Direct drive/rim drive/idler drive vs. belt drive?

Lewm

There is effectively no damping effect available from the two opposed magnets. Eddy currents are proportional to field strength times relative velocity divided by electrical resistivity. The configuration used results in low relative velocity. The electrical conductivity of available magnetic materials is quite high - NdFeB magnets have about 100 times the resistivity of copper.

For all: A distinction needs to be made between velocity dependent drag, which will tend to stabilise the system against speed variation and classical friction (velocity independent) which will not. Hydrodynamic drag and eddy current effects are in the former camp, standard bearing friction and stylus drag are in the latter.

Mark Kelly

Lewm
what Quiddity is relating, as I seem to understand it, is that eddy current 'friction' is very much on the minimal side with the magnetic repulsion, almost levitation, ring magnet concepts. Also recall those magnets are only about 1/4" wide rings. To support this, it is told, that if these platter are (disconnected from the drive) pushed by hand seem to run 'forever' and thereby VERY MUCH differently behaving the 'Platine Verdier' mentioned by example.

Now go figure yet some more ... :-)
Axel
PS: a difference in VFT of .75g, now I'm running at 0.75g with an Empire S1000ZE/X (0.25g! - 1.25g spec) as compared to 1.5g spec. for a 'M20FL super' give the my controller a lot more 'pain in the a...' - it take just longer to settle. This is for me a clear indication about what friction (needle and/or bearing) does in terms of motor/controller loop-feedback/response...

Mark, Thank you for putting us back on the right track, as you always do. I had read somewhere else that the Verdier develops an eddy current effect by virtue of its apposed magnets, so I assumed that the same might be true of the Clearaudio. Are your remarks re the effect of bearing friction in agreement with Win's description of the virtues of the Verdier?

Lew,

Maybe I spoke out of school because I believe I am the one who may have confused the issue. Unlike either Clearaudio or Verdier, my turntable uses an eddy current motor. At least, I believe neither of them uses one. Anyway, I also am a believer in the use of hydrodynamic drag, as Mark calls it, so any reference to friction drag was maybe the source of confusion.

Win
Saskia Turntables

As one who has just wasted the better part of a beautiful hot Sunday afternoon trying to assemble my Lenco in its slate plinth, only to fatally smudge the professional paint job on the PTP3 (it will need to be redone) and find that I had ordered the wrong very fancy push-button switch, I am in no position to take issue with anyone else's feaux pas. Who knew that "off-(on)" in the Mouser catalogue is not the same as "off-on"? I now know. This is not really OT because I am talking about assembling an idler drive tt.