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... -What? -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...

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