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How to choose potentiometer

Discussion in 'DIY Motion Simulator Building Q&A / FAQ' started by DonCorleonez, Mar 15, 2016.

  1. Arihant

    Arihant New Member

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    thanks but actually there is a problem because i want to limit the movement in +/-45 deg and the smcutility has a min clip value of 255 so with this value and the specs of my 360 hall sensor, if i set the center reference value to 2.5V or 512(adc value) the movement will reach an undesire +/-90 deg. and the solution to avoid this without use gears is changing the limits of the clip value to 512 for example , so im figuring out how to change it in the ino file.
  2. Arihant

    Arihant New Member

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    i think a found a solution, in order to represent the movement of one sensor to other, for example a hall sensor 360CW can be represented as a 180cw mapping its input values to the desires output values, in a +/- 90 deg movement centered in 2,5V [512 ADC] the 360cw sensor goes from [255] to [766] and the 180cw sensor from [0] to [1023] , so we just have to map these values in the Feedback variable , im going to try it and check how smooth it goes
  3. ChargedBoost

    ChargedBoost New Member

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    These pots are listed at 1000megOhms minimum, I keep reading 10k ohm min/max. Looks like neither of you had issues... but..?

    Also, is there any advantage to going with the 180* vs the 360* for the same price? If the resolution is the same (12bit), then the 360 should give you a little more leeway in mounting errors, yea?

    180*: 6127V1A180L.5FS TT Electronics/BI | Sensors, Transducers | DigiKey
    360*: 6127V1A360L.5FS TT Electronics/BI | Sensors, Transducers | DigiKey

    Spending more on 3 pots than I did on all my motor controllers is giving me anxiety. Thanks!
  4. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    You could technically get away with 90*, if you don't use more that 40 degrees up and down, which would be the ideal, but personally I use 180 for an extra bit of headroom, see here: https://www.xsimulator.net/community/threads/hall-effect-potentiometer.4948/#post-48019

    With high accuracy, long life and unable to be damaged by over rotation, Hall sensors may have a higher upfront cost, but are good value over time.
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  5. ChargedBoost

    ChargedBoost New Member

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    Good point on the higher cost vs probably not having to replace them every few weeks (or so it seems from some of these posts!).

    I've checked out that thread and re-read that post several times this morning... from what it seems, no matter if you get a 90*, 180*, 360*, every degree is still worth "12 bits", right? So, if you use 90* of a 90* sensor, you're still only using the same 1080 bits of data that you'd be using if you used 90* of a 360* sensor... I think?

    Meaning, a 90* sensor seems like it would be more accurate, but in reality, it's exactly the same. But I assume this can't be the case, because why would they even sell smaller than 360.

    I design construction power systems, this small electronic stuff is strangely foreign to me and it's uncomfortable to admit that, haha!
  6. ChargedBoost

    ChargedBoost New Member

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    I went ahead and ordered the 180* versions. If I go beyond 90* in any direction I'm in trouble anyway. Thanks noorbeast!
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  7. Snapdi

    Snapdi New Member

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    Thank you so much for this recommendation. I was having a terrible time 3d printing gears and designing a system with a hall effect sensors. they were not cheap in Canada (28$CAD) each, but well worth it.
  8. Matthew Bangerter

    Matthew Bangerter Member Gold Contributor

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    6127V1A180L.5FS potentiometers seem to be out of stock everywhere, has anyone found a suitable replacement hall effect potentiometer?
  9. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    Any Hall sensor with these specs should do the trick: Hall Effect Sensor, Position, 180°, Flatted 4.5 V to 5.5 V, Pin, Cylinder Rotatable, 200 mV

    Technically you could get away with a 90 degree hall sensor (45 degrees up and down), but personally I think a bit of headroom is worth the compromise in resolution.
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  10. Matthew Bangerter

    Matthew Bangerter Member Gold Contributor

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    Thanks @noorbeast i spent a couple hours poking around and I found 90s and 360s in the above potentiometer but as you say 180 is really the ideal for my sim. Trouble is I haven’t been able to find many other manufacturers who make a 180 hall pot. Most are 360s and the only others I have found in 180 are one by CALT that is $42 and one by P3 that is $67 which is really more than most would be willing to pay for a POT. Mouser claims to be getting more in stock in a month or so, so I may just place an order with them and wait it out unless I can find something comparable. This one seems to be a bit of a unicorn!
  11. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    Tech related shortages are a pain and global phenomenon at the moment, it looks as though in Australia the likes of Element14 anticipate stock later this month and as they are a global distributor that likely applies elsewhere: https://au.element14.com/bi-technol...fs/sensor-hall-0-2v-20v-to-10v-pin/dp/2319662
  12. Matthew Bangerter

    Matthew Bangerter Member Gold Contributor

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    Amen to that! I found this interesting site that shows stock across all vendors. looks like some company(s) that use(s) these made some massive bulk buys in september and december. Good to know other vendors are expecting them next month as well
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    Last edited: Apr 1, 2022
  13. Zed

    Zed VR Simming w/Reverb Gold Contributor

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    Hey Boost, they actually are different but in practice it’s not a huge deal. It’s the same kind of thing with “filling” an ADC. You get the best resolution if you use all the bits but that may or may not matter.

    First off, 12 bits is 4096 steps and 10 bits is 1024 steps. With a 10 bit resolution over 180 degrees, that makes each step equal to 0.17 degrees. 10 bits over 90 degrees is 0.088 degrees per step - twice as fine of step size. If the actual range of motion matches the sensor, you can “see”/resolve smaller motions. But use too big of a range sensor (e.g. using a 180 degree sensor for 45 degrees of motion) and the smallest motion you can resolve is 4 times as the size as if they match properly.

    For example and just using whole (unrealistic) numbers so it’s easier to think about, if you have 45 degrees of travel and your ADC can resolve 1 step per degree, you could detect a 1 degree movement with 45 total steps. But use a 180 degree sensor and you wouldn’t see a change in output until you move 4 degrees since 45 steps over 180 degrees is 4 degrees per step.

    So which range of sensor you use matters but in practice, with enough bits of resolution, it may not be a big deal. There’s other considerations but that’s the jist of it.

    The bigger problem comes in going the other way - you simply can’t use a 45 degree sensor in a 180 degree application. In a feedback loop you really don’t want your sensors to run out of range or things can break.

    (edited for clarity)
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    Last edited: Apr 2, 2022