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Characteristic length in Mechanism/Simulate


Characteristic length in Mechanism/Simulate

Hi all,

in Pro/Mechanism you have to adjust the parameter called "characteristic length" to improve the absolute tolerance (the other parameter is the relative tolerance).

The manual says:

"The characteristic length is the sum of all lengths of the parts divided by the number of parts. The length (or size) of a part is the length of the diagonal of the bounding box that completely contains the part."

But this default value is taken following the rule in automatic?

In the 1st picture attached (prima), 10 is the value that appear always, with any part/assembly.

In the 2nd picture (dopo), I've pushed the button "Restore default", and the number changes every time.

I think, in the second case, ProE applies the rule.

Is it correct?

At the end, I wonder if the value of the rule, the default value (if is true what I think), is always the best value.

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Hello Giulio,

normally the calculated setting should be the default and you can manually overwrite it in the Model Properties under Mechanism.

When you specify a non-default value in one model, other models should not be affected.

However, if the value has been set in your assembly template, then it will be inherited by all new models, so it may appear as if the value is always set.


I've investigated at work and 10 is set on a template.

But I would want to have the confirm that the default value follows the rule and it does automatically "the sum of all lengths of the parts divided by the number of parts".

Well, first of all there is no reason to doubt the manual.

And then you can simply test it:

  • If you look at the value in an empty assembly (no template), an arbitrary value of 1 is assumed (this is what the manual does not say)
  • If you add a part with a certain length (use something like sqrt(27) for side length of a cube, to get a nice number, 9 in this case), then the assembly has the expected value. Add / remove parts and observe the formula is always used...

You're right.

I've tried to insert some parts with a predetermined characteristic length and the "default value" is always correct.