flavio81
pfm Member
sq's Kuzmaesque with Geddon update and drag,
What turntable is that? "Kuzma-esque"?
The graphs look fantastic !
sq's Kuzmaesque with Geddon update and drag,
683 wasn't there, so it's 687.Many thanks Paul, was the file from my post 683 or 687?
Flavio, it's a Kuzma Stabi/s 12" version. But I have replaced the bearing, subplatter,platter and motor with Lp12 parts and built a PSU based on a large isolating transformer and simple phase shift capacitor network. The real improvement comes from modifications to the bearing which has increased drag.
Flavio, you can polish your bearing all your like, it might make a tiny difference to the rotation of your deck. I wouldn't waste my time trying it.
The issue seems to be that because of the low number of motor poles, and the large variation in attraction between rotor and poles across the course of one motor rotation that the motor will 'peak' as elements pass come towards other, increasing its ability to pull the belt, and 'trough' as the motor elements pass each other. The PL71 polar graph is a perfect example of this effect.
Adding viscous damping to the bearing adds a constant, almost linear load to the bearing. The idea being that the increased load from drag swamps the variance in attractor between motor elements as it rotates. This would seem to be proved true by the results achieved.
So you could polish your bearing to a mirror finish and that might even out bearing drag, but it will do nothing to damp the motor variance and it really is the effects of this 'cogging' in the motor that ruins speed stability.
If you had a huge heavy platter and very weak motor, then maybe bearing smoothness would be important enough to worry about. In most decks it isn't.
The issue seems to be that because of the low number of motor poles, and the large variation in attraction between rotor and poles across the course of one motor rotation that the motor will 'peak' as elements pass come towards other, increasing its ability to pull the belt, and 'trough' as the motor elements pass each other. The PL71 polar graph is a perfect example of this effect.
Adding viscous damping to the bearing adds a constant, almost linear load to the bearing. The idea being that the increased load from drag swamps the variance in attractor between motor elements as it rotates. This would seem to be proved true by the results achieved.
That is interesting, I had always wondered why multi-motor designs like the Voyd worked and that could be the answer - if you align the peaks and troughs from different motors, you get a smoother total torque. It would be interesting to be able to directly measure these torque ripples, I note from a quick internet search this data is not on any motor spec sheets.
This idea has been used on the Bauer DPS
This is still an ongoing project.I am not sure you are still interested.
At the moment I'm not willing to support it, so it seems best to keep it in house.In the process of building my diy turntable I became interested in measuring its performance. Are you willing to share the software you are using?