That is a most interesting report, Marc. It raises many questions which I hope you or Vic can answer.
I had no idea that it takes 20 minutes for the speed to stabilize. Why is that? I had assumed that rim drive/idlers get the platter up to speed quickly and then stay that way. You write that it is up to speed in 3 seconds, but then I'm confused about why it is not stable at that point. How much does the speed vary during that 20 minutes and then how long does it take for you to confirm the speed before you play an LP? My SME takes about seven seconds for the speed to stabilize according to the blinking light on the motor controller.
Also curious is why the speed needs to be checked before each listening session after the 20 minute stabilization period. If it is stable, then why does it need to be checked? How does the system know when it is operating at the correct speed? Is the platter speed checked, or the motor speed, or both? Is there perhaps some degree of designed slippage between the wheel and platter?
I had thought that high torque motors were used to get platters up to speed quickly. If you don't listen for 20 minutes, why not use a low torque motor if the platter has enough inertia to combat stylus drag? Then it can get to speed gradually and perhaps vibration would be less of a concern.
Why does the system go out of correct speed and need to be adjusted after several days? Does vibration change the contact between the wheel and platter? And what method do you use to check for speed accuracy? Have you noticed any change in speed from stylus drag? If so, I presume you are then confirming speed while playing an LP.
Even with the fairly heavy platter on my table, it does slow down very slightly due to stylus drag, so I confirm speed with either the KAB strobe or TimeLine while a record is playing. I know ack does the same with his VPI. The only table that I have seen evidence of not slowing down with stylus drag is Halcro's Victor DD, and that video shows three arms all playing. Perhaps David's massive American Sound platter is immune also. I have met one audiophile who claimed to be able to hear stylus drag on all belt driven platters weighing less than 100 lbs so he got a heavy platter and replaced his rubber belt with magnetic tape for tape drive and reported a more stable speed.
A German designer was designing a turntable with intensional belt slip with a massive platter weighing over 100 lbs. The idea was to get the platter up to speed fairly quickly with an idler wheel and then to disengage the wheel and let the thread drive take over only occasionally slightly speeding up the platter when it slowed down, but never slowing down the platter because the thread would start to slip once the correct speed was achieved. I don't know if this table went into production.
Sorry for all of the questions, but I am curious now about the design intentions behind your Trans Fi direct rim drive table.
Never heard of motor warm up time either Peter, it doesn't make any kind sense! Regarding seeing any visual signs of cartridge drag, I can't seen any visual evidence (KAB, Ortofon or built in strobes) of it with any of my tts and that's with a 6.5 gram tracking Neumann. One caveat, I use a 0.5 kva industrial AC regenerator for all the motors.
david