Recommended DC motors for turntable

[mratx]

Does this group have any recommended DC motors for driving lathe turntables? I'm assuming a high torque brushless dc is the way to go, but didn't know if anyone has a specific recommendation based on experience. I know Flo had used a Premotec on his modified portable lathe, any other suggestions? I'd like to drive a fairly heavy 16 inch platter.

Thanks,

Mark

[flozki]

hello Mark
the premotec was just laying around... not the reference.
and it only works with belt driven TT's as they dont run stable on direct.

but if you go the belt way you find cheap some bldc with electronics for 30-50$ esy
happy cutting
f.

[dmills]

I am playing with a Yaskawa coreless direct drive servo motor SGMCS-05B3C11 as a direct drive on a 14 inch platter, 5nm =~ 50kgcm of torque which should be fine.

One thing I did find is that the servo driver seems to chop at 6kHz, which given the very low running torque can wind up audible in the air, unsure as yet if it will show up on the disk, might need to add a sinewave filter between the drive and the motor, or build an analogue driver, we will see. One nice thing is that being coreless there is NO cogging.
Currently hoping the bearings will quiet down when it has run a few days or I might have to rethink using the motor bearings for the platter support, it is not BAD but well, given the playback curve ANY LF rumble would be bad news.

Speed range is 0 - 200RPM, and it has a fairly high count optical encoder so the speed feedback is nice and tight.

These are **expensive** new, at least most of the time, but you do sometimes get a deal on fleabay, think I paid about a hundred quid for mine (And then the same again for the cable harness, grumble I hate surplus places that cut cables).

One slightly boring detail is that the servo amp in 'internal control' mode can hit 33.3RPM but not 100/3rpm, so if I want the speed to be exact I will have to put the drive in torque mode and wrap a PLL around it. Might be easier to leave it at 33.3 and just jigger the sample rate in the digital doings to fix the minor error up there, not a big deal either way.

I will warn you off the NSK version of the same idea, their driver doesn't have speed as a first class citizen, only position, and I have never gotten it to not cog like a bastard.

[uvoscillator]

would be bad news.

hey hey, any news about this motor exploration yet?

[dmills]

Ask me for anything but time...

I am increasingly convinced that I will wind up doing my own motor driver for the thing as the servo loop is overly difficult to stabilise when swinging a heavy platter at near zero torque, it is just not where that drive electronics really lives, which is a little annoying.

[farmersplow]

I have also come to the conclusion that it is necessary to develop our own drive electronics.
BLDC motors on the market are always based on torque or fast running.
Both are negative for a turntable drive.
It is therefore necessary to ensure that the motor is designed for slow synchronisation, which is usually the case if the motor has a large number of magnets (coils) and the magnets are inclined.
(That's why I built a motor like this).

The three Hall sensors are not sufficient for control. An encoder that can recognise at least 1000 positions per revolution is required for position control for speed stabilisation.
This is necessary to ensure a correspondingly constant speed even with varying torque.
The optimum solution in such cases is field-orientated control (FOC).
This sinusoidal commutation method also relies on a programmable controller to calculate the stator currents required to drive the rotor based on the motor's current feedback.
(This requires a very fast microprocessor, which is much faster than that of the Auduino)
I am working on the development

Thomas

[farmersplow]

I have also come to the conclusion that it is necessary to develop ... bla bla bla...
Thomas

Addition: This is for direct drive