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In the Forum: Analog Playback
In the Thread: Copper Mat on a Micro Seiki Gun Metal Platter

Post Subject: From a physics perspective...Posted by chaslieb on: 1/30/2016

I don't understand why people are using the flywheel with the same thread coming off the motor to go around both the turntable platter and the flywheel. I also don't get why the flywheel is supposed to be used with a slipping thread at all. To make it simpler, if we look at the transmission of energy from the motor unit to the turntable platter like filling a bucket with water, the motor's goal is to keep the platter spinning at the same rate, which would in our terms mean keeping the water level the same in the bucket. The drag of the bearing, drag of the stylus and friction of the thread or belt are all reducing the amount of energy stored by the rotating platter. We can think of them as holes in the bucket.

The thread used to transmit energy is designed to slip on the platter. This clearly protects the motor from burning out, but also prevents speed variations in the motor from having an effect on the speed of the platter. If there is a slight increase or decrease in speed, the thread will slip and not transmit these micro variations to the platter. The same slippage which serves a purpose for a motor to platter, makes the thread a useless device to couple a flywheel to the turntable platter. If we go back to the water example, a flywheel adds energy storage and should make our bucket larger so that the small holes draining energy, by the bearing or by the stylus drag, have even less effect on the water level. In practice, the use of a thread to couple the flywheel to the turntable platter is like a small pipe attaching two buckets of water. When the water level in one goes down it will take time for the other to level it off because the transmission of energy, like the transmission of water between the buckets is not instantaneous. This can create an oscillation between the transmission and response between the motor, platter and flywheel and could be predicted to create speed instability. This situation is worse than having no flywheel at all! A solid coupling of energy, like simply stacking platters or an idler wheel between the platter and flywheel will ensure a tight coupling and instantaneous transmission of energy, like making a bigger bucket. If a belt is to be used between the platter and flywheel, it must be a rigid belt, meaning that it will not stretch or contract. Rubber is useless for this purpose. It also must grip both the platter and flywheel and therefore a coating that gives it such grip to avoid slippage is necessary. from what items are out there, only a non stretching fabric or plastic belt with some sort of gripping coating should be considered. Given the different job to be accomplished by the thread drive from the motor, which is meant to slip, and the tight coupling needed to make a flywheel effective it is amazing to see people who set up their turntables the exact opposite way; with the thread connecting the flywheel to the platter and the belt between the motor and platter. Probably just as bad are those who use a single thread to connect the motor, turntable and flywheel.

Looking at the microseiki.nl site I see that they say their flywheel should only be used with a thread. Considering the implications based on the coupling issues, I cannot guess why. Also, I see people say that the flywheel was meant to augment the air bearing and not the oil bearing. Given that the air bearing should have less friction losses than the oil bearing, I don't understand this either. It seems like the greatest benefit would not be to the air bearing which already has the advantage of less friction, but to the oil bearing that has more friction losses and therefore more to gain by added energy storage. I have not heard the flywheel used with thread or belt in any system and this analysis is solely scientific, and has nothing to do with anyone's personal experience in their system. However, in my way of thinking, math helps explain the subjective phenomena we perceive, so I put these thoughts out there to suggest a possible way to approach the use of the flywheel that may provide a benefit.
Charles

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