6 ms·

Not this shit again... Look closely at the picture of the test chamber in the article. Do you see Helmholtz coils surrounding the entire apparatus? Nope. http

Not this shit again... Look closely at the picture of the test chamber in the article. Do you see Helmholtz coils surrounding the entire apparatus? Nope. https://en.wikipedia.org/wiki/Helmholtz_coil https://en.wikipedia.org/wiki/Helmholtz_coil It's the same story as the EMdrive: they run something at high current, without cancelling earth's magnetic field. high current + earth magnetic field = force. This method is used to move satellites: https://en.wikipedia.org/wiki/Magnetorquer https://en.wikipedia.org/wiki/Magnetorquer

imglorp 6y ago
Wouldn't you want to run tests in multiple orientations to cancel Earth fields anyway? Similar to how you would run a Michaelson-Morley interferometer experiment.
- commonjcb 6y ago
  The torsion balance introduces fixed biases, and can be operated only in XY plane. So in theory you're right, in practice it's not possible. Not canceling earth's magnetic field (an easy thing to do) when measuring microNewtons at high currents is just very poor experimental practice. Unprofessional. Amateur.
  - deleted 6y ago
    [deleted]
- marsokod 6y ago
  You could but that may be a bit complicated to set up, while Helmholtz coils are dead easy to make and install. It's just a frame, copper wires, 3 power supplies, a magnetometer and a PC (even an Arduino could drive it).
mdorazio 6y ago
Be careful here. Magnetorquers do exactly what the name says - they create torque, which manifests as rotation around a point. If a device demonstrates linear force, it's likely to be a different effect (electrodynamic), which currently requires a rather long tether to work [1]. [1] https://en.wikipedia.org/wiki/Electrodynamic_tether https://en.wikipedia.org/wiki/Electrodynamic_tether
- commonjcb 6y ago
  Right, or we can just link to the physical law itself: - Lorentz force - the force on a current carrying wire. No need for a long wire. It's in the range of micro-Newtons for few Amps, for 10cm, at earth magnetic field: https://en.wikipedia.org/wiki/Lorentz_force#Force_on_a_current-carrying_wire https://en.wikipedia.org/wiki/Lorentz_force#Force_on_a_curre... "When a wire carrying an electric current is placed in a magnetic field, each of the moving charges, which comprise the current, experiences the Lorentz force, and together they can create a macroscopic force on the wire (sometimes called the Laplace force)."
firebaze 6y ago
I find it quite hard to believe that this obvious question wasn't challenged by anyone. To me it is like questioning if any of the people involved prior to publishing this news are capable of solving 1+1. It's basic. I don't think of the relevant people as idiots.
mleonhard 6y ago
A 2013 paper by Fearn & Woodward makes no mention of the earth's magnetic field. After skimming the paper, I think their experiment is flawed. "Experimental Null Test of a Mach Effect Thruster." https://arxiv.org/pdf/1301.6178.pdf https://arxiv.org/pdf/1301.6178.pdf "The motion of the beam is damped by a pair of aluminum plates attached to the beam that move in the magnetic field of an array of small neodymium-boron magnets. The power circuit was extensively shielded to insure that stray fields did not compromise the results."
Aesthetys 6y ago
I’ve never understood this position with the EMdrive and similar technologies; wouldn’t magnetic propulsion revolutionize low-earth-orbit travel, or whatever the ceiling is for pushing against Earth’s magnetic field?

imglorp 6y ago

Wouldn't you want to run tests in multiple orientations to cancel Earth fields anyway? Similar to how you would run a Michaelson-Morley interferometer experiment.

commonjcb 6y ago
The torsion balance introduces fixed biases, and can be operated only in XY plane. So in theory you're right, in practice it's not possible. Not canceling earth's magnetic field (an easy thing to do) when measuring microNewtons at high currents is just very poor experimental practice. Unprofessional. Amateur.
- deleted 6y ago
  [deleted]
marsokod 6y ago
You could but that may be a bit complicated to set up, while Helmholtz coils are dead easy to make and install. It's just a frame, copper wires, 3 power supplies, a magnetometer and a PC (even an Arduino could drive it).

mdorazio 6y ago

Be careful here. Magnetorquers do exactly what the name says - they create torque, which manifests as rotation around a point. If a device demonstrates linear force, it's likely to be a different effect (electrodynamic), which currently requires a rather long tether to work [1]. [1] https://en.wikipedia.org/wiki/Electrodynamic_tether https://en.wikipedia.org/wiki/Electrodynamic_tether

commonjcb 6y ago
Right, or we can just link to the physical law itself: - Lorentz force - the force on a current carrying wire. No need for a long wire. It's in the range of micro-Newtons for few Amps, for 10cm, at earth magnetic field: https://en.wikipedia.org/wiki/Lorentz_force#Force_on_a_current-carrying_wire https://en.wikipedia.org/wiki/Lorentz_force#Force_on_a_curre... "When a wire carrying an electric current is placed in a magnetic field, each of the moving charges, which comprise the current, experiences the Lorentz force, and together they can create a macroscopic force on the wire (sometimes called the Laplace force)."

firebaze 6y ago

I find it quite hard to believe that this obvious question wasn't challenged by anyone. To me it is like questioning if any of the people involved prior to publishing this news are capable of solving 1+1. It's basic. I don't think of the relevant people as idiots.

mleonhard 6y ago

A 2013 paper by Fearn & Woodward makes no mention of the earth's magnetic field. After skimming the paper, I think their experiment is flawed. "Experimental Null Test of a Mach Effect Thruster." https://arxiv.org/pdf/1301.6178.pdf https://arxiv.org/pdf/1301.6178.pdf "The motion of the beam is damped by a pair of aluminum plates attached to the beam that move in the magnetic field of an array of small neodymium-boron magnets. The power circuit was extensively shielded to insure that stray fields did not compromise the results."

Aesthetys 6y ago

I’ve never understood this position with the EMdrive and similar technologies; wouldn’t magnetic propulsion revolutionize low-earth-orbit travel, or whatever the ceiling is for pushing against Earth’s magnetic field?