topic Re: unable to change expression in parameter dialog box in Fusion Design, Validate & Document Forum

unable to change expression in parameter dialog box

Anonymous — Sat, 14 Nov 2015 00:24:53 GMT

Hi there,

I have encountered issue when I try to edit the expression in the parameter dialog box, and it prompts "units do not evaluate", where there is no unit in my expression. Please help! I truly appreciate it 🙂

It also prompts error when I tried to multiply my ctr_R with my cap_a together, and my guess is Fusion360 expects millimeter instead of millimeter * millimeter, so I divide everything by a variable called 'dumb' which has value of 1..Am I doing/understanding this correctly?

Thanks,

Jason

Re: unable to change expression in parameter dialog box

Anonymous — Sat, 14 Nov 2015 01:47:01 GMT

A new problem arose.. I tackled it with user parameters to get rid of the units, but after I put everything in, it won't compute..

As you can see from the screenshot, the value for X is clearly not 1440, and no matter what value I give for ctr_R, X is not changing..!

please help, thanks!

Re: unable to change expression in parameter dialog box

TrippyLighting — Sat, 14 Nov 2015 02:13:47 GMT

I am not sure this is related, but you also have an icon in the timeline highlighted in yellow. That's a warning sign that something is wrong with that object.

You should take care of that before attempting to do further calculations.

Unless, of course it turns yellow as a result of a failed calculation.

Either way, it's worth checking that out.

Re: unable to change expression in parameter dialog box

HughesTooling — Sat, 14 Nov 2015 09:42:51 GMT

Can you export the design as an f3d file and attach to this thread.

Mark

Re: unable to change expression in parameter dialog box

HughesTooling — Sat, 14 Nov 2015 11:01:21 GMT

I think I've found the problem, I thought I test using just numbers to make it easy to set up. What I found is ^ doesn't work if the base is a negative number and the exponent is less than 1.

This works.

But with a negative base it doesn't.

If you change 0.5 to 2 for example it works.

Mark

Re: unable to change expression in parameter dialog box

Anonymous — Sat, 14 Nov 2015 21:32:12 GMT

but my values are all positive, and I think the reason why it doesn't work when the base is negative is because the base of ^0.5 has to be greater than zero. I have attached my f3d file here and I appreciate you guys' help!

Re: unable to change expression in parameter dialog box

HughesTooling — Sat, 14 Nov 2015 22:41:17 GMT

I miss read but in your equation you have (1-cap_a*cap_a) which is -35 so your expression was 2*20*(1-36)=-1400. So that's -1400^0.5 I'm not sure what you've got in the second screen shot and file. Also I can't get it to work with parameters in mm but here's an example with unitless parameters.

So you have 2 problems, one setting your equation up using mm parameters and two -1400^0.5 will not work because the base is negative.

Mark

Re: unable to change expression in parameter dialog box

HughesTooling — Sat, 14 Nov 2015 23:06:22 GMT

If I change your expression to 71 - cap_a^2 so you get 35 instead of -35 I get this. See parameter test and Test2.

Mark