Magnetic turntable bearing - Page 13 - diyAudio
Go Back   Home > Forums > Source & Line > Analogue Source

Analogue Source Turntables, Tonearms, Cartridges, Phono Stages, Tuners, Tape Recorders, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 4th July 2007, 02:22 PM   #121
YNWOAN is offline YNWOAN  United Kingdom
diyAudio Member
 
YNWOAN's Avatar
 
Join Date: Jan 2007
'Triumph' I have given a bit of thought to your '3mm tide' problem and can only conclude that it is due to the magnets being mounted out of square relative to the platter and/or the bearing housing. My own version of the bearing (which is quite different to your own) definately does not suffer from the problem you describe.

I also bought my most recent magnets from 'Supermagnetman'.
  Reply With Quote
Old 5th July 2007, 07:25 PM   #122
Triumph is offline Triumph  Netherlands
diyAudio Member
 
Triumph's Avatar
 
Join Date: Jun 2005
Location: Holland
Picture of my mk2 version. Notice the three adjusting screws at the bottom and the alu ring with three screws on the top.

But still it fails. I think because of the great push and pull forces, short type bearing etc.

Thanks for pointing me to "supermagnet" more magnets available than in Germany.
Attached Images
File Type: jpg magn bearing mk2.jpg (20.1 KB, 848 views)
__________________
Triumph
  Reply With Quote
Old 5th July 2007, 07:31 PM   #123
diyAudio Member
 
Join Date: Jan 2003
Location: Musicville
Quote:
Originally posted by Triumph
Picture of my mk2 version. Notice the three adjusting screws at the bottom and the alu ring with three screws on the top.

But still it fails. I think because of the great push and pull forces, short type bearing etc.

Thanks for pointing me to "supermagnet" more magnets available than in Germany.
I doubt your present design is ever going to work. If you can tilt the magnets or even move them laterally on the shaft using those brass screws, the ability to control parallelism between the magnets as the platter rotates is gone. You have to fix the magnets in position permantly and concentric with the axis of rotation. It is really simple if you think about it. Good luck.
  Reply With Quote
Old 5th July 2007, 08:55 PM   #124
YNWOAN is offline YNWOAN  United Kingdom
diyAudio Member
 
YNWOAN's Avatar
 
Join Date: Jan 2007
'Triumph', I'm afraid that I completely agree with the comments made by 'Vinyl-addict'.

The problem is not because of the "great push and pull forces" as such, or because of the "short type bearing". The problem exists because the magnets are not truly parallel to each other and/or are not perpendicular to the bearing shaft. Your adjustment solution is cunning but is difficult (if not imposable) to adjust to a significantly fine degree. I'm afraid the problem has to be engineered out at a more fundamental level.
  Reply With Quote
Old 6th July 2007, 08:11 AM   #125
oshifis is offline oshifis  Hungary
diyAudio Member
 
Join Date: Mar 2004
Location: Budapest, Hungary
Could this excellent magnetic floating idea be applied to a DIY linear tracking tonearm? Smaller weigth, smaller (bar) magnets...
  Reply With Quote
Old 6th July 2007, 10:57 AM   #126
diyAudio Member
 
Join Date: May 2006
Quote:
Originally posted by oshifis
Could this excellent magnetic floating idea be applied to a DIY linear tracking tonearm? Smaller weigth, smaller (bar) magnets...
I think the problem is the stability of the tonearm. I've been racking my brain, trying to figure out how to do it......so far my brain isn't up to the challenge! LOL
__________________
People in audio whom I admire.... Henry Kloss, Edgar Villchur, John Dahlquist, Bowers and Wilkins, Theil and Small, Don Keele, our own Nelson Pass. In short VISIONARIES.
  Reply With Quote
Old 6th July 2007, 01:29 PM   #127
diyAudio Member
 
Join Date: Feb 2006
Location: Willy, VIC
Quote:
Originally posted by oshifis
Could this excellent magnetic floating idea be applied to a DIY linear tracking tonearm? Smaller weigth, smaller (bar) magnets...
Unlikely. The application would fall foul of Earnshaw's theorem, which states that stable magnetic levitation with static magnets is not possible.

The thrust magnet schemes so far discussed get around this by using the bearing shaft as the mechanical "leash" element. This transfers the dynamic instability consequent to Earnshaw's theorem into rotational and especially precessional instability. I would be very interested to see whether anyone who has developed a completely floating magnetic bearing has actually measured these movements.

I can't see how you could achieve the same mechanical leashing with a linear tonearm. That doesn't mean it couldn't be done.
  Reply With Quote
Old 6th July 2007, 04:32 PM   #128
diyAudio Member
 
Join Date: Jan 2003
Location: Musicville
Quote:
Originally posted by Mark Kelly

The thrust magnet schemes so far discussed get around this by using the bearing shaft as the mechanical "leash" element. This transfers the dynamic instability consequent to Earnshaw's theorem into rotational and especially precessional instability. I would be very interested to see whether anyone who has developed a completely floating magnetic bearing has actually measured these movements.
Hi Mark, I did measure "vertical" movement on the bearing I made. I mentioned it on the previous page.
  Reply With Quote
Old 6th July 2007, 09:42 PM   #129
Aengus is offline Aengus  Canada
diyAudio Member
 
Aengus's Avatar
 
Join Date: Apr 2004
Location: Victoria, BC
Default Tonearm levitation

Could something like the drawing work? I'm envisioning the tonearm attached to a shortish angle-iron shaped magnetic structure which is trapped between two longer angle iron shped magnetic structures of opposing polarity. The two longer structures are embedded in a cylinder which is free to rotate in the vertical plane, allowing for warps and lifting the tonearm - or perhaps the tonearm could be hinged to its magnetic structure....

Seems that whichever axis the trapped structure tried to move along, it would be opposed by the outer structures - but perhaps this merely proves that I'm bad at thought experiments.

Regards.

Aengus

[Edit] Sorry, the image quality isn't great - by the time I'd converted to a .gif and then shrunk it, I lost a lot of detail. Luckily, my verbal explanation is impeccably clear.
Attached Images
File Type: gif drawing1.gif (20.8 KB, 1072 views)
  Reply With Quote
Old 6th July 2007, 11:22 PM   #130
diyAudio Member
 
Join Date: Feb 2006
Location: Willy, VIC
No, definitely won't work.

There is nothing to constrain the movement of the "floating" element except the magnets. Earnshaw's theorem says that they cannot achieve stable equilibrium so the system will move until some mechanical constraint is reached.

I would guess that the inner angle will tilt relative to the outer angle until the two lodge against each other but that's only a guess.

The problem briefly stated is this: a turntable platter only requires one degree of freedom, that of rotation around the Z axis. the sleeve bearing serves to constrain 4 of the other degrees (X and Y rotation and X and Y translation), leaving the magnetic bearing to constrain the last (Z translation). Since the disequilibrium forces from instability in the Z translation constraint will show up as X and Y translation and X and Y rotation (eg the platter will attempt to move sideways or rock) the sleeve bearing constrains them (adequately if it has really good tolerances, inadequately if not).

A tonearm however requires at least two degrees of freedom - If we assign the tracking direction as the X axis it requires translational freedom along this axis and rotational freedom about it. If a magnetic bearing is designed to supply the constraints on Z and Y translation then the instabilities again will show up in X translation and X rotation which are by definition not constrained. You therefore need a mechanical constraint which rather defeats the point.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Air Bearing Spindle DD Turntable monsieurphot Analogue Source 18 12th April 2008 07:05 AM
Other bearing for turntable use? Zero One Analogue Source 4 27th May 2006 01:13 PM
DIY turntable bearing bigbulb Analogue Source 9 11th July 2005 02:16 PM
Turntable bearing Tee-Rex Analogue Source 3 5th May 2005 06:55 PM
turntable bearing design sc351cobra Analogue Source 1 24th March 2005 10:30 AM


New To Site? Need Help?

All times are GMT. The time now is 08:38 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2