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Resonance for motorcyclist? Tank slappers.

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  • Resonance for motorcyclist? Tank slappers.

    .
    If there is one thing that we know about it is resonance - the benefits and pitfalls. Have a look at this video, noting carefully at T= 0.55 secs:

    https://www.youtube.com/watch?v=-k26h7XOpHo

    Is this a resonance effect in a mechanical system?

    If so, can we solve it for these petrol heads?
    .
    Last edited by wrtner; 03-02-2014, 03:17 PM.

  • #2
    I think more its a problem from the damper and her distance, that they are not exact tie. Remember how a turning wheel usually stays stable in on Direction like a Spintop. There must be another Force what try to pull it back beside the hands at the handlebar. If you would have a direct control over the the linkage, the wheel would stay in the direction where it is brought to.

    They need to check the sealings often from her dumpers or replace the whole dumpers oftens, that it got less space at the linkage.
    Theorizer are like High Voltage. A lot hot Air with no Power behind but they are the dead of applied Work and Ideas.

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    • #3
      Originally posted by wrtner View Post
      .
      If there is one thing that we know about it is resonance - the benefits and pitfalls. Have a look at this video, noting carefully at T= 0.55 secs:

      https://www.youtube.com/watch?v=-k26h7XOpHo

      Is this a resonance effect in a mechanical system?

      If so, can we solve it for these petrol heads?
      .
      It's certainly a resonance effect in my opinion. A very complicated one to model because of the various directions of applied forces.

      The hard part for me to figure out is the role the driver plays.
      i.e. Would the handle bars still oscillate if he let go of the handle bars?

      Comment


      • #4
        It's natures way of eliminating showoff idiots that do wheelies in traffic.

        For the more science based part I'd say the sudden startup to high speed generates a lateral torque that is trying to find a stable spot as it gains speed. The riders spring loaded arms resisting that to try to keep it centered result in the oscillation continuing. The solution is simple .... don't do wheelies.

        BTW I'm not anti-motorcycle. I have one and ride too.
        There is no important work, there are only a series of moments to demonstrate your mastery and impeccability. Quote from Almine

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        • #5
          Originally posted by ewizard View Post
          It's natures way of eliminating showoff idiots that do wheelies in traffic.
          It can happen any time when both wheels are on the ground, I'm not a biker so I don't know what actually causes it, but I do have biker friends. Counter-intuitively the solution is to accelerate. Slowing down will cause a more violent oscillation and flip you right off. You could say that the energy is transferred into the side to side "amplitude" if the wavelength of the oscillation is not increased through acceleration.
          http://www.teslascientific.com/

          "Knowledge is cosmic. It does not evolve or unfold in man. Man unfolds to an awareness of it. He gradually discovers it." - Walter Russell

          "Once men died for Truth, but now Truth dies at the hands of men." - Manly P. Hall

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          • #6
            I wonder if we can produce an equivalent electronic tank circuit as a stepping stone to suggesting a remedy

            What do you think of this scenario?

            AC power supply:
            As the wheel comes down and hits the road, there will be an oscillation depending upon the tyre pressure. This oscillation drives the resonant circuit.The frequency is a function of tyre pressure and the voltage will be a function of the speed with which the tyre hits the ground.

            Inductor/capacitor:
            The frame will have a "springiness", and a natural frequency. The frontforks will contribute in some way.

            What else?

            Comment


            • #7
              The phenomenon seems to be significantly more pronounced with lighter weighing individuals. For example in the video they show a boy and a girl who experience dangerously violent tank slapping. Perhaps shifting the center of gravity forward can minimize tank slapping and make it more controllable. One way would be to shift the body weight forward by pressing down with your feet / trying to stand up while leaning forward your torso as the front wheel comes into contact with the road's surface. In other words, there must be a skill to minimize tank slapping and skilled bikers would know. Of course this would require a suitable and maintained suspension system adjusted to the weight of the bike and the person riding it.

              Other things worth observing would be the design of motorbikes, their make / models specifically, to see if some of them are more prone to violent tank slapping than others. The second thing might be the tires specifications as well as the air pressure in them. Things like diameter and tire width and shape must be making a contribution to the overall effect. Last but not least, the braking system of bikes or the braking habits of the bikers more prone to tank slapping should be noted.

              I think that with such simple but important skills and experience derived from such observations the problem should become easy to handle.

              Comment


              • #8
                It's not a matter of wheelies or wheels hitting the ground.

                Speed wobble

                Wobble, shimmy, tank-slapper,[1] speed wobble, and even death wobble are all words and phrases used to describe a quick (410 Hz) oscillation of primarily just the steerable wheel(s) of a vehicle. Initially, the rest of the vehicle remains mostly unaffected, until translated into a vehicle yaw oscillation of increasing amplitude producing loss of control. Vehicles that can experience this oscillation include motorcycles and bicycles, skateboards, and in theory any vehicle with a single steering pivot point and a sufficient amount of freedom of the steered wheel, including that which exists on some light aircraft with tricycle gear where instability can occur at speeds of less than 50 mph; this does not include most automobiles. However, coil-sprung vehicles with a track bar setup such as the Jeep WJ, XJ, ZJ, TJ, and JK with both stock and after-market suspension lifts may also have this problem. The initial instability occurs mostly at high speed and is similar to that experienced by shopping cart wheels and aircraft landing gear.

                Theory

                Sustained oscillation has two necessary components: An underdamped second order or higher system and a positive feedback mechanism. An example of an underdamped second order system is a spring and mass system where the mass can bob up and down (oscillate) when hanging from a spring.

                If shimmy can not be designed out of the system, a device known as a steering damper may be used which is essentially a notch filter designed to dampen the shimmy at its known natural frequency.

                In two-wheeled vehicles

                Wobble or shimmy begins when some otherwise minor irregularity accelerates the wheel to one side. The restoring force is applied in phase with the progress of the irregularity, and the wheel turns to the other side where the process is repeated. If there is insufficient damping in the steering the oscillation will increase until system failure. The oscillation frequency can be changed by changing the forward speed, making the bike stiffer or lighter, or increasing the stiffness of the steering, of which the rider is a main component.[2] While wobble or shimmy can be easily remedied by adjusting speed, position, or grip on the handlebar, it can be fatal if left uncontrolled.[4]

                Since shimmy frequency is independent of bike speed, gyroscopic effects "are clearly not essential to the phenomenon."[2] The top five influences on wobble have been found to be lateral stiffness of the front tire, steering damper, height of bike center of mass, distance of bike center of mass from rear wheel, and cornering stiffness of the front tire.[3][5]

                An academic paper that investigated wobble through physical experimentation and computer modeling concludes: "the influence on wobble mode of front tyre characteristics, front frame inertia and chassis stiffness were shown. In particular, it shows that [by] increasing front tire inflation, chassis stiffness, and front frame inertia about steering axis and decreasing sideslip stiffness of front tire, wobble mode damping is improved, promoting vehicle stability."
                Speed wobble - Wikipedia, the free encyclopedia
                http://www.teslascientific.com/

                "Knowledge is cosmic. It does not evolve or unfold in man. Man unfolds to an awareness of it. He gradually discovers it." - Walter Russell

                "Once men died for Truth, but now Truth dies at the hands of men." - Manly P. Hall

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