I will admit that I am a complete noob (discovered this program about four weeks ago) and this is probably a simple case of my having no clue what I’m doing. I am playing around with various features in blender, and currently trying to use physics to simulate realistic-looking positions for fallen objects. However, when I tried to use this to knock over a chair I’d built, it consistently failed to actually lay on the ground, instead choosing to ‘fall’ upright, even when I placed it on the ground upside down (think Weeble Wobbles). This problem was fixed when I moved the center of the chair to higher up in the mesh, but the problem remains that the chair is acting less like a real, massive chair than it is a real, massive ball with some massless bits of chair sticking out of it.
To summarize, is there any way to get some ‘weirdly’ shaped object like a chair to act like its mass is distributed over it rather than focused at the center point?
Please tell me if I’m not being clear enough or if this isn’t the right place. There is no obvious (at least to me) place to post questions about physics.
I tried playing around with the radius and that didn’t seem to do anything. Changing the collision bounds seems only to determine the shape of an object for collisions, which makes sense (I’m using convex hull, since triangle mesh lets parts of it fall through the floor). What I’m asking about is some way to have the mass of the chair distributed over its surface, or something, rather than concentrated at its center point.
The main purpose of the center of mass, is still to define the point where rotations happen most likely. And therefore you won’t be able to change it. And of course, this is also the best realistic property. This is especially crucial, if you make e.g. a car for a game, where you really have to adjust its physical properties.
You already found out, how you can move its center of mass (switching to editmode and moving all the vertices away from the origin).
So, maybe you could also subdivide your chair more often, to make it detect collisions much better.
Thank you for your welcome and advice, though I think you are misunderstanding my problem. What I want to know is, is there any way to get objects to act like their mass is actually distributed over the mesh in some way. Now that I’ve been thinking about it a bit more, it might not actually be necessary, since any such effect can be duplicated by moving the center of mass, but it would certainly be more intuitive. Thanks for responding anyway.
I think you still are misunderstanding. I don’t actually have a problem right now, I just want to know if it is possible to say, concentrate the mass of a barbell at the two ends instead of only defining a center of mass and putting all the mass there. If there isn’t, or if you don’t know, then don’t worry about it. But thanks for responding anyway.
Ah, sry I tried a little and now I think I know what you mean(after looking up the word “barbell”) Sry, I’m German.
Well, considering a barbell, you can look at the object as three objects connected in some way. To achieve something like that, you could use the “Rigid Body Joint” constraint in the constraints panel. I just created a simple scene to get your idea. I modelled a chair and attached a UV Sphere via the Rigid Body Joint constraint to it. It was able to influence the chair physically (by pulling on it). I still don’t really know how to set the pivot point of the constraint correctly, but I’m pretty sure, that this is it, what you’ve been searching for, isn’t it?
Just try to attach the weights via this constraint to the bar of your barbell and tell me if it helped.
Thanks again for the advice. I realized something stupid that I was missing, and I’m pretty sure that I can do everything I need to with the center of mass, but the Rigid Body Joint constraint is a fun thing to play with and seems like it should be useful, especially with simple things you don’t want to add a whole rig for. Thanks for looking so deeply into this, and have a nice weekend yourself!