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      CommentAuthorbloodymedia
    • CommentTimeJan 14th 2010 edited
     
    Seansays:
    In a typical motor, as you go faster, the back EMF increases, the current flow drops, which means your torque drops in line with the speed, because with no back EMF the torque imparted to the wheel is always the same whether you're doing 1rpm or a million rpm but power output is obviously, torque is obviously, energy over speed so...


    Example of a torque curve of an electric motor:


    Speed, current, power vs. torque
    • CommentAuthorjoshs
    • CommentTimeJan 14th 2010 edited
     
    Posted By: bloodymediaSeansays:
    In a typical motor, as you go faster, the back EMF increases, the current flow drops, which means your torque drops in line with the speed, because with no back EMF the torque imparted to the wheel is always the same whether you're doing 1rpm or a million rpm but power output is obviously, torque is obviously, energy over speed so...
    Sean the Sociopath either never got past DC brush motors, or is hoping his audience didn't. The way they've thinned away all but the insanely gullible, the latter has a reasonable probability.
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      CommentAuthoralsetalokin
    • CommentTimeJan 14th 2010 edited
     
    Orbette graphs:


    • CommentAuthorjoshs
    • CommentTimeJan 14th 2010
     
    How can that possibly be? With no BEMF surely Georgiana Orbette cannot transfer increasing input power to the output monotonically? Say it isn't so! Say that the Orbomination with its tight rheostat adjusted tolerances, and shyness from measurement could still be free of coupling!
    • CommentAuthorspinner
    • CommentTimeJan 14th 2010 edited
     
    Thanks for the graphs!
    Bloodymedia's first one is showing a typical AC asynchronous el. motor torque curve (at 60Hz), that's why there's a steep drop all the way to zero (1800RPm), when rotor catches the rotating field of a stator. Working RPMs are usually a few percent lower (on that graph cca. 1775RPm), where max. output (not torque) is reached.
    DC motor torques are usually more flat, and drops to zero far outside the nominal RPm area.

    Al's graphs are interesting, they're showing the same characteristics (and problems) as eOrbo - namely the very poor overall efficiency (I estimated Orbo to have some 3% efficiency, Al's graph shows 2%), a lousy starting torque (typical el.motors have quite high value at 0 RPm), which is in accordance with the main principle of Steorn's gizmo - make a poorly coupled pulse motor and swear it is OU because it "has no BEMF"...

    No wonder that they discovered "an anomaly" of a wind turbine generator back in 2003...
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      CommentAuthorNoSideSam
    • CommentTimeJan 14th 2010
     
    Probably just a coincidence, but it’s interesting that Orbette’s peak efficiency occurs with an input voltage around that being delivered by the battery in Orbo.
  1.  
    Posted By: NoSideSamProbably just a coincidence, but it’s interesting that Orbette’s peak efficiency occurs with an input voltage around that being delivered by the battery in Orbo.


    Yep, I noticed that too. You must bear in mind, though, that I have bearing and shaft issues. High radial loads...washboard roads....er....um.....

    Anyway, Orbette now has a new straight 5 mm shaft, brand new TRex 450 main shaft, and some nicer ball bearings, slightly beefier than even the stock TRex mains. I've ditched the bent black gearshaft from the little BladeCP heli and its tiny bearings, made a new better mount, and so forth. It is much smoother now, but of course these bearings are a bit draggier. I just realized I haven't washed them out yet, though, which will make them run better.