The Wonderful World of Turntable Design AKA: Dave's Fugly World Of TT Wank

[bmtell]

Yes. How much more meat he can fit before he becomes wider than he is tall.

[Jim]

@bmtell

I think Jim’s thought experiments mostly include meat and his belly.

…don’t forget the naked women!!

[Jim]

@bmtell

Yes. How much more meat he can fit before he becomes wider than he is tall.

Pots, kettles…

When’s the last time you saw your winkle?

[crimsondonkey]

@Jim

When’s the last time you saw your winkle?

Crimewatch

[loo]

@Valvebloke

It doesn’t confirm his statement, only the physical effects that he ‘predicts’ on the basis of his statement. He’s right that a single rotating platter would tend to cause the boat that it’s on to rotate in the opposite direction, and that two counter-rotating platters wouldn’t. But his explanation that friction is involved in this is horse-poo. If you think about it for a moment you’ll realise that friction tends to drag the object which is supposed to be stationary in the same direction as the moving object, not the opposite direction. The reason the boat turns the other way under a single platter is the much more fundamental principle of conservation of angular momentum. As we spin the platter up from stationary we give it some angular momentum. Since, between them, the platter and the boat had no net ang mom to start with, they must still have no net ang mom once the platter’s spinning. So the boat must acquire equal and opposite ang mom to that of the platter, which it does. If there are two platters then their ang moms match and the boat doesn’t have to spin.

How does the boat spin in the opposite direction? Surely it would spin in the same direction as the platter, if it counter rotated there would be no twisting effect to worry about

[bmtell]

@loo

How does the boat spin in the opposite direction? Surely it would spin in the same direction as the platter, if it counter rotated there would be no twisting effect to worry about

It is because of reasons.

And the laws of physics.

[Valvebloke]

@loo

How does the boat spin in the opposite direction? Surely it would spin in the same direction as the platter, if it counter rotated there would be no twisting effect to worry about

What the electromagnetic force in the motor does is to set up a ‘push’ between the rotor (attached to the platter) and the stator (attached to the boat, or the earth) . The push acts on both the rotor and the stator. If the stator is attached to something really massive (strictly something with a large moment of inertia, but that often involves a large mass) then it hardly moves. The rotor does all the moving and the platter goes round while the boat or earth stays almost still. The way that a force results in opposing motions is more familar to us if we think of motions in a straight line rather than rotary motions, but the principles are the same. If you’ve ever been in one boat and pushed against another boat you’ll know that when you start pushing both boats move. If one is heavy and one is light then the heavy one doesn’t move much and the light one moves a lot. And they move in opposite directions (away from one another). The same’s true of rotation.

You’re right about the twisting effect though. There really is nothing to worry about.

VB

[mmichbam]

[akaYoda]

https://static1.squarespace.com/static/52699379e4b01768fee82182/t/52ed81c0e4b02959f854329c/1391296974560/?format=500w

I like this. The platter speed is locked by measuring the actual speed of the platter itself multiple times a second so no variations irrespective of load. The arm is massive and machined of multiple metal types to kill any resonances.

[murrayjohnson]

That kind of motor control isn’t particularly new though. I was looking at one of these in a hifi shop a week or so back. A very elaborate suspension system providing vertical isolation. No isolation afforded for horizontal excitation though. The stylus / groove needs to be isolated in all 3 planes if possible.

[Pan]

What is this? I like the big look.

[chelseadave]

It would make an ideal pottery wheel.

[Ruprecht]

@Pan

What is this? I like the big look.

It’s the hernia MKII which takes over from the very popular traction pro MKI.

[Valvebloke]

@chelseadave

It would make an ideal pottery wheel.

It would make a pretty decent fairground ride !

VB

[akaYoda]

@murrayjohnson

That kind of motor control isn’t particularly new though. I was looking at one of these in a hifi shop a week or so back. A very elaborate suspension system providing vertical isolation. No isolation afforded for horizontal excitation though. The stylus / groove needs to be isolated in all 3 planes if possible.

Hi

Genuine question but isn’t horizontal easier to isolate against, thinking the symposium roller block type arrangement with the deck sat on the moveable platform .

[ICHM]

I would like one of those.

[rmsshipbroker]

It’s very you.

[loo]

Nice pic showing how the Koma drives its dual platters

[BobC]

Round profile drive belt, stop that.

[ICHM]

@rmsshipbroker

It’s very you.

I know.