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Flexible Shaft

Discussion in 'General Electronics Discussion' started by Bremme, Dec 9, 2017.

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  1. Bremme


    Oct 6, 2016
    I have a flexible shaft and would like to have a buzzer telling me the max torsion has been reached.

    I was thinking adding a small magnet and Hall Sensor at both end. This way, when the shaft is at rest, both sensors are aligned. When in action, this shaft becomes twisted up to ½ turn (180°).

    My challenge is to have a buzzer turned on when the torsion reaches 180°, neither before nor after.

    I was thinking using an EXCLUSIVE-NOR gate (4011 or else). When the shaft is not twisted (no force applied), both magnets (or their absence) result with the same levels (HH or LL). When the shaft is active (transmitting a torque), the two magnets are not aligned anymore. This results in different input s to the X-NOR gate so the buzzer can be turned on.

    My problem is to have the buzzer turned on only after as much as ½ turn (180°) of torsion is reached and this at any speed. So, a time delay can’t be applied.

    Suggestions are welcome, even a complete different approach. Thank you.

    Attached Files:

  2. dorke


    Jun 20, 2015
    Your hand drawing skills are impressive:).

    I don't know if it is feasible here,but maybe an optical approach may be simpler.
    Using an "optical fork sensor" instead of the Hall sensor ,and instead of the magnet use a "light blocking attachment" bulging from the shaft (or a slotted disc type) .
    Using two of those on the end points of the shaft (180° locations) will tell you precisely when you reach the desired point.

    Logically an XNOR will not work here,you need to "logically AND" the result of the Ex-NOr with the B sensor being at 180° the expression (notA) AND (B).
    Bremme and kellys_eye like this.
  3. kellys_eye


    Jun 25, 2010
    If you can suffer the noise, use two micro-switches operating off cams attached to the collars of the shaft connectors.

    In the event of electrical failure you would still 'feel' the point of maximum torque as the clicks occurred.
  4. Bremme


    Oct 6, 2016
    Thank you for your reply.
  5. Bremme


    Oct 6, 2016
    Thank you very much for taking your time to give me this usefull answer. I appreciate.
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