EDIT 03 APR 2024: I WAS WRONG. As of this post, I have no idea why, but somehow I can now enter trig functions using parameters with units. See the screenshot:
If your design includes trig functions, you must create unitless parameters. You cannot reference parameters with units to create a unitless parameter, so you must start with unitless parameters. LOL
@g-andresen wrote:Hi,
Please illustrate this statement with an example.
günther
EDIT 03 APR 2024: I have since settled on a different formula for theta:
acos(Scale_Length / ( sqrt(( Scale_Length ^ 2 + ( ( String_Width_Saddle - String_Width_Nut ) / 2 ) ^ 2 )) )) * 2
Here is a calculation of the angle of the sides of a quadrilateral, in this case a trapezoid. It is the angle that the E strings of a guitar are from each other, as they are not parallel. The formula is:
180 deg - ( 2 * atan(Scale_Length / (String_Spacing_Saddle - Spring_Spacing_Nut / 2 )))
In the first image, I have successfully created this parameter using the above formula, with unitless parameters as inputs:
In the next image, I have replaced with formula with 0, and then added units to two of the inputs. I then pasted in the same formula:
This was overlaid, but was not included in the screenshot:
Other attempts with a different strategy also failed. I first attempted to simply add units to the unitless parameters shown earlier, but they were locked out. Normally a down caret and a drop down menu appears if you hover over the unit, but this did not appear. This also seems to happen to the first parameter added, whether it was used in a formula or not; it is forever locked out of changing units.
In the following image, a formula without trig functions was successfully created using parameters with units as inputs. Also, note that units are mixed. Additionally, the parameter "Scale_Length" is FOREVER locked to inches as units. Whether other parameters depend on it as an input or not, it cannot be changed. This is something I have been able to repeat across new, blank designs.
In the following image, I removed the units from the formula "Fret_01", and is no longer valid.
Note the error message:
In other words, parameters are not consistent or robust. I haven't shown this, but it is impossible to create a new unitless parameter using an existing parameter with units as an input, as a workaround. This means if I foresee possibly needing Trig in my model, I have to start out of the gate with unitless parameters ONLY. It's weird.
This makes it very difficult to work with mixed systems, such as a guitar neck with a 24-inch scale length but modeled in metric, or any number of other scenarios. It is far simpler and more robust to model with native units, for example a 650mm scale length of a classical guitar fretboard and a 25-1/2" scale length of a Fender Jazzmaster fretboard, as configurations of the same model. With the current limitations I described here, this is impossible if parameters have units.
You should cancel the units by dividing by the units. If you multiply two MM dimensions the result is square MM, this is standard behaviour in all the solid modeling programs I've used. Also from the meany times this has come up before, according to @TheCADWhisperer taught in basic math, but I personally can't remember being taught this.
Here's your example with parameters with units canceled.
Mark Hughes
Owner, Hughes Tooling
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I can confirm that this works, but this a stupid workaround and a complete waste of time and effort. This means I have to create an entire extra set of parameters just for calculations, just to satisfy the embargo on units.
I imagine it must also be possible to include the extra text in the formula too. I'll test that.
@laughingcreek wrote:
It's not work around.
Disagree. This is definitely a workaround.
just cancel out your units appropriately in the formula.
This is probably the least worst option. I came to the same conclusion.
Units Matter.
If I weren’t an American, I probably wouldn’t even be having this conversation. If you have a choice and you choose inches, you’re part of the problem, but I’m not talking to Johnny Paycheck here - I’m talking about policy on a national level.
FWIW-trig formulas can usually be avoided by drawing the sketch in fusion and letting it find the value you're looking for. Less room for human induced math errors that way.
Disagree, and context matters. Sketches should be as simple as possible and important parameters should be stored and calculated in Global Variables, aka Parameters in Fusion 360. If I had to use sketch entities in my sketch that exist solely to avoid calculations, then I have to do that every time I need to refer that value. This is not good practice, and often not even possible.
The Fusion user base has adapted to its deficiencies with workaround after workaround like this. The application is and has been just one more update away from being usable for real work.
EDIT 03 APR 2024: I WAS WRONG. I have no idea why, but somehow I can now enter trig functions using parameters with units. See the screenshot:
Hi,
@Fully_Defined wrote:...
Disagree, and context matters. Sketches should be as simple as possible
...
This should then also be the case for equations.
Why are you using the old Greek?
günther
@g-andresen wrote:
Why are you using the old Greek?
TOUCHEZ!!!
I started with inverse tangent, actually, but then I ran into problems with units in trig formulas and got sidetracked. I acknowledge that your formula is better, and thank you for posting it!
