Potentiometer

is there any restrictions to using a Potentiometer on our robot?

just wire it with the correct gauge wire for the breaker, and connect it correctly to the cRIO, not a motor controller. Oh and make sure the parts are under the $ limit. other than that I think you will be fine.

What are you planning to use the potentiometer for? :slight_smile:

Typically potentiometers are going to be wired into a port on the analog breakout which provides power and is already downstream of a breaker.

that works too, just another way of saying meet the wiring resrictions! (hey, mebbe its a ginormous one and needs 10 amps or something :ahh: )

Actually, it would be a fairly tiny one by Ohm’s Law, assuming we’re talking 12V since its through a breaker

V = IR
12 = 10R
R = 1.2 ohms

Our pots are nearly 5000 times ‘bigger’! Of course, I’m just being silly now.
Back on topic, why do you say not to connect it to a speed controller? The position control mode on Jaguars can use the potentiometers (though I don’t personally find it actually works that well).

EDIT:
Actually, since you’d be dissipating about 120W, you would need a fairly large physical pot to absorb that kind of heat!
Ok, really I’m gonna put on my serious face now :slight_smile:

Matt

If you are asking if you can use a potentioimeter the answer is yes. If you are asking how to connect it check the following FIRST document:
http://usfirst.org/uploadedFiles/Robotics_Programs/FRC/Game_and_Season__Info/2011_Assets/Kit_of_Parts/Analog_Breakout%281%29.pdf page 5 for this:

[LEFT][FONT=Cambria-Bold][size=3][FONT=Cambria-Bold][size=3]How do I connect a potentiometer?[/size][/size][/FONT][/FONT][/LEFT]
[FONT=SymbolMT][size=3] [/size][/FONT][FONT=Calibri][size=3]Connect the wiper to the input pin – Top row.[/size][/FONT]
[LEFT][FONT=SymbolMT][size=3] [/size][/FONT][FONT=Calibri][size=3]Connect the other two pins to +5 and ground – Middle and bottom rows.[/size][/FONT][/LEFT]

[LEFT]As for the Power required if you use a 1kΩ you would only dispate 144 mW at 12 volts and with a 10kΩ of course 14.4 mW. 1/4 potentiometer would be fine. [/LEFT]

[LEFT]A good 10 turn pot works wonderful for positioning feedback.[/LEFT]

We found an old pot in our junk drawer that we are using to get feedback for our arm. Why would you want a sensor that can turn 10 rotations when your arm may only move 180 degrees. Aren’t you using a small range of the possible output voltage?

So true… A 300 degree one should be fine for most apps but I was thinking of a tower type of application that would have multiple motor rotations. One train of thought problem…

And I didn’t think of using it on a idler or a sprocket. Can’t wait to try that out on the next bot :slight_smile:

One more thing. I was expecting the output voltage to be linear (constant angle/voltage) but we found that not be remotely true.the first 40 degrees give us roughly a change of .3 volts but the next 45 degrees gives us a change of 1.7 volts. Is this normal?

One analog input vs many digital inputs… I’d go analog…

It sounds like you picked up a “log” or “audio taper” pot. They’re used as volume controls. We accidentally mounted one on our 2004 robot’s wrist joint, and it was ridiculously difficult to program for.

If I were you, I wouldn’t use it. Get yourself a “linear taper” one. You’ll be a lot happier.

Not all pots are linear. Some are called "audio taper and have a logarithmic function to adjust sound volume so turning the pot approximates what your ear perceives as linear. I’ve also run into some very strange special purpose pots made on the surplus market. These have a very odd response. Pots aren’t that expensive. Go buy one that’s linear, and of good quality if your arm’s position is going to depend on it. Remember, if you are using a feedback circuit to help drive your arm, then the quality of the pot becomes a safety issue!

Ignore the troll. (location listed as /b/, ridiculous suggestion, rookie year 1919, etc.)

before that it was “4 chan /b/ board” but agreed. The first rule of internet usage: Never feed the trolls.

were too busy feeding the watchdog and the watch puppies :ahh:

Can we train the watchdog to hunt trolls? Should get rid of those pesky watchdog not fed errors and clean up the forums. Win-win.

If you’re looking for good potentiometers, I would suggest Spectrol or Bourns.
I have a 10-turn Spectrol pot myself. Its linearity is rated within 0.25%.
(typical pots don’t HAVE a rating for linearity)

Of course, feel free to try a cheap potentiometer, and see where it gets you.

…But if you do buy a cheap potentiometer, or actually, most potentiometers (but cheap ones mostly). Even though they rotate at 270 degrees, don’t expect to get all 270 degrees of data from it. Cheap ones get probably 200 degrees of reliable data. Decent 270 degree ones maybe a little more.

My point: don’t get a potentiometer that will just have enough rotation to work. It won’t.

Agreed, plus you want to be able to sense your soft limits before you’re right on top of them, which requires some extra room at either end of the range.

We’ve used 300 degree pots for about 250 degrees maximum range, with some breathing room.

Matt