[sdiy] Two parameter mechanical controller thoughts....

bbob fluxmonk at gmail.com
Fri Jun 7 14:07:24 CEST 2019

i'd go wireless - bluetooth or ble from whatever controls are on the
carriage, and a time-of-flight sensor to measure the carriage position.
there's probably a lot of hardware bits you could repurpose from folks
developing diy 3d printers for the carriage mechanics.

On Fri, Jun 7, 2019 at 7:19 AM thresholdpeople via Synth-diy <
synth-diy at synth-diy.org> wrote:

> If I were going to build it, I'd lose the softpot and replace it with a
> mechanical drive mechanism - either something built onto linear bearings,
> something on a guide rail, or a telescoping slide - turning either a
> 10-turn pot, depending on the gearing of the mechanism, or an encoder.
> Check out McMaster for different possibilities -
> https://www.mcmaster.com/linear-bearings. These types of things can be
> DIYed as well.
> With a rigid carriage on some sort of guide rail system it'll be easy to
> mount an additional encoder, and an LED or anything else you need there.
> For wire management, if you want it real clean and fancy something like a
> cable and hose carrier will do it.
> Boris
> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> On Friday, June 7, 2019 2:13 AM, Pete Hartman <pete.hartman at gmail.com>
> wrote:
> At the risk of depriving myself of a market advantage....
> If you haven't seen videos of the Collidoscope, go to youtube and watch
> now.
> The control mechanism -- encoder sliding in a slot on some kind of
> carriage that presses down on a softpot underneath -- strikes me as a
> really appealing and expressive means of controlling two parameters
> simultaneously. However, they don't provide a lot of mechanical detail at
> the micro level (that I've been able to find... they call out the encoders
> and the wiper for the softpot etc, but not the carriage mechanism).
> I've been thinking about how this could be accomplished as just a CV
> generator -- one CV that reflects the position in the slot, and one that
> reflects the position of the encoder. Would be good to use an LED shaft
> encoder as well, so you could light the LED with a brightness that reflects
> the level of the encoder, so you can look at a glance and see what both CV
> values are, roughly.
> The tough problem to solve here, of course, is the mechanical carriage. I
> need 4 signals and ground to deal with the encoder and an LED. Maybe only 3
> signals, but I'm going to go with 4 cos it's symmetrical. Don't want to use
> a set of wires rolling back and forth for the signals because they will
> wear out and break off.
> My first thought is something to somewhat mimic a slide pot. PCB that
> holds the encoder, has a hole for the wiper screw. Glue a nut to the PCB on
> the bottom side, screw the wiper through it and adjust for the height to
> the soft pot on a PCB underneath.
> PCB has 4 spring contacts (two on each side of the encoder) that ride on
> bare traces on the PCB that comprises the panel These are on the "top" of
> the carriage PCB, pressing up against the panel. These are the 4 signals.
> PCB rides on a pair of rails that are made to be soldered into the panel
> PCB, tied to ground, and the PCB has a pair of bare traces that connect
> into its ground. So the rails carry the ground to the carriage PCB.
> SO here is where my ignorance of what's out there takes over... is there
> anything like this rail "out there" that I could buy off the shelf? What
> about the spring contacts? I'm concerned about the rigidity of the rails --
> pressing down on the encoder while it's in the middle of travel shouldn't
> be able to deform the rails. What about twisting of the carrier PCB? I
> don't want it to rotate off the rails. Presumably if the encoder has a
> reasonably loose rotational resistance it won't be a problem, but I don't
> think that's a good thing to assume. I have a bunch of copper wire of
> various thicknesses, and my initial thoughts about this were I could
> prototype using that as springs and rails, but I definitely don't think
> copper has the necessary rigidity for a 100mm long throw in the slot, which
> is what I'd want to have.
> Is there some other approach that would work better/more reliably? Are
> there pre-made slide pots that have encoders built into their shafts? Am I
> missing some other prior art on how this could be accomplished?
> Obviously I'm inspired by the Collidoscope; it's not a particularly novel
> mechanism. But it's not something that "exists" in a form generally usable
> for synths either.....  At least not that I've seen.
> Thoughts?
> Thanks
> Pete
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