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

O.K. here is one for all the physics majors and engineers.

Does a high mass platter being belt driven offer the same steady inertia/speed as a direct drive or idler drive?
Is the lack of torque in the belt drive motor compensated for by the high mass platter. Object in motion stays in motion etc. Or are there other factors to take into consideration?
I am considering building up a Garrard 301 or Technics SP10, but is it all nonsense about the advantage of torque.
I am aware that the plinths on these tables can make a huge difference, I've got that covered.
My other options would be SME20 or Basis 2500 of Kuzma Stogi Reference etc.
If I have misstated some technical word, please avert your eyes. I don't want a lecture on semantics, I think everyone knows what I mean.
Thanks in advance.
mrmatt
clarkie
4 posts
 
I would just like to add my five-penneth.

Aren't the idler wheel and belt drive systems completely differing technologies/sciences? On the one hand (Belt) you have a large mass in rotation, a motor that only really pushes when the platter slows, and a flexible drive system (belt). One the other (idler) you have a clamp sytem where the idler wheel (inside rim) pushes the platter away from the centre bearing or (outside) pushes the platter towards the bearing. The platter is trapped between the bearing and the idler. (Depending where you are standing both idler types are the same.)

I don't see how a comparison can be made. They are just different and both work well or badly depending how well they are engineered and built.

:-)
quiddity
119 posts
 

Clarkie

I can't see where the distinction lies. In both cases you have a passive inertial element (the platter), an active source of energy (the motor, which also has inertia of its own) and a transmission (belt or idler) which links them.

The motor's function is to replace the energy lost from the system. The transmission's function is to adapt the speed of the motor to that of the platter.

Most of the distinctions made betwen belt and idler can be viewed in terms of how lossy the transmission is, it historically having been the case that belt TTs were made with a much lossier form than were idlers.

I think the inertia of the motor is also important but misunderstood.

Mark Kelly
t_bone
1,182 posts
 
Mark,
This aspect of inertia of the motor is something I did not really understand the last time it came up (because I assume you are not referring to motor inertia the way the Micro SZ-1 motor does it). If you were talking about that, then I can start to see where you see the similarities between an idler with a high inertia motor and a belt drive with high inertial motor where the belt slippage issue is addressed by bringing the slippage away from the belt-platter interface and to a kind of clutch mechanism which allowed the motor to more or less "apply" the belt to the platter with even force on both drive side and lee-side of the turn.
quiddity
119 posts
 

T-Bone

Maybe you have me confused with someone else.

I have never advocated the use of any form of slip in a turntable transmission. I understand the theory of it being used in an attempt to reduce cogging but I think it's the kind of half baked idea propounded by people who really don't understand the mechanics of TTs. You will have noticed that there are a lot of them about.

I have pointed out many timnes that belt creep (and idler creep) is an inevitable consequence of using compliant coupling materials but that could not be construed as advocating its deliberate introduction.

Mark Kelly
t_bone
1,182 posts
 
Mark,

I have not mistaken you for someone else. I am aware of your issues with belt creep. In fact, because I was trying to dance the long way around a subject which I think may be of commercial importance to you, I ended up mis-communicating. Please ignore my comment.

Play on ladies and gents...
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