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[Physics] Questions about inertia drive, absolute rotation changes without thrust...

Discussion in 'Nerd Out Zone' started by NeonSturm, May 20, 2015.

  1. NeonSturm

    NeonSturm Back Into Space

    • Member
    Below are 2 theories of mine.

    #1 Absolute rotation changes : rotate solely with energy, not thrust

    TurningWheels.png XY, Z is the depth - toward / away from you.

    The centre of mass is in the picture's centre.
    The rotation we are talking about is the whole picture around Z.

    Now you start spinning the wheels with the same directions around Z.
    The inner rotation doesn't change the pictures's rotation much, but the outer does.

    Additionally you have the option to flip them 180° around the X-axis (from picture).
    One clockwise, one counter-clockwise to preserve the Z-axis vector.​
    This should give a quick burst, turning around Z.

    (if you can't imagine that, leave the "Nerd out Zone" :p :D)​

    #2 Inertia Drive

    TurningWheels.png Again these 2 wheels! :)

    But now, you turn left one in opposite direction (mid=both-up, left/right=both-down).

    They don't move along Z (depth axis) while you start spinning them.
    According to the theory that the more you approach the speed of light, the higher your mass gets, these wheels should have increased mass now.

    At least while you start moving them along Z.

    While moving them along Z, you stop spinning, reducing their mass to normal.
    v_total = sqrt( v_aroundXY + v_alongZ )

    When you now also stop moving them along Z, you should require less force than when you start their movement while they were spinning.​

    I would be happy if somebody can explain me what I am missing, if I am missing something.

    It's a bit difficult to build an experiment IRL, because of the time you have to stop spinning and the air-resistances on earth.
    And games don't have accurate enough physics to allow such experiments while dedicated software often lacks visual feedback.

    Remembering a BUG in KSB (Kerbal Space Program):
    You could build 2 fuel tanks connected with a pipe,
    start spinning and transfer fuel between tanks to change the inertia vector of it.

    The transfer didn't affect the object which has these fuel tanks.​
    NeonSturm, May 20, 2015
    Last edited by NeonSturm; at May 20, 2015
  2. PsychoticLeprechaun

    PsychoticLeprechaun Designer & Web Developer

    • Dev Member
    I think you should try to produce more fuller descriptions of what you are getting at. I'm having trouble understanding exactly what you mean in your explanations.

    If I understand the second one correctly, though, your suggestion is that by rotating the wheels and thus increasing the effective mass of the object travelling you can then stop that rotation to gain a "boost" to acceleration? If so, that is flawed. Sure, stopping the rotation will do that, but you would need to A) spin the wheels really fast to gain an observable effect and B) even then, the effect of this process is to simply slow down initial acceleration, not speed up acceleration on the stopping of the rotation of those discs; if you had never spent time with those spinning discs, you'd be travelling at a faster speed.
    PsychoticLeprechaun, May 20, 2015
    Last edited by PsychoticLeprechaun; at May 20, 2015
  3. NeonSturm

    NeonSturm Back Into Space

    • Member
    I have made an animation in blender. (With logic)
    But #1 is difficult to make - 2 rotations at the same time around 1 axis mess with the coordinate system.

    Attached Files:

  4. Sevio

    Sevio Back Into Space

    • Member
    These wheels just act like reaction wheels.

    If you're not invoking anything more than standard physics with this thought experiment, conservation of momentum states that you're not going to move any faster or slower by spinning up wheels inside your ship. You'll make your ship rotate around the Z axis if both wheels start spinning in the same direction, but its (lack of) acceleration in the Z direction is unaffected.

    You can turn your ship about your Z axis as many times as you like while the wheels are running but the rotation will stop when you spin the wheels down.
    Last edited: Jul 29, 2015
    Sevio, Jul 29, 2015
    Last edited by Sevio; at Jul 29, 2015
    joppiesaus likes this.
  5. Sevio

    Sevio Back Into Space

    • Member
    By the way, while you can use solely reaction wheels to control your attitude in space, real spacecraft still rely on thrusters for a couple reasons:
    • Reaction wheels can saturate. Outside influences like drag from the Exosphere or solar wind will tend to build up a rotation in the spacecraft over time. You can counter that with reaction wheels but they have to start spinning faster and faster to keep the spacecraft oriented. Eventually you have to offload the momentum by firing thrusters.
    • Reaction wheels are heavy. Since you need a thruster system anyway for the above reason, wheels that are strong enough for "fast" (for spaceflight standards) turns will probably weigh more than the fuel mass used over a mission's reasonable lifetime, as spacecraft don't need to make significant turns that often.
    For these reasons, reaction wheels are usually kept small, only used for very fine attitude control and to absorb only enough drag-induced momentum until it's just enough to be cancelled by a thruster firing.
    Sevio, Jul 30, 2015
    Last edited by Sevio; at Jul 30, 2015
    PsychoticLeprechaun likes this.
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