How a quarter shrinker works

This machine is capable of shrinking coins. What you’re looking at is actually a 3D model of the Geek Groups impulse generator, which is called Project Stomper. The model is used to explain how induction shrinks a quarter to the size of a dime.

The grey chamber to the left is a reinforced containment device. It’s a safety feature to keep people in the same room as the Stomper safe from flying particles which may result from the forces this thing can put out. You see, it uses a mountain of magnetic energy to compress the edges of a coin in on itself.

As the video after the break illustrates, the main part of the machine on the right starts off by boosting mains voltage using a microwave oven transformer. This gets the AC to 2000V, which is then rectified and boosted further to get to 6000V DC. This charges three huge parallel capacitors which are then able to source 100,000A at 6 kV. When it comes time to fire, the charge is dumped into a coil which has the coin at its center. The result is the crushing magnetic field we mentioned earlier.

This isn’t a new concept, we featured a different coin crusher build in the early years of Hackaday’s existence.


  1. addidis says:

    Nice post. I was wondering exactly how you shrink a quarter.

  2. tomdf says:

    Forgive my ignorance, when the coin gets smaller, what happens to it’s internal structure? Do the atoms and molecules get squished closer together? I’ve never really understood density. Like, how can steel be less dense than lead if they are both completely solid. Magic?

  3. magnotto says:

    Help me out here.. How does a “crushing electromagnetic field” crush this non-iron object?

    Or is it that the induced currents just heat it?

    • Steve says:

      magnets don’t just effect ferrous metals. Depending on the strength of the magnet, just about anything can be effected in one way or another. If you want to test this, make a pendulum out of aluminum foil and swing it from side to side. then do it again under the same conditions but put a neodymium magnet beside the path of the pendulum. it will go ALLOT slower

      • willrandship says:

        That would be, specifically, demonstrating eddy currents. Eddy currents occur when a magnetic field pulls on the electrons in a conductor, IIRC. And, since everything is somewhat conductive, voila.

        FYI this is how generators work. The windings of copper match the flow of the eddy currents, turning mechanical work on the magnet into moving electrons.

    • Steve says:

      I love coin shrinkers, I really do! I just can’t get over the fact that they are machines that cost thousands of dollars that literally eat money and poop out condensed slugs with images of presidents as if they aged 30 years. hey if you put a glass of water in it would you get a block of ice?

      • JB says:

        Hard water? :P

      • JB says:

        Not intentional to poop on their parade, but…

        “Defacement of currency is a violation of Title 18, Section 333 of the United States Code. Under this provision, currency defacement is generally defined as follows: Whoever mutilates, cuts, disfigures, perforates, unites or cements together, or does any other thing to any bank bill, draft, note, or other evidence of debt issued by any national banking association, Federal Reserve Bank, or Federal Reserve System, with intent to render such item(s) unfit to be reissued, shall be fined under this title or imprisoned not more than six months, or both. ”

        They recorded themselves and posted it online.

    • maglinvinn says:

      there’s a lot of articles out there that explain how aluminum slugs are the choice ballistic solution for naval coil guns currently in production…

      meanwhile, the way i understand it, the 10 turn coil is actually like a transformer, and the coin represents a single turn. Between getting very hot (the coins are almost too hot to the touch immediately after a discharge) and the emf fields, the coin collapses in on itself, or rather, its magnetic field.

      instead of trying to accelerate a mass out of a barrel, imagine trying to hold that mass in place and subject it to those same forces uniformly.

      meanwhile, The Geek Group does have another impulse generator:

      that can send a non magnetic aluminum can soaring, imparting so much force that the can, while not in motion, resists the acceleration to the point that its bottom caves in. That unit also turns harddrive platters into funnels … there’s a particularly amusing point where a plastic pony (yes, my little pony) sitting on the ring offers enough resistance that the ring fails under its feet and the legs are sticking through. meanwhile, the only mechanical motion in that device is the high voltage contactor to discharge the circuit. long story short, there’s a incredible amount of energy being discharged in a very short window of time, and we’re able to capture that and do some amazing things with it… which is the point of being a geek.

  4. nato says:

    So 6kV @ 100,000A = 6*10^3*10^5 = 6*10^8 watts = 0.6 gigawatts. Run two of these simultaneously and you basically have “one point twenty-one gigawatts of electricity!!!”

  5. Darren says:

    There must be a better application for this than mangling a quarter. Is the effect the same for objects of homogeneous material (say a steel slug), rather than the sandwiched materials from which quarters are made?
    The graphics are nice tho….

  6. Drake says:

    Their 3d software needs a steadycam …

  7. backSlider says:

    So if you ran a coin through this enough times you would get a ball or a rod? Or maybe an hour glass? That is a ton of power. How efficient is this compared to a press and hydraulic motor?

  8. spliff666 says:

    This isn’t very convenient for those of us that need to shrink things whilst on the go, but I’m sure this will be overcome once they release a handheld version

  9. maglinvinn says:

    hey guys, i have the pleasure of being on the team that developed this particular crusher, and i’m excited to see it receive such a popular response. We have run coins multiple times in the system, but after the first go they have a tendancy to destroy the cap blocks that hold them in the coil. We’ve also shrunk tube stock in the machine, with very interesting results. Stomper, being the Mark IV variant of the machine was developed specifically to shrink coils, and we’re already working on V and VI variants, though the powers that be don’t want me to say anything about those :) The first three MKs of this build were strictly testing of the capacitors and charging circuits. MK3 didn’t have the benefit of a blast containment, and i am the proud owner of a shirt that has an interesting gash in it where a peice of the copper coil decided it was time to illustrate why that was an important feature.

    of all the comments i see, nato, yours amuses me the most. consider it done. There’ll be, come hell or high water, a video demonstrating the magnetic prowess of 1.21 gigawatts.

  10. tmbomber says:

    Here’s a video showing initial testing and the first successful run:

  11. n0lkk says:

    With the understand nothing can be perfect,I’d have to say the geek group may have created the ultimate hackerspace. I really don’t keep up to date on their projects, so I wonder if this is a new reiteration of thumper. The animation doesn’t resemble the last thumper I have seen. This might be the portable version they mentioned they where working on. In any event they are an awesome devices that store & discharge an awesome amount of potential electrical. energy. The comparison of the capacitor bank charge & discharge times is an interesting fact.

    • tmbomber says:

      This is Stomper, Thumper’s still there. The portable version you heard about, Kicker, was finished about two months ago. A portable ring launcher, Tosser, was finished last week. So The Geek Group now has four impulse generators.

      Oh, and as to squishing. A member took a quarter into his college metallurgy lab and found the “Rockwell Number” increased a bit. In theory that means the volume decreased “a little bit” :)

    • chrisboden says:

      Hey there guys. This is Stomper, not Thumper. The portable version is Kicker (a smaller version of Thumper). I’ve submitted links of all of the recent projects to HaD and haven’t seen any post or gotten any responses. The Geek Group is certainly interested in sharing with HaD and I would welcome a contact there to get a hold of for submissions and first peeks at our latest work.

  12. Frank Cohen says:

    Pretty damn cool. Now I know how to shrink coins should the need arise.

    Incidentally, I watched some of the Geek Group videos on YouTube earlier today. Anyone else find Chris Boden to be a more-annoying version of Kevin Rose?

  13. Whatnot says:

    If you invert the flux capacitor you can drain a liquid from it that when rubbed on 20 dollar bills turns them into 50 dollar bills.

    But I guess they can’t mention that for legal reasons.

  14. maglinvinn says:

    i think mentioning:

    might be handy, since the other video states the higher price for these unique bits of the geek groups history :) regardless of price, the first half of the video captures exactly why i enjoy giving my time and energy away for free to the geek group, starting with irresponisbly loud noises and ending in motherfucking robots. :P

  15. Solenoid says:

    I guess it’s like Cave Johnson said: “isn’t about why, it’s about why not!”.

  16. meistro says:

    How about popping a lump of coal in there? Will it come out all nice and sparkly?

  17. shrinkage says:

    Could you do this with an arduino? I mean, could you shrink an arduino using this?

  18. bigattichouse says:

    I’ve always wondered why the principle wasn’t combined with the Farnesworth Fusor, just to see if you can create “pulse fusion” instead of the nice little orbits you see whenthey operate in star mode… not saying it would increase useful energy production – but you might increase output.

  19. agtrier says:

    A machine for shrinking money? What for? Inflation does the same trick all by itself.

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