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Old 3rd January 2018, 06:57 AM   #1621
niffy is offline niffy  England
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Quote:
Originally Posted by nocdplz View Post
I think it can be reasonably applied to the stylus a drag of 2-3mN and 5- 6mN of side force.
5-6mN is way to much side force. With a typical cartridge this level of side force will result in a lateral tracking error of about a degree. It will not be just the stylus/groove that will be misaligned but also the coils/magnets of the cartridges generator. If you are accepting this level of side force your lateral tracking error is likely to be as bad or even worse than a conventional pivoted arm. It really does appear that side force/bearing friction is the biggest problem with pivoted tangential arms not the geometry.

Niffy
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Old 3rd January 2018, 07:21 AM   #1622
nocdplz is offline nocdplz
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Completely right* Niffy, but at this stage I just want to understand if this mess can move or not, using what I called the "skipping force", the maximum available.
If it does there will be the problem of using as little as possible with the most appropriate techniques, for now it is only a matter of vectors and after the Syrinx better understand everything before than after.
Speaking of side force, how much do you need on a good linear on bearings?

Carlo
*far, far worse than a good old Baerwald
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Old 3rd January 2018, 08:52 AM   #1623
niffy is offline niffy  England
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Hi Carlo,

The side force required to overcome bearing friction with a linear tracking arm is dependent upon the type of bearing used.
With an air bearing the fiction is very close to zero so only a miniscule side force is required, measured in uN rather than mN.
With mechanical linear tracking arms the amount of friction is dependent upon the coefficient of friction of the bearings and the mass of the carriage. An arm using ball race bearings running on borosilicate glass will have a coefficient of friction between 0.006 and 0.01 dependent upon the quality of the bearings. An arm like the clearaudio which, if I remember correctly, has a mass of about 75g would require around 4.5mN side force to overcome bearing friction. (i am assuming that clearaudio uses very high grade bearings) So better than a conventional pivoted arm when looking at lateral tracking error but not by a huge margin.
With my arm using jewelled pin bearings running tungsten carbide wheels on a tungsten carbide rail the coefficient of friction is 0.0017, much lower. With my carriage mass of 55g the side force required to overcome friction is about 0.9mN.

Niffy

Last edited by niffy; 3rd January 2018 at 08:56 AM. Reason: Missed a zero
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Old 3rd January 2018, 09:19 AM   #1624
nocdplz is offline nocdplz
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very, very low: must be really excellent bearings.
The data you quote are taken at the cart point or at the stylus? if I remember correctly the side force to a cart with friction applies according to the cosine. I think it is also essential to have a very short arm like yours, in spite of azimuth problems on warps. Do air bearings have laminar flows? because if not could be tricky with resonances.
Lots of questions better to talk on your forum, someday
Carlo
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Old 3rd January 2018, 09:21 AM   #1625
niffy is offline niffy  England
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Hi Carlo,

Measured at the stylus.

Niffy
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Old 3rd January 2018, 09:43 AM   #1626
nocdplz is offline nocdplz
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unbelievable. So the cart glides with just a bit of that forces: evidently i' ve a lot to learn about bearings, and tonearm building
thanks carlo
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Old 3rd January 2018, 12:03 PM   #1627
nocdplz is offline nocdplz
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Hi Twice.
I've done an overlay on the dimensions and layout that you sent me to work on it: you managed to reduce errors in an incredible way. It would be nice to use standard diameter pulleys that can be bought, to allow a construction without a lathe
Even if the solution with runout could be feasible (I tried just for fun) now seems really unnecessary: + - 0.5mm of overhang is completely inaudible. And then, since i'm stupid, i like to K.eep I.t S.imple.
On this basis I think it's possible to make a mock-up, but since to be useful will almost be like making the working arm, before I'll have to re-study a bit of Static, to see what kind of forces can be found on P (and HP).
carlo
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Old 3rd January 2018, 01:40 PM   #1628
2wice is offline 2wice  South Africa
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Hi Carlo

I think there is merit in this new design and would love to see you make it work.
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Old 3rd January 2018, 04:22 PM   #1629
nocdplz is offline nocdplz
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Not even if the tonearm moving against the moving pivot rotation will work.

Yes, there is something strange that I can not understand, but does not convince me: that knee joint that must open for 40 e.g. I tried to break down the forces and the torque on the pulley HP seems to act against, but should be impossible trough the bearing. Before doing even the mock up better to have clearer ideas on what happens.

Your solution seems to have less problems and is easier, if the pulleys can be kept in contact in the right way

Carlo
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Old 4th January 2018, 03:02 AM   #1630
dtut is offline dtut  United States
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Carlo,

Some construction thoughts: I assume you are using ceramic hybrid bearings. Try those made for yo-yos.

An angular contact or a deep groove bearing is a good idea for the top bearing in the support column because it carries so much of the vertical load. The others can be radial.

Check out preloading: Bearing Preload Facts and Information - NMB

Consider alighiszem's binding force link at #1525 if you are going to use the cantilever design in Birch B #1605.

Side and stylus forces aren't the only ones. Gravity is a trouble maker for PLTs. The axes for horizontal movement have to be as vertical as possible or the wand motion becomes erratic.

Horizontal effective mass builds up quickly.

You may have to add half the belt thickness to the pivot diameters to be accurate.

I haven't quite figured it out, but it may be that skating can be our friend.

The parking problem I mentioned is about Birch designs with a bearing at point B. The headshell is very close to the platter at rest. Your design and the two arm design solve this.

I'm going to be traveling for about ten days. I try to stay in touch.

I agree with 2wice at #1628
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