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I want to sense position along a slightly curved metal rod (length 100mm, diameter 5mm) for a project. For the wiper element, I'll be using steel wire of diameter 0.3mm, the length of which runs perpendicularly along the rod's length. I've tried wire-wound techniques, but they pose issues for my project such as durability and a lack of surface smoothness. I'm thinking of creating a new rod with the same dimensions made out of a material that would be durable enough to withstand heavy usage. I was looking at carbon based plastic materials since they offer high resistance, but am open for advice. I want to be able to mould the material into the shape of the rod in question.

Is this a good way to go, and if yes, what material would suit best?

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  • \$\begingroup\$ How much usage are you anticipating? One person's "heavy usage" is another person's "light usage". Every day? Every hour? Continuous? \$\endgroup\$
    – jonathanjo
    Commented Mar 30, 2020 at 8:06
  • \$\begingroup\$ @jonathanjo Thanks for asking! In any session I'll be using it for an hour or two with gaps of a few seconds at most in between usages. The frequency of these sessions will vary; at times it could be a session each on a couple consecutive days, and at other times once in a week. \$\endgroup\$
    – Teetow
    Commented Mar 30, 2020 at 15:25
  • \$\begingroup\$ @Teelow It sounds like some kind of exercise machine! I forgot to ask what kind of accuracy/repeatability you need. \$\endgroup\$
    – jonathanjo
    Commented Mar 30, 2020 at 16:15
  • \$\begingroup\$ @jonathanjo Sorry for not being more specific! I'm building a fretted musical instrument based on the sitar for which the rod(s) I mentioned would act as frets. The instrument provides room for an impressive amount of string bending, and I want to be able to accurately capture the continuous movement of the string along the frets. While I don't know what metric is used in this case to measure accuracy/repeatability, I would ideally want it to be as accurate as possible, especially since I plan on mapping these values to, for instance, pitch values on a soft synth, for which accuracy is vital. \$\endgroup\$
    – Teetow
    Commented Mar 30, 2020 at 16:44
  • \$\begingroup\$ Post all that information into your question instead of burying it in the comments. It is essential if the reader is to understand your question. See my answer to Expressiv MIDI guitar implementation for a much simpler method. \$\endgroup\$
    – Transistor
    Commented Mar 30, 2020 at 17:38

1 Answer 1

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Consider:

  • electrically conductive 3d-printing PLA -- you could use it straight, or you could 3d-print the pieces. It's only "conductive" compared to normal plastic. It has a resistance of a few ohms per centimetre (but obviously depends entirely on shape)
  • nichrome wire -- such as often used in (unwound) electric guitar strings, used for heating
  • various other antistatic protection plastics

A search for conductive plastics found TECAPEEK, which looks like the kind of stuff you're after.

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  • \$\begingroup\$ @jonathango Thanks for the suggestions. I feel PLA will offer way more resistance than is necessary, but I'll still keep that option open. The TECAPEEK plastic on the other hand does have the ideal specifications, so I'll definitely look into that more! \$\endgroup\$
    – Teetow
    Commented Mar 31, 2020 at 17:20
  • \$\begingroup\$ @Teetow have fun with your project, let us know how it goes. NB: mind you have some way not to measure the resistance of the musician. \$\endgroup\$
    – jonathanjo
    Commented Mar 31, 2020 at 17:34
  • \$\begingroup\$ @jonathango Will share updates! And yes, I'll bear that in mind. \$\endgroup\$
    – Teetow
    Commented Apr 1, 2020 at 3:56

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