Hackaday Links: December 11, 2011

Drilling square holes

We’re still a bit baffled by the physics of this, but apparently it’s possible to drill a square hole with a round bit. This video shows square holes being milled using a cutter which is offset from the center of the bit. [Thanks Jordan]

LED Motorcycle headlight driven by mains

[William] found a way to use a big capacitor and bridge rectifier to run this H4 LED headlight bulb in a mains sconce lamp.

Electronic slide whistle

Here’s an electronic instrument that [Dorian] made. It uses a linear potentiometer and a button and works much like a slide whistle would.

Robot rocks out to Daft Punk

[Adrian] didn’t just make a robot arm out of CD cases and a mints tin. He built the arm, then made a music video featuring it.

More light-pipe sensor experiments

[Uwe] has been working on an input sensor using a flexible light tube. It is a similar idea to these optical flex sensors, but [Uwe] tried several variations like filling the tube with alcohol.

23 thoughts on “Hackaday Links: December 11, 2011

  1. The square drill bit is based on the shape of the Reuleaux Triangle.
    Near the end of the video linked to my name you can see how it works. Because the triangle does not have a fixed center of rotation it wobbles around within a holder, which leads to the awful clunking sound you hear in the video.

  2. “The reactance of the cap means it will drop the voltage down but not dissipate much power as the current will be out of phase with the voltage. Hence the drop is efficient (i.e. no heat). ”

    It’s true that it won’t create heat at the point of consumption, but a large capacitor like that will create a parasitic current that will cause your pole transformer to heat up. While the power to the load is indeed VxI, the transmission losses still follow RI^2

    Large amounts of parasitic current may also trip breakers even though it doesn’t transmit any power down the wire.

  3. How much ripple current is that cap seeing?
    We did a project that took 5Vpp and stepped it up to 8VDC, and used a capacitor multiplier. Not quite what he’s doing. But anyways with a 40 ohm load we had on the order of 100s of mA flowing through the cap. It was only rated for 1.4A. Anyways with 60 times the voltage, I can imagine there could be an issue with the amount of current that cap is passing. Combined with the ESR of electrolytics being pretty high…it may fail. And I don’t see any fuses/protection.
    Might want to re-think that one. I got a 120 to 12VDC converter for halogens bulbs at about $6 at the local home depot.

  4. When the light is turned on, the cap is initially discharged (ie it’s a short circuit wrt the current) therefore the leds will get a 120 V spike. If they don’t die immediately is because they already have resistors inside, but they’re calculated for a 12V supply, so they won’t last long.

  5. oh may i add using mains to light an LED is nothing new

    we used LEDs and 100k ohm resistors as indicators for blown fuses

    place a 100ohm resistor with an LED and a diode or just 2 LEDs … like

    they can take the voltage just fine

  6. Re: square holes, this wouldn’t be a surprise if you remembered playing with Spirograph. Did you know that there’s a direct correlation between the decline in Spirograph and the rise in gang activity?

  7. Electric Slide Whistle, for v.2 he should buy a cheap trombone and build this into is, they have electric guitars, don’t that.

    Drilling Square Hole, no mater how many people try to explain it all I have to say is, “Drill square holes, WFT!?!?”

    1. But it’s not really really drilling a square hole. Just something that approaches a square.

      The mechanism itself is kinda like a scotch yoke, but in two dimensions instead of one. If you can imagine a slot being cut by a pin in a slot guide, you can imagine a mechanism that does the same for two axis at a same time, drawing a square-sort-of.

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