Turning Gravity Into Light - Smarter Every Day 146

Hey, it's me Destin. Welcome back to Smarter Every Day. If you've ever watched Smarter Every Day, you know that I spend a lot of time off the grid. Right now I'm in the Amazon rainforest, and I don't really know what this thing is. I think it's some kind of termite… thing on a tree. I don't know. Anyway, so one thing about being off the grid or in a developing nation is light is always an issue. Right now I'm using a headlamp. I've done this all over the world. I've done this in Africa; I've taken showers by headlamp. It's an important thing.

But what if you live off the grid so far that you don't have access to batteries? Check this out. I'm about to make light in the middle of the rainforest alone, with nothing but gravity. This is awesome. I'm gonna have to put this head strap camera on because I don't have enough hands, but check this out. So there you go. I'm in the middle of the rainforest powering a light with nothing but gravity, and that's a pretty big deal because humans have powered things with gravity for thousands of years, but we've never done personal source lighting.

So we're gonna figure out how this thing works because that's obviously the next question: how does it work? Let's go to the UK where the offices are, but let's make a pit stop on the way. Harnessing the energy of gravity to power things is not a new idea at all. In fact, here at Salisbury Cathedral in the UK, they've been using the power of gravity to power something for hundreds of years. It's a clock, and we're about to go mess with it and see if we can come up with any bright ideas.

The cathedral at Salisbury is over 750 years old. It's home to beautiful choral music, one of the original copies of the Magna Carta, and what's claimed to be the oldest working mechanical clock in the entire world. Clock expert Chris McKay agreed to walk me through the ancient technology of powering something using gravity.

"So it's ancient technology."

• "It's very ancient technology."
  "Clocks generally work backwards. Most machinery is you turning something fast and making it slower. With a clock, you've got a, you know, slow, faster, and sort of fast as if it were. The motive power is this thing here. This is a weight, and it's suspended by some pulleys which go all the way up. So the rope pulling on here tries to turn this wooden barrel. And in fact, it's turning it now. But at a very slow rate, and the rate is being governed by the escapement."

• "There it goes."
  [bell tolls] [machinery sounds] "And it's stopped with a pawl and ratchet here. The pawl and ratchet's very clunky, isn't it? It's really loud, so it's like you have this nice sound with the chimes, and then you have this [kunk kunk kunk kunk kunk]."

OK, so there's two takeaways to remember about clocks powered by gravity. Number one: they take a slow moving object and speed up the movement with gears. And number two: there's an escapement that regulates the release of potential energy.

Let's go to London. "Hey, what's up man, I'm Destin."

• "Pleased to meet you."
  "Jim."
• "Jim?"

This is Jim Reeves, co-inventor of GravityLight. Jim told me that he had visited Kenya where he had met people who had to use kerosene lamps at night so their children could do their homework. Children can get burned, the soot causes respiratory problems, you've got to pay for the kerosene, and think about it. You're burning an open container of fuel inside your house. It's a fire hazard.

Jim let me inside the secret lair where they developed GravityLight. I wasn't really surprised when we took one apart and found a DC generator on the inside. "OK, so now what we're gonna do is we're gonna set up the GravityLight prototype up here without a cover on it, and we're gonna look at how it actually works. So I would expect that the side under tension is where it's gonna be moving slowest, and near the gear on the, or the belt on the motor with the generator, they're the same thing by the way, that's where it's gonna be driving fastest, so let's check it out."

So the weight on GravityLight moves very slow and takes over 20 minutes to fall. So how is this slow motion converted into something fast enough to move that generator? The clock in the church had really large metal teeth capable of holding back that large weight. But GravityLight is just made of plastic. Wouldn't those teeth just break off under such a large load?

Jim taught me something interesting about how gears work. "If you have two gears touching on the outer diameter, only one tooth is engaged at any time. But if you have a gear running on the inner diameter of another gear, multiple teeth are engaged at the same time, which has serious implications for the life of the gear."

"So if a gear is mounted internally, then you get multiple teeth touching; therefore, you transmit the force over multiple teeth, and so you decrease the contact stress."

• "Exactly."
• "Increasing the life of the gear."
• "Precisely."

"I went to school for four years and you just taught me something. Thank you so much." Think about that. One side of the mechanism is closest to the weight, so the forces are larger. Jim uses internal gearing here to distribute that load across more teeth. The further through the drive train you go, the fewer the teeth you have to engage because the torque gets lighter and lighter as the speed runs faster.

Eventually, they're even light enough so that the generator can run with just a small rubber band, which has the added bonus of being quiet at high speeds. "When you said the motor itself is at 1600 RPMs?"

• "That's right. That's one of the reasons why we use a belt at the end, because if you did that just with a spur gear, it'd sound like a bag of nails."

"So the secret that you guys have uncovered to creating light with gravity with these low powered LEDs is using ancient technology, which is just falling weights. But the way you've done it is distribute the load on the teeth in a very particular way so that these things last a long time and they don't break or wear out."

• "Exactly."
  "That's genius."

OK, so we talked about the gearing, but what about the escapement? Why doesn't the weight just speed up until it hits the ground? LEDs are way more efficient than traditional bulbs, but there's something else. LEDs have a voltage limit. Once the generator turns up to a certain speed and that voltage limit is reached, the LED won't let it turn any faster. It acts just like the escapement in a clock. In fact, if you hang ten rocks on it, or gang 12 rocks on it, it's always gonna fall at the same rate.

This is how GravityLight can run for so long. "One of the advantages of GravityLight is there's no limit to that reservoir of power as long as you're willing to go back over and re-hoist the weight off the ground. You can let that run all night for no cost."

So there you go. Jim and his team are using their technical talent to provide a safe, clean, sustainable alternative to kerosene lamps. I love this story. I think it's because the solution was so obvious, but nobody connected the dots. All we had to do was apply an ancient technology to a technology that we have now. You're getting Smarter Every Day. Have a good one.

"So you plug the audio plug in the side of the product, and that interrupts the power to the LED so you've got a really bright task light. You can turn off…"

• "What, like a child's schoolwork or something at night, light homework?"
• "Exactly."

"What we're attempting to do here is to provide a really cost effective solution to people, really. But one of the ways in which we're doing that is to market the product in on-grid markets for people who might be wanting to put something away for the next hurricane or the next tsunami when the power's gonna go out. Because GravityLight has no batteries in it, it doesn't degrade over time. So you can store it under the stairs, and it's still gonna be ready to go for you whenever you need it."

"If you'd like to learn more about the GravityLight project, I'll leave links in the video description, and thank you very much to Shell for connecting me with Jim and letting me learn more about this project. It means a lot to me. I've spent a lot of time in Africa and South America, and I think it's really important. Thanks."

So to summarize everything that we've come up with here, this weight pulls this chain.