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Making a reliable potentiometer

  1. Aug 27, 2016 #1
    Long story short : I need a good solid semiconductor material besides pencil lead

    I can't find any potentiometers that I can insert my own shaft into so I decided to try to make my own. The shaft is about 0.25" in diameter so it's not something big.

    Anyways, I know I can use pencil lead as a semiconductor to make a potentiometer but I get the feeling the device will eventually wipe off the material. I need a good solid semiconductor, maybe something I can cut with scissors?

    Thanks in advance.
     
  2. jcsd
  3. Aug 27, 2016 #2

    berkeman

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    Making your own potentiometer material and wiper material seems problematic. Can you say more about why you can't just use some standard potentiometer and adapt it to your application?

    BTW, I'm attaching a very helpful tutorial on potentiometers from Bourns FYI... :smile:
     

    Attached Files:

  4. Aug 27, 2016 #3
    Pencil lead is not a semiconductor.
    It's graphite (carbon), which is a normal conductor, but not a very good conductor.
    I don't know if there are substances with similar properties but more hard wearing, but a lot of commercially made variable resistors do use carbon.
    (and yes wearing down of the carbon track is often a mode of their failure)
     
  5. Aug 27, 2016 #4
    It will be used on the shoulder of a robotic arm to determine it's position. It needs to be mounted on the outside of the arm, which has a small shaft coincidentally to keep the joint on the axis.

    I looked online for potentiometers but...they are ridiculously bulky and have an unnecessary shaft of their own.

    Here is a rough sketch, please excuse the quick drawing work :D The red part is where I would like the potentiometer to be.
     

    Attached Files:

  6. Aug 27, 2016 #5

    berkeman

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    Have you considered using rotary encoders? That would be more reliable than even commercial pots, and I believe that this is how such robot position sensors usually are done...
     
  7. Aug 27, 2016 #6
    I've heard of them but never considered them, I'll check them out, thanks!
     
  8. Aug 27, 2016 #7

    Nidum

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    Yes - encoder is a far better solution .

    If you must use potentiometers then get some ordinary ones and use the resistance tracks and wipers from them in your own assembly . Old style radio ones are best sources of bits .
     
  9. Aug 27, 2016 #8
    The only problem I'm seeing though with the encoder is that they would probably consume more power since they require an additional chip. Price is also a factor, and I would need to build a more complex code to handle the number of clicks to determine the position. I don't mind paying more, but over time things do break and having to replace encoders might be more of a headache than a potentiometer.
     
  10. Aug 27, 2016 #9

    davenn

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    a rotary encoder will last a lifetime compared to a "pot"
    you would be very wise to take the suggestion offered by Berkeman. It is the usual way for position determination


    Dave
     
  11. Aug 27, 2016 #10

    billy_joule

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    I also recommend an encoder but if you're set on a pot the a thumbwheel pot may suit;
    b503.jpg
    Or a slide pot with a push rod could also work.
     
  12. Aug 29, 2016 #11

    sophiecentaur

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    If your Robot is going to be in any way autonomous, you are going to need an ADC to convert the output of a home made potentiometer. Why not cut out the middle man and start with a digital position encoder? Fit and forget. These things are modern and very reliable. There is a good reason why they don't use analogue pots on control knobs these days.
     
  13. Aug 29, 2016 #12

    Nidum

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  14. Aug 29, 2016 #13
    They do have potentiometers in them however they don't report back their position to the controller for some reason. I guess it's just how they're built for simplicity.

    Okay I will take your guys advice and try out some encoders instead.
     
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