DC Motor Whirligig Generates Power

Everyone knows that if you spin the shaft of a DC motor, it will generate power. [Vapsvus] has found a novel way to do this with no direct mechanical connection to the shaft. He simply taped a loop of string around to the motor can. This effectively turns the motor into a whirligig. Flip the motor to give the string a few twists, then pull on the two loops. The string unwinds and then winds back up, just like the toy we all grew up with.

The interesting thing is that the motor generates usable power when being spun like this. [Vapsvus] connected two LEDs to the motor’s leads to show what’s happening. The white LED glows when current travels from positive to negative, and the red LED glows when current travels from negative to positive.

What’s going on under the hood is all about momentum. As the motor can starts to spin, the heavy iron rotor remains still. Power is generated. Eventually, friction and torque from back EMF cause the rotor to spin as well. By the time the rotor is spinning, the motor can is already reversing direction.This generates even more power with current traveling in reverse.

Sure, this isn’t exactly practical, but we’d love to see how far it could be taken. Add a super capacitor, and we bet it would be more efficient than the magnetic shake lights which were popular a few years back.

Whirligigs are usefully little devices. Not only do they keep children entertained, you can use them as centrifuges.


25 thoughts on “DC Motor Whirligig Generates Power

  1. Thanks
    Great demonstration, isnt delta rotational momentum great stuff, might I
    suggest explore that with a configuration of the Faraday Paradox in a3D
    3 motor rotating mass re exploiting the static (non moving) magnetic field
    when the magnets are rotating, hence the claimed “Paradox”, what fun :-)

      1. Thanks Pez,
        Merely the luck of the draw, np Pez though is that a tortuous Seinfeld euphemism for what ? ;-)

        Um, lets not be shy, blow our horns obviously with ear muffs on & have some fun :-)
        The Faraday paradox intrigues me in more than 1D (linear axis I mean) as the issue of a rotating
        coil whilst also in a rotating magnet But, evident static fields suggests we can push against a non-bound
        or rather a fully non-tethered “stator” ie being space *alone* with nil foundation beyond that !

        I’m still working on this as time permits but, realise I have to develop another line of instrumentation
        to garner some definitive evidence but FFS (!); food, women & various entertaining biological functions
        beckon so stridently – what am I to do … mutter mutter ?

        These days anonymous nicks are quickly becoming passe, lets lift the paradigm…

        Cheers for now,

  2. Nice, I guess it could power a simple blinking circuit for POV effects… And maybe the strings could be replaced by wires to extract the energy and power a non-rotating circuit…

    1. I’m sure the wires would break fast. Maybe keep the string for strain relief and run a few strains of magnet wire along the string although I still think the wire would still break before too long.

  3. Hehe, funny and clever!

    Was saving this idea for a “Hobo Phone Charger” project, for when one get lost in the woods with nothing but a discharged phone and shoelaces, or somethin’, and needs to charge the phone or die.

    P.S. Some people might simply die without their phone even when not lost in the woods!

    1. Adding a flywheel to the rotor, which both would be stationary would increase the inertia making more current! Power takeoff would be through some flexible twistable wires along one of the strings. This is clever in the most intelligent way: You have taken a cheap commonplace dc motor and substituted a complex expensive gearbox with a piece of string to make a 5 cent phone charger! The beauty of it is that most of us have had sufficient knowledge of dc motors and a button on a string most of our lives to invent it, but you were the first to put the marbles together. Brilliant.

      1. Thank you, but I’m not sure I was the first who thought about it, and also I’m not the person who made the video from the article. I had a similar idea some months ago, when saw the button string toy from my childhood used as a blood centrifuge. I was then thinking about a survival kit made out of a small magnet and a piece of wire, a kit so flat that can be easily kept in a wallet or in a phone’s case. I told about it some months ago to a friend, then kept the idea for a project in the Hackaday Prize competition, for Wing, Wheels and Walkers phase. Long story short, I didn’t enter the competition until 2 days ago, only a week before the deadline. So it was time at most for only one project.

        I had to choose between these 3 of these new ideas of mine:
        – Hobo charger
        – Reinventing the wheel as a holonomic drivetrain
        – An slowed down articulated pendulum running in lowered gravity (on Earth)

        I picked the second idea for the Hackaday 2017 “Wing, Wheels and Walkers” competition. And here I shamelessly plug a link to it, because now I’m too upset (feel scooped) to be modest: https://hackaday.io/project/26004-the-robot-with-balls-experiment

        Of course, I don’t expect people to believe my story, but it’s true.

          1. Phew! I was afraid being guilty in the first place for lots of typos, bad English and bad manners. For the rest of the accusation – pleading not guilty, not my fault!

            Seriously speaking, I was very frustrated while typing those messages, and now I regret them. I wish I could delete those messages, especially the second one, but it’s not possible.

            Lesson learned: To chill down before typing.

      2. I came to mention the flywheel. Although.. there isn’t a lot of clearance in there between the shaft and the string. If the flywheel touches the string it might just cause it to spin with the motor housing and there goes your power generation.

        I’m not sure how to use this to charge a phone though. Like probably 99% of everyone here that was one of my first thoughts too. How do you get the electricity from the phone to the motor though? wires running along the string to a stationary phone would break very fast as well as rob the system of the momentum that helps re-wind it. Actually placing the phone in the middle with the motor would change the center of rotation so that it is no longer right down the shaft. Would it turn as efficiently? Would it turn at all?

        This may be one of those really cool ideas that just can’t be moved beyond the toy stage. That’s ok though.. it’s a nice toy!

        1. Maybe a super cap placed behind the motor, parallel to it? Charge up the cap then stop, discharge into the phone, charge it up again, repeat… It kind of sounds like moving a lake with a bucket.

  4. Interesting and neat, but certainly NOT more efficient that the “shake” lamp. The motor requires quite a lot of acceleration to make the rotor (now more like an oscillating stato-rotor; in Czech we have a perfectly fitting word “kotva” = “anchor”) move in relation to the stator. In contrast, you don’t have to shake the “shake” rod at all, just flip it one end up, the other down and vice versa. Requires much less energy.

    1. I’m not sure of that – especially when you consider the human factor. The shake light requires you to accelerate your entire arm up and down to generate power. While this requires tension to be applied and released. Which do you think would tire you out faster? I’d say the shake light.

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