This is Leonardo, we call him Leo.
This is Calvin's little brother.
He loves to bounce.
And it's a good way to get him to fall asleep.
The trouble is, after he falls asleep in my arms,
when I put him into his crib, he often wakes up.
So I figured out, if I bounce him in his crib,
when he falls asleep, I can stop bouncing it and he stays asleep.
It's a heavy crib.
It'd be great to have a bounce-o-matic
that would automatically bounce the crib
to help Leo get to sleep,
and so that I could sleep, too.
My idea is to make a hinged platform
with springs and a motor that will bounce the platform.
I'm going to use a loud saw.
So to protect my hearing, I'm going to use ear plugs.
And to protect my eyes, I'm going to wear safety glasses.
Now I'm going to cut some 2 x 4s,
and figure out how to arrange them
to make a bouncing platform.
The way I have this set up right now
is actually upside-down,
so this will be a surface that's against the floor.
And the crib will be under here.
What do you think about when you think about bouncing?
I think about springs.
These springs will make it easier to bounce the crib.
I'm going to need a hinge down at this end,
and I'm going to need space to allow the crib to bounce
without crashing into anything.
When you bounce something like this,
you'll notice there's kind of a certain speed
it wants to bounce at.
That's called the resonant frequency.
Frequency is the speed at which an object vibrates.
If I want Leo to bounce fast,
I'll put the springs far away from the hinge.
If I want him to bounce slow,
I'll put the spring close to the hinge.
This is more like how I bounce Leo to sleep.
Just to measure how fast I bounce,
I'll pretend the drill is Leo.
Perfect.
I'm going to put the 50-pound weight on the crib platform,
and I think it'll weigh about the same as the crib plus Leo.
Instead of bouncing by hand,
I'm going to add a motor to bounce for me.
I'm going to repurpose the motor from inside of a car door.
It's the motor that makes the windows go up and down.
Motors need power.
This is a power supply.
What's great about this one is, it's adjustable.
As I change the voltage, the motor's speed will change.
That's important, but I've got to do something special,
because a motor goes around and around,
and I want this crib to bounce up and down.
The motor's going to spin a shaft,
and I'm going to attach something heavy to the shaft
that's off-center,
so that when the shaft spins,
the off-center thing swings around.
It'll help me convert rotational motion
to up-and-down momentum.
It'll be just like the vibrating motor in a phone, just slower.
Rather than try to make
something difficult and complicated
to attach to the square shaft,
I can just use another motor as the heavy thing.
(laughing)
(power supply falls on board)
All right, it works.
When the motor's speed matches the natural frequency
of the bouncing platform,
we should see it shake a lot more.
(yells and laughs)
Time to do a little fine-tuning with the weight on top.
There's a pretty good bounce going,
but I want it to be a little bit slower.
This is a little faster than I bounce Leo.
So I'm going to take my springs
and move them closer to the hinges.
Look at what's happening.
Big bounce, small bounce-- big bounce, small bounce.
Big bounce, small bounce.
The reason it's going big bounce, small bounce
is because the frequency of the weight
going around and around
is faster than the natural frequency
of the bouncy platform.
What I need to do is
match the frequency of the weight going around
to the frequency of the platform.
That's what we call resonance.
This wave shows the frequency or speed of the motor.
And this wave shows the natural frequency of the platform.
When they're the same frequency and the waves are lined up,
I'll have resonance, and the bounces will be bigger.
I'm going to change
the frequency of the weight going around
by changing the motor speed.
And when it gets into resonance,
we should see the bounces get all big.
(laughing)
It's actually crashing into itself,
it's bouncing so well.
I added spacers to give the platform more room
to make bigger bounces.
Now I'll try the bounce-o-matic with Leo in the crib.
You feeling tired?
Perfect timing because Leo's ready for his nap.
(Leo panting)
Yeah, it's time.
Let's try out your new crib.
(weight rocking)
(Leo panting)
It's working.
Is that a nice gentle bounce, buddy?
(whispering): This is great-- it worked.
The motor is bouncing Leo's crib,
and he's fallen asleep,
and I didn't have to bounce him myself.
Nice.
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