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Old 15th April 2016, 02:28 PM   #1
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Default DD pancake motors

Looking at my motors stash ready to start playing with the backlog of DD projects and thinking I ought to have a late model pancake motor for experimentation. I have one, from a JVC, but it's 2 phase and run with a FDD controller. Trying to find out if anyone made 3 phase pancakes (coils glued onto PCB style) in the 70s or 80s that found their way into anything affordable? So far my limited searching suggests most of the pancakes were in fact 2 phase.
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Old 15th April 2016, 03:09 PM   #2
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Have found one. Pioneer PL-200
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Old 16th April 2016, 03:17 AM   #3
Bare is offline Bare  Canada
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Why? a pancake motor?
Hunt around in RC aircraft Motors. Very sophisticated motors of surprisingly good precision... really cheap too at from 10$ to 200$ (if nuts)
Wayyy better machinery, by My observations than those foisted onto Audio gear .
Add in a decent Electronic speed control: 10/20$ and a suitable Battery and you can dial in rpm feed back precision TT makers barely even dreamed about.
Audio is technology's forgotten stepchild these days.
Look elsewhere for genuine surprise
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Old 16th April 2016, 10:27 AM   #4
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Yeah right. An RC heli motor will turn a platter directly. I did say DD. Given a cooking technics from 30 years go was quartz locked I assume you though I was talking about the all over the shop motors in cheap belt drives?

I want to test a theory/myth. the myth is that iron cored motors (such as used in the SL-1200) 'cog' and coreless motors (pancakes) don't and maybe mess with some 21st century contol schemes for BLDC. All for lolz, no sonic improvments expected
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Old 18th April 2016, 06:06 PM   #5
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I can show you a graph of 1210 motor speed per revolution as. 360 degree chart. The number of motor poles are blatantly obvious.

Cordless motors still cog, just more gradually, more like a shaded pole ac unit.
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Old 18th April 2016, 06:58 PM   #6
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I would be interested as the plots from the pink fish thread on that have vanished when I looked for them a couple of days ago. Step one is to replicate those. Step two is to see if newfangled drive methods actually make any difference
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Old 18th April 2016, 06:59 PM   #7
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Coreless motors don't have any inherent cogging, but for constant torque you need enough phases and large enough field poles so that you can switch phases through constant gap flux. That is, for simple "hard" switching.

Think of it as a bunch of underhung speaker coils.
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Old 19th April 2016, 09:55 AM   #8
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Bill, you're right they've all gone, i kept my own, but not the 1210 ones. Anyway, you could blatantly see the poles as a series of flat spots on the circle. it was almost an octogon.
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Old 19th April 2016, 10:02 AM   #9
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You could, I just never printed it to analyse what the magnitude was or check if this was visible as FM across the band. I'll check some of George's measurements to see if he has any evidence from his tests.
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Old 23rd April 2016, 06:14 AM   #10
benb is offline benb  United States
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Quote:
Originally Posted by Andrew Eckhardt View Post
Coreless motors don't have any inherent cogging, but for constant torque you need enough phases and large enough field poles so that you can switch phases through constant gap flux. That is, for simple "hard" switching.

Think of it as a bunch of underhung speaker coils.
I was shocked to read many years ago that the 1200 used square-wave drive - I assumed all DDs drove their motors with nice, low-distortion sine waves.

Sine waves would surely be a large improvement, but even sines likely won't give absolutely constant torque, due to the nonlinearity of the magnetic field vs. distance (something like inverse square or inverse cube). It should be possible to measure the torque an energized coil makes vs. the angle of the platter pole piece to the coil, and do an inverse function to generate "true" constant torque.

Quote:
Originally Posted by sq225917 View Post
Bill, you're right they've all gone, i kept my own, but not the 1210 ones. Anyway, you could blatantly see the poles as a series of flat spots on the circle. it was almost an octogon.
I saved the big pinkfish thread a few years ago when I saw it mentioned on diyaudio, if you can give me post numbers, I can likely find and post the plots, maybe even find some of the .wav files posted there.

I wrote some code to read frequencies in a .wav and output data for gnuplot, which is apparently exactly what the person in that other thread did.
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