Arctangent formula units

[Anonymous]

I noticed strange behavior while entering expression into edit dimension box IV sp3. I entered “atan (1/2)” where 1 and 2 are sides of the triangle. When I click on the dimension to edit value I got “atan (1 deg / 2 deg)”. I think 1 and 2 should be in linear units or unitless. Is it a glitch or I am missing something?

Thanks
Igor

[dan_inv09]

Inventor automatically assigns the units that apply to the dimension to any numbers that don't have them.
Your angle should be in degrees so any number you do not type a unit for will be assigned the unit of degrees.
If you want something else just type it yourself.

Be careful if you are using another dimension in your formula.
If you want atan(d0/d1) you will be okay because d0 = .2 in and d1 = .4 in
but if you have atan(d0/2) it won't work because it expects degrees and it will assume it's inches/degrees. You will have to explicitly type atan(d0/2 in)

[Anonymous]

If I remember my trig correctly arctangent does NOT expect angular units as an argument. It expects unitless value. The result it returns should be in angular units (degrees). So if IV assumes units for the values of the sides of the triangle I type it should assume linear units , not degrees. Result is still correct just formula looks wrong. I posted this in case ADSK wants to fix it.

Igor

[dan_inv09]

I messed up my description of what the error would say, I should have actually tried it first.


I thought Inventor was just putting in units based on what the dimension was but I just tried it with other trig functions and it put deg for those. Maybe it just assumes deg for any trig function.

It's probably best to avoid letting Inventor guess what units are needed in any formula.

[Inv_kaos]

It doesn't matter what units they use, the actual expression used by atan must be unitless, since they cancel out who cares. Inventor would assume degrees because the output of the function is degrees. If you want to change it to "mm" or "in" or "lengths of string", go ahead but I wouldn't waste time on it since it will not affect your result.

Regards
Stew

[Anonymous]

Inventor should not assume that argument of the function is the same units as a value returned by the function. If that is a glitch it may matter in some other places. In case of atan units cancel out so it works, just looks ugly. You are right, we should not waste time on it - ADSK should.

Thanks for listening.

Igor