnitude? With this you should get the sinusoidal behavior that you would expect.

If this is what you've done, I would expect the correct answer.

Post a few screenshots of the graph you've got from the analysis.

    C
    ChrisKaswer16-PearlAnswer
    16-Pearl
    May 23, 2023

    One way that will absolutely work every time is to support each bearing position by a "General" constraint. This offers you the ability to individually select the DoFs you wish to constrain and will calculate reactions in all constrained directions for each joint. Even if you "think" you've over-constrained the model, it will work. It also allows the ability to apply stiffness and damping in any of the 6 DoFs as well. I've used this approach to model an ICE crankshaft with exact results for reactions at every main bearing and crankpin joint. This is the best (I believe only) approach to use when you have more than 2 bearing supports along a shaft.

     

    Cheers

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