Pull it back and then release the car to watch it go.

In this video, we're gonna look at the gears,

the spring, and that clicking noise you hear

when winding up the car.

(spring clicking)

That's coming up.

(electric buzzing)

(lightning explosion)

(upbeat music)

If you want one of these toy cars to move forward,

you can either push it.

You could build a track

and use gravity to move the car forward.

Or my personal favorite are the cars

with the pull back mechanism.

No batteries required.

Just firmly press down,

pull back the car to wind it up.

Now release it and watch it go.

Let's take a look at how this works.

Take the case off the car and we're left with the chassis,

four wheels and a motor.

The front wheels spin freely.

There's nothing special about them.

The motor is only connected to the back wheels.

Now if you wind it up,

you can see some of the gears moving.

Let's open this up to see what's going on.

There's five gears here.

And right behind the biggest gear

is a twisted piece of metal.

It's called a Torsion Spring.

The more you twist this, the tighter it gets

and the more energy it stores.

Once released, it will quickly unwind

if allowed to do so.

This spring fits quite snug inside the circular hole.

If I pull it out, then the spring immediately expands.

And it's not so easy to put back in.

So be warned if you try this on your own toy car.

On the large gear, there are some curved extensions

sticking out the side.

These fit right around the center of the spring

as the gear turns, the spring does too.

When the car is pulled back, there's a chain reaction

of gears turning.

This is called the gear train

and it's what causes the spring to wind up.

Let's take a step back for a moment

and talk about gear ratios.

I have two gears here of different sizes.

If the big gear turns once, the small gear

will turn around more than once.

Now imagine the small gear

had another larger gear attached to it.

We could repeat this again with another smaller gear here.

Turn the first gear just a little

and the last gear turns a lot.

This concept is used in the mechanism

for a pull back car.

Now let's take a look at the car gears.

There's one attached to the axle

and there's one right next to it.

These always move together whether the car

moves forward or backwards.

We've seen the large gear.

Now these two gears have a mind of their own.

This one helps winding up the car.

And this one helps unwind the spring

and push the car forward.

The wind up gear can slide up and down

to engage or disengage with the teeth

on the large gear.

On the side, there's a diagonal slot

that makes the sliding possible.

When we start pulling back the car,

the wind up gear engages with the large gear.

When the car is released and starts moving forward,

the gears move the other way

which disengages the wind up gear

so it's no longer in contact with the large gear.

Now during this time, the wind down gear

is doing the exact opposite.

The car is pulled back, the wind down gear

is disengaged from the large gear.

You can see it doing a little dance

while it tries to stay out of the way.

When the car is released, the wind down gear

slides into place just as the wind up gear

slides out of place.

The Torsion Spring is causing the large gear to spin

which then moves the gears

which then turns the wheels on the car.

This is where the gear ratios come into place.

The largest gear moves only a little

and the back wheels of the car turn a lot.

This is part of why the car can travel so far on its own.

When the spring has released all of its energy,

the car keeps going on its own momentum.

The large gear will stop

and the wind down gear will disengage again.

This time, both of these gears are out of place.

This way, the car continues to move forward

with minimal interference from the large gear.

Imagine if the car abruptly stopped when this happened.

It wouldn't be a very fun toy.

Now because of the gear ratios,

you can move the car back and forth

while firmly pressing down and it's still winds up the car.

Watch the large gear here.

Pull back the car and the large gear winds up a lot.

Push the car forward the same amount,

and the large gear only unwinds a little.

Back and forth.

Back and forth.

Overall, the spring is still winding up.

One last mystery is that clicking noise you hear

when you pull back the car far enough.

(spring clicking)

This is actually a clever fail safe

to prevent you from over winding the mechanism

which might damage the spring or the gears.

On the outside of the spring, you'll see a little loop

which fits into these slots around the outside.

When the spring has enough tension,

the loop will slip into the next slot.

This is what causes the clicking noise.

The sound means your car is just about wound up

as far as it'll go.

My name's Jared and I'm a 3D animator here on YouTube.

I like making videos about how things work.

If you'd like to help me make more videos,

click here to visit my Patreon page.

Thanks for watching and I'll see you next time.

(upbeat music)