Why Machines That Bend Are Better

What do this satellite thruster, plastic
tool, and micro mechanical switch have in common? Well they all contain components
that bend, so-called compliant mechanisms This episode was sponsored by SimpliSafe. More about them at the end of the show. Now about a month ago I was giving
a talk in Utah hence the suit and that’s where I met
this guy, -Larry Howell professor of mechanical engineering. So it’s always been considered to be bad to have flexibility in your in your machines.
Well we’ve tried to take that that thing that everybody hates, that is trying to
avoid and say how can we use flexibility to our advantage? how can we use that to
do cool stuff? Now Professor Howell literally wrote the
book on compliant mechanisms -that’s the most cited book
-but he’s pretty nonchalant about his work just watch how he introduces this mechanism he developed to prevent nuclear weapons from going off accidentally: actually in safing and arming of nuclear weapons. And so if…
-Yeah And so if you want….
-Hang on, hang on hang on What-ing nuclear weapons?
-Safing and arming Safing and arming
-yeah so if there’s anything in the world that you want to be safe it’s
not going to accidentally go off I feel like this is – it doesn’t even need saying
but yes nuclear weapons obviously you don’t want them to go off. What I don’t
understand how this is gonna keep the nuclear weapons safe. Now I want to come
back to this device and explain how it works once we understand why compliant
mechanisms are best suited to this task [that’s cool] So let’s start with
something basic. Probably the first compliant mechanism I ever designed was
this thing. What it is is a compliant mechanism that is a gripper so you can
put something in there and it will get actually a really high force. I can put
that in there and and it breaks the chalk What have you put your finger in
there and squeeze it? You would scream in pain, would you like to try? -I would like
I would actually like to feel the force OK, you need to squeeze it yourself though or it’s…
-Really? well all right, I’ll squeeze until you scream in pain Aaahh hahaha That very quickly got incredibly painful it felt
like having my finger like in a in a vice. That looks suspiciously like vice
grips but now with these flexible components where the hinges are. What I learned in my visit with Professor Howell is that compliant mechanisms have a
number of advantages over traditional mechanisms but I thought he needed kind
of a clever pithy way to remember all of these advantages. So I came up with the
eighth P’s of compliant mechanisms and the first of those is Part count.
Compliant mechanisms have reduced part count because they have these bendy
parts instead of having things like hinges and bearings and separate springs.
This gripper is just a single piece of plastic but achieves a similar result to
the much more complicated vice grips. Like how much does it amplify the force?
This will get about thirty to one so I could get for one pound force in, get
thirty pounds out. That’s pretty good It seems like that would be super cheap
-and really inexpensive so this we just made here in our shop but you can imagine
also injection molding that – that would cost like cents
-yep this would cost cents the other thing is because of its shape you could extrude it and then just chop
them off and that would be cool. So the simple design allows different production processes to be
used which lowers the price these switches for example achieve in one
piece of plastic what is normally done with springs, hinges and many rigid
plastic pieces also a good fidget device how long can these last? -we’ve had these in
our fatigue testing machine. We’ve been able to go over a million cycles without
failure What have we got there? All right, Derek I’ve got a quiz
-uh oh quiz for you okay, I’m gonna
-elephant I’m gonna Very good! okay I’m gonna push on elephant’s rump
this direction okay? I’m gonna hold this and that little dot right there, is that
dot when I push on it, is it gonna go left, right, up or down? Um… I just you know what I wanted to guess
without even thinking about it? Yeah, please do. I’m gonna say like up and in -okay
-and I kind of feel like that because like that would be a logical way for an
elephant to hold its trunk -okay but also because like if this is all going over then I feel like
this is gonna kind of extend there and that’s gonna get pushed up in there.
– ah, good thinking well I don’t know is that good thinking? that’s well it’s
thinking at least so… this is designed so that when you push on that it
actually just rotates in space it doesn’t move at all.
-I knew you were gonna pull some sort of trick it’s a trick question! now since I was fooled by it I
had to try it out on my friend the physics girl. That’s so trippy. That is so cool! I don’t understand – what?! it’s modeled after the mechanisms you use in wind tunnels where you want to have say
a model that’s that’s attached here but you move it and all you want to do is is
control its its angle and move it around in a wind tunnel. don’t displace it but be able to change the angle. Devices like this demonstrate that
compliant mechanisms are capable of producing very precise motion, which I
personally found pretty counterintuitive because these objects are made up of
flexible parts but maybe that shouldn’t be surprising because compliant
mechanisms don’t suffer from backlash for one thing. So backlash occurs when
you have a hinge which is basically just a pin in a hole and it’s moving in one
direction and now if at some point the motion reverses it doesn’t happen
instantaneously because there’s some give in the hinge. This also causes wear
and requires lubricant and that is why compliant mechanisms have better
performance than their traditional counterparts. This one though is my favorite.
That is is one of my favorites too. It’s just so pleasing, right? Ahhh, that sound is so satisfying. This actually, believe it or not was inspired when we
were doing things at the microscopic level, where we’re building compliant
mechanisms on chips. We had to be able to make these
compliant mechanisms out of silicon, which is as brittle as glass.
-mm hmm And if you’re trying to make something like this out of glass, right? it’s it’s crazy
hard but that also means once we figured out the design we could make it in a
material even like PLA which is also you know not the ideal compliant mechanism
material. So you can get on our website and get the material… and get the files to
make this yourself I’ll put a link in the description ya- that also has a nice
feel and I snap to it has a really nice snap I like when it comes out, it’s like
‘gunk’ you know like there’s something about that that’s really it’s very
pleasing. So these things actually move? oh yeah, yeah yeah
-I need to see this okay all right we’ll do it were those etched on there?
– yeah those are etched and so just using the same process as used to make computer chips. So another advantage of compliant mechanisms is that they can be made with
significantly smaller proportions because they take advantage of
production processes like photo-lithography And we have motion that we
want at the microscopic level -that’s brilliant. Plus since they simplify design
compliant mechanisms are much more portable meaning lightweight which makes
them perfect for space applications. This here is something we did with NASA
making a hinge that could replace bearings for say deploying solar panels.
This is titanium, 3d printed titanium but what’s freaky about it is you get that motion
which people expect but there’s a piece of titanium that can bend plus
minus 90 degrees, 180 degree deflection that is solid titanium. –
That is one piece of titanium that is 3d printed There’s no alloy, nothing to make it flexible.
-yep, this is yeah and even freakier than this is this guy right there. So that looks
like a crazy beast but every part in there has a purpose. All these flexible
beams here are the two inputs and again we did
this with NASA for a thruster application where you can put a thruster right there
and now with our two motor inputs we can direct that thruster in any direction.
That titanium device moves that, you notice that’s just all bending and then
there’s no pinch points for the fuel lines or electrical lines coming in. Here, this single piece of titanium allows you to use one thruster in place of two. Okay, that is a clutch, so the idea is if you spin it up really fast because it’s
flexible this outer part will actually start coming outwards and then if
there’s a drum around it it’ll it’ll contact with that drum and spin that thing
-oh so this like kind of oh that kind of comes out like so
-when it gets spinning really fast and then you’re you essentially engage this this outer drum so this is
like the way that a chainsaw would work or something like that because you get
it spinning fast enough and then it engages the chain and then it turns it
over -centrifugal force
-yeah wow that’s cool so So here this is made in plastic so that it
you know you can see it but in reality it’s gotta be a lot stiffer so here it is made in steel
-What? So hang on, you’re saying that that thing, which is made of steel
yup You spin it up to a certain speed and then it expands and engages a drum that is around it -yep so idle with no motion but then at a certain speed that
are what we designed it for it will speed up to that rpm You speed it up and it engages
-Yup I had no idea like I have learned something today So let’s come back to the safing and arming device for nuclear weapons. Its purpose is to ensure that no random vibrations say from an earthquake
inadvertently disable safeties and arm the nuclear weapon. Now one of the
requirements was that this device be made as small as possible. They had made those as small as they possibly could using traditional methods even using things like what the Swiss watch manufacturers were using. With compliant mechanisms they produced a device out of hardened stainless steel
where some components were the size of a human hair. This is high-speed video, here the device is operating at 72 Hertz meaning this
little hole makes two complete revolutions each second. The way it’s
meant to work is an arming laser shines on the rotor wheel and when the proper
input is given to the system the wheel rotates a notch. If all the proper inputs
are given then the hole lines up with the laser beam and crazy things happen
from there. So it is essential that this device’s performance is perfectly
predictable even if it sits unused in a silo for decades. So are these now being
used on nuclear weapons? You know, it turns out they don’t tell us what they
do with their nuclear weapons and so we design them, we made prototypes we tested
them and then it goes what they call behind the fence. And… where it’s all classified and, you know we don’t know what happened, so… hey this episode was supported by
viewers like you on patreon and by SimpliSafe, incredibly effective
reliable home security. Now I started thinking seriously about home security
one day when there was this police helicopter circling overhead and it
turned out that the house across the street had been broken into. SimpliSafe makes it easy to protect your home.
they sent me a kit including a base station, camera and multiple sensors and
the setup was simple it only took me about an hour to complete. The system is
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thank you for watching

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