Direct drive vs belt vs rim vs idler arm

Peterayer - that lurching almost disappears when he puts a constant load on the platter at the end which I thought was quite interesting.

We all know the TT in Halcro's video was the Transrotor Fatbob.
I dont think it is representative of a true "high mass" or "high inertia" TT for the following reasons -
Platter is only 11kg - even Brinkmann suggest minimum 15kg
Drive belt is elastic rubber - should be thread or inelastic material
Most high intertia TT's use a small pulley and drive the platter at the perimeter. Because of this gearing ratio it enables you to run the motor much faster and reduce the cogging effect by increasing the number of poles per revolution.
eg HM 1800rpm/4poles = 216 poles/revolution vs DD 33.333rpm/20poles = 20poles per revolution.
The Fatbob is driven by small pulley, small subplatter which means the poles per revolution will be significantly less than the 1800rpm scenario, but more than the DD.
So the Fatbob to me is an inbetween deck - mid mass platter , low speed motor, elastic drive and no speed correction.

What is really disturbing is that despite what was demonstrated the magazine reviews describe its superior ability on timing rhythm and pace.

When I cued up the same track on the Fat Bob, the recording became even more believable. The timing, rhythm, and pace were improved over the Leonardo’s.

Obviously the reviewers system went from really bad to just bad.

Dover,
Can you comment on how the Transrotor system might differ to those of Linn, Rega, VPI et al?

Dover, Sorry for being such a "creep". I do recall your citing Kelly's formula. It just seemed to me that he later modified his ideas. As I said, I may be wrong. If all I can do is to try to remember what someone else wrote, I am no authority. Anyway, from now on I will wear suspenders.

Halcro - Breaking newsflash -
This Fatbob could have the magnetic drive, where the belt drives a subplatter and it relies on magnets on the platter to "lock" to the attracting magnets on the subplatter. They say it reduces wow and flutter by a factor of 10.
Personally I would call this floppy drive - maybe thats the issue, certainly not as direct as a DD, idler, or thread drive..
http://www.positive-feedback.com/Issue50/transrotor.htm

The main difference is the heavy platter in comparison to the Linn/Rega/VPI. The VPI's are driven around the perimeter of the platter, so they run higher speed motors.
As far as motor for the Transrotor goes, I couldn't find any specs on the Transrotor whether its ac or dc. I assume no error correction but you could measure the back emf in the motor and use that to control speed, but there is nothing measuring the platter. As Richardkrebs says you have to engineer the motor/drive system/platter as a group. From what I hear in the video, my old Roksan, Sota & Townsend Rock TT's, which use rubber belts, would be more speed stable than the Fatbob.