3D Printed Resistor Elements / Controllers

deltamodulator

I ws thinking of what I could 3d print with this conductive filament that I have here and it occurred to me to make a controller. I imagined two bars, as shown in the attached image. Long story short, I was able to measure the resistance along the length to be 10k Ohms for the full length, 5 kOhms for the half way point, and about 1 or 2 kOhms in close proximity. So it could be a pot.

Actually it's kind of silly to print a flat structure on a 3D printer, but this was just for starters. any shape within reason is possible. For example, a bolt or a torus or a spiral. there are lots of possibilities.

Well, I'll keep you posted.

Les

3D printed Resistor Controller - 1.jpg

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3d printed resistances

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Vo1t · Posted: Mon Jun 27, 2016 10:13 am Post subject:

A spiral would allow you to change pitch smoothly by spinning your finger, then quantized jumps by swiping across spiral zones. Smooth or Jumps in one easy controller, this is genius!

deltamodulator · Posted: Mon Jun 27, 2016 11:05 am Post subject:

blue hell · Posted: Mon Jun 27, 2016 3:04 pm Post subject:

I like that spiral idea .. but apart from the practical issue of how to turn it into a voltage source ... I'm trying to work out some math on it .. the resistance per unit length would have to vary with the spiral's length, or the angle (defining a spirial in polar coordinates as r = a.Phi).

Say .. you want a move of one step (corresponding to a 2.Pi 'rotation') to amount to a semitone, or maybe to a 3rd .. or maybe 3 semitones would be a nice step value ... Now depending on if you want linear or exponential control from it the resistance will have to vary in some way.

Let's assume linear then for every 2 Pi the resistance change would need be the same, but the path length increases with angle, so the track will have to get wider to get the same resistance per unit length.

In the end you will want expo control ... probably ... like a 1 Volt change will give a frequency change of 1 octave for a controlled oscillator .. so maybe the resistance change could be matched to that .. but I didn't dare to think of the math involved in that yet. EDIT: But an expo converter could be used as well of course to go from linear to expo.

Anyway ... not only is it an interesting controller idea, it's an interesting math puzzle too :-)

Edit2 : I was assuming a higher pitch on going out on the spiral more, but could invert that too, in the case of expo control that would prolly result in a narrower trace going outward ... which may be more practical for playing it?

blue hell · Posted: Mon Jun 27, 2016 3:14 pm Post subject:

Oh, and for constructional ideas, maybe the approach people use for ribbon controllers could work. Basically that is a resistive element separated from a good conductor by some spacer, such that when you press at some point the resistor gets connected to the conductor there. There should be plenty of practical info about ribbon controllers on the webs, and at least three ideas on this forum as well.

deltamodulator · Posted: Mon Jun 27, 2016 5:08 pm Post subject:

Funny you should mention the idea of putting another resistive layer underneath the spiral, as I was reflecting on just such a notion. Thanks for taking it a step further and informing me that this is how ribbon controllers work.

The variation of voltage change with radius could be adjusted by varying the thickness of the spiral in the z direction. With 3D printing we of course control the vertical, at least to some degree. Also this opens up the possibility of all manner of crazy structures, spirals wrapped around spheres, cones, a flute controller that looks like a flute, or whatever.

I'd be interested in what might conjure up in your bright mind in the 3D printing space - I've always held you in high regard mentally as you know Jan.

Les

deltamodulator · Posted: Mon Jun 27, 2016 9:02 pm Post subject:

Excitement! I thought and thought of a way to do this. You see, it's not very simple because well, of a hundred problems. It became clear to me, as if divine inspiration guided my thoughts (which we know is true), as I created the CAD file.

It turns out that by interlocking two spirals I was able to make a varistor! This will be my first product. Vo1t, would you like to be the first customer? The model shown is defined by the following parameters:

deltamodulator · Posted: Tue Jun 28, 2016 2:23 am Post subject:

I printed one stronger fingerPot and it turned out well. This one is 12k max and about 6k min, plux ig is less sensitive but perhaps smoother, ah I can't tell really just from meter readings. Have to hook it up to an oscillator to really know...

Les

Finger Pot 2 - 1 (1).jpg

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Finger Pot 2 on left, Finger Pot 3 on right

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RingMad · Posted: Tue Jun 28, 2016 4:32 am Post subject:

Cool stuff!

.:James:.

Grumble · Posted: Tue Jun 28, 2016 1:38 pm Post subject:

I'm sure that by useing an Arduino with an apropiate conversion program it is very possible to get the right voltages.

deltamodulator · Posted: Tue Jun 28, 2016 1:57 pm Post subject:

deltamodulator · Posted: Tue Jun 28, 2016 2:39 pm Post subject:

I have been just playing around with the sensor for a while now and I'm concluding that a better way of making electrical contact is necessary. It keeps behaving somewhat erratically.

So later tonight when I get back into this I'll use some m3 hardware that I have in a Harbor Freight kit and use that to establish really good electrical AND mechanical connections. Then the results will be more readily evaluated.

Also I think it is picking up the 60 Hz from the body in air, so I will make a ground contact to minimize that.

Les

deltamodulator · Posted: Wed Jun 29, 2016 8:04 am Post subject:

I secured the electrical but not mechanical connections and the device became somewhat more expressive. Next I will make a couple of wiring mods and get some mechanical stability to improve the sensitivity.

I am a bit disappointed of this device as a controller per se, as it is less expressive than I had imagined in my mind. It is, however sufficiently expressive to be fun as a wonky control of sound, very exploratory and interactive. Fun for play.

I am thinking of designing multiple port versions and adding a mechanical base for the things.

Also I have one for sale. I'd like to see $5 for it if anyone wants to buy it. Basically it replaces one potentiometer in a test circuit or even in a small enclosed system. I'll also put the files up on Thingiverse for anyone who wants to print their own.

I can't promise any other items for sale yet because printing these things is a bit hit or miss and I can't guarantee to have anything in stock at any given time...

Les

deltamodulator · Posted: Wed Jun 29, 2016 12:29 pm Post subject:

OOPS I forgot that I cannot ever sell anything for any amount. Sorry bout that.

Les

deltamodulator · Posted: Thu Jun 30, 2016 5:52 pm Post subject:

Never mind anyway, I do not seem to be able to reliably create these things.

Sigh.

Les

deltamodulator · Posted: Sun Jul 03, 2016 5:28 pm Post subject:

well some good news - I posted it to Thingiverse and it was well received.

http://www.thingiverse.com/thing:1655695

Les

Grumble · Posted: Sun Jul 03, 2016 9:26 pm Post subject:

Just thinking: isn't it possible to fill up the space between the windings of the spiral with a printed isolator?
So than you get a more mechanical stable device.

deltamodulator · Posted: Sun Jul 03, 2016 10:25 pm Post subject:

deltamodulator · Posted: Sun Jul 03, 2016 10:54 pm Post subject:

Here is the test fixture photograph.

Les

Finger Pot 2 - 1 (2).jpg

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Finger Pot in test fixture

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Grumble · Posted: Sun Jul 03, 2016 11:49 pm Post subject:

Ow.. I think I completely misinterpreted Your meaning of how to use this device...
I thought that by moving a finger over the spiral you would introduce a kind of "shortcut" between the windings of the spiral.
Please enlighten me Rolling Eyes

how is this contraption ment to work?

deltamodulator · Posted: Mon Jul 04, 2016 12:24 am Post subject:

Hi Grumble,

I thought the same thing before I built it and hooked it up to an Arduino and wrote the Processing code. The shorting of the finger does nothing because the finger is an insulator compared to the winding's resistance which is in the neighborhood of 10k Ohms to 100k Ohms.

Instead, what I found is that the thing is flexible to the point that you can push the coils together to create shorts, and you can slide the resulting short along the length of the coil by moving laterally. This is the smaller change in Resistance.

To learn to play it well would require understanding and mastery of technique. Also I feel that a larger loop with more coils would be very beneficial.

Les

Grumble · Posted: Mon Jul 04, 2016 4:15 am Post subject:

What if you suspend the coil over aluminum foil and ground the foil?

deltamodulator · Posted: Mon Jul 04, 2016 4:45 am Post subject:

Then the coil would short out and have zero resistance at all times. Perhaps what you suggest is to place the coil on a surface that was 3D printed in the same material,and that would be interesting to try, yes. I had thought of that before but rejected it as hard to print.. Maybe I should try that next...

Les

Grumble · Posted: Mon Jul 04, 2016 4:47 am Post subject:

Is the coil to weak to be suspended over foil at a height of a few mm's?

deltamodulator · Posted: Mon Jul 04, 2016 5:49 am Post subject:

Well, the coil is springy and it flexes downward if you lift it. It can be made thicker and wider to stiffen it up though, but then it would be tough to control. It can also be made thinner and narrower like the first one I made, in which case it has very high resistance and also is not durable enough for an instrument. The happy medium seems to work best.

Les