Airpumpless Ladegaard Tangential Arm - diyAudio
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Old 16th April 2004, 08:08 PM   #1
sreten is offline sreten  United Kingdom
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Default Airpumpless Ladegaard Tangential Arm

Whist pondering the design of this arm :

http://www.aiko.com/roscoe/airbearingarm.html

and dice45's airpumpless arm :

http://home.t-online.de/home/bernhar...LT-2_index.htm

It struck me that the airflow of the Ladegaard design
could be replaced by a magnetic repulsion bearing.

My estimates indicate that as long as modern magnetic
materials can support say > 500% of their own weight
this should be entirely feasible, at 500% the lateral
mass of the arm would only be increased by 20%.

A small price to pay for no airpump.

Or have I missed something ?

Anyone know what the actual percentage is for modern
magnets ? I would of thought its a lot more than 500%.

sreten.
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Old 16th April 2004, 08:21 PM   #2
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Why not indeed. Only contra-indications I "feel" are that the magnetic circuit of a magentic Ladegaard version would be very "open". So it would generate a large stray field. And while a lot of people atround here dismiss magnetic bearings for platter because of possible cogging, I'm afraid that this is a far larger problem with an arm that is not actively driven. I mean a platter has a large mass and even larger inertia and is driven, so any cogging will be not much of a problem. But the Ladegaard is "driven" by the groove only.

I really need to put mine together. All parts are already finished (more or less) but I never get around finishing the job. Only problem I have is that making the holes 0.3mm drilled through the AL profile, it generates a lot of resistance, so I need a bloody large compressor instead of an aquarium pump....
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Old 16th April 2004, 08:28 PM   #3
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by Havoc

Only problem I have is that making the holes 0.3mm drilled
through the AL profile, it generates a lot of resistance, so I
need a bloody large compressor instead of an aquarium pump....
I read somewhere you cover the holes (on the inside) with
electrical tape and then puncture this with a hypodermic.

Edit : sorry I misread, you have a pressure problem, not airflow.

sreten.
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Old 16th April 2004, 08:45 PM   #4
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Hi Sreten

Can you say more about your idea? I assume you'll still need some guiding rails/bearings, right?
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Old 16th April 2004, 09:06 PM   #5
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by analog_sa
Hi Sreten
Can you say more about your idea? I assume you'll still need some guiding rails/bearings, right?
you make something very similar to the Ladegaaard arm except
the guide and slide are magnetic material and add magnets.

The slide could be split into two small slides spaced apart,
for stabililty and minimum added mass.

The guide uses bog standard ceramic magnets.

The slide(s) use small high power modern magnets, these
need to be just powerful enough for levitation in the guide.

Should work ?

sreten.
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Old 16th April 2004, 09:07 PM   #6
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Hi Sreten,

It’s true that magnetic bearings can carry a lot of weight. But they also act as a (non-linear) spring and as such are, uhm well, very springy. Wonder how you gonna deal with this. This is also the case with air-bearings but that “bearing” is very thin and much stiffer.

Cheers
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Old 16th April 2004, 09:13 PM   #7
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by Pjotr
Hi Sreten,

It’s true that magnetic bearings can carry a lot of weight. But they also act as a (non-linear) spring and as such are, uhm well, very springy. Wonder how you gonna deal with this. This is also the case with air-bearings but that “bearing” is very thin and much stiffer.

Cheers
Yeah, I was wondering if it would simply refuse to stay in the guide.

But no fear, I have a solution for that - you add another
repulsion system above the arm to keep it in the guide.
This would be a very simple overhead flat linear system.

But I'm beginnning to see the problems :

If you make a stiff triangular repulsion bearing any misalignment
of the surfaces will impart a side force. And any uneveness of
the magnetic field would do the same, this is cogging ?

And there's the vertical resonant frequency to consider .

sreten.
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Old 16th April 2004, 11:43 PM   #8
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Hi Sreten
What about trying Your idea but with fieldcoil instead, You would get an adjustable system...
If coil is in guide rod there would be several adjust/control options?
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Old 17th April 2004, 12:05 AM   #9
dice45 is offline dice45  Germany
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Hello all,

not wanting to be a naysayer, but Nd-magnetic stray field? in the presence of 4 air-spaced unshielded phono leads with a 0dB-level of 200-600 µV? ... and cogging too has been mentioned ... that alone is reason enough not to do it.

While you are musing about Ladegaard-improvements, why not try to feed the air to the slider instead to the rail? Why not figur out a way to lead/guide the (ultra-thin & flexible) air hose in a way that the air hose pull helps the slider to move continuously centerwards?

One hint: with the air fed to the slider, you need only 4 nozzles (with pockets) at the ends of the slider's bearing surfaces and you have 100% nozzle coverage. Hence you can carry much more weight with the same pump as the air pressure does not collapse.

And another hint .... keep the nozzle pockets as small as even possible as they store pressurized air ... => could cause oscillations at higher frequencies.
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Old 17th April 2004, 01:12 AM   #10
sreten is offline sreten  United Kingdom
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Was just a thought, wondering if magnetic is possible. I don't
pretend to know much about air bearing arms, other than what
appears to be common sense, and I'm sure their are people
who've given air bearing arms a great deal of thought.

Quote:
not wanting to be a naysayer, but Nd-magnetic stray field? in the presence of 4 air-spaced unshielded phono leads with a 0dB-level of 200-600 µV? ... and cogging too has been mentioned ... that alone is reason enough not to do it.
DC magnetic fields are not a problem. Don't think cogging is either.

Quote:
Why not figur out a way to lead/guide the (ultra-thin & flexible) air hose in a way that the air hose pull helps the slider to move continuously centerwards?
Just point out that the arm generally travels much further back
and forth at the eccentric frequency than it does at the very
slow average speed towards the centre. IMO helping the slow
average speed towards the centre is not a technical issue.

regarding the basic idea :

With the comments so far I can see as usual the problem is far
more complicated than it first appears. And modification of
design using a different system is far from a "good" solution.

Pjotr :

You say magnetic bearing can carry a lot of weight - interesting.

If this is true then a very small system is required.

I need to give this some further thought.

P.S. all :

I'm just as interested in why it can't work as if it can.

sreten.
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