[HN Gopher] Expanding Racks [video]
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Expanding Racks [video]
Author : doctoboggan
Score : 121 points
Date : 2025-06-12 05:02 UTC (17 hours ago)
(HTM) web link (www.youtube.com)
(TXT) w3m dump (www.youtube.com)
| downboots wrote:
| Is there a standard way to formally describe a mechanical
| machine? Similar to how a .obj file defines a 3d shape? Some
| standard way of describing piece types, interactions, properties,
| movement ranges, etc.
|
| Then one could have a computer use the format to learn/find
| interesting configurations based on a catalog like
| https://507movements.com/ especially if paired with simulation
| like done in this Disney research project using gears and
| linkages https://www.youtube.com/watch?v=DfznnKUwywQ
| trws wrote:
| I'm rather hoping there's something better, but various CAD
| formats support specifying assemblies of objects, and joints
| between those objects that can represent properties like that.
| Often this comes with at least some level of simulation, or if
| not simulation imposed constraints like in the FreeCAD assembly
| workbench, allowing you to move connected parts in the assembly
| but only through the range permitted by the "joint". I quote
| that because that includes things like meshed gears, linear
| slides, ball joints, all kinds of things like that some of
| which I would not call joints as such.
| imtringued wrote:
| Well, the problem is that FreeCAD is in the wrong here, but
| you are also making mistakes as well.
|
| * The correct term for "slider joint" is "prismatic joint".
|
| * "ball joint" should be "spherical joint" (nit picking, but
| still)
|
| * "Revolute joint" and "cylindrical joint" are correct
|
| Now comes the list of things which aren't joints and should
| be called constraints instead:
|
| * Distance Joint
|
| * Parallel Joint
|
| * Perpendicular Joint
|
| * Angle Joint
|
| * Rack and Pinion Joint
|
| * Screw Joint
|
| * Gear Joint
|
| * Belt Joint
|
| Now to your mistakes. There is absolutely nothing wrong with
| calling revolute, prismatic and spherical joints joints. They
| are joints, they do what joints do, hence the name joint. The
| physical interface is your responsibility as the designer.
| zonkerdonker wrote:
| It's an intriguing idea, but the scope of any such formal
| definition would essentially be the entire scope of physics,
| materials science, thermodynamics, etc. For much more bounded
| problems (like that very fun website you linked) I think
| something like that would be more attaintable, but still
| challenging.
|
| Take the example of the differential gearing shown. I doubt
| there exists any functional differential/mass produced assembly
| that looks exactly like the example presented. The concept of
| differential gearing may be able to be broken down into more
| symbolic representation of forces and motion, but at some point
| it becomes simplified to the point of impracticality.
| downboots wrote:
| All models are wrong, some are useful.
|
| Form follows function.
| aa-jv wrote:
| The movements from your first URL are actually from a 100-year
| old book, and its chapter on mechanical terminology (which has
| been oddly stripped for the web page) might be a good start:
|
| https://www.thalia.at/shop/home/artikeldetails/A1032836899
| IIAOPSW wrote:
| You know, I find myself thinking the same thing sometimes. And
| the closest I can think of would be some mapping of force
| transmitted through linkages on to current transmitted through
| wires and from there its the same formalism as electronic
| circuits. Though the usefulness of the abstracted form really
| depends on what you're trying to compute.
| GistNoesis wrote:
| In robotics the URDF format can be used to specify and simulate
| rigid-body systems. You can also check various physics engine
| input file formats like MuJoCo (MJCF format). (It's just some
| variant of XML).
|
| If you want soft-body dynamics, you can have decompose your
| objects into particles of different types which interact,
| (examples are liquidfun or powder toy). (It's just a list of
| particles and a particle-particle interaction matrix) (More or
| less base on Smoothed Particle Hydrodynamics).
|
| If you want something more serious, you'll have to look at
| finite-element based multi-physics tools, like Ansys or Comsol,
| which will allow you to specify the various domains and solve
| the differential equations on each domains.
|
| If you want to go very small scale you have Molecular Dynamics
| tools with standards like GROMACS.
|
| If you are more into the topological optimization, you can use
| neural networks to represent the quantities which are of
| interest to you and Physically Inspired Neural Networks (PINN),
| or neural ODE, or "sim-to-real" tools, in which case you'll
| probably be using pytorch.
|
| Or text if you use WorldSim like LLM tools and only need an
| abstract representation. Agents playing with CAD software tools
| will probably standardize some convenient way to solve
| engineering tasks.
| burnt-resistor wrote:
| I find telescopic crane boom internals interesting because they
| can have more than a few sections that all nest within each
| other. There's an Australian channel CEE that has an ongoing
| restoration of a Frena crane by disabling some of the sections as
| unnecessary for practical use because it can place loads way, way
| into the air (albeit at the expense of capacity and stability).
| Gravityloss wrote:
| The Stem Boom is another somewhat mind bending mechanical idea.
| You have a roll that when opened, creates a boom. This can be
| very small when stored and very long when unfurled. Or two
| rolls that together form a boom.
|
| https://ntrs.nasa.gov/api/citations/20170003919/downloads/20...
| mitthrowaway2 wrote:
| A similar mind-bending idea is the helical band actuator:
|
| https://en.m.wikipedia.org/wiki/Helical_band_actuator
|
| https://www.pacospiralift.com/solutions/spiralift-solutions/
| chii wrote:
| another good video is this channel, which explains exactly how
| a telescoping boom works in somewhat detail (using a standing
| desk as an example: https://www.youtube.com/watch?v=UVTDMO7rlhs
| edweis wrote:
| Are such racks tech used at an industrial level?
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