Nottingham spacedeck motor - driving me crazy

As you may know, that motor is never "off". The push you give to the platter seems to engage some sort of clutch to then drive the platter properly. My guess is that there is some critical loss of torque for some reason, such that the motor cannot get going up to mechanical advantage needed for 33 rpm, but it is probably barely OK to get going using the 45 rpm part of the pulley. To test that, you might try starting it at 45 and then flick the drive belt down to the 33 pulley, see if it can then stabilize at that speed.

There's no clutch in the Spacedeck's motor. It's a simple AC synchronous motor, intentionally too weak to start the mass of the platter from a stop. The Spacedeck's designer, the late Tom Fletcher, argued that the motor's real job is just to keep the platter rotating. He believed that motors powerful enough to put the platter in motion were therefore oversized for their real job and vibrated too much. I vaguely recall experiencing the original poster's problem once. As I recall the issue is really that the motor (which is on a separate chassis or pod) has moved slightly closer to the platter, reducing the belt tension and causing it to slip on the pulley. Replacing the silicon belt with a string fixed the symptom because the string has greater "traction" than the OEM belt. My suggestion is to clean the belt with some cold water and dish soap, put it back in place, and move the motor away from the platter a small distance.

Thanks, Rob. You are most likely correct. Fletcher's idea of how to use the motor was closely allied to that of Lloyd Walker, except Lloyd uses a much heavier platter than did any of Tom's designs (well, never saw an AnnaLog or a Dias in the flesh). I never experienced this particular issue with my Hyperspace. Occasionally I noted that the motor had crept too close to the platter, but it still worked fine to bring it up to speed. So, why does this Spacedeck work fine at 45 rpm but not at 33 rpm? I would think that belt slippage would be a factor at either speed.

45 RPM is harder for the motor to pull than 33 1/3, like trying to get your car moving in 2nd gear instead of first. If it will work at 45, the problem is not the motor.

I suspect that the reason the belt doesn't slip at 45RPM is because the 45RPM pulley has a larger diameter than the 33RPM pulley. Since the grooves for both speeds on the Spacedeck's platter are the same diameter, the belt must stretch to accomodate the bigger pulley. That stretch probably means that the belt is pulling "harder" on the 45RPM pulley than on the smaller one. The distance between the motor and platter seems to be critical. I have a PDF copy of the NA dealer manual and it calls for 6mm between the two pieces.