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  • #76
    Originally posted by RKW
    Fortunately here you can just update your "Buddy / Ignore Lists" and the rest is magic ;-)
    Yabut, if you do you will eventually miss something good. All those guys do come up with some good stuff.
    Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
    ~Practitioner of the Electromechanical Arts~

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    • #77
      Agreed. It was just a suggestion for folks who just can't take it anymore. My list is actually empty on this forum.

      Originally posted by Weston Bye
      Yabut, if you do you will eventually miss something good. All those guys do come up with some good stuff.
      "Work hard. Tell everyone everything you know. Close a deal with a handshake. Have fun!"

      -- Harold "Doc" Edgerton

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      • #78
        Definition of torsional rigidity.

        (mechanics) The ratio of the torque applied about the centroidal axis of a bar at one end of the bar to the resulting torsional angle, when the other end is held fixed.

        No radius of gyration involved in torsional rigidity. If you study the equation it may help you with your misunderstanding.
        The radius of gyration also defines the torque moment of inertia.

        That doesn't matter because you cannot determine the rigidity of what may be in the box. You have no reference point and the phase shift measurement doesn't give one. The most you can say is that the entire system isn't rigid, but we already knew that since nothing is rigid.

        So, the question is still unaswered. What can we discover about what is in the box?
        Free software for calculating bolt circles and similar: Click Here

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        • #79
          One last time:

          torsional rigidity = applied torque divided by the angular deflection.

          This is a mathematical definition, no amount of verbal diarrhoea can obscure the fact.

          Phil


          Originally posted by Evan
          The radius of gyration also defines the torque moment of inertia.

          That doesn't matter because you cannot determine the rigidity of what may be in the box. You have no reference point and the phase shift measurement doesn't give one. The most you can say is that the entire system isn't rigid, but we already knew that since nothing is rigid.

          So, the question is still unaswered. What can we discover about what is in the box?

          Comment


          • #80
            Originally posted by Evan
            So, the question is still unaswered. What can we discover about what is in the box?
            Can you supply a sketch of what you described in words? The configuration is not clear to me.
            Allan Ostling

            Phoenix, Arizona

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            • #81
              One last time:

              torsional rigidity = applied torque divided by the angular deflection.

              This is a mathematical definition, no amount of verbal diarrhoea can obscure the fact.
              You don't know the angular deflection ( of what is in the box), only the ratio.

              --------------------------------------------------------

              Allan, I will later but right now I don't have time as my wife is due home from work and I have a few chores to do.
              Last edited by Evan; 04-16-2010, 05:50 PM.
              Free software for calculating bolt circles and similar: Click Here

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              • #82
                Originally posted by Evan
                Allan, I will later but right now I don't have time as my wife is due home from work and I have a few chores to do.
                Where's your sense of priority?

                I'm hung up on the coupling. Presumably not this:

                Allan Ostling

                Phoenix, Arizona

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                • #83
                  The following is an extract from your post 71 regarding the "box" experiment, the section in bold is you measuring the angular deflection over a fixed length (between the two points on the shaft). So how can you now claim you don't know the angular deflection. The whole point of the procedure is to measure the deflection. You could more easily measure the deflection at the point you applied the torque relative to the fixed end, this would not then require any penetration of the box itself.

                  OK, one very last time: the torsional rigidity equals the applied torque divided by the relative angular displacement of the two pointers.

                  Phil
                  .....................................
                  There is a small slot at each end of the box into which we may insert a small rod so that it protrudes very slightly from the slot to act as an indicator. We apply a torque to the output with a torque wrench. We then are able to observe how much the indicator rod at each end moves. We find that at a torque of 100 ft lbs the indicator at the end with the torque wrench moves twice as far as the indicator at the other end.

                  That tells us how much relative deflection of the pointers occurs when a torque of 100 ft lbs is applied to the one end of the stub shaft sticking out of the box.
                  ......................................

                  Phil

                  Originally posted by Evan
                  You don't know the angular deflection ( of what is in the box), only the ratio.

                  --------------------------------------------------------

                  Allan, I will later but right now I don't have time as my wife is due home from work and I have a few chores to do.

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                  • #84
                    I use a torque meter that operates as Evan describes almost every day. It is a Torquetronics device manufactured by Torquemeters Limited in the UK (www.torquemeters.com). It has a toothed wheel on each end of the measuring section, monitors the relationship of the ends by means of magnetic pickups, and the signal conditoner reads out torque, speed and power. It must first be calibrated by the use of a calibration arm and dead weights, but you don't need to know anything about the physical properties of the shaft. There is one exception: If you wanted to temperature correct the data without deadweight calibration at multiple temperatures, you would need to know the change in modulus with temperature. Luckily, this function is built in to the signal conditioner. One of the drawbacks of this type device is it is a dynamic torquemeter only, in that you cannot measure torque without significant relative motion between the pickup and the toothed wheel. In order to allow static calibration, the manufacturer has developed a clever device that interposes a motorized symmetrically toothed section in the magnetic path at both ends of the measuring section. When this is spinning, you can calibrate the non-rotating shaft. It is locked in place during normal use. The one I use is rated for 0-100 lb-ft of torque at 60,000+ rpm. We run it at 60krpm routinely, and it is very sensitive. I can consistently resolve performance changes of less than .05 lb-ft.
                    Davis

                    "Nothing is impossible for the man who doesn't have to do it himself"

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                    • #85
                      Originally posted by RKW
                      We all know or work with someone we get tired of listening to so you just learn to ignore them after a while. Fortunately here you can just update your "Buddy / Ignore Lists" and the rest is magic ;-)
                      Originally posted by Weston Bye
                      Yabut, if you do you will eventually miss something good. All those guys do come up with some good stuff.
                      True,
                      I have two people in my list but they are people who, when they post never make sense to me.

                      Evan isn't one as I find him far more entertaining than Channel 4 either when he's right on a subject or when he's wrong which is usually the same thing

                      I tend to think of him as The Champ, named after the Austin Champ. Here's the Tiffiepedia link. http://en.wikipedia.org/wiki/Austin_Champ

                      This was interesting in that the reverse gear was in the rear diff giving the vehicle 5 syncromesh forward gears and 5 syncromesh reverse gears which means Evan can backpedal out of an argument just as fast as he got into it

                      .
                      .

                      Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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                      • #86
                        OK, one very last time: the torsional rigidity equals the applied torque divided by the relative angular displacement of the two pointers.
                        You are making unwarranted assumptions. The item in the box may not be under torsional load. It could be bending, or under compression, tension or shear.

                        You are not able to measure the angular displacement of the pointers. They are inserted in slots in the box into a receiver that you cannot see and you have no idea what the radius of motion is. There is no way to determine it and even if there was it may not represent the average state of the machine.

                        All you can discover is the torsional rigidity of the entire system but you can't even determine that using the measuring system I have described. However, you can calibrate the measuring system in terms of absolute torque transmitted.

                        Try again.

                        No need John.
                        Free software for calculating bolt circles and similar: Click Here

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                        • #87
                          Originally posted by interrupted_cut
                          I use a torque meter that operates as Evan describes almost every day. It is a Torquetronics device manufactured by Torquemeters Limited in the UK (www.torquemeters.com). It has a toothed wheel on each end of the measuring section, monitors the relationship of the ends by means of magnetic pickups, and the signal conditoner reads out torque, speed and power. It must first be calibrated by the use of a calibration arm and dead weights, but you don't need to know anything about the physical properties of the shaft.
                          And. yet another person apparently thinks it's magic........

                          You do, of course know "a physical property of the shaft"...... you absolutely MUST or it cannot work.

                          What you know is that it deflects a certain amount per newton-meter or whatever as reflected in the change of signal......

                          You don't know how much that is in "real" units, and it doesn't matter........ But you DO FOR SURE know how many "magic torque meter units" it deflects per unit of torque applied......

                          And, the only reason you don't know the actual real deflection is that you were too lazy to correlate "magic torquemeter units" to "real" units, since after all you don't have to. But that information is available, you know just about all the things you need already.

                          There just is no escaping it...... you gotta know "how much" it changes per unit torque or your meter reads only "Bubba twisty units".

                          It's called calibration..... and it isn't just an incidental detail...
                          1601

                          Keep eye on ball.
                          Hashim Khan

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                          • #88
                            Sorry Jerry. You don't even know it the box contains a shaft.

                            What you know is that it deflects a certain amount per newton-meter or whatever as reflected in the change of signal......
                            No. All you know is that it produces a particular signal when loaded to a certain torque. You have no idea how much it deflects or what the torsional rigidity of the shaft is. All you know is that it isn't rigid just like every other bit of matter in the universe.

                            The torque meter does not inform you about the shaft.
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                            • #89
                              I'm pretty sure the box contains a cat....
                              Location: Saskatoon, Saskatchewan, Canada

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                              • #90
                                And it's name is Schrِdinger...
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