Homemade Gravity Light Doesn’t Last Long but Proves the Concept!

gravity light

After being inspired by the Deciwatt Gravity light, [Steve Dufresne] decided he wanted to try making his own as a proof of concept.

The Gravity Light by Deciwatt is an innovative device designed for third world countries to help eliminate expensive lighting like kerosene lamps. It has a small weight on a pulley which can be lifted up in under 3 seconds. During its slow descent down the weight provides light for 25 minutes! It’s affordable, sustainable, and reliable. It’s also mechanically impressive, which is exactly why [Steve] decided to try making his own.

He’s using a single LED, a small DC motor, a few pieces of wood, an old bicycle wheel, some bicycle chain, and a few jugs of water. The water is connected to the chain which is looped over the smallest gear on the bike. The generator is then powered by a belt wrapping around the outside of the rim. This gives the motor enough speed to generate electricity for the LED. His current design only lasts for about 3 minutes, but he’s already working on the second iteration. Testing systems like this really give you an appreciation for the effort that must have gone into the real Gravity Light.

Stick around after the break to see it in action.

72 thoughts on “Homemade Gravity Light Doesn’t Last Long but Proves the Concept!

    1. It’s beautiful, isn’t it? It always seems like the most fun developments are those that just bring together ideas that nobody saw to try before.
      Modern electronics powered by such an old, simple idea. Outstanding!

  1. He needs a 10 to 1 reduction in gearing maybe even a 100 to 1 to give that motor enough speed to really slow down that weight fall. Problem is I think he will overspeed the motor before he get’s there as that much weight will easily overwhelm the small motor he has.

      1. air vanes will just waste energy. he doesn’t want to add drag as that prevents the energy from being used to make light.

      1. Most of the music boxes I have seen use an air vane as pointed out above those waste energy. Perhaps more idea would be a mechanism that is literally more like a clock with an adjustable escapement.

        1. Ideally, you’d want to size the generator and choose a gear ratio such that the input energy is exactly transformed to the optimum light output, less losses of course.

      2. If just the drag from the generator isn’t enough to govern the speed, then it’s not geared up enough. That is, rather than use a governor, exploit that excess energy by increasing the step-up ratio in the drive train.

  2. From the GrivityLight website:
    “GravityLight Lux output: variable between 5 and 15 Lux.
    As a comparison, a basic kerosene lamp is quoted as providing between 1 and 6 Lux.”

    I don’t know what kerosene lamp they used, but I have some at home that produce more like 500 Lux. And burn the kerosene very cleanly, without producing any odor.

      1. When I think Kero lamp, I also envision a petromax lamp such as in your post. I suppose that is considerably more costly than the other style you mentioned.

      1. I wander what mantle they used for the pressurized kerosene lamp, because the old ones, containing radioactive Thorium, give much more light than the new ones without thorium.

  3. yetihehe i think the idea of this hack is to be environmentally friendly and kerosene is hardly environmentally friendly.

    it may be possible to use some super capacitor and joule thief to power the led after the motor stops.

    Tom Hargrave the same is still used to power clocks today you can get tall grandfather clocks that uses weights and even has an electric winder.

        1. Why is he anti-science? His analysis of the subjective nature of the term “environmentally friendly” is spot on. He is mearly saying that kerosene isn’t ‘evil’ simply because its a fossil fuel.

          1. in a way any large sale use of fossil fuel is evil.

            the earth is/was a balanced system any use of an “outside” energy like the million year old accumulated solar energy that is fossil fuel unbalances the system sending it into chaos.

        2. “So you are anti-science then?”
          What makes you say that? Can you be any more specific? And, if it’s a legitimate question, no, I’m not anti-science at all.

      1. You are right that kerosene “saved the whales” but the implication that a kerosene substitute would not be environmentally friendly would be absurd. Obviously people wouldn’t suddenly shift wholesale back to whale oil because this lamp was cheaper than kerosene.

        1. “implication that a kerosene substitute would not be environmentally friendly”

          Your inference doesn’t mean that that’s what I implied. I simply can’t see what’s “environmentally unfriendly” about kerosene, since I don’t subscribe to the warmingist dogma.

    1. I want to try a super capacitor, but don’t have one yet. Yesterday I did put together a full wave bridge rectifier circuit along with a 4700uF 35V capacitor which took advantage of both halves of the AC cycle and managed to brightly light three of the LEDs and smooth out the lighting. That, and with a counterweight added, has the run time now at just over 8 minutes, a big improvement over the 2 minutes I had when I made the video.

      1. Using a large super capacitor or even a large rechargeable battery could enable enough current drain from the motor such that it slows itself and wouldn’t require a counter weight. The more current you can sink, I imagine you could use heavier weights that pack more energy but would still move slowly due yo the back EMF of the motor.

    1. Why not make a methane version, and use the farts of a person to generate electricity?

      (In fact, biogas is already used in many countries, for light and cooking)

      1. And every 20 or 30 minutes, pick yourself up off the chair, which is now on the floor, and raise the seat (and yourself) to the starting position again. In the dark.

        I thought something like a handle on the loose end of the chain, that you could just pull, like the weights in a grandfather clock, exploiting the ratchet in the hub.

  4. The fun thing will be to see how this plays out “in the field”. Some of the electricity generating stoves that have been developed for similar markets have reportedly become popular because the purchasers (men) can charge their cell phones while the users (women) cook. We’ll see where the Deciwatt concept winds up.

  5. NEAT writeup and riffs on existing hacks are oftentimes more fertile learning tools than is first apparent. Nothing teaches us like making a WORKING model and 25 minutes light for 3 seconds winding is indeed quite useful.

    There’s also a factor of scale to consider. Let Hackerdom’s fertile imagination raise a million weights to have their useful descent uplift many. Sometimes the Hacking of our MINDS to think differently is the greatest win of these hack’s bigger footprint.

    HOW big of a “Steamless Steamtech ” Evocative BEAST can we scale this? Someday up to and including oh- charging things at events. A category of Field Day bonus for LARGE Gravity Genny?

    Booths @ Hack/Make events powered by Ferris Wheel sized drums and a wheeled trolley on a LONG angled cable, trading height for diagonal… Raise the weight by dedicated hackers pulling block&tackle or other Pyramid building tech.

    Anyone up for collaborating on a series of Grandiose Gravity Generators:?

    Wifey thinks me mad as I dictated voice recorder notes for a winding drum able to hold how many dozen stories of lift *ANCHOR CHAIN* as added mass. Hell, Leave the anchor on and wrap it in scrap mass. But Seriously- the DCPM motor axles of various things already having wheels with suitable rim for cable winding could be a neat Categorical Basis.

    I’m wondering if many other standard bidirectional gearbox motors could be a quick to deploy incarnation of the Gravity>Electricity hack? . Includes steppers, Anyone who has ever moved a printerbot axis and seen things getting powered by that stepper>genny effect should be thinking on some applications of it.

    Building a Light Bulb would tie in nicely and doing so is on my round tuit list.

  6. OK how about eliminating the water weight gravity feed and chain and move to an alternative method? Namely elastic potential energy. Keep the same rig as before, however, add a large elastic band to the center hub of the bicycle wheel (like a rubber sheet from a physical body workout kit, inner tube, or a black bungee cord). Then attach the other end of the band to a hook mounted horizontally off of the center hub by a few inches or feet.

    Now wind it up by turning the bicycle wheel backwards. Then when you feel it’s tight enough, release it. Since your motor-generator appears to have gearing it will slow down the release of the potential energy. In this case the more friction at the generator the better as it will introduce longer event timing.

    To govern the amount of electricity generated to the LED you might think about a Zener diode or a IC voltage regulator. Think about upgrading your LED to a high-output jumbo LED. You can also look at a solar light and try copying it’s NiCd rechargeable battery configuration to store electrical energy for discharge over a longer period of time. A high-value electrolytic capacitor is OK but a NiCd will last longer. The generator will recharge it.

    I don’t see why you need a bridge rectifier as a brushless PM motor is not generating AC. It is DC and needs no rectification. An induction motor is AC and can be used in power generation too. What type of motor do you have?

    If you take a 6VDC brushless PM motor out of a old toy car, it has a large gear box. That gear box will gear down the torque significantly allowing a slow release of potential energy from the elastic band. It is noisy though. Add a lot of lubricant to the gear box to reduce noise and wear to it’s plastic gears.

    I think if you can keep your voltage output at about 1.5 volts DC you’ll be OK. A voltage regulator can do that. However, if the generator output voltage tends to run high, you may need a heat sink on the diode, transistor, or IC. Of course a dropping resistor will help too but if the rig slows down too much the dropping resistor becomes a bit problematic as the voltage may go lower than that.

    All in all a really cool project to play with… GOOD LUCK!

    1. I like the elastic band idea – basically a different way of doing a windup spiral spring as in watches I think.
      The motor is a microwave oven motor used for slowly turning the tray. It’s a synchronous motor and definitely AC – I’ve since checked it on my oscilloscope. That’s what confirmed for me that a bridge rectifier would be a good idea, instead of throwing away half of each cycle.
      I was thinking of putting in a zener diode to protect the LEDs from too high a voltage. But the 4700uF, 35V electrolytic capacitor I added just after the rectifier never seems to get above 4.5 volts, unless I really let the wheel turn fast. I guess all that excess capacity is a lot to get fill with the LEDs in place. But of course, unanticipated things are what the zener diode would be for.
      Looks like there’s a lot of room for fun with this one yet. Thanks.

    2. There’s a project I saw on TV, I think in Africa, maybe it was Asia…

      Anyway a kids’ playground had the roundabout rigged to a mechanism, every time the roundabout went round, it drove a piston pump (some clever, and heavy-duty engineering). It pumped water from a well, up to a small water tower. The idea was just to provide water to people. The water tower meant you could get a drink without having to drag the kids out of bed.

      Anyway, that was a great idea. Something similar to generate electricity might not be a bad idea. I know farmers work hard, but they could come up with a schedule between them. Have a low-voltage grid that drives lights in each home, and phone chargers.
      You’d have to match power demand to size. Obviously the more users you have, the more volunteers you have to work it.

      Human power can do all sorts. If you can wind a radio by hand, you can light some houses with a few men powering a generator. It could even use an gravity as a storage mechanism instead of batteries.

      That might be one way this system could work. Scale it up to a decent size. If a few neighbours can split the cost, the better. Hang a pulley from a tree, with a rope with a weight on the end. The generator stays on the ground. In the day, men pull the weight up by the rope. At night it’s rigged to start, and lights up several people’s houses.

    1. Rechargeable batteries have a comparatively small life cycle. Fine for a first-world toy, not so useful if you’re going to use the entire battery capacity every night.

    2. Advantage is MORE FUN Steve’s way! :-)

      A clock mainspring is problematic as not only is it hard to find but is difficult to mount and setup. A piece of flexible rubber is a bit less a problem and easy to implement.

      The benefit in using the microwave table motor is it has a gearbox. Gearing down is highly beneficial in governing torque speed. Also a oven rotisserie motor too. However, I like using PM motors for generators as it removes the need for conversion. However, you can easily step-up AC with a transformer if you need more voltage. You could get that 6vdc toy motor from a local thrift store or while driving around town dumpster diving. Or just ask your empty-nest neighbor who is throwing out all those toys piling up in his garage. “Hey Joe… how much for the old PowerWheel?” “Ah you can just take it Steve. I don’t need it… my son’s in college now. He doesn’t need it any more.”

      Now where to get the big rubber band? “Honey? Have you seen my workout exercise rubber belt?” “No sorry hon… haven’t seen it!” (you liar!) :-)

  7. The Deciwatt itself is useless. The light it gives off is pretty useless, it’s very dim. The basic problem is, to generate enough power by gravity to provide useful light, you’d need a big, strong generator (or at least strong gearing) and a strong frame, to handle the large weight needed.

    The Deciwatt’s one good idea, is to have the “weight” as a bag the user fills with dirt. It’s the same bag the item ships in, so nice for not having to ship weights anywhere. It could scale up to a bigger bag, since you could fill the bag a shoveful at a time, then tip out at the bottom.

    But as it is, you can’t generate a large amount of light, for long, from gravity, with an inexpensive generator.

    For the effort needed to get real light, you may as well go the whole hog and get people to take turns on a bicycle gen. Or some other source, something that uses cooking heat might be good. But this idea is fundamentally doomed.

    1. Fundamentally Doomed is a term overused in many contexts. I could go on further but why?

      Some of these Hacks are of their greatest utility in promoting engineering creativity= Breaking Sets so to speak. Breaking Sets as in BRAKING SETS gave us Regenerative Braking to illustrate the logical inference in action:>

      If we had funding for a contest to prove that YES, we CAN Generate Useful Light with a CHEAP riff on the foundation elements of falling mass>electricity>LIGHT?

      I was idly speculating and my wild arsed hack paths came up with a battery box stacked power chair simply rolling down a ramp. Getting it up raises a ton of hacking contests for how-to… Arch Reactor’s space has a few old Power Chairs that might do well on their space’s driveway ramps…

      Windmill and rope capstan winch with human operator as Zen Energy Mindfulness?

      1. Yeah, the idea of gravity energy storage itself is not necessarily doomed. There’s 2 giant lakes in Wales that smooth out demand on the UK’s electric grid, pumping water from the lower to the upper one at night, then generating during peak.

        I should’ve been specific. It’s ideas like the Deciwatt that won’t work, simply because it can’t be done tiny-scale. To generate useful power you need strong, good. mechanisms. Little plastic doo-dahs won’t do it.

  8. My bike dynamo has 3 parts. The tire touching generator feeding a bridge of .170 volt or so diodes and a 1.1 watt led. No regulator, current limiter, nuthin! It goes to full light at a walking pace and flying downhill no worry. The generator delivers the old standard of bike bulb lighting going back to German standards. 6 volt-3 watt. Voltage depends on load of course. The generator is the built in current limiter limited to about 300mA. No governor needed as the magnetic flux slips when the thing saturates, so there is no additional drag as I go above that walking speed. It’s not near max current for the LED. I’d think that walking pace efficiency would work with dirt or sand hauled up a tree or set of poles. That LED would be like a piece of daylight to the poor that pay for the many markups for that dollop of kero.
    Kero and batteries are gotchas in the third world, much like utilities in the rest of the built-up world. The rocket stove tries to curtail the use of charcoal which is a dirty inefficient fuel.
    As for “clock” motors (microwave turntable) as generators I doubt it not much flux. Stepper motors are much better as a generator. I rocked one back and fourth the size of half an oatmeal can and ran a car radio. One out of a printer ran a cheap keyboard as a test for a future human powered e-keyboard, batteries not needed. The bike setup is left on in the daytime, it could light up to 6 LED’s in series according to one forum. They just wouldn’t get to full until full level speed. ]
    Try a printer motor mounted in a backpack frame with an arm or linkage to tap a little leg motion, charge on the go!

    1. “What if we could have two weight instead of one?? so we get a kind of cycle and it keeps rotating with endless power??”

      Go for it! It shouldn’t be hard to throw together a prototype I’d really like to see something like that!

  9. One thing I would like to see is more self-powered exercise equipment
    (or even exercise equipment that powers the gym).

    It seems silly to have to plug in a treadmill, exercise bicycle, stair-climber, etc.
    Running a motor for people to exercise on.
    Better to have them exercising to turn a generator, or other energy storage device.

    I like the playground idea. I volunteer doing forest restoration in a park that is next to a school. When I see all the energy being expended in the school yard, I keep thinking it would be great to harness that energy to do something useful.
    (Of course have to consider how long it would take to recoup the embodied energy in the energy recapture system.)

    1. I once used an exercise bike in a gym (ONCE and once only!) that did just that. The displays didn’t light up til you’d got a bit of a pedal going. I suppose there was a battery or cap to keep the data in the onboard computer safe when you stopped for a while. It’s handy because you don’t need cables strung over the floor (which is probably not allowed).

      Treadmills have motors for tilting, and also to move the road itself. The action of treadmill running is different from dragging the conveyor backward with your feet. I don’t think it’d be useful for exercise AND generating power. I think they’ll always need a decent power supply.

      Regarding the playground, yep, it’s invaluable when it’s pumping your only source of water, but almost useless when you already have that infrastructure, or just don’t need it.

      1. I can’t help but wonder at the mentality that will drive to the gym, where they’ll pay to walk on a treadmill, then shower up and drive home. Geez, why not just walk to the gym and back?

  10. whatever the setting, the only energy available is = mgh
    with 5kg and 2 meters, this is 20joules
    and 20 joules is 0.2W during 100 sec
    or 0.02W during 16 min !

    1. Pretty sure you missed out g in your calculation:
      Should be – 5kg*9.8*2=98J
      Which would be 0.1W, or 100mW. This is more than enough to drive a small LED, even at 20% efficiency

  11. I proposed elastic potential energy using several hard rubber bungee bands with hooks. But since this is in Africa I think hydroelectric should be explored. Steve’s bicycle wheel rig could still be used. However, he would need to modify it so that the wheel could be dipped into a strong stream of water like a brook, river, rapids, waterfall, etc. He would have to add wood or plastic paddles (i.e. spoons bent at right-angle) around the circumference of the wheel. They could be held on by small diameter metal hose clamps or large nylon tie-wraps.

    The paddles would catch the water stream and rotate the wheel endlessly (or until the next drought season). The base would need to be anchored (i.e. sandbags) so the stream would not carry the rig away. A long extension cord would be needed to run the power wire to your tent or hut nearby,

    Steve could test this at the local good-current river near his house or set up his lawn hose in a kiddie swimming pool to test this idea. The river would need good human-or-vehicle access and a good flat shoreline for him to approach river and setup the rig. Also he would need the landowner’s permission to be on that property.

    This idea is also very old indeed. Remember Nikola Tesla’s AC generators used by Westinghouse at Niagara Falls? Except his were huge. If Steve could somehow miniaturize this idea to a portable system he may just have a patent to file. Who knows?

    1. To expand on this hydroelectric idea… I saw a movie with Clint Eastwood that depicted the gold rush miners in California in 1840’s. They found a way to increase a river current’s pressure by using large diameter pipes compressed to a small diameter. This would cause a jet-stream effect of sorts which allowed them to hydro-dynamically strip-mine for gold. This idea could be built into Steve’s rig using several lengths of PVC pipe from Home Depot or Lowes. They have adapters to join together different diameters of pipe. That way if Steve only had low current rivers near his house he could increase the flow to the rig with PVC pipes. Using 45° elbow joints he could extend the PVC pipes up a waterfall area to higher elevation allowing gravity assist to the water stream. This idea would take a lot of tolerance from the land owner as it might look CRAZY and dangerous.

  12. THIS should have been the “Developed on Hackaday” project. Something like the GravityLight should be open-source.

    I normally not the lefty, love the world type; but if you’re gonna act like you care about poor people in Africa, and ask for CROWD FUNDING to do your R&D and production, then IMHO, you shouldn’t be trying to make a buck off of it, no matter how small your profit margin may be.

    Kudos to Steve for his initial success, I hope he keeps going, finds inspiration and gets to something close to the performance of the Deciwatt one and lets the world have it for free.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s