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Anyone here ever make a hot-wire foam cutter using PWM with the Propeller? — Parallax Forums

Anyone here ever make a hot-wire foam cutter using PWM with the Propeller?

ElectricAyeElectricAye Posts: 4,561
edited 2009-10-09 05:52 in Propeller 1
I'm faced with making some curvy shapes from foam and, rather than hack my way through it all with a bone saw, etc., I thought about using PWM to control the current through a hot wire. Considering how cool the Propeller is and how hot are the intellects here, I also pondered the possibility that somebody here might have figured out a nifty way to monitor the wire temperature so it could be niftily controlled. Anybody have any thoughts about - or experience with - this?

many thanks,
Mark

Comments

  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2009-10-09 04:18
    ElectricAye said...
    I'm faced with making some curvy shapes from foam...
    Airfoils for an RC glider, perhaps? smile.gif 'Sorry, no direct experience, though.

    -Phil
  • ElectricAyeElectricAye Posts: 4,561
    edited 2009-10-09 05:19
    Phil Pilgrim (PhiPi) said...

    Airfoils for an RC glider, perhaps?

    Alas, if only I had the time for such frivolities. No. No RC fun for me. This is to cut foam insulation for one of the instrumented devices that fits in the freezer we use for testing. I thought about using that expandable stuff you squirt from a can, but I can't bear to deal with that stuff. Last time I used some, some of it magically got transported into my hair and on my clothes. So I thought I'd try a hot wire this time and take my chances with burning down the building.

    Any chance some of your fancy IR detectors could accurately monitor the temperature of a hot-wire somehow???

    BTW, Phil, the Mosfets you helped me with last week are holding up very nicely.

    thanks!
    Mark
    smile.gif
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2009-10-09 05:28
    Mark,

    'Glad the MOSFETs worked out! smile.gif

    The resistance of the wire may increase as it heats up. If that's the case, you could measure temperature indirectly by monitoring the voltage across it and the current through it. But I don't think my friends who cut airfoils have any special controller for the wire except for simple current limiting. I'll check tomorrow and see.

    -Phil
  • ErNaErNa Posts: 1,752
    edited 2009-10-09 05:50
    surely it's right to measure the resistance to determine the temperatur. The wires from old power resistors might be appropriate. I also found strong thin wires in the cable to the ignition sparks of a combustion motor. As a hot wire expands, it may be usefull to measure the length of the wire, which has to be preloaded by a spring. As the wire may have different temperatur due to cooling at the cutting area, measuring length and resistance gives an information about uniformity of temperatur and so to control the speed.

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  • ErNaErNa Posts: 1,752
    edited 2009-10-09 05:52
    By the way: as the wire will draw much current at a low voltage, it may be appropriate to use an old switching regulator from a motherboard.

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