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In the Forum: Analog Playback
In the Thread: Idler Drive - Rumbling Into The Future?
Post Subject: N-set number of idlers or beltsPosted by Romy the Cat on: 7/31/2010
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 N-set wrote:
The only purely theoretical point which is intriguing for me
in the whole multiple drive idea is whether one can achieve a uniform "floating" rotation:
the forces perpendicular to the spindle balance out
and the spindle rotates without (too much) intercation with bearing's walls.
Is it reliably, repeatedly and proveably achieveable
under dynamical condictions in practice?

 
I have no answers but I have a theoretical contra-argument. Why do you feel that uniform "floating" rotation is possible only with N amount of drives?  Let look in this deeper. A single drive would it be idlers of belt transmitting moment to platter has errors (slips, bends, elasticity…  etc). Those errors make a platter to reset microscopic backlash in bearing. The minute deviation of speed is not truly a problem but the platter rocking back in force while it clears the micro freedoms between mating element of bearing is a problem.
 
Now we presume that let say 3 idlers or belts driver the platter at 120 degree and they create more uniform rotation. Yes, the errors of each idler or belt is less critical and now it transmits 1/3 of moment. However, why we are under a presumption that idlers or belts errors have random character. What will happen if idlers or belts errors took place in near same time? We just have no control over it as the idlers and belts are not synchronized.  Now, let see how a single idler or belt work. The force of the moment from ONLY side permanently offset the backlash of the bearing, creating a mechanical biasing of the bearing errors. So, the theoretical conclusion is that a single drive is better.
 
In reality there is only two known to me ways to address the problem that agree with my theory. First is to make the bearing longer. The longer bearing shaft is less left-right backlash. The EMT 927 is way ahead in it that any other turntable. Second is increase the platter mass in order to make the platter do not sense the idlers or belts errors.  A large platter weigh has own issues with bearing but this is a whole other subject…
 
The Cat

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