Kind: captions
Language: en
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 simply
safe 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 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 on I feel
like this is it doesn't even need thing
but yes your weapons obviously you don't
want them to go off well 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
you need to squeeze it yourself though
well squeeze my cream pain that very
quickly got incredibly painful it felt
like having my finger like in a in a
vise that looks suspiciously like vice
grips but now with these flexible
components where the hinges are what I
learned in my visit with Professor how
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 piece 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 a amplify the force
just look at about thirty to one so I
could get for one pound force and get
thirty pounds out so that's pretty good
yes 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 and we 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 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 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 where we got there all right
Derek I've got a quiz quiz for you
okay I'm gonna elephant I'm 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
I just you know what I wanted to guess
without even thinking about that 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 okay but also because like
if this is all going over they feel like
this is gonna kind of extend there and
that's gonna get pushed around there
good thing what I don't know is that
good thinking that's well it's just
thinking at least so that's just design
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 something it's a 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 it's
modeled after the mechanism see 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
devices like this demonstrate the
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 where
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 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
making the
on chips we had to be able to make these
compliant mechanisms out of silicon
which is as brittle as glass 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
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 mechina and get the files to
make this yourself I'll put a link in
the description ya-huh also has a nice
feel and I snap to it has a really nice
snap I like when it comes out it's like
gum 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
where there's edge down there yeah those
are etched and so just using the same
process is 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
brain 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 if that motion
which we 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
yes 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 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 and
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 it's been that
thing oh so this like kind of oh that
kind of comes out like so any 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 and then yeah wow that's cool so
here this is made in plastic so that it
you know you can see it but in reality
it's gonna be a lot stiffer so here it
is made in steel so hangin you're saying
that that thing which is made of steel
yeah you spin it up to a certain speed
and then it expands and engages it from
there 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
engage it yes 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 in arm
the nuclear weapon now one of the
requirements was that this device be
made as small as possible they made
those as small as they possibly could
using true
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
devices 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 at their nuclear weapons and so we
design and we made prototypes we tested
them and then it goes what they call
behind the fence
where it's all classified you know we
don't know what happened
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