♪ ♪ NATHAN: Otis is my downstairs neighbor.

(chuckling) So, Otis wants me to build a series of backyard ninja training obstacles, which I think is awesome and super fun.

This young ninja needs to train to jump, dodge, crawl, and balance, so I'm making a ninja obstacle course.

And I'm going to use it as an opportunity to help explain how to use different kinds of fasteners.

Fasteners are things we use to hold stuff together.

My plan is to make four obstacles-- a hurdle, which is a bar to jump over; hanging bags to dodge and punch; a tunnel to crawl through; and a balance beam.

To join materials, fastening methods apply holding force so the parts can't come apart.

And sometimes I'll need to add clamping force, squeezing the parts tightly together.

First, I'll make the hurdle for jumping.

I've got this hurdle upright that I made by putting some screws in.

Now the screws I'm not using to fasten to the deck.

That would be permanent, and it would put a hole in this nice, beautiful surface.

Instead, I want a temporary way to hold this securely.

One of the easiest ways to do that is with a simple clamp.

So this has applied a lot of clamping force.

I don't really want this clamp sticking out in Otis' way when he jumps over this hurdle.

So I'm going to use a device called a ratchet strap.

(clicking) This is a good example of a temporary fastening technique.

Now that the ratchet strap is in place, I can take off the blue clamp.

And look!

It's still in place.

I'm going to put one more on the bottom.

(clicking) Perfect.

(straining) I'm going to use this 2x4 as the other upright for the hurdle.

To attach the base, I'm going to use screws.

This style of screw is called a drywall screw, or sometimes a deck screw.

Screws like this are awesome, because they apply holding force and clamping force.

Now, it's always best to pre-drill a hole through the first board.

If they're not lined up and there's a gap, watch what happens if I try to screw the boards together without pre-drilling.

(whirring) (squeaking) I can't tighten the screw anymore, I have holding force, here, but there is no clamping force.

It didn't squeeze the two boards together.

Now, instead, if I pre-drill a clearance hole, the clearance hole allows the screw to still turn, meaning it's going to suck that top board down against the bottom board, clamping them together and holding them.

Nice and tight.

(whirring) Nice.

I'm making a bridge with two ladders for a swinging bag obstacle.

Now, we need to securely attach these ladders together.

I'm not going to use screws or nails or bolts, because that would damage the ladders.

So, instead, I'm going to use a rope.

If you only learn one knot, my opinion is you should learn the bowline.

You make a loop.

This like the tree.

And the end of the rope is a bunny rabbit.

The bunny pops out of the hole, runs around the tree, and goes back down the hole.

That's it.

This is a bowline.

Now we can load this up really tight by hanging on that loop and it will not come undone.

There's the holding force.

You can also tie a bowline with string, or wire, or anything that you need to hold securely in place.

I'll wrap the rope around a few times and then tie it off to make it tight.

I can do the same thing up at the other end to clamp the bottom of this ladder to the staircase.

This is a zip tie.

You take the small end, and you put it through the big end.

Inside the big end is a tiny mechanism that lets the small end only go one direction-- the tightening direction.

If the one zip tie you have isn't long enough to go around what you want to grab, you can add a second one to it, or a third one, or a fourth one.

The downside is they're not reusable.

Now I attached the first bag already, but if I want to move it later, I can't without cutting the zip ties, so instead of attaching the rest of the bags this way, I'm going to use a great temporary connector called a carabiner.

The gate opens and closes to let you attach things to it, and to let you use the carabiner to attach things together.

Carabiners come in different sizes and different strengths.

Using a carabiner, I can take off the bags and reposition them as needed.

It looks good, so far.

I'm going to build a tunnel for Otis to sneak around through.

One of my favorite fastening techniques for cardboard?

Tape, and specifically duct tape.

I like duct tape because it's fast, it's easy to use, quick to pull off the roll, and it holds very securely.

Tape is particularly good at holding things in shear.

(strained): I cannot pull this off.

However, if you peel it off, it comes right off.

If I tear it, it barely takes any force there, either.

I formed a corner with two box sections and I'll connect them with tape.

If I add tape to the outside, it'll actually peel off pretty easily.

I want to make the tape hold itself in shear and the way that it's strongest.

So I put duct tape on the inside of the tunnel, and to make it resist tearing, I covered it with packing tape.

The advantage of packing tape over duct tape is that you can't tear it.

(straining) Instead it just stretches.

Which is actually awesome, because if you stick this on, and the parts are applying forces that make it want to tear, packing tape will not fail like duct tape will.

(tape screeching) The ninja obstacle course will end with a balance beam.

To add some challenge to the balance beam, I'm actually going to use the screws a little bit wrong by not pre-drilling.

I'm going to add a space that'll make it tip just a little bit, making it more challenging.

(chuckles) Nice.

Do you think the swing could become a part of the obstacle?

That's a really good point.

The tripod swing I built will also become one of the challenges.

Ready?

Go!

♪ ♪ ♪ ♪ And high five!

Got it!

A pretty good little obstacle course for young ninjas.

Okay, ready?

Go!

♪ ♪ (chuckles)