Numeric Fields with Multiple Length Divisions and Additions

nicholas_aarestad

Hello all, I've run into a bit of a roadblock using numeric fields with multiple configuration variables.

I am attempting to define a configuration variable's upper limit as a function of other configuration variables. Specifically, the (approximately) correct equation is:

(#X / 2) - (#Y / 2) - 1in

Where #X and #Y are both lengths. 

However, while I've tried a bunch of different ways of phrasing this, I can't seem to find one that Onshape will accept.

Specifically, I've tried:

(#X / 2) - (#Y / 2) - 1in
((#X / 2in) - (#Y / 2in) - 1)in
#X / 2 - #Y / 2 - 1

I've found a previous question which lead me to the reference manual's page on numeric fields (super interesting!) but all of its examples involving length are extremely basic.

Can anyone guide me in the right direction with this?

Thanks in advance!

ilya_baran

Ah, yes, I didn't read the original post carefully enough.  Yes, you can't use a configuration variable to define a limit on another configuration variable.

chris_8

I've gotten stuck on syntax too, so I know how you feel.  Variables are case sensitive, so make sure those are identical.  Spaces between the number and unit designation make a difference.  This worked for me:
#X/2 - #Y/2 - 1 in

example:
https://cad.onshape.com/documents/097cd417dd0132907147b98d/w/829548ea8fccc921c00968ba/e/47a28d79fb61d6a117853a34

nicholas_aarestad

chris_8 said:

I've gotten stuck on syntax too, so I know how you feel.  Variables are case sensitive, so make sure those are identical.  Spaces between the number and unit designation make a difference.  This worked for me:
#X/2 - #Y/2 - 1 in

example:
https://cad.onshape.com/documents/097cd417dd0132907147b98d/w/829548ea8fccc921c00968ba/e/47a28d79fb61d6a117853a34

Thanks for the suggestion! Unfortunately that syntax doesn't seem to work in my document. I'm wondering if it has to do with that I'm using Configuration Variables instead of Variables (from the toolbar), and if there's a restriction that I can't seem to find documentation for on not being able to use Variables or Configuration Variables to set the limits of another Configuration Variable (which I guess there would be some significant edge cases related to that).

ilya_baran

If #X and #Y are lengths, your first expression and @chris_8's equivalent expression is valid. It really shouldn't matter if there's a space between the number and the unit -- please file a bug if you find otherwise.
The problem with the second expression, ((#X / 2in) - (#Y / 2in) - 1)in  is that #X / 2in is an area, not a number (as one might think) -- the unit here is multiplied, not divided -- e.g., 1/2 in is half an inch.  Doing (#X / (2 in) - #Y / (2 in) - 1) in will do what you intended.
The problem with the third expression is you're subtracting a number (1) from a length #X / 2 - #Y / 2

Hope this helps.

nicholas_aarestad

Apologies for the double post, but I realized I didn't link any sort of demonstration document-- here's an example with three Configuration Variables set up, where I've tried setting #H's maximum and minimum as a function of the other two configuration variables.

nicholas_aarestad

ilya_baran said:

If #X and #Y are lengths, your first expression and @chris_8's equivalent expression is valid. It really shouldn't matter if there's a space between the number and the unit -- please file a bug if you find otherwise.
The problem with the second expression, ((#X / 2in) - (#Y / 2in) - 1)in  is that #X / 2in is an area, not a number (as one might think) -- the unit here is multiplied, not divided -- e.g., 1/2 in is half an inch.  Doing (#X / (2 in) - #Y / (2 in) - 1) in will do what you intended.
The problem with the third expression is you're subtracting a number (1) from a length #X / 2 - #Y / 2

Hope this helps.

Thank you for the response! It makes sense that the last two wouldn't work-- honestly, I put them in there as an example of a couple of things that I had tried before I found the documentation.

While I thought that this was originally a syntax thing, I can see now that the error message this gives me is "Enter a Number or Number with Units" which I suppose might imply that a function of other Configuration Variables or Variables is not a valid input, so it's probably more related to me not understanding the limitations on the feature.

ilya_baran

Ah, yes, I didn't read the original post carefully enough.  Yes, you can't use a configuration variable to define a limit on another configuration variable.