Nottingham stepped motor

I just recently bought a used spacedeck but still need an arm for it. While doing some inquires I can across this bit of information. That nottingham is the only TT manufacture that uses a stepped motor and that stepped motors are the worst possible choice because of 'cogging'. Brushless motors and syncronous motors have some rumbling but do not have cogging and are therefore better. DC motor,with precious metal brushes, eg Maxon are the best. (this last part I think I understand) Could someone explain the sonic effects due to cogging, and is this really a problem with nottingham TTs.
Each "cog" of an AC motor gives the rotor a magnetic push. When the rotor is between cogs it coasts, and decelerates due to friction. The rotation of such a motor is a series of pushes and coasts. It never turns at one stable speed. The more cogs per revolution and the lower the torque, the closer to stable such a motor will be. But it can never be "perfect".

It's important to isolate the platter from such speed instabilities. The usual way is a stretchy belt, whose elasticity is meant to absorb these micro-variations. Unfortunately, an elastic motor/platter coupling leaves the system vulnerable to stylus drag, which can dull transients, audibly smear strings and female vocals and reduce transparency of complex passages. It takes a pretty revealing system to reveal these effects, so the stretchy belt compromise is often fairly effective.

A better approach, obviously, is to use a DC motor that doesn't have cogging problems in the first place. (It has other problems of course, there's no free lunch, but they are subtler and easier to overcome.) With a quiet, non-cogging motor you can use a non-elastic belt that rigidly couples platter to motor. Now the system can overcome stylus drag. A good direct drive TT would also want a stable, quiet motor of course.

Nott' uses a very low torque AC motor, so the difference between its push and coast stages is minimized. This should help eliminate audible cogging effects. Those with direct experience with Nott TT's could say more.

Below is an interesting thread comparing a Spacedeck with a VPI Scout. After the Spacedeck blew away the Scout, they swapped stock motors and also tried a Teres DC motor.

On the Scout:
- VPI motor was bad (unhappy Scout owner)
- Nott motor was better (pissed off Scout owner)
- Teres motor was best (Scout owner bought it, probably should have bought a Nott' or Teres in the first place!)

On the Spacedeck:
- VPI motor would not fit (no big loss, apparently)
- no detectable difference between Nott motor and Teres
That speaks pretty well for Nott's engineering.
This is one of the quitest tables on the market,and all of thier tables use the same motor, this is one of the best aspects to the design.You will never hear anything bad from this motor, a little info can be a dangerous thing
I have had a space deck for a month now. I was concerned about the motor because you can feel it vibrate when it is stopped. I bought it because when it played, it was very quiet and seemed to sound right. A definite improvement over the Scout that I auditioned.
I think the Nottinghams in general are good sounding tables. Apparently they have made a good working system using the items they have selected.