Two diameters... non iLogic solution?

[oransen]

I have a cylinder with a diameter DiamAtt and it has some material taken away by another cylinder, with a diameter of DiamColl. Here's a picture:

So when DiamColl or DiamAtt changes Dcoll is calculated.

I have the iLogic to calculate Dcoll:

Dim RagColl as Double
Dim RagAtt As Double
RagColl = DiamColl/2.0
RagAtt = DiamAtt/2.0
If RagAtt < RagColl Then
    Dcoll = Sqrt((RagColl*RagColl) - (RagAtt*RagAtt))
Else
    Dcoll = 0.0 
End If 

This works, but the triggering of the rule seems a bit hit and miss. So my question is:

Is there a way of achieving this without iLogic but directly inside the parameter formula column?

TIA!

[MechMachineMan · Accepted solution]

You better believe it.

https://knowledge.autodesk.com/support/inventor-products/learn-explore/caas/CloudHelp/cloudhelp/2014...

sign(ragcoll - ragatt) - returns 0 if negative, 1 if positive -- your if statement when used multiplicatively

sign(ragcoll*ragcoll -ragatt*ragatt) -- needed because Sqrt(negative number) returns "nan(ind)"

THUS:

in one line:

sign(ragcoll - ragatt)*SQRT((ragcoll*ragcoll - ragat*ragatt)*sign(ragcoll*ragcoll-ragatt*ragatt))

Returns 0 =  0 * SQRT((ragcoll*ragcoll - ragat*ragatt)*0) if ragcoll < ragatt

returns SQRT((ragcoll*ragcoll - ragat*ragatt) =  1 * SQRT((ragcoll*ragcoll - ragat*ragatt)*1 if ragcoll > ragatt

Also, be careful of your units.

[CattabianiI · Accepted solution]

Try this:

sign does the work of your If

abs avoids the square root on negative numbers

sign(RagColl - RagAtt)
sqrt(abs((RagColl*RagColl) - (RagAtt*RagAtt))) * ifRes

Anyway, for your iLogic code, make sure you haven't checked the "Don't run automatically" in the iLogic options.

[CattabianiI]

I just read the @MechMachineMan's answer that get also the sign of the argument of sqrt, and it clearly works, but if RagColl is less than RagAtt, Dcoll is equal to -0, yeah don't worry and treat that -0 as zero, but getting negative sign by the square root can be weird.

[oransen]

Thanks all for you help!