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Torque Acceleration Braking Crabbing Momentum Inertia Part 1

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  • Torque Acceleration Braking Crabbing Momentum Inertia Part 1

    A slot car motor is fixed to the chassis and is immovable, the rear axle is fixed to the chassis and is immovable. The motor armature and the motor housing create the same amount of torque in the opposite direction and cancel each other out.

    This same force happens in a slot car in the opposite direction when the brakes are applied.

    To demonstrate this force I mounted a piece of plastic 5mm x 70mm off the rear of my test chassis.

    The motor used in this test makes 480g/cmTs @ 12Volts.

    The test was conducted at 16Volts.

    In each test the crown gear was mounted on the opposite side of the pinion.

    The composite PHOTOS show the first four frames of each test. The first frame is before power is applied. The second, third, and forth frame show the car lifting it’s front wheels and accelerating away.

    At no point in any of these photos does the striped bar twist in either direction from the torque forces.

    At 16Volts the torque is over 640 grams, almost ten times the weight of the car.

    When the brakes are applied at maximum RPM, a force almost this great is applied in the opposite direction.

    Dave
    Last edited by davejr; 10-05-2008, 05:34 AM.

  • #2
    At no point in any of these photos does the striped bar twist in either direction from the torque forces.
    C'est vrai!

    Cleverly demonstrated, Dave.

    Comment


    • #3
      At no point in any of these photos does the striped bar twist in either direction from the torque forces.

      Originally posted by Wet Coast Racer View Post
      C'est vrai!

      Cleverly demonstrated, Dave.
      Yes, but in the test photo strips, the lane tape seems to get more wrinkled as they progress from left to right. I have no idea what this means.

      It is a good demonstration of the theory though. Thanks Dave.

      Greg

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      • #4
        If I understand this correctly . . .

        The striped bar doesn't twist because it is fixed to the chassis, which cannot twist unless one wheel lifts. With acceleration transferring nearly the whole weight of the car onto the rear axle, the rear end is kept firmly in contact with the track. This in no way indicates a lack of twisting force within the chassis. It does indicate that the twisting force is overcome by the acceleration, which keeps it level.

        The torque in the system comes from the electromotive attraction and repulsion of the armature inside the magnetic field of the motor. Every other torque is a reaction to this electromotive force. As the armature revolves, it pulls and pushes the motor case in the opposite direction. This force is applied to the chassis. The chassis can't twist because of the reasons in the paragraph above.

        Try it with the motor loosely mounted, and the motor will spin around inside the chassis.

        Try it with a rear axle that can pivot, relative to the chassis and the motor, and the whole chassis will lean to one side.

        Try this: lift the car up at the tail, with one finger under the chassis, with the guide in the slot. Give it a burst of throttle, and the car will roll on you finger and the guide, dipping to the left. When you hit the brakes, it will dip to the right side.

        Comment


        • #5
          In actual running the motor in an inline set up will exert a twisting force on the chassis which can cause torque steer and wheel hop. Your test cannot show this, but years of racing has shown this to be true, that is why all Grp 7 slot cars are angelwinders. If you tried to run a multi segment cobalt mag Grp7 motor inline it would twist the chassis to the point that it would be totally ruined.


          Tom

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          • #6
            This test stated that the twisting force in the chassis is canceled by the opposing forces of the armature and motor housing. It also stated the motor and axle were solidly fixed to the chassis, which causes the cancellation of this force.

            The force felt by lifting the car and revving the motor is the moment of inertia created by the acceleration of the mass of the armature. This force is instantaneous and only appears when the armature is accelerated or decelerated. When this force is applied to an accelerating or braking car the value is so low it is almost negligible.

            With a heavier more powerful motor, the moment of inertia would be greater and create a force that could cause handling problems.

            Dave

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            • #7
              Take out the magnet of a revell Porsche 550 and take it for a ride on the slippery original wheels, and the car has a strong tendency to push the rear out to one side while accelerating. Put on some grippy tires and/or some weight and the problem dissapears. I'd say this shows that the motor does put some force on the chassis, but it's small compared to the accelerating force.

              Comment


              • #8
                Originally posted by davejr View Post
                At 16Volts the torque is over 640 grams, almost ten times the weight of the car.
                I think this is a VERY interesting understanding of the power that is in that motor! But even further and sort of what 356speedster was referring to is that a properly setup car CAN handle this amount of torque, with the proper tuning - tires, weight possibly, etc. - that counteracts this amount of torque.

                I think it would be interesting to see this same test run on box stock RTR's with whatever they come with and then once "tuned" show the difference it made. I bet the results of the tests will end like this one began, but the box stock RTR's with no tuning will definitely display the twisting affect.

                Awesome testing as always Davejr!
                PD2

                Comment


                • #9
                  couple questions, observations:

                  what is the purpose of this exercise?


                  in pic #4 of the 2nd set, the bar looks closer to the track on the right side, indicating (to me) torque loading twisting the chassis.

                  Comment


                  • #10
                    martini917k

                    The forth frame of the second set of photos, the bar on the car is parallel to the track. The bar, and the reflection of the bar, are parallel to each other, this indicates that the bar isn‘t closer on the right side. The angle you see is an optical illusion caused by the camera not being perpendicular to the slot.


                    Dave

                    Comment


                    • #11
                      okey dokey

                      but what is the original purpose of the exercise?

                      Comment


                      • #12
                        martini917k

                        This is just a discussion of the force created by a slot car and how they effect the handling and performance.

                        Dave

                        Comment


                        • #13
                          Guys, I apologize, but I can't keep my mouth shut any longer.

                          So all the torque is cancelled out between the armature and the motor housing? That means that slot cars can't function at all, since there's no torque left to drive the wheels...

                          The physics misunderstandings that are being passed off as fact are wearing me out. There is such a clear misunderstanding of concepts like 'moments of inertia' and 'torque', and I'm tired of being the heavy and rushing in to correct all the bogus stuff. A more powerful motor does not in any way change the moment of inertia, by the way. From what I'm reading, you're treating 'moment of inertia' as being time related, much the way people mistakenly refer to 'light-years' as a measure of time, even though it's actually distance.

                          Please stop. I don't have the time to keep correcting all this mess, and all that's happening is that people are getting a worse understanding of physics. The fundamental mechanics are lacking here, and I'd encourage anybody interested in it to go read the first 16 chapters of their nearest physics book.

                          Comment


                          • #14
                            Hibbeler makes a good Physics book

                            Comment


                            • #15
                              Originally posted by Mark View Post
                              Hibbeler makes a good Physics book
                              Available in bookstores everywhere!

                              Comment

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