Parameter calculations

[cfairfowl]

Hello,

In the parameters I want to enter a formula =sqrt(((sleeve_Inside_Dia)/2)^2)-((plate_Thickness/2)^2))

so inventor will calculate the offset to the back face of a plate inside a round sleeve from the axis.

This works OK in Excel but not in the parameters.

Am I doing something wrong? or perhaps the parameters table doesn't support this kind of input?

Thanks in advance....

Chris.

[JDMather]

You can do it - but you will have to cancel out units (so that they are not squared, example mm^2).

Attach your *.ipt file here if you can't figure it out.

[cfairfowl]

Thank you very much for the prompt reply JD.

I hope you can open my ipt file. Its a master geometry file of sketches for parts for an assembly.

I'll be be changing certain parameters such as OD of sleeve from 36" to say 22 - 24 inches depending on the project. I would like to automatically change the distance from the axis of the tube (sleeve) to the back face of the stiffener/centraliser plates, because the plate has a square face landing on the curved surface of the inside of the sleeve (round tube) I need to bring the face back slightly so only the edges of the plate touch the sleeve's inside face.

I'm using the adjacent side of a triangle (inside radius of sleeve (tube) and half the plate thickness) to establish the slight difference in distance required to bring the plate in towards the axis of the tube slightly.

I will appreciate greatly any help you can give me as once I've got my head around this I can make other adaptations to control other geometry.

If you require further clarification I'm at cfairfowl@hotmail.com

Thanks again,

Kindest regards

Chris. 

[Sergio.D.Suárez]

Hello, I was looking at your file, could you tell me where to find the user parameters

"sleeve_Inside_Dia"   "plate_Thickness"

I could not find them, then the function could not be evaluated, maybe they have another name and you have to change them in the equation, greetings

[cfairfowl]

Hi,
I will go through it and rename some parameters and add sleeve inside diameter. I used OD and subtracted wall thickness.

Kindest regards Chris

[Sergio.D.Suárez · Accepted solution]

As I told you before, I think you should check the name of the parameters involved.
I've tried these two and the formula works

sqrt(( Spring_OD / 2 ul ) ^ 2 ul - ( SH_Thickness / 2 ul ) ^ 2 ul)

Check and comment, so that we can all solve your problem, regards

[cfairfowl]

Thank you very much,

That works, Brilliant! I didn't know about using the  / 2 ul

Thanks again - much appreciated.

Kindest regards.

Chris.

[chris.harbour]

i can see that forcing constants to be ul can solve some issues, but why cant it just work out a simple equation like this.

i seem to remember that the square root of 25 is 5

[johnsonshiue]

Hi Chris,

Inventor parameter expression is unit sensitive. But, the function like sqrt() isn't. You will need to make it unitless. Try this.

sqrt(B2_L/1 mm)

Then it should work correctly.

Many thanks!

[chris.harbour]

Hi John, thanks for the reply.

I tried : sqrt(B2_L / 1mm) but got 50mm as the result...

So I tried sqrt(B2_L * 1 mm) and got 5mm. Yea.

Thanks for pointing me in the right direction.

[johnsonshiue]

Hi Chris,

I forgot to add some detail. To make it work, you need to ensure unit type consistency. For example, sqrt(B2_L/1 mm) returns a unitless value. You will have to convert it to the length value with a unit. So, it should be sqrt(B2_L/1 mm)*1mm.

Many thanks!

[cfairfowl]

Hi, I want to calculate an arc using the degree of an angle dimension, I have tried adding the ul to the angle but it doesn't like it. I'm a novice at this so any help would be appreciated. (500x2x3.14159)/360x2.436

The 2.436 is the angle dimension in deg. If I can change this to a ul value instead of a degree value it will give me the length of the arc that I can then subtract from another dimension.

Thanks in advance for any help. Cheers....

[johnsonshiue · Accepted solution]

Hi! The correct equation should look like this. Please avoid using approximated PI value. It should be PI.

( 500 mm * 2 ul * PI ) / ( 360 deg ) * 2.436 deg

Many thanks!

[cfairfowl]

Brilliant.... thank you very much. Like I said I'm a novice at this....

This worked for me, variables are

SL model parameter (straight section) is equation 1500 mm - (Bend_Rad * 2 ul *pi)/(360 deg) * Arc_Angle

Result = straight section of a bent plate. 

Bend radius is 500mm angle is a driven from a displacement distance. 

Thanks again. Chris