Pot rotation question

[David]

This isn't off topic, but I can't reveal why until later.  It seems to me I read (I think it was here) that full rotation of a pot was about 270 degrees.  Does this mean that given a 1M linear pot, it would turn 27 degrees to give you a resistance of 100K?

[Samuel]

This sounds like a job for MultiMeterMan....

[David]

Yeah, I know I can always do it that way.  I just wanted to see if it could be determined mathematically.  I do have a very sane, sound reason.  I just don't want to reveal anything until I've got my ducks lined up...

[keko]

given

that full rotation of a pot was about 270 degrees...

it would take either 'about' 27 degrees' turns to give 100 K resistance, or 27º turns to give 'about' 100K resistance.

hope this helps  :twisted:

well....I might be completely wrong, but taking from your thoughts, I figure I might wire a pot to a radio controlled servo, and start from there.

[The Tone God]

Most pots rotate 318 degrees.

Andrew

[Mark Hammer]

It is difficult to assure how much resistance change occurs per unit rotation across the entire length of the conductive element, largely because you have both the amount of surface contact made by the wiper, the role that wiper tension plays in that, and other things that pot makers know much more about than I do such as how to produce tight tolerance conductive elements and decent low-resistance riveting of lugs to element.  Pot tapers are not promises so much as ball-park estimates, and the same goes for resistance values.

Matching a pair of even high-quality pots for change-per-unit-rotation is hard enough that many high-end audio manufacturers (booteek preamps, etc.) use ganged multi-position rotary switches and 1% resistors to produce the needed matching between channels as one tweaks volume or EQ-ing.

In principle, though, production of a pot as nominally "linear taper" means that it comes usefully close to providing a 1:1 relationship between per cent rotation and per cent maximum resistance.

[David]

OK.  I'll settle for a roughly linear relationship.  Now all I have to do is figure out how high you have to lift a 6-to-8 inch long lever connected to said pot in order to move it 27 to 32 degrees.

Where's that trig book?

Yes, I'm crazy!  But I'm on to a concept that is just crazy enough to actually work!   :wink:

[Mark Hammer]

Now David, please tell me you are not planning on having a wah-wah played by having circus midgets jumping on a see-saw connected to a pot! :roll:

[Samuel]

It's the only logical conclusion.

[David]

Very intuitive, Mark!  However, at 5'9", I hardly qualify as a midget.  Some days, though, I do feel like my job is a circus!

All right, since you figured it out, I might as well come clean.  I THINK I may have come up with a way to build a wah actuator with parts available even in my small local hardware store.

[Ansil]

cool.    are you sure you arne't a midget..    5'9" is pretty short isn't it.?

i dont' remember that has been too long ago since i saw that height.. lol.. sorry just yankin your chain

[David]

Yank away.  Keeps me down to earth.

[Ansil]

sorry i have too..  but hey dont' let it get you DOWN.. LOL..  nah it sucks being this tall sometimes. i mean i am only 6'3" but it is hard to find clothes.  shoes..  lol 14 EEEE

[Mark Hammer]

My son takes size 15.  No more shopping for sneakers OR socks at Wal-Mart.

[R.G.]

All right, since you figured it out, I might as well come clean. I THINK I may have come up with a way to build a wah actuator with parts available even in my small local hardware store.

Remember that the exact value of resistance in the wah pot isn't what matters - it's how much the wah pot varies the amount of signal passing from the collector of Q1 to the base of Q2.

I hope I'm not stealing your thunder, but one way to do this is to disassemble the pot (ala "The Secret Life of Pots" at GEO) and paint over the ends of the pot's resistive element's travel with conductive paint or copper sticky-foil, leaving only your 27 to 32 degrees uncovered. On a 1M pot, that would leave only 100K of the whole 1M uncovered (on a linear pot, anyway) and would give you a pot with a 100K value but only a short range. That's got some promise for a full pot-style rocker with a short effective rocking travel.

[David]

R.G -

Couldn't I just cop out and buy (shudder) a "Hot Potz" or something of that ilk and take care of the "problem" that way?

Also, I get the impression that what you're really saying is that the rotation of the pot needs to be limited to the range you want.  Could this not be achieved by using stops on the actuator to mechanically limit the travel range of the pot?