How far out to place motor from platter

Manitunc, assuming stretching the belt does not change the angular velocity of the motor it will not change the platter "speed" as this depends on the motor's rotation and the ratio of the platters diameter to the pulley's diameter. Changing the length of the belt by stretching does not affect the "speed". Changing the tension can affect the sound though. I have a Nott. Hyperspace whose motor shaft bearing had become "hogged out". Increasing the belt tension by moving the motor further from the platter made the sound unlistenable. Moving it in as close as possible and still maintain rotation made things bearable. Needless to say, a new motor improved things a lot.

John,
Stretching the belt necessarily make it thinner, and therefore, the radius of each pulley changes as the ratio is determined by the radius to the center of the belt at each end. And thats assuming that the increased drag from the side loading of the motor and platter bearing doesnt also slow the platter down. I know on my Transrotor Fat Bob, I can hear it slow down as I pull the motor farther away. There is a point of perfect tension, and it is different on each table/motor/platter/belt

Doug, Your comments are a perfect rationale for why I have become a devotee of idlers and direct-drives. You make a good point about the trade-off associated with having the motor pulley close as possible to the platter, but are we conflating belt "creep" with belt "slip"? I had not thought of that (mostly because I only worry about belt creep after the third slice of pizza). I was actually repeating a statement once made by Mark Kelly, or at least I thought I was. If the idea is flawed, then I probably misinterpreted Mark. There are two better solutions to belt creep. One is using a capstan-like device to keep the belt close to BOTH the pulley and the platter. (One commercial turntable does that, I think.) The other is to use two platters, one driving the other, with the belt wrapped in a way described by Mark and maybe also implemented by RS Labs, such that it is in contact with most of the circumference of both the driver and the driven platters.

I can only imagine one reason why the motors must be equidistant. First, it would seem obvious that we want the two motors to be as identical as possible in all parameters. If so, then it follows that we want their drive pulleys to be rotating at identical speeds, or as identical as possible. Therefore the belts need to be of the identical circumference. From that, does it not follow they would be equidistant from the spindle?

Third try. My last two posts never got posted. In the above post, I misspoke; the 2-platter solution to belt creep is commercially implemented in the 47 Labs turntable, not the RS Labs one. (In fact, RS Labs does not make a turntable, so far as I can tell.)

John, I owned a Hyperspace. Great turntable. As I recall, David Fletcher's crude instruction sheet advised placing the edge of the pulley practically touching the edge of the platter, a few mm's apart. When I later read about belt creep, I understood better why he did so. A Walker Audio Motor Controller made a profound improvement in the sound of my Hyperspace, much to my amazement.