Ellipse perimeter formula - length of a panel

[autodesk_inventor_user]

I am trying to input ellipse formula into the part parameters so I get the lenght of the part.

p=2*PI*Sqrt(((a*a)+(b*b))/2)

According to Inventor Help, this should work:

Sqrt()

Return the square root of the argument.

Sqrt(25) = 5 Sqrt(100) = 10 Sqrt(3) = 1.732051

Any ideas why it does not for me?

Basically Inventor highligst red and wont accept Sqrt(value).

Thanks.

[JDMather]

You have to get the units matched as well (for example Sqrt(1mm) for a length doesn't make sense.
But do you really need to calculate this - could you use sheet metal and let Inventor calculate?

[autodesk_inventor_user]

I have units in mm and when input Sqrt(25mm) it still will not accept it.

I wanted to use the part I have, inputting for its length ellipse perimeter formula divided by 2 because my part is a half of epllise. This is nothing complicated enough to go into lenghts of converting the ipt ino sheet metal part. I should be able to input formula using minor and major axxis value and should be done.

Well, it would be done in one minute if Inventor accepted the formula.

[cwhetten]

Inventor's functions are case-sensitive.  It's not Sqrt(), it is sqrt().  When I input your formula with the case correction, it works just fine.

-cwhetten

[rdyson]

One way

[JDMather]

Sounds like a unit mis-match to me.  mm^(1/2) doesn't make sense.

Also - sounds like if you know the major and minor axis this is a trivail problem with no calculations required.
What is minor axis
What is major axis
What is material
What is thickness?
How will the part be manufactured?

[autodesk_inventor_user]

( 2 * PI * sqrt(( ( 1790.7 ul * 1790.7 ul ) + ( 1968.5 ul * 1968.5 ul ) ) / 2 ul) ) / 2ul

This formula works for my perimeter.

Just wondered, tried to input: pow(1790, 2)  to have 1790 raised to 2 power. Did not work. Any ideas?

[cwhetten]

The correct syntax is pow(1790;2).  Note the use of a semicolon instead of a comma.  You may also have some units issues here depending on which unit your result needs to be.

As for your original ellipse formula, you don't need to do everything with 'ul' units.  Your original formula works just fine when a and b have 'mm' units (when you use sqrt() instead of Sqrt(), of course).

-cwhetten

[autodesk_inventor_user]

Thanks.

Thats kinda weird that Inventor Help shows functions starting with capitol letters (Sqrt) and uses comma instead of semicolon for power function. Its confusing.

Thanks.

[cwhetten]

What version of Inventor are you using?  I am using 2011, and the help file shows the correct information.

[autodesk_inventor_user]

2011.

When I go F1, ilogic, functions, math functions, other math functions, it displays the info the way I described it.

[cwhetten]

Yes, you're right.  I see.  Those functions are only correct in the iLogic editor.  You use them in your iLogic code.  The functions I was talking about are in your Parameters editor.

You can find the ones I was refering to here:  F1 > Autodesk Inventor > Assemblies > Functional design > Functions, prefixes, and algebraic operators.

I never noticed until now that they are not consistent.    That's really unfortunate that we have to remember two different syntaxes for each function, and which one applies in which environment.   No wonder there was confusion! 

-cwhetten

[autodesk_inventor_user]

Good to know.

Final version:

( 2 ul * PI * sqrt(( ( pow(( d62 / 2 ul );2 ul) + pow(( d63 / 2 ul );2 ul) ) / 2 ul )) ) / 2 ul

[SBix26]

No need to use the pow function, just use the exponentiation operator: ^

So the formula simplifies a bit:

( 2 ul * PI * sqrt((( d62 / 2 ul ) ^ 2 ul + ( d63 / 2 ul ) ^ 2 ul ) / 2 ul )) / 2 ul

[autodesk_inventor_user]

Thats even simpler!

Thanks.