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Author: Subject: Stiffness Conversion
phelpsa

posted on 11/12/10 at 02:31 PM Reply With Quote
Stiffness Conversion

I have a lever twisting a bar. I have the stiffness of the bar in Nm/rad and the length of the lever, how do I get the rate at the end of the lever in N/m?

Cheers






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Mal

posted on 11/12/10 at 02:50 PM Reply With Quote
Your 2 sets of units are comparing eggs with cheese.
Rotational stiffness is the moment (or torque) needed to produce unit angular deflection.
If you want to convert Nm/ radian to Nm/ degree, divide by 57.3, which is 2xpii.

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indykid

posted on 11/12/10 at 02:52 PM Reply With Quote
it won't be a linear rate at the end of the lever, but divide the Nm/rad by the length (in m) of your lever and that will give you the force required to deflect the lever 1 radian.

divide the N/rad by the angle (in radians) travelled and that should get you somewhere near.

try make whatever linkage you use rising rate






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matt_gsxr

posted on 11/12/10 at 03:06 PM Reply With Quote
Adam,

The length of the lever comes in twice.

Firstly for the torque i.e. F x L (where X is the cross product if you want to be precise, but if things are perpendicular its just the multiple)

Then a second time, because low levers cause a smaller change in the deflection angle of the tube.




Matt

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phelpsa

posted on 11/12/10 at 05:16 PM Reply With Quote
Managed to find it in my solid mechanics notes. Shows how much attention i pay to what im taking notes on...

Cheers anyway guys!






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phelpsa

posted on 12/12/10 at 02:10 AM Reply With Quote
Finished










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