Kind: captions
Language: en
this is one of the strangest materials I
have ever seen it is not sticky at all
you can't even stick like regular tape
to it
but if I drape it over this tomato
it holds it up
unless you turn it upside down in which
case it just falls off
now does it only stick to fruit no it'll
stick to a water bottle or a bag of
chips basically any approximately smooth
surface and that's because this material
is made to mimic gecko skin
artificial gecko skin comes out of
Professor Mark kokoski's Stanford lab
and it has now been used on robotic
grippers on Tiny robots that can pull
way more than their weight
on a robot that floats around the
International Space Station and even
enabling a person to scale a glass wall
Spider-Man Style
it all started with a competition to
make a robot that climbs a vertical wall
without suction here's sticky tape
everybody's familiar with it you press
it on and it sticks sticks pretty hard
actually and then you peel it off here's
Gekko material and the first thing you
notice is that it's actually it's not
sticky at all but if I lift it from the
middle I can lift the football you might
say well you could do that if you had
this other sticky tape right well yes
but if I had the other sticky tape it
wouldn't do that and that's important
because if you're a small robot trying
to climb a wall
you can't afford to have something like
chewing gum on your feet because then
every step you take is effort what you
want is something that only grabs when
you need it to
and that that's kind of the main
principle of Arc Echo inspired adhesive
here this is an early prototype of the
sticky bot gecko inspired robot this got
us into a long effort to understand what
is it that makes gecko adhesion work
having something which grips but is not
sticky
geckos are incredible climbers they
scale walls and even walk on ceilings
but for a long time we didn't know how
they did it they don't use hairs or
spikes like spiders or other insects you
might think they'd have tiny little
suction cups at the end of their feet
but their adhesion is actually way
stronger than suction cups a gecko can
easily hang its entire weight from just
part of one toe the clue to how this
works can be seen if you zoom in on a
gecko's toe these are called lamellae
they're regions of stocks which are
called site and the site Branch into
these incredibly fine structures called
spatulae which are you know less than
one micrometer across and that's
important because the physical principle
they use to stick is actually incredibly
weak it's not like an ionic bond where
atoms are attracted to each other
because one is positive and the other is
negative it's not even a hydrogen bond
like in water where part of the molecule
is slightly positive and the other part
is slightly negative no geckos rely on
the attraction between neutral atoms
so how does that work
say a gecko is climbing up a glass
window the gecko atoms are neutral and
the glass atoms are neutral but at any
particular instant the electrons around
an atom are not perfectly evenly
distributed about the nucleus they may
be a little bit more on one side than
the other and this makes the atom
momentarily a little positively charged
on one side and a little negatively
charged on the other side now if there's
a neighboring atom really close to it
say an atom for the glasses within a few
nanometers this charge can induce a
complementary charge imbalance on the
glass atom so now the electrons from the
glass atom are attracted to the nucleus
of the gecko atom and vice versa there
is a very weak force of attraction
between Gecko and glass and this is
known as a van der waals Force if
Android's forces are at least in part
why Gage blocks smooth flat pieces of
Steel can stick together it's there all
the time if you have a car with you know
you can put these like vinyl sheets on
the back window so that your kids don't
get like excessive sun when the car seat
that's also Van Der waals Force but
generally we don't notice Van Der waals
forces we don't feel them with our
fingers because at least on the
molecular scale our skin is incredibly
bumpy touching a piece of glass is like
putting a mountain range on top of a
flat plane there aren't many points of
close contact geckos overcome this using
all those tiny branches
so this means that when the gecko puts
his foot down it has a very large
intimate area it's almost as if you were
pouring glue on the surface and letting
it flow okay and that's what makes the
adhesion work replicating the gecko's
intricate branching structures is
currently impossible we cannot make what
the gecko has we can't that structure
that really fine branching structure
sophisticated branching structure but we
can make a more crude approximation
under a microscope you can see that the
artificial gecko adhesive is covered in
rows of sharp wedges the tips are around
one or two micrometers wide that's a
hundred times narrower than a human hair
to create such fine structures requires
a labor-intensive process a block of wax
is used as the base for a mold and then
a razor blade is repeatedly pressed into
the block creating wedge-shaped indents
a silicone polymer is poured into the
mold and a backing material is attached
this is silicone so it's called silguard
170. okay and it is a type of silicone
yes after about 24 hours the adhesive is
cured and ready to go and that's what it
looks like
but the mold can only be used a few
times before the quality of the adhesive
declines and you have to start all over
again
this sharp wedge structure which has
this kind of interesting property that
when you first bring it up to a surface
the only part in contact is these tips
so therefore it's not sticky because
there's no no vandivals Force worth
mentioning as you load it in Shear these
things all bend over
and we get a much larger in fact almost
continuous contact area and so like the
gecko we have some Van Der waals forces
to work with and that's what give us
adhesion
so to make the adhesive stick you have
to pull it parallel to the surface
that's known as a Shear force and you
have to pull it in the direction that
will bend the wedges so that they make
contact with the surface if you pull it
in any other direction it won't stick
this makes it easy to pull the adhesive
straight off the surface I mean there is
basically no contact force and so the
way we clean this is just with tape
because tape doesn't stick
they used this property to create an
incredibly small and lightweight robot
called micro tug it weighs just 17 grams
but is able to pull a 20 kilogram weight
that's the equivalent of a human towing
a blue whale
just six of these tiny robots can tow a
car
the gecko adhesive is on the underside
of the micro tugs so when they're
pulling the car the material is in shear
and it sticks tight to the ground but as
the car moves forward this Shear Force
decreases and so it's easy for the robot
to pick itself up and move itself
forward
the amount of pulling Force attainable
depends on the area of adhesive that's
in contact with the surface so they've
developed a method for measuring this by
Shining Light through acrylic so what it
does is Led across the acrylic and
whenever there's a contact with the
surface if if fluctuates a ray and it
shows you exactly where the contact area
is one square inch of contact area can
support the weight of about four and a
half kilograms or 10 pounds
since the adhesive is directional to
grip an object two pieces of adhesive
are attached in opposite directions so
when you pull up both sides are in shear
and so they both stick
two opposing pads of adhesive were
actually tested on a robot on the
International Space Station it's called
astrophy think of it as like a drone a
UAV only actually uses a fan to push
itself around inside the International
Space Station and the idea is that it
could be there to take video or or fetch
something for astronauts our proposal
was how about it should be able to float
along gently and stick itself to a wall
for example or or pick up a big box
our goal is to get that blue LED to turn
green because there's no gravity you
don't actually need a lot of force but
you do want to be able to grab very
gently and and release easily and so we
got the gecko adhesives up in
International Space Station and it works
just as well up there as it does down
here this went to space this was in the
space station this was in space station
for about a year and a half wow
this principle can be extended to three
pieces of adhesive so that when you pull
them all in they can stick to a flat
surface when it's at rest these things
are sticking up just a little bit and
then when you pull there then they
become flatter right yeah the entire pad
doesn't touch because it's both surface
is not perfectly flat and then once you
activate it
oh yeah I could totally see that
so I'm going to unplug the power so
there's absolutely no power to it at all
and still attached to the surface yeah I
was thinking that you'd have to keep the
motor on but it just sort of like locks
in position or what I don't know there's
tiny bit of tension it just stays there
forever
there are lots of potential applications
for this material but the most obvious
one is for robotic grippers since the
adhesive sticks well with just a small
Shear Force it's great for picking up
delicate items like produce these are
meant to be sort of like smart gecko
Palms basically so we're trying to grasp
with minimal squeezing we're not even
really engaging the ratchet mechanism
there yeah so it's like less than a
Newton it could also grab bulky items
or Palm a basketball
now can the gecko adhesive pull a car
they have hooked this one up to this
rope which is connected to a winch here
but the winch is not actually secured it
is Tethered back to four pieces of gecko
adhesive which are just sitting on this
pipe so the question is can these four
pieces of gecko adhesive anchor the
winch as it pulls that car back
okay
oh yeah it's moving
foreign
[Applause]
how much does
like there was nothing holding it on
as wild but of course the application
everyone wants is to be able to climb a
building and this was actually a PhD
project for grad student Elliott Hawks
it was a challenge because he had to get
enough gecko adhesive in contact with
the glass at any one time to support his
whole weight let me know if you want me
to try to climb a building with gecko
adhesive and maybe even go a little bit
faster
foreign
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