Building a tachometer for a spindle motor?

Discussion in 'The Projects Forum' started by spinnaker, Dec 28, 2015.

  1. spinnaker

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    I would like to build a tachometer for a spindle motor. Where I am struggling is how to sense the RPM. The two methods I have come up with so far is Hall sensor and a laser (which I am not even certain I can do).

    Both have downsides. The advantage of a Hall sensor is it is fairly straight forward and easy to implement. The downside is there will be weight (the magnet) on the spindle shaft and I am concerned that will throw off the balance. The motor will only be spinning at most 40K RPM. Do I need to even be concerned about that small magnet causing an issue?

    A laser has the advantage of having virtually no weight on the spindle other than the target material. But much more complicated than the Hall sensor option. More important it could present a safety issue, especially since the device would be permanently mounted.

    Any other ideas on how to do this?
     
  2. paulktreg

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    Slotted wheel through an opto?
     
  3. spinnaker

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    Not sure if I would be able to get a wheel on the spindle and where would I get such a wheel other than to fabricate it?
     
  4. strantor

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    Why you say this?
    Why you say this?
     
  5. OBW0549

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    You might be able to use a reflective optical sensor. Take a narrow strip of the spindle's circumference and paint half of it black and half of it white, and put the reflective sensor up close to the painted strip. Or, print out an alternating black-white-black-white pattern on a strip of paper and fasten it around the spindle.
     
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  6. strantor

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    If you wanted to take it a step further and print out an encoder disk for absolute or quadrature operation, there's apps for that.

    https://www.google.com/search?q=enc...hUKEwiEwLeA3v7JAhXHOyYKHTx7DLcQ_AUICigA&dpr=1
     
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  7. Picbuster

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    Dec 2, 2013
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    Please inform us how this spindle motor is constructed. some motors, depending on construction, have an extra winding for this purpose.
    This extra winding is sensing the rotor allowing to measure the 'slip' between the connected phase and the actual rotation.
    @ 40K rpm and a few grams on a diameter of 4 cm will make your whole house resonate.
     
  8. MaxHeadRoom

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    I have recently used the QRE1113 retro-reflector for rpm detection, some have used just a spot of white paint on the shaft, In my case I used 3M reflective tape.
    I have also used the IR opto slot type, in which you can also get the dual head type if you need to set up quadrature signals for direction detection.
    If you go with a small button magnet for the hall effect type, you can use one each side for counter balance and either count each pulse or use the bi-polar latch type for a single pulse/rev.
    Max.
     
  9. spinnaker

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    Don't know yet. I don't have it yet. Just blue skying for ideas. I am fairly certian it does not have it's own internal sensor as it is a cheap spindle and motor. But who know maybe it does???
     
  10. spinnaker

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    It is the Hall sensor itself is what has the bipolar latch feature, correct?

    The QRE1113 has both the emitter and sensor?
     
  11. MaxHeadRoom

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    There is the normal bipolar which senses either pole, and there is the latch which requires the opposite polarity to unlatch, all built in.
    The QRE1113 is all in one retro reflector, requires a resistor for the IR diode and a load resistor for the photo transistor.
    A member that used to be around, THE_RB, commercially designed one for a 20krpm router, see SuperPID pdf.
    http://www.vhipe.com/product-private/SuperPID-Home.htm
    Max
     
  12. spinnaker

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    Thanks Max! Now you just gave me more ideas to expand the project. I never thought of a temperature sensor. :) I like using those Dallas one wire sensors.

    Maybe I will even add my own controller. :)
     
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