Direct drive vs belt vs rim vs idler arm

Mosin - no worries. The silk thread I use only seems to slip fractionally on start up, but the 20kg platter can be up to speed in less than 1 rotation, depending on how I tension it, which I think is pretty good considering the pulley is only about 10mm versus the 20kg platter. This suggests the silk has very good grip. With the high mass platter it does drive the motor pulley as well. If I turn the motor off, the platter/thread will drive the motor for a while. The designers original intent was that the silk should be "chalked", I presume for a controlled slip, but I prefer direct. The silk lasts a long time as in can go for a year or two. The only breakage I've had in 20yrs is when I've moved the deck and once when I went on holiday for 6 weeks and left the TT running ( I think high humidity weakened the silk fibre ).
Timeline speed checked on playing records inside/out etc and it's rock solid. These things all come down to the quality of the implementation, whatever direction is chosen.

"These things all come down to the quality of the implementation, whatever direction is chosen."

Exactly. :)

First, belt drive tt's in general have high mass platters.

Tony, some belt drive decks have high mass platters, but MOST? Some certainly do, but I would venture to say that most belt drive decks on the market, both new and used, do not have or were not designed with platters that I would characterize as high mass platter.

But I guess it depends on what you consider to be "high mass".

I'd say that high mass would be something like 100 times greater than the mass of the record. That would be about 15 kg.
This discussion got me in the mood to check my platter speed again. After playing several records the tt was warmed up and I know from measurements before that warmup is critical. I had a small bit of drift (about 0.5Hz out of 3150 Hz) after setting the speed several months ago. I dialed speed back in and had some good results: -0.01%/+0.02% Wow&Flutter and the speed plot over time shows a sine wave with a 5 second period. I believe the +/- speed variation over 5 seconds is the control system holding speed about the setpoint (At any rate I feel these values are well below audible detection and are an order of magnitude better than the records themselves.) This app is a very good objective measurement tool, I think, for dialing in speed and checking to see if your tt is operating within the manufacturer's specifications. No more, no less.

Here's an interesting test for those of you who have belt drives, especially those with rubber belts like the VPI's. Place your finger lightly on the belt where it leaves the motor capstan and is being pushed to the platter. Feel that vibrational energy that's being transmitted to the platter? You don;t feel it as much on the other side of the belt, where it is being pulled off the platter to the capstan.

A simple solution is to place something fairly heavy and smooth up against the belt between the capstan and the platter to help dampen and absorb that vibration.

I don;t feel any of that with my silk thread, and I would bet there is little to feel also with mylar tape.