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A $5 Lamp Powered Solely by Gravity

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Re: A $5 Lamp Powered Solely by Gravity

#31

Post by icoder »

duskwuff wrote: post #24
tonyarkles wrote: post #5

Earlier quoted context omitted.

If you read some of the followups and tweak the math a little bit, it works out reasonably well. Instead of 20kg and 1m, 20lb and 2m, which comes out about the same (49.42mWh). If you have to lift it every half hour, that's 100mW for a half hour. That's more than enough power to get a useful amount of light out of an LED. For example, this LED uses 68mW https://www.sparkfun.com/products/531 and is marketed as "so bri…

That's assuming a perfectly efficient dynamo and no mechanical losses. (Which are both huge assumptions.)

Exactly, and since they state that they think they can make it twice as efficient, that would mean they run at max 50% now.

Re: A $5 Lamp Powered Solely by Gravity

#32

Post by sliverstorm »

Lagged2Death wrote: post #10

Some people get excited by F1 racing, the Bugatti Veyron, or stuff like the latest iPhone, telling you they are technology enthusiasts or engineering fans. But if you ask me, it's always at the low end of things - like this project - where the really inventive, exciting engineering happening. Sure, something like an F1 car is impressive after a fashion, but considering the price, yeah, well, it better knock my damn s…

You're just paying attention to different constraints. Engineering with zero constraints is pointless- but an F1 car operates within all kinds of constraints that are not money. You just aren't familiar with them.

Re: A $5 Lamp Powered Solely by Gravity

#34

Post by kevinh »

bmelton wrote: post #15
Jach wrote: post #13

Earlier quoted context omitted.

It's not very useless. The title suggests a perpetual motion machine, so I was wondering what that was doing on HN. Knowing you have to lift it first (from the article or from the comments) is important to know and lets one think this isn't necessarily made up.

If you had an infinitely long rope and access to an infinitely deep chasm, then there's no reason it wouldn't be considered a perpetual motion machine.

With an infinitely long rope and an infinitely deep chasm there would not be substantial gravity pulling it downward to have perpetual motion.

Re: A $5 Lamp Powered Solely by Gravity

#35

Post by lusr »

ars wrote: post #30
pdonis wrote: post #6

Earlier quoted context omitted.

Um, please read the entire previous thread before dismissing this as a hoax. As you can see from a number of posts that I and others made there, the light is comparable to a kerosene lamp, which is what it's intended to replace. It is not, of course, comparable to the kind of light we in developed countries are used to, but that's not what it's intended for.

Using the numbers above and the typical LED efficiency you get 5 lumen of light per half hour ASSUMING perfect mechanical efficiency. http://www.wolframalpha.com/input/?i=20+kilogram%E2%80%90for... A simple wax candle produces 11 lumen. And there is no way you will get anywhere near perfect efficiency. So at best, this will product maybe 1/3 of the light from a candle. If you directed that light into a small spot, it…

Why are you limiting your scenario to only one of these lights?

Re: A $5 Lamp Powered Solely by Gravity

#37

Post by retube »

ColinWright wrote: post #2

Previously submitted and seriously doubted: http://news.ycombinator.com/item?id=4889266 In that thread[0] revelation[1] said: At perfect efficiency, this seems to give you about 55mW for a hour, if I asked Wolfram correctly (for 20kg lifted one meter) - [2] - So probably a hoax. [0] http://news.ycombinator.com/item?id=4889426 [1] http://news.ycombinator.com/user?id=revelation [2] http://www.wolframalpha.com/input/?i=…

well here's the agency behind it... pretty elaborate if it is a hoax: http://www.therefore.co.uk/our-work

Re: A $5 Lamp Powered Solely by Gravity

#38

Post by fhars »

lusr wrote: post #35
ars wrote: post #30

Earlier quoted context omitted.

Using the numbers above and the typical LED efficiency you get 5 lumen of light per half hour ASSUMING perfect mechanical efficiency. http://www.wolframalpha.com/input/?i=20+kilogram%E2%80%90for... A simple wax candle produces 11 lumen. And there is no way you will get anywhere near perfect efficiency. So at best, this will product maybe 1/3 of the light from a candle. If you directed that light into a small spot, it…

Why are you limiting your scenario to only one of these lights?

Because if you used a sufficient number to light a room you would have to hire people to lift the weights continuously, and if you have to to that, it would be far more efficient if you hired them to generate electricity using a pedal powered generator, because that is still the most efficient way to transform human labor into electricity.

Come to think of it, pedalling for the time it takes to lift the weight and charge a supercap that will them provide electricity to the LED might still be better.

[Edit: Lets do the math: 100W effective for 30 seconds gives you 3000J electrical energy stored in the cap, drained over 3600 second provides an average of 830mW for an hour.]

Re: A $5 Lamp Powered Solely by Gravity

#39

Post by tjic »

tarice wrote: post #7
dsl wrote: post #4

Not to nitpick, bit it's not powered by gravity, it is powered by people going over every 30 minutes and lifting a weight back up to its top position. EDIT: Apparently people don't understand that using gravity to generate energy is a thing, and the title "Powered Solely" suggested someone found a way to do that.

People couldn't lift the weight without consuming energy from food. Doesn't mean that it's powered by food. The machine converts gravitational potential energy to electromagnetic radiation. People generate the gravitational potential energy by lifting the weight using kinetic energy, which was likewise created by converting chemical energy. It's easier just to say "Gravity" because, without gravity, it wouldn't work…

> People couldn't lift the weight without consuming energy from food. Doesn't mean that it's powered by food.

Actually, it does, and that's the perfect way to analyze this. Food is good for keeping humans alive, but it's a pretty foolish fuel to burn in a human engine to accomplish things. It's perishable, it's eaten by rodents, it's hard to transport, and more. I chuckle darkly when someone tells me that something is "green" because it's human powered. Growing food isn't free - it uses conventional energy sources to harvest, transport, etc., and it's a ton less efficient than just burning that fuel directly.

Re: A $5 Lamp Powered Solely by Gravity

#40

Post by tjic »

zem wrote: post #21
Lagged2Death wrote: post #10

Some people get excited by F1 racing, the Bugatti Veyron, or stuff like the latest iPhone, telling you they are technology enthusiasts or engineering fans. But if you ask me, it's always at the low end of things - like this project - where the really inventive, exciting engineering happening. Sure, something like an F1 car is impressive after a fashion, but considering the price, yeah, well, it better knock my damn s…

indeed! having lived in india, i get particularly excited by projects that could provide grid-free lighting and clean water to rural areas. also, a quick plug for my blog [ http://aleverlongenough.wordpress.com/ ] rounding up projects like this - it was unfortunately short-lived because life got busy, but i hope to restart it in 2013.

> i get particularly excited by projects that could provide grid-free lighting and clean water to rural areas.

The best way to provide lighting and clean water is via the grid: power lines and water pipes.

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