Micro SX-8000 II or SZ-1

The SZ-1 motor has a built-in flywheel (which helps to make the motor box 6kg heavier than the SX8k2 motor unit) which also has an air bearing, and the floating flywheel is supposed to make the drive even smoother. The flywheel, will of course, raise the overall moment of inertia a bit as well (though not by a lot).

note: I am not sure where the VK gets their moment of inertia number. 26 tons/cm2 is way too high. Given the size/weight of the platter, you'd be physically limited to about 4t/cm2 - which is still pretty good (the biggest direct drive tables were less than half that, but they had torque going for them too).

Dear T bone: You are right, the number is 3.5 tons/cm2 for both: the 8000 and the SZ-1.

regards and enjoy the music.
Raul.

The required figures are in the link provided above.

The motor / flywheel has an inertia of 5.1 x 10^-3 kg.m^2.

It turns at 750 rpm, so the inertia referred to the platter is multiplied by the square of the gearing ratio.

22.5^2 = 506.25 so the total moment of inertia = 506.25 x 5.1 x 10^-3 kg.m^2 which is 2.58 kg.m^2.

In the perfectly ridiculous unit of tonnes.cm^2 this is indeed nearly 26.

Thanks Raul. I remember that number now (which I bet is for platter only; the motor flywheel would add another 8-10% to that number for the SZ-1). I think the Verdier and the highest-end Final Audio tables may have a higher moment of inertia (as would the table that Dertonarm put together a while ago) because of slightly massier platters, but it wouldn't be too much bigger (in the case of the Verdier at least) and I could probably suffer through ownership of the SZ-1...

Wonder why more people don't build dual-voltage motors (one high-voltage motor rim drive motor for start-up and another for maintaining speed on a belt drive). If you did that, you could run a VERY big flywheel and use the outside of your flywheel as your belt pulley, which would mean that you'd largely eliminate the belt tension issue (which Mark Kelly has written about). And this, in turn, makes me think back to the big thread about massy platters, belt drive vs DD, and alternate drive mechanisms that got reasonably technical.

T-bone

The problem with that idea (besides complexity) is that you lose most of the advantage of running an external flywheel because your gearing ratio is much reduced. Using the effective mass analogy as given above, a 5 kg flywheel of 150mm diameter coupled "outside to outside" would add about 3 kg of effective mass to the platter.

As a contrast, the motor arrangement in the "Saskia" table adds an effective mass of about 85 kg.

In any case there are other ways of addressing the limitations of belt drives regarding creep (which is what I assume you mean by "the belt tension issue". There will be a completely new take on the issue exhibited at RMAF come October if everything goes to plan.


Mark Kelly