Thor’s Hammer Build Recognizes Its Master’s Hand

electromagnetic-thors-hammerOnly those who have completely insulated themselves from modern pop culture will miss the meaning of a Mjolnir build. It is, of course, the mythical hammer wielded by Thor, and only Thor. It’s a question of being worthy; a question solved perfectly by this electromagnetic Mjolnir build.

Using an electromagnet is smart, right? Just plunk the thing down on something metal (that is itself super-heavy or well-anchored) and nobody will be able to pick it up. It starts to get more interesting when you add a fingerprint reader, allowing only Mjolnir’s Master to retrieve it from atop a manhole cover.

But for us the real genius in the build is that the hammer isn’t burning power from the four 12V batteries most of the time. All of the people in the video below could have picked up the hammer had they first nudged it off the metal plate with their foot. The build uses a capacitive touch-sensor to enable and disable the microwave over transformer used as the electromagnet. An engineering trick like this really separates the gods from the posers.

We hate to admit it, but this is probably a cooler build than the Telsa-Coil powered Mjolin that [Caleb] built a few years back. Still, his held up as the best for many years, and if you’re going to be displaced this really is a build worthy of the new title: coolest Mjolnir hack.

[via Engadget via Taxi]

52 thoughts on “Thor’s Hammer Build Recognizes Its Master’s Hand

      1. I don’t know, have you ever seen those electromagnetic door locks? There’s no chance you can bust one of those open because the field is so strong. I don’t think a permanent magnet in the same size restraint could outperform that.

        1. I have worked in the security industry for a long time, typical mag locks are rated at 1200lbs. This looks like it wouldn’t fit a full size mag, half mags are just that, usually rated about 600lbs.

        2. you can easily bust past them, most are set to release after a certain amount of time due to safety reasons. I.E. people trying to flee a fire, after 60 seconds of constant pushing they release.

          They also set off the alarm when they do it, but they release.

          1. where’d you get that information? or did you just invent it?

            now you can drill the windings and that will permanently release the lock. Works great on a double door where there is a gap between the two doors and the mag lock is straddling the two doors.

            Other simple maglock defeat is just tape some cardboard to the lock face.
            door will sort of lock but can easily pushed open.

          2. how would they sense the torque pushing against the door? you would need a bit of sensors and circuitry for that, and that adds cost. Most of the locks I’ve seen installed have an emergency exit switch nearby that opens the circuit to the lock.

          3. @andres:
            These don’t measure the force applied. They use a certain amount of current to hold the plate to the electromagnet. Forces beyond the strength of the magnet simply overpower the magnet. (AKA the breakaway force) If you’ve ever tried lifting a magnet off a metal surface, or seperating two magnets, you’ve already experienced this. If you notice, as soon as you put enough force into seperating it, it suddenly moves. This force can even be tested.

    1. if you watch carefully, right around 1:00, the coil is only active when someone’s hand is near the handle. So most of the time it is just sitting there doing almost nothing. I guess you could stand there holding on to it for a hour or 3, but i’d get bored well before then. Though i have to wonder if a rapid kick to the handle would knock it over without engaging the magnet.

  1. There are places on the internet where you can buy some fairly strong neodymium magnets. Flux path switching can be more of an art than a science at times. (unless you’re willing to for go the garden shed aproch and actually do the math)

    1. My thought would be to put the RFID in the toe of the guy’s shoe. That way the authentication process would start before he even bends down, so he could grab it straight away. The current situation where he holds it for a second before it lifts kind of hurts the illusion too. If the magnet released the exact moment he grabs it, it would be perfect.

  2. +10 points for finding a new use for a MOT. Is he just running DC through the primary – with the secondary removed?

    I wonder what voltage he is using and if it’s a 110V or a 220V primary? Any guesses?

    I am guessing the SLA’s are 12V and they’re seriesed.

  3. Next V2.0, add a shock sensor that engages the magnet when it is bumped. Leave the magnet engaged for a random period of seconds so they don’t figure out the nudge, wait, nudge wait.

  4. How about this? Put the powerful electromagnet in a base unit instead of the hammer like a low-profile wooden box on the ground. Run the power off of 110 VAC (or 220 in non-USA) mains with the flat power cable (i.e. air-conditioner cable) hidden under a long narrow carpet. Use a standard common sledge hammer with nothing embedded in it at all. The box would hold the hammer down 100% of the time and with great force even through wood.

    Off to the side of the box and far enough away is a laptop with a shotgun microphone or parabolic dish (i.e. plastic salad bowl?) with a microphone aimed at the box area. A program running speaker-independent voice recognition (standard for Windows 7 and up I think) is listening for a secret phrase. When it hears it, it sends a signal to the USB or parallel port to fire a releasing relay for a few seconds. The relay is in series with the mains to the box.So that no one can master the secret phrase it uses a rolling password scheme which changes the pass-phrase after every use and never repeats same pass-phrase. Of course the MASTER knows all of the phrases and sequencing by heart (i.e. open sesame, etc.). The MASTER has no gadgets on him/her only their voice (and maybe a cheat sheet of sorts :P ). A small incandescent lamp could be installed in the box to indicate magnet is engaged or disengaged.

    In battery-only scenarios where there are no mains, one could save on battery power by installing a PIR security motion-sensor at the box which detects anyone approaching and turns on the electromagnet for lets say 1-5 minutes. The more you move around the longer the hold is. Of course the same pass-phrase release scenario with a smaller gauge under carpet wire to release battery voltage to box.

    Of course you could probably use an Adruino instead of a laptop. And since an Arduino would be smaller, you could probably hide everything in the box including a local microphone. The only cable coming out would be the mains cable. However, if battery-operated no cables or wires at all. It could all be self-contained. With the small Netbooks today you could probably do the same thing just bypass the clam-shell display closing sleep switch or use a tablet with USB access.

    I know someone can improve this kernel of an idea…


  5. Fingerprint sensor is in a weird place and too slow to react, making the trick obvious. Other than that, nice build. A remote to turn the magnet off and let some kids feel like they are ‘worthy’ would be a nice addition.

    1. A remote in general might be easier, but I can see the attraction in keeping it in one piece. This really is a loyal hammer, only it’s owner will ever be able to lift it.

      For the time it takes to react to the fingerprint, just “take the strain”, make a grip, then pretend you’re tensing your muscles or something. Bit of drama for the couple of seconds it takes.

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