Placeholder Image

Subtitles section Play video

  • 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... -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.