Ultimate direct-drive : the platter IS the rotor.
The 10kg and 33cm pure copper platter has no magnets inside and is moved solely by implementation of induction coils creating Foucault currents - linear induction.
Despite the theoretical perfection of linear induction, variations of temperature on the shaft's lubricant calls for Quartz regulation through a frequency generator and a PLL loop....
The PX-100M started very much like a contemporary Micro Seiki with a separate tonearm base ; it then became a sort of "in-between" with a custom dustcover and then what was finally produced, with perhaps a penultimate sample with a layer of glass added atop the platter...
Despite making the cover of Radio Technology (01'82) and Sound Mate (03'83) and seeing an in-depth article in MJ, the 100M is an x-rare item with a production run of probably 100 units (or less) which was barely advertised in Japan, like the contemporary Lo-D TU-1000 (also Micro-engineered) : the highest s/n spotted so far is #59 (#1211 0059).
It seems, however, that the PX-100M is a very fragile item, difficult to restore with predictible results regarding stability. Maybe why Onkyo quickly stopped mentioning it in its japanese catalogs - or not.
There are two known units in the UK, one of which was imported from Germany, the other from a much more southern area, outside Europe. Another is still in Germany and there should be at least two in France...
A NOS/NIB PX-100M here, and a bashed one here (s/n 1205 0033).