What really gets me is how something that looks off balance ends up being super stable. This shape makes you rethink what balance actually means. It's not just about equal forces. It almost feels like the shape knows where it wants to land every time.
A new pyramid-like shape always lands the same side up
141–150 of 175 posts
Re: A new pyramid-like shape always lands the same side up
#142Earlier quoted context omitted.
If the constraints are that an object has to be of uniform density, convex, and not containing any voids, then you cannot choose where its centre of mass will be, other than by changing it shape.
That isn't true. Look at the pictures. It has the same outer shape, that is all that is required for the geometry. And for center of mass, you set the positions for the bars, any variations in their thickness, then size and place the flat facet, in order to achieve the same center of mass as for a filled uniform density object of the same geometry. As the article says: > carefully calibrated center of mass Unless an…
> Unless an object has internal interactions, for purposes of center of mass you can achieve the uniform-density-equivalent any way you want. It won't change the behavior.
That is true, but they are using a very heavy material for a small part and very light material for the other. So in this case the center of mass is almost on one of the faces of the polyhedron.
Re: A new pyramid-like shape always lands the same side up
#143Earlier quoted context omitted.
I was expecting to see the photos, but the jpg are linked there instead of visible. IIRC you were using a self-made CMS for your blog, with more support for math formulas. Does it not allow images?
Everyone complains about how crap my website is, so in this case I've just exported a page from my internal zim-wiki. Yes, it can have photos, but it doesn't give any control over sizing or positioning, so I'm providing links for people to click through to. It's the middle of my working day and I'm in the middle of meetings, so I don't have time to do anything more right now.
To be fair, I don't think there is anything wrong with clickable links instead of embedded images.
Re: A new pyramid-like shape always lands the same side up
#144I wouldn't really call this a "shape" since the highly manipulated center of mass is what is actually doing the work here. I would call this an object or rigid body.
Re: A new pyramid-like shape always lands the same side up
#145Math has a PR problem. The weight being non-uniform makes this a little unsurprising to a non-mathematician, it's a bit like a wire "sphere" with a weight attached on one side, but a low poly version. Giving it a "skin" would make this look more impressive.
It appears unsurprising because it is unsurprising.
Re: A new pyramid-like shape always lands the same side up
#146Earlier quoted context omitted.
>useful as a tamper detector If anyone's actually looking for this, check out tilt and shock indicators made for fragile packages. https://www.uline.com/Cls_10/Damage-Indicators https://www.youtube.com/watch?v=M9hHHt-S9kY
These shock watches and tilt watchers are quite expensive. I wonder how much must be the package worth to be feasible to use this kind of protection
Fun fact: MythBusters used shock watches extensively when testing anything involving impact, because they were massively more reliable than any of their digital instrument.
Re: A new pyramid-like shape always lands the same side up
#147Earlier quoted context omitted.
Everyone complains about how crap my website is, so in this case I've just exported a page from my internal zim-wiki. Yes, it can have photos, but it doesn't give any control over sizing or positioning, so I'm providing links for people to click through to. It's the middle of my working day and I'm in the middle of meetings, so I don't have time to do anything more right now.
To be fair, I don't think there is anything wrong with clickable links instead of embedded images.
I don't mind the image links. The text weight and contrast could use some work.
Re: A new pyramid-like shape always lands the same side up
#148Earlier quoted context omitted.
https://www.thingiverse.com/thing:1985100/files
Does it work when 3rd printed? How sensitive is it to infill options or infill density variations?
You need 100% infill to ensure it's working for the right reason.
I've got one mostly working with quite a lot of sanding
Re: A new pyramid-like shape always lands the same side up
#149I wouldn't really call this a "shape" since the highly manipulated center of mass is what is actually doing the work here. I would call this an object or rigid body.
I agree with you.
Re: A new pyramid-like shape always lands the same side up
#150I wouldn't really call this a "shape" since the highly manipulated center of mass is what is actually doing the work here. I would call this an object or rigid body.
It’s both. To work you need a polyhedron constructed of a series of polygons, here triangles, and one of those triangles has to have its center of mass outside the base of the object in all orientations. Otherwise the weight will pin it down instead of tilt it over.
That’s why in the one orientation it tips back before tipping sideways: the center of mass is inside the footprint of right edge of the tetrahedron but not the back edge. So it tips back, which then narrows the base enough for it to tip over to the right and settle.