Hummina Shadeeba said:
And the wheels on same fixed axle or both wheels on bearings?
sorry man, i initially overlooked this.
yes, both wheels on the same axle would be the simplest to construct.
but that's not a requirement as long as the two rims run (very closely) parallel to each other.
so they can be physically separated but otherwise are co-axially aligned.
Hummina Shadeeba said:
I assumed using one polarity the iron wouldn’t be thrown so far or something but now:
I don’t think there’d be any hysteresis in the all N up motor as the teeth would be exposed to the same continuous field as the rotor rotated all the same continuous polarity past the teeth.
not switching from one extreme to the other, sure the loss would be less but you wouldn't have a continuous field if the rotor is moving.
the field intensity is varying in both magnitude & direction as the magnet passes by the iron core (say left to right) even if the polarity remains the same.
magnetic domains are commonly depicted as tiny compass needles.
if a compass could be placed on the end of a stator tooth the needle will move following the N as it swings across.
but unlike a compass needle with a friction-free bearing that responds instantly, magnetic domains are stuck in molasses.
actually the word molasses (or inertia) are not a particularly good analogue since both imply a linear relationship when it is more of a step response almost like a detent (stiction maybe??).
if you've ever magnetized a screwdriver that's hysteresis.
wikipedia said:
When an external magnetic field is applied to a ferromagnetic material such as iron, the atomic domains align themselves with it. Even when the field is removed, part of the alignment will be retained: the material has become magnetized. Once magnetized, the magnet will stay magnetized indefinitely.
now the very next sentence following the above quote talks about requiring the opposite polarity to demagnetize.
since this case is specified all N, demag won't happen but the domains are still in motion regardless.
however before they can get moving it takes a certain amount of field strength to first get unstuck from the position they're locked into which robs some energy.
now any magnetic field that passes thru a conductor produces a current (how a genny works) & this is what happens when a domain moves thru an iron core.
since iron is not the best electrical conductor, it's relatively high resistance converts that current into heat.
is this particularly hi speed?
[youtube]MglUIiBy2lQ[/youtube]
WRT to the ball-track, cogging would be the energy-well represented by the hill/valley in the track.
hysteresis & eddy-current are the source of loss equivalent to friction, both air & rolling (even though a motor has both of those too).
if there were zero loss, then the ball or rotor would continue moving (almost) indefinitely just like things do in the vacuum of outer-space.
in either case the source of loss may seem small but it can have a seemingly large dramatic effect that is due to the relatively large (by comparison) energy-well.
as the system drops out of balance from small, gradual, continual accumulated loss it falls to ground giving up it's potential energy store.
as i get a little older,
i get a little bolder.
then roll it down a little hill.
good times.