Angle of suspended disc? Rhino or GH

Hi
I wonder how I could get the angle (degree) of a suspended disc when the center of suspension is moved from the center in one axis or maybe in GH, tilt the disc in x degrees and find out the distance moved in one axis? Hope that some one could point me in the right direction because I dont know where to start…
Suspended_Disc_01.3dm (189.7 KB)

Hi Per,

The disc will hang so that its mass centroid is immediately below the point by which it is suspended. Your disc appears to have no thickness, so it will rotate 90 degrees, regardless of the distance offset.

A solid disc with thickness will be off vertical. The angle from level will be arctan(2*offset/thickness) assuming the disc density is consistent throughout its volume.

HTH
Jeremy

image

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Hi Jeremy! And thank for reply!
And uhhh, me and math is not a great combo… I do understand that if the disc has a thickness it will effect the centroid. I thought to make it a bit simpler to use just a disc with no thickness…
My objective is: if I move the point of suspension (say) 10mm in x-axis what angle will the disc be in?
Or if I want the disc to hang in (say) 32 degrees how much do I have to move the point of suspension in the x-axis? Hope that you understand what I mean?!

And would it be possible to make a GH-def with a slider tilting the disc and it would tell me what distance from the centroid I should place my new point of suspension? Stupid question, shure it would be possible but I dont know how… :frowning:

If the disk has no thickness then it will just rotate 90 degrees and hang straight down if you suspend it anywhere other than at the centroid.

Here’s a partial GH solution that allows you to set an angle and tells you how far the offset from the centre of the top face has to be to make that happen.

It won’t give you the right answer for the “no thickness” disc.
It won’t give you the right answer when the angle is so great that the point of suspension would have to be on the rim of the disc.

It’s dealing with these sorts of special cases that adds significantly to the time it takes to write a programme and I only have a little time available for this. But you can always draw the disc in 2d as above at a steeper angle in Rhino, draw a line directly up from the centroid and measure where it intersects the rim.

SomeDisk.3dm (48.4 KB)
TiltingDisc.gh (26.7 KB)

HTH
Jeremy

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Hi Jeremy and thank you for being patient with me! I was not aware of the fact that it would do that if it had no thickness, maybe I should have done some real time experiments first to see the physics. And thank you so much for the gh-def, did not know that I had to translate the degrees to radians first!! The disc do have thickness, it is supposed to be laminated glass 2x4 mm. So I guess I was a bit stupid thinking it would be easier with just a flat disc. Learned some more today :wink:
Best regards
Per

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