This is the Reuleaux triangle bearing, a mechanism which takes advantage of the unique properties
found in objects of constant width which allow them to roll like a ball.
But it took a lot of experimentation to get this thing to work – let's get started.
Hows it going guys angus here from maker's muse.
Last year I became obscessed with solids of constant width – these curious looking forms
which, when rolled under a flat plane, act like spheres or balls – Their unique geometry
maintains a constant distance from bottom to top no matter what orientation their in,
which made me ponder if a bearing of some kind could be possible using them.
My first attempt was a basic roller bearing with 2D forms packed around it, and I concluded
that although these objects do maintain a constant width, their center point actually
changes throughout the rotation which resulted in the shapes either falling out due to insufficient
support or colliding with each other, resulting in more of a sliding motion than true rotational
movement you see in a normal bearing.
That video went on to get loads of hits and many of you had really neat ideas on how this
could be resolved to make a true functioning reuleaux triangle bearing – so I got to
work.
The first and by far most popular suggestion was to implement what's known as a cage – a
supporting structure which spaces the balls in a regular ball bearing, allowing them to
rotate freely while keeping them separated and not rubbing up against one another.
The crazy thing about shapes of constant width though is they do not trace a circular path
as they rotate, but instead, in the case of the realeux triangle, trace a square.
It's this property which sees them used in special square hole drilling jigs.
So therfore, the cage has to look like this!
This cage looks visually stunning, and I had really high hopes... but sadly, like before,
the shapes tended to slide rather than roll.
Their center of mass means the force of getting past each sharp angle was much harder than
just simply sliding along one of the curved faces, and they also had to revolve up and
against the bearing cage.
I had a go at extending the faces to mate with the 45degree bearing overhangs in an
attempt to create more contact and thus more friction to cause them to roll... but nope,
no dice!
Another suggestion was the idea of constraining each shape with an additional ring, however
because the centerpoint changes during rotation it can't just be fixed, it needs to in fact
be a slot.
So in this version the centerpoint of the objects are losely fixed to the ring with
an M6 screw tapped into the plastic.
This allows them to smoothly rotate as well as move up and down, but still be constrained
at 120degrees apart from eachother.
Theoretically if every surface mated perfectly and we didn't have this annoying thing called
tolerance to deal with, I see no reason why this shouldn't work... but alas, more sliding!
But it ALMOST works.
So I thought to myself, what If I could just give these shapes a tiny bit more friction
to work with?
I grabbed rubber bands and popped them around the shapes – and they rolled!
The rubber bands take up any small inperfections in the 3D Prints and causes them to turn instead
of slide, although I did notice just how much more difficult it was to move the shapes past
the peaks compared to the gentle curved part of the triangle.
Encouraged however, I went ahead and designed a modified version which uses a semiflex insert,
printed on my modified Cocoon create with the flexion extruder – the rest of these
parts by the way were printed on the Prusa mk3, mostly fillamentum vertigo grey and gold
happens PLA.
Also if you're wondering how I achieved this surface effect, I simply turned top or bottom
layers off in Slic3r prusa edition and used cubic infill.
Looks pretty swanky hey.
But by this point I was growing frustrated with how hard it was to rotate the shapes
past each curve, so I caved and went about modifying the realeaux triangle ever so slightly
to give it rounded corners.
Turns out creating a rounded releaux triangle isn't a super trivial exercise however!
You need to pay really close attention to the tangential relations of each part to ensure
it's truly a shape of constant width and not 'almost but not quite'.
And this is its final form – slightly rounded with a thin semiflex insert to provide just
a little bit more traction to encourage rotation.
You have no idea how overjoyed I was when I tested this out and it worked – it works
SO well, exactly how I envisioned it when I first attempted this rediculous concept
all those months ago.
It's satisfying to turn and doesn't get caught up, although interestingly the rubber inserts
tend to migrate slowly around the shape – I'll have to investigate that later.
But for now, it works...
so what to do with it?
Well, how about hooking it up to a motor.
So there you have it guys, a working relaux triangle bearing turned into a kind of kinetic
sculpture, and while the use of solids of constant width has pretty much no advantage
over circles or spheres in a bearing that I can see, it definitely looks incredible
while in motion.
I'd like to say this is the end of my mad descent into these forms but honestly I don't
think I'm quite done yet, I've got just a few more wacky ideas to test out in future.
And it is my aim to empower your creativity through technology and if you would like to
join me I'd love for you to subscribe.
Also a huge thanks to my patreon supporters for making all of this possible – there
was some pretty crazy late nights involved in this project including this clever idea,
yeah I have no idea what I was thinking.
And your generous support keeps the channel going, you can expect to have the files for
the final version and instructions posted up shortly.
Thanks for watching guys.
Bye!