On Sat, Jun 27, 2009 at 1:25 PM, William Beaty <[email protected]> wrote:
> On Sat, 27 Jun 2009, John Berry wrote: > > > After re-reading I still fail to understand your contact point thought, > but > > is it merely to produce a magnetic field in the shaft? > > A Faraday motor has a radial current in a disk, and a magnet to produce a > b-field perpendicular to the disk. This produces a torque between the > disk and the sliding contact at the edge (but zero net torque on the > permanent magnet.) If instead we remove the magnet and place a coil on > the copper disk, and route some current through the coil, the motor still > spins. If instead of a coil, we carve spiral slots into the copper disk, > which forces the current to have a circular component as well as radial, > the motor still spins. Sure, makes sense. > > > DOH! I wrongly called these "self-acting" Faraday motors, but the real > term is "self-excited," as with standard DC generators where the generator > output is used to "excite" the generator's own field coil. If we short > out a self-excited Faraday motor, then spin the shaft, it starts > generating a current. But this only works above a certain RPM, where > the output energy is greater than the resistive losses. > > > If we used a magnetized shaft, north at one end south at the other would > > this still be required to create the effect? > > That would work. A magnetized shaft would turn it into a conventional > Faraday motor. Ah, but it wouldn't. At least not on the shaft. If you had say a magnetic dipole shaft and tapped one end and the center then you would get a force as the "magnetic lines of force" exit that half of the shaft then you would get a net rotational force as the current cuts across. However if the current cuts across both poles then it encounters as much magnetic field exiting as entering over it's length resulting in opposite twists at each end. > > I'm looking for an effect which would drive an all-copper ball bearing > motor into rotation. > > > > Is the force you are envisioning one that puts a torque on the individual > > ball bearings? > > Yes, a relative torque between each bearing and the ring enclosing them. Ok, above I am speaking to the ability of an current in the shaft to generate a force and I find none. I am not yet considering how the ball bearings or rings might react.
