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Torque measurement of rotating shaft

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  • #16
    Now you are going to have to have some sort of filter to clean out all the noise in the system.

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    • #17
      Originally posted by Evan
      Meauring the twist doesn't require knowing anything about the shaft, only the load.

      You do need to know the diameter of the shaft, and the length between measuring points to calculate the twist.

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      • #18
        No but turning the twist into a torque value does require that you know something about the shaft. If he knew the load he could calculate the torque directly by measuring the rpm, but that is not the case.

        Phil

        Originally posted by Evan
        Meauring the twist doesn't require knowing anything about the shaft, only the load.

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        • #19
          Originally posted by Evan
          Meauring the twist doesn't require knowing anything about the shaft, only the load.
          I see that others have already dealt with this.........

          One DOES assume that a numeric measurement with some basis in normal units and reality is wanted......
          1601

          Keep eye on ball.
          Hashim Khan

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          • #20
            You do need to know the diameter of the shaft, and the length between measuring points to calculate the twist.
            No but turning the twist into a torque value does require that you know something about the shaft. If he knew the load he could calculate the torque directly by measuring the rpm, but that is not the case.
            Nope. All you need to know is how much twist is produced by a particular amount of torque on the output. That can be a purely relative value that is determined by an experienced operator who can tell when the system is close to it's limit. All the other possible methods face exactly the same issue if an absolute value of torque is required to be known and that is somehow measuring the actual torque on the output.
            Free software for calculating bolt circles and similar: Click Here

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            • #21
              I wonder how much twist a suitable shaft can withstand and still return to its original 'alignment'- for what it's worth, I just had a thought, so I'll contribute it-

              Have the piece of shaft, the drive couplings on both ends, and two pieces of reasonably close fitting tubes placed end to end between the couplings. Clamp the ends of the tubes to the shaft at the ends where the couplings are. While at rest, scribe a mark across both tubes where they meet. If you twist the shaft, those marks will go out of alignment. How far out is determined by how much you twist the shaft.

              You can calibrate that by putting a known force on the end of a known length of bar that's attached to one end of the shaft. Scratch the mating marks across for each torque value you apply. In this case, you might want a range up to maybe 1200 ft/lbs if you'll be routinely measuring roughly 800 ft/lb.

              In operation, you read it using a strobe light to freeze the markings, or you could trigger the strobe from the rotating shaft.
              I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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              • #22
                No but turning the twist into a torque value does require that you know something about the shaft.

                Originally posted by Evan
                Nope. All you need to know is how much twist is produced by a particular amount of torque on the output.
                That would be "knowing something about the shaft"........
                1601

                Keep eye on ball.
                Hashim Khan

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                • #23
                  Nope. All it is is knowing the relative alignment of each end of the shaft to the other. That does not reveal the properties of the shaft nor does it matter. That isn't what is being measured. It is a value that is directly coupled to the torque load and can be calibrated in absolute terms without even knowing what size or shape the shaft is.
                  Free software for calculating bolt circles and similar: Click Here

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                  • #24
                    Originally posted by Evan
                    Nope. All it is is knowing the relative alignment of each end of the shaft to the other. That does not reveal the properties of the shaft nor does it matter. That isn't what is being measured. It is a value that is directly coupled to the torque load and can be calibrated in absolute terms without even knowing what size or shape the shaft is.
                    So, a shaft on a system has 0.7mm relative movement on the circumference between two marks 3 meters apart. End of data.

                    What is the torque on the shaft in NM?
                    1601

                    Keep eye on ball.
                    Hashim Khan

                    Comment


                    • #25
                      In case you missed it here it is again.

                      All you need to know is how much twist is produced by a particular amount of torque on the output. That can be a purely relative value that is determined by an experienced operator who can tell when the system is close to it's limit. All the other possible methods face exactly the same issue if an absolute value of torque is required to be known and that is somehow measuring the actual torque on the output.


                      It still doesn't require knowing anything about the properties of the shaft.

                      So, a shaft on a system has 0.7mm relative movement on the circumference between two marks 3 meters apart. End of data
                      By the way, we don't even need to know that much. All we need to know is that there is a timing difference between when the marks pass the sensors and that also doesn't need to be quantified. The most we need to know is that X timing difference corresponds to N torque.
                      Last edited by Evan; 04-13-2010, 11:59 PM.
                      Free software for calculating bolt circles and similar: Click Here

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                      • #26
                        Evan, you said you don't need any data on the shaft, and I'm holding you to it...

                        What's the torque? Come on, give...... inquiring minds want to know.


                        Oh,, you mean you need MORE DATA? Like the relation of torque to deflection in that particular shaft?

                        Ah, so you DO want to "know something about the shaft", even though you SAID you didn't need to know that....

                        Originally posted by Evan

                        By the way, we don't even need to know that much. All we need to know is that there is a timing difference between when the marks pass the sensors and that also doesn't need to be quantified. The most we need to know is that X timing difference corresponds to N torque.
                        Which would be "knowing something about the shaft".....................

                        We will now return to step one and repeat......... in different words, but coming back to the same thing.......Since a timing difference on a particular size shaft at X rpm, i.e some actual physical system, corresponds precisely to a distance......

                        All you can get without SOME form of absolute calibration is an "assumed" relative relation between an "assumed" maximum output, and some distance ot timing difference, whichever you prefer to call it. "we are at about 76% of what we think is maximum, but we don't know the actual maximum number"........
                        Last edited by J Tiers; 04-14-2010, 12:07 AM.
                        1601

                        Keep eye on ball.
                        Hashim Khan

                        Comment


                        • #27
                          You can measure the torque on the output end of the shaft with a dyno. That is all you need to know to calibrate the system. If you don't understand that I can't make it any simpler. That doesn't give you information about the properties of the shaft since it doesn't even tell you the amount of deflection that takes place. You don't need to know that.

                          The only information that you obtain is a phase difference between input and output. That is enough.
                          Last edited by Evan; 04-14-2010, 12:12 AM.
                          Free software for calculating bolt circles and similar: Click Here

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                          • #28
                            Originally posted by Evan
                            You can measure the torque on the output end of the shaft with a dyno. That is all you need to know to calibrate the system. If you don't understand that I can't make it any simpler.
                            Ah, but you only NOW want this dyno, which anyone would realize right away is one possible way to do it.

                            before you said you didn't NEED it.......

                            of course a dyno is not the only way......

                            If you know dimensions and material of the shaft, you can come reasonably close to reality with a calculated value for teh torque to deflection figure..

                            I understand this is how ships power was figured at various speeds, I don't seriously believe that the whole system was hooked to an underwater dyno system with 200,000 HP capacity while the ship was floating in the harbor.
                            1601

                            Keep eye on ball.
                            Hashim Khan

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                            • #29
                              before you said you didn't NEED it.......
                              I said no such thing. Go back and read the postings Jerry. The dyno is for calibration which is precisely what I said in two different posts.

                              For the third time:

                              All the other possible methods face exactly the same issue if an absolute value of torque is required to be known and that is somehow measuring the actual torque on the output.

                              I don't seriously believe that the whole system was hooked to an underwater dyno system with 200,000 HP capacity while the ship was floating in the harbor.
                              Yes it was. It's called a propellor. That is exactly how some dynomometers work.
                              Last edited by Evan; 04-14-2010, 12:20 AM.
                              Free software for calculating bolt circles and similar: Click Here

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                              • #30
                                Originally posted by Guido
                                Been brainstorming this problem and a solution for years. Should have been more detailed with the problem of wanting to measure/display HP and torque on the dashboard of a Peterbuilt moving down the highway at speed. Idea popped up when we saw how turboprop engines display torque in real time. A nonlinear pressure guage is mounted on the panel, with pressure from engine compressor stage number so-and-so measured and displayed. The pressure guage displays in ft-lb of torque.

                                There's gotta be a market for a device to be added to an over the highway diesel truck tractor, which would reliably display torque/HP. Instant operator visual of motor performance.

                                Everyone's thinking and input is appreciated.--G
                                Way back in, oh maybe 1958, my dad and I were driving west on the PA Turnpike on the section that climbs towards the eastern-most tunnel. We had a similar conversation, just from the standpoint that it would be interesting to watch the changes due to throttle changes. That section of road was kind of twisty, and the grade wasn't particularly constant.

                                We came to the conclusion that some sort of way to measure the movement of the motor mounts would be a possibility, but we had no way to calibrate it.
                                Our conversation drifted off to other things of similar importance.

                                By the by, I don't know if big trucks have the engine/transmission set up the same way that cars did then, but the torque measured that way would have to have the torque multiplication of the torque converter (if one is used) and the transmission factored in if one really wanted to know the actual torque at the crankshaft. I'd suspect the torque converter factor to be a tad-bit on the un-constant side.

                                I haven't been over that stretch of highway in quite a few years, but I'm sure the road no longer follows the path it did then. They might have even bypassed the tunnels.

                                -bill

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