#1 By: the_ether, September 10th, 2013 14:48
I have the following minimalist structure which will obviously fall over without support. I'd like to design the minimalist possible structure to act as a stand. Is there any tool that will help me with that? I've seen that there is the Volume Moments command but, a) I'm not sure how to interpret the results to tell me in which direction the object would fall; b) I'm not sure the results would tell me that a stand I attach would be good enough to stop the structure falling.
(P.S. Feature wish: it would be nice to have an arrow that could be drawn to indicate the rotational force).
#2 By: djnelson75, September 10th, 2013 16:40
Sounds like you need to have a structural engineer take a look at it. Hint. Hint. Depending on what the structure looks like there are a bunch solutions to your problem, but yes you need something to resist the rotation moment created by the cantilevered element, which Rhino isn't going to be able to tell you. You will need something like SAP or Scan and Solve for Rhino to get your answer.
#3 By: Al Worth, September 10th, 2013 19:42
For the extremely basic case of static stability - no perturbing forces like wind or things bumping into it - it's pretty straightforward. Just use Rhino to find the center of gravity of the structure and project it vertically to the ground. You will need to have some additional structure of some sort which is attached to your structure and extends to cover the point on the ground directly beneath the center of gravity. Kind of like keeping your feet under your hips if you don't want to fall over.
If you can assume your structure is extremely stiff, you can also make some assumptions about how far you would like the structure to be allowed to rotate and still return to it's initial position. Then you must make the added "foot" large enough to cover the area on the ground which contains the projections of all possible allowed locations of the CG. The supporting "foot's" bottom surface must be of such a shape that as the structure rotates, it's center of gravity will rise. This will make the structure want to return to it's rest position. This is called positive static stability.
It starts to get more involved if it's a flexible structure subject to various types of loading.
Does this help?
#4 By: the_ether, September 11th, 2013 16:24
Thank you both. Of course, another method is to use a base made of a different, more dense material or which is larger and placed on the opposite side of the centre of gravity. But certainly using Rhino's Volume Centroid command is somewhat helpful.
#5 By: Al Worth, September 11th, 2013 17:12
Absolutely! The objective is to get the part of the structure that is supposed to touch the ground to be under the center of gravity. (or conversely, to get the center of gravity over the part of the structure which is supposed to touch the ground.)