Parametric Related - Adding Equations.

robert_melascaglia

Greetings

Lets say I placed a rectangle in a sketch, and dimensioned the short-side (w) ; could I then use an expression such as h=1.5w as the long-side?

thanks,

Robert

Jake_Rosenfeld

@robert_melascaglia

Variables are set using the Variable feature in the Part Studio. If you create a Variable feature before the Sketch feature, you can define w as whatever length you want, and then use "#w" as width and "1.5 * #w" as the length.

https://cad.onshape.com/help/Content/variable.htm

robert_melascaglia

Thank you Jake - I will investigate; although I was sure Onshape had that covered.

mahir

The Measure Value FS is handy for things like this if you don't want to create the variable ahead of time, or your relation is based on a measurement that is not directly dimensioned.

robert_melascaglia

The Measure Value FS - I will give that a try also, thanks.

robert_melascaglia

Hello All

I have another question with a graphic pertaining to "equation constraints."

1.  I have two "construction lines (in red)" at angle "alpha (in green)."

2.  I would like the line G-F (in blue" to be one-half the angle "alpha."

How do I constrain the line G-F so it will always behalf as mentioned in 1 and 2 above.  Thanks for your time - Robert.

owen_sparks

Hi. I'd use a variable, defined above your sketch in the feature tree, and then drive those angles in the sketch using the dimension tool.

Cheers, Owen S.

NeilCooke

@robert_melascaglia you could also draw a construction arc (shown as a in your diagram), constrain a point to the midpoint of the arc then constrain the line to the point. 

robert_melascaglia

Neil, nice solution; I'll let you know how that goes, thanks.

mahir

Similar to @NeilCooke’s solution, you can use sector lines along with an equal constraint between them all. This would let you make one angle be any fraction of another angle. Although, I would opt for using Measure Value and a variable if it got any more complication than 1/4. 

robert_melascaglia

Neil - your the man.

The line-angle made a "mad dash" for that mid-arc point; thanks.

robert_melascaglia

mahir said:

"Similar to @NeilCooke’s solution, you can use sector lines along with an equal constraint between them all."

How would I construct the "sector lines", and constrained them how?  I tried to work that out but somewhat confused, thanks for your assistance - Robert.

mahir

Here’s an example where the right side angle is constrained to be half of the left angle. Mind you, I would use @NeilCooke’s method for something as simple as getting half an angle. But sectors are handy for more complicated fractions. 

robert_melascaglia

Okay, I see; that is also interesting and I will try, thanks.