Andrew's Blog

Joule Thief (now with Pancakes)

Since this is the first post I’ll just cover a simple-yet-effective idea. The flat motors from floppy disc drives are commonly referred to as pancake motors (due to their shape). I’ve always wanted to do something with the stators from pancake motors, simply because I think they look fairly good, as components go.

These motors are very good for hacking. They normally have their own board that is mechanically separated from the rest of the drive which makes them highly accessible (I had to unscrew a sum total of 6 screws to get at each of mine – and three of those held the stator down). The boards themselves sometimes have motor drivers and position sensors (and so forth) that in this case are not used, but in other projects could be useful. Removing the coil from the board without breaking the wires is an exercise in patience and care. I find that applying gentle upward pressure and repeatedly heating each pad in turn is the most successful method. Remember that if one or two wires break, the situation can be recovered because we only need 2 sets of coils (the stator pictured has three sets).

Unilluminated Joule Thief

I used two of the three sets of coils to make the toroid component of a joule thief circuit. The LED is supported by its legs and extends out from the middle of the stator and points back on itself to illuminate. Since I am no electronics expert I work largely by trial and error, in these cases the resistor needed for the joule thief is typically ~ 0.1kohms but since it is so variable I suggest using a variable resistor (0 to 5kOhms will suffice) to work out where the resonance is, measuring the resistance and replacing it with a fixed resistor of approximately equal value.

In related news, the stators from DC β€œtoy” motors work very well electrically, however they look fairly rubbish because they are so hard to illuminate.

With pancake motors I think the effect is fairly good for a minimal outlay of components, effort and time. Also the flower/sun like resemblance is promising for decorations, jewellery etc. Versions of the Joule Thief circuit utilising motors present in small (CPU) fans and laptop CD drives would be ideal embellishments to clothing. Although there is not really much to working out which wire is which on the stator I will write an instructable detailing how to do it (in a short while). In the mean time, more pictures (Bear in mind that these pictures are taken at a long exposure in the dark, results may vary);

Update: I realise that the red version appears very different to the yellow version in the pictures, with the red seeming much more “hazy”. I believe that this is caused by the camera, both units looked pretty much the same by eye, and both photographs were taken using the same equipment. The pictures of the yellow version are a much more accurate representation of their actual appearance (Just imagine it in red πŸ˜› ).

Update: The instructable has been published. It is accessible at this address.

3 responses to “Joule Thief (now with Pancakes)

  1. jason brooks December 9, 2010 at 2:14 am

    A novel idea. I like the the look of your setup and may use it for an enhancement of my Borg costume. On another note I wonder if your motor would spin if you used a good configuration of JT circuits. All those pulses and electromagnetism may work some magic.

    • thouton December 9, 2010 at 3:38 pm

      Hi Jason,
      For a borg-esq look you might want to mount it on a larger piece of circuit board (for example the main board from a CD-ROM drive) and then shape the board to fit a contour around other pieces, thus giving a more integrated appearance than a perfectly square unit…You might also want to experiment with the stator from a PC fan (bigger fans are easier to use, I have broken all my small fan stators by accident, they are very delicate), it is connected differently than a pancake motor but it looks very cool. (Instructable is on the way, promise…).

      I don’t think this circuit would be capable of driving a motor as well as an LED, simply because it requires the voltage spikes for the LED, which would be negated somewhat by the spinning rotor. Having said that I’m no electrical engineer and could well be wrong.

      I have had the idea to use a motor like this to spin one or more untethered ball bearings around it’s circumference, however this would require a motor driver and probably an MCU as well. Also, It would probably be best to not use as part of a costume because if it runs out of batteries you will loose all the ball bearings.


      P.s. Good luck with the costume!

  2. Masud January 12, 2013 at 11:12 am

    Great hack, I made my Joule Thief by a small toroid from CFL circuit, but I never thought of this. The most amazing part is, it looks like a flower.

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