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Loss of power over junctions

  1. Dec 29, 2013 #1
    Good day. I was wondering what the extent of resistance/voltage drop occurs over junctions that are made off movable parts and brushes. Electrical trains tend to get the voltage from brushes so it can't be too great, also brushed motors.

    In my case I was planning to run an electric brushless motor, but it is situated on a moving part, so either it was making long wires that can bend and twist a little, but that takes some space which would make my mechatronic machine larger. But then ofcourse I figured a simple coal brush or whatever like they use in brushed motors, and since this moving part will be moving far less, slower then in a brushed motor, it should last, my only concern left was weather there was a great amount of power loss in the junction between the brush and the moving part.

    I made a quick sketch of the concept, the moving part moves +/- 30 deg, around an axis.

    Attached Files:

  2. jcsd
  3. Dec 29, 2013 #2


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    Staff: Mentor

    Assuming you don't get arcs, it is just a regular resistor: P=I^2*R
    Lower currents (and therefore higher voltages for the same power) are better, but can lead to problems elsewhere.
  4. Dec 30, 2013 #3


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    A carbon / graphite brush will be less reliable and more bulky than a coil shaped like the hair springs in a meter.
    You can wind say a two turn coil of metal tape to carry power to the moving part.
    I would consider cutting strips of 0.010” brass shim from a model shop. Size will depend on power.
    Avoid passing current through metal bearings. It is better to use an extra flexible conductor.
  5. Dec 30, 2013 #4
    Thanks for the input,

    I tried to get a mental picture of this but couldnt with my current education. Is there a name for what you are mentioning? Id gladly study a better solution than a carbon brush.

    Also, a flexible conductor is a possibility, that is how the original concept was. I then recently have been leaning over to brushes due to advantages on size, a brushed solution takes less space then a flexing wire, my original concept had empty spaces for wires to move around in.

    Brushed solution: possible power loss but less spacious

    Flexing wire solution: efficient but space and engineering difficulties.
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