Tables That Feature Bearing Friction

Air would be a poor choice for a drive mechanism since it is compressable. Hydraulic fluid on the other hand is not compressable. Driving the platter with hydraulics would be an alternative choice. A pressurized bearing could also be utilized.

I'm not a turntable expert, just a bmw tech. I believe some models of Jeep/Chrysler used hydraulic cooling fan motors powered by the P/S pump due to the fact they are quieter. Perhaps a similar system could be made for a turntable? Just throwing out ideas.

Dear Rhljazz, a fascinating idea. This is something really worth discussing. You happen to have any links to technical exploration and the required periphery?

Hello Dertonarm,
>The "air-pulse" drive (no pulse would exclude a problem) has some considerable problems while looking close to a theoretical ideal first. It not only will require considerably (really serious...) periphery, but indeed a "assist"-motor to bring the (high mass) platter to requested speed first and than de-coupling.<

Weren't you asking about "all out",no compromise, no commercial consideration approaches? Did I not explain some of the caveats? Yes, the periphery would be expensive, but maybe not as expensive as it appears(remember, this is not about a commercially viable project).
The Onkyo PX-100M eddy current drive turntable does feature an idler drive just to bring it up to speed within half a revolution, then the eddy current drive takes over(and it has a break too). It can be done...
Platter speed needs to be monitored, which in turn can govern the force of the air(or any other driving) "pulse". It will have a VERY slow recovery time, but(that is where my chronometer analogy comes in) the disturbing influence of the drive system could be minimized.

To assess which principle is superior, we'd have to build two(or more) otherwise identical turntables that can be driven by more than one means. I have done this several times many years ago, Chris Brady has done this more recently, so his assesment holds merit, even if some may not agree with all of his peripheral design choices.

I suggest opening another thread to discuss that there is VASTLY more to building an excellent turntable then the drive principle, even though nothing else matters if the record doesn't spin at (as close to)constant speed to begin with.

Dertonarm, I didn't ask you any questions, I just showed that your approach is just as far from or as close to being perfect as some other approaches, at least from a conceptual/theoretical point of view. But that part of the discussion was doomed from the start... and yes, it's not neccessary to repeat yourself yet again.

Nevertheless, have an enjoyable and relaxing Easter weekend!

Frank

Dear dertonarm: Good to hear it, happy holidays.

regards and enjoy the music.
Raul.

I believe some models of Jeep/Chrysler used hydraulic cooling fan motors powered by the P/S pump due to the fact they are quieter.

I would speculate that the main reason for using a hydraulic motor is more to do with the high-temperature environment in which the fan motor must operate, especially if used on the back side of the radiator. At these temperatures, copper conductors get pretty lossy, and when running a 12V motor (drawing 20-30 amps), they start to really add up . . . in windings, commutators, brush leads, wiring, relay contacts, etc. And then you've got make up for those losses in power generation . . . and when a cooling fan is most important is when the vehicle isn't moving, hence engine speeds are low, and the alternator suffers from poor effeciency. In this application . . . hydraulic makes lots of sense.

But for a turntable, both air-vane and fluid-vane motors are far from vibration-free and cogless (go to an auto-body shop and listen to their air-vane-powered tools) . . . so there will be similar challanges as electric magnetic motors. Maybe an expanding-chamber screw-type armature fed by high-pressure hydraulic fluid? Then the problem is that you've got NO speed feedback, not even the fixed-frequency rotating magnetic field in an electric motor, and there's been disapproval voiced for a feedback speed control system.

Believe me, I'm not completely poo-poo'ing the idea, but rather will be extremely impressed if these challanges (and all of the others that I've not thought of) are able to be solved. And of course I'll want to read all about it, so do keep us posted.