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

[rsdio at audiobanshee.com]

Pulleys, belts, and similar solutions involve rubber that stretches, breaks, cracks, and eventually deteriorates over time.

Have you ever used a set of digital calipers? They have a pattern that is read optically, so the system knows where the slider is positioned at any time. 0-calibration is usually necessary on the affordable ones. I believe that the pattern is basically the same as the quadrature in a rotary encoder, except that it’s straight - not circular. I’m not sure how easy it would be to build something like this, but if possible then it would be a lot less problematic than something with long rubber bands.

I’m also thinking of optical mouse technology, where any surface can be used, despite the lack of a precise pattern. Also no idea how difficult it would be to adapt this sort of optical mouse technology to a sliding controller, but I imagine that aluminum rails have enough of a surface for an optical sensor to track, at least as well as a mouse.

The real questions are whether these would be too difficult to custom-make, and whether the precise pattern of the calipers would be needed for usable control, or if the optical mouse solution is good enough.

Another idea is that any system might benefit from having a center calibration marker, or something similar, so that the slider doesn’t have to be moved to one of the ends to reset the calibration.

Brian

p.s. this thread keep mentioning “soft pot,” but I’m not clear about what folks mean, exactly. Are we talking about rotary encoders (versus potentiometers)? … or is there some other distinction to a “soft pot” that folks are focused upon?


On Jun 7, 2019, at 11:40 AM, Pete Hartman <pete.hartman at gmail.com> wrote:
> I've been kind of stuck on pulleys having their axes perpendicular to the panel/pcb surface, but if they are parallel....  Ok.  That can replace the soft pot without taking up a lot of space, and makes some aspects of this simpler.  Still need a rail; those linear bearings at McMaster are spendy, but I haven't looked to see if there are less quality solutions that are "good enough" from elsewhere.  The idea of having 4 x 100mm controls on a module is a minimum $160 just for the hardware, not counting encoders, pulleys, etc. is kind of daunting for a DIY project.
> 
> Pete
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