Icsaszar - again stylus drag
it is difficult to feel certain things without putting hands and eyes on; with traditional arms there is no direct experience. So I did again the guide test with the string from the middle point to show in pictures what happens. Without any guide this carriage goes to the end of rail, but now advances by 2-3 mm at best - it can barely stretch the splines of a 0.1 mm fishing line. Difficult to rely on this
Now I'm thinking a set up to make direct measurements of stylus drag and side force; If some result will emerge I'll post
carlo
it is difficult to feel certain things without putting hands and eyes on; with traditional arms there is no direct experience. So I did again the guide test with the string from the middle point to show in pictures what happens. Without any guide this carriage goes to the end of rail, but now advances by 2-3 mm at best - it can barely stretch the splines of a 0.1 mm fishing line. Difficult to rely on this
Now I'm thinking a set up to make direct measurements of stylus drag and side force; If some result will emerge I'll post
carlo
Attachments
Carlo,
I was very sorry to read The Syrinx did not perform as hoped. It's still a beautiful arm and I believe the 'string gadget', one of the most interesting ideas on this thread recently, can still be effective. I think it's possible the binding bearings problem can be solved with a different sled using radial load ball bearings.
I really appreciate your excellent work, careful tests, and thoughtful explanations. If I can help with The Syrinx or a Birch arm, please let me know.
Alighiszem: Thanks for posting the binding ratio link. It answered some long-time questions for me. I think the 2:1 ratio may be important in any design using a pivot arm like the Birch.
Walterwalter: I hope you are going to post your arm.
I'm convinced from my own experience, and now from Carlo's work, that the dominant force working on any tonearm is the side force and that stylus drag contributes very little, if anything, positive. My test and Carlo's seem to indicate that side force is as much as a magnitude larger than stylus drag.
Phivates and walterwalter are right: The stylus is stuck in a rut and the resulting force moves the arm, any arm. With pivots, stylus drag is only a factor in skate; in parallel trackers, it's irrelevant; and in PLTs, its role is minor at best.
PLTs, including Frank Schroeder's, extend at a specific rate determined by the designer's choice of geometry and the side force acting on it.
I was very sorry to read The Syrinx did not perform as hoped. It's still a beautiful arm and I believe the 'string gadget', one of the most interesting ideas on this thread recently, can still be effective. I think it's possible the binding bearings problem can be solved with a different sled using radial load ball bearings.
I really appreciate your excellent work, careful tests, and thoughtful explanations. If I can help with The Syrinx or a Birch arm, please let me know.
Alighiszem: Thanks for posting the binding ratio link. It answered some long-time questions for me. I think the 2:1 ratio may be important in any design using a pivot arm like the Birch.
Walterwalter: I hope you are going to post your arm.
I'm convinced from my own experience, and now from Carlo's work, that the dominant force working on any tonearm is the side force and that stylus drag contributes very little, if anything, positive. My test and Carlo's seem to indicate that side force is as much as a magnitude larger than stylus drag.
Phivates and walterwalter are right: The stylus is stuck in a rut and the resulting force moves the arm, any arm. With pivots, stylus drag is only a factor in skate; in parallel trackers, it's irrelevant; and in PLTs, its role is minor at best.
PLTs, including Frank Schroeder's, extend at a specific rate determined by the designer's choice of geometry and the side force acting on it.
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I was planning to do simple and cheap prototype of this arm; but due to personal work am not finding any time. I suppose we can use anti biasing string and weight to help whatever little stylus drag is there. Put an antibiasing string and weight as shown in following picture. In typical turntable the stand which holds the bias weight is fixed but here it is not so the forces act in both direction pulling both wands A and B. So the tonearm(B) moves forward. The weight can be adjusted. This way we solve both antiskating and tonearm moving forward problem.
Regards
Attachments
Thanks for supporting Doug, I'm stil in mourning** - With syrinx the problem seemed the bearing upon the horizonthal pivot, but with this second attempt with advanced bearing? Consider too that when the record is stopped, that bearing slides back (like in left photo) pulled by the splines of a 0,1 line, and not in axis! I think, and not from now (#1391) that the Baerwald geometry is much smarter than what it looks because the offset generates centripetal force (too much. unfortunatly) that aids to rotate the arm. With 0 offset maybe forces are quite balanced, and side force must be generated also by some cantilever offset, following next grooves of the spiral. Maybe experts may enlighten me.
Measures (attachment)
Basically a ballistic pendulum; the idea is to measure the forces by angular displacement. (h = potential energy), in fact, all values - length, mass of pendulum and peripheral velocity are known. Stylus drag and side force are calculated as the mass of the bullet. Maybe before losing time in other mistakes if someone helps me I'll be happy.
carlo
ps - your measure seems realistic: found 1,1 resistance on syrinx and it does'nt move, the new one has lower with same result - what's VTF used? - ** pps - consolation: 3Points now beautifully playing .
Hiten: seems clever, keep us informed
Measures (attachment)
Basically a ballistic pendulum; the idea is to measure the forces by angular displacement. (h = potential energy), in fact, all values - length, mass of pendulum and peripheral velocity are known. Stylus drag and side force are calculated as the mass of the bullet. Maybe before losing time in other mistakes if someone helps me I'll be happy.
carlo
ps - your measure seems realistic: found 1,1 resistance on syrinx and it does'nt move, the new one has lower with same result - what's VTF used? - ** pps - consolation: 3Points now beautifully playing .
Hiten: seems clever, keep us informed
Attachments
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Regarding side force
Hi dtut,
With an unmodulated record the side force required to make the stylus skip will be equal to the tracking force as the wall of the groove is at 45°. With a modulated groove the amount of side force will be dependent not only on tracking force but also on the frequency and amplitude of that modulation. Cartridge compliance and damping will also have an effect. It is not easy to calculate the side force required cause skipping for a modulated groove but the required side force will be less than for the unmodulated example, e.g. less than the tracking force.
Just because the stylus is not skipping does not mean that all is good and well. The side force might be only just below the point where skipping occurs. With most cartridges set at the recommended tracking force the cantilever will be deflected from tangency by about 3° before skipping occurs.
The whole point of tangential tracking arms is to reduce lateral tracking error to as close to zero as possible. Making an arm that is geometrically perfect but has high bearing friction, that causes the cantilever to be deflected by several degrees, will result in a worse lateral tracking error than with a conventional arm.
With a good tangential arm the side forces have to be as close to zero as possible so that the cantilever remains tangential. Stylus drag on the other hand is always going to be in the 0.5-2g range, dependent upon tracking force and groove modulation. You actually want stylus drag to be an order of magnitude greater than side force not the other way around.
With any pivoted arm stylus drag will translate into skating force that is itself a sideways force. Apart from causing skating force stylus drag is not really a problem. ANY sideways force is a problem as it will result in a lateral tracking error and that is a problem.
Hi Carlo,
An arm as beautiful as the Syrinx has no right not to work. I'm sure that with your craftsmanship you will get a working arm before long.
Niffy
Hi dtut,
With an unmodulated record the side force required to make the stylus skip will be equal to the tracking force as the wall of the groove is at 45°. With a modulated groove the amount of side force will be dependent not only on tracking force but also on the frequency and amplitude of that modulation. Cartridge compliance and damping will also have an effect. It is not easy to calculate the side force required cause skipping for a modulated groove but the required side force will be less than for the unmodulated example, e.g. less than the tracking force.
Just because the stylus is not skipping does not mean that all is good and well. The side force might be only just below the point where skipping occurs. With most cartridges set at the recommended tracking force the cantilever will be deflected from tangency by about 3° before skipping occurs.
The whole point of tangential tracking arms is to reduce lateral tracking error to as close to zero as possible. Making an arm that is geometrically perfect but has high bearing friction, that causes the cantilever to be deflected by several degrees, will result in a worse lateral tracking error than with a conventional arm.
With a good tangential arm the side forces have to be as close to zero as possible so that the cantilever remains tangential. Stylus drag on the other hand is always going to be in the 0.5-2g range, dependent upon tracking force and groove modulation. You actually want stylus drag to be an order of magnitude greater than side force not the other way around.
With any pivoted arm stylus drag will translate into skating force that is itself a sideways force. Apart from causing skating force stylus drag is not really a problem. ANY sideways force is a problem as it will result in a lateral tracking error and that is a problem.
Hi Carlo,
An arm as beautiful as the Syrinx has no right not to work. I'm sure that with your craftsmanship you will get a working arm before long.
Niffy
NiffY : 0,5 > 2g - have you measured? How? And with 0 side force what can move a tonearm (pivoted or linear)? and how?
It seems to me that Doug found SD an order smaller than SF, and me too: that's why we want to make some measures after the words we've read around. That things are complicated and variable is known, so as in every test is necessary to reduce them as possible, even at the cost of non-exhaustive results
carlo
Thanks for "beautiful", but for me a superb racecar that does'nt move is simply an ugly paperweight. There something deeply wrong in that design, all advices to find it are welcome. And yes, in ten years i've made a dozen working tonearms of different types, toghether with more than dozen mistakes
It seems to me that Doug found SD an order smaller than SF, and me too: that's why we want to make some measures after the words we've read around. That things are complicated and variable is known, so as in every test is necessary to reduce them as possible, even at the cost of non-exhaustive results
carlo
Thanks for "beautiful", but for me a superb racecar that does'nt move is simply an ugly paperweight. There something deeply wrong in that design, all advices to find it are welcome. And yes, in ten years i've made a dozen working tonearms of different types, toghether with more than dozen mistakes
Hi Carlo,
0.5-2g drag.
Most cartridges fall in the tracking force range of 1.5-3g. The coefficient of friction between the stylus and record falls in the range 0.3-0.6 dependent upon groove modulation, stylus profile and vinyl composition. The drag is the tracking force multiplied by the coefficient of friction. Roughly rounded that gives the 0.5-2g. Most cartridges will fall in this range. Of course there are the odd example of cartridge that are going to have higher or lower tracking force and some stylus profiles and vinyl compositions that will result in differing c.o.f.
If we assume that the bearing friction is zero and there is no skating force then the only sideways force acting on the stylus will be that required to track the arm. (I am of course ignoring the sideways force due to groove modulation as this occurs at a frequency above that at which the arm moves)
As you are aware force = mass x acceleration.
The mass in this case is the effective mass of the arm.
With a perfectly centred record the arm tracks sideways at a near constant speed so there is zero acceleration.
Any mass x zero acceleration = zero force.
In reality there is always some bearing friction plus the flexibility of the wires so the side force is never going to be absolutely zero.
With a record that is not perfectly centred the arm has to be accelerated back and forth. A basic formula for determining the peek magnitude of this force is
Force = effective mass x angular velocity squared x twice the eccentricity.
All unit have to be SI. So effective mass is in kg , angular velocity in radians per second, and the eccentricity in metres. (Twice the eccentricity is equal to the amount you see the arm move from side to side) The resultant force is in Newtons.
As an example :
If we have a typical cartridge with a 15um/mN compliance mounted on an arm so total effective mass is 17g. The record revolves at 33 1/3 rpm (3.49 rad/s) and the eccentricity is 0.2mm. This is pretty typical/average.
The peek sideways force will be. 0.08mN.
(The average sideways force is this force divided by root 2. Which is 0.058mN.)
0.08mN is tiny. With our 15um/mN cartridge this would result in a stylus displacement of only 1.24um.
If the cantilever of our cartridge is 5mm long we can easily calculate the angular deflection using simple trigonometry. The deflection would be 0.014°.
There are more comprehensive formulas that take damping and resonance into account. I thought including them here would over-complicate this description and they give very similar results at this frequency, 33 1/3rpm.
So yes, there are side forces required to track the arm across the record but these are absolutely miniscule and do not cause any significant lateral tracking error. The tracking error due to friction is going to be much more significant.
I hope that this clarifies things.
Niffy
0.5-2g drag.
Most cartridges fall in the tracking force range of 1.5-3g. The coefficient of friction between the stylus and record falls in the range 0.3-0.6 dependent upon groove modulation, stylus profile and vinyl composition. The drag is the tracking force multiplied by the coefficient of friction. Roughly rounded that gives the 0.5-2g. Most cartridges will fall in this range. Of course there are the odd example of cartridge that are going to have higher or lower tracking force and some stylus profiles and vinyl compositions that will result in differing c.o.f.
If we assume that the bearing friction is zero and there is no skating force then the only sideways force acting on the stylus will be that required to track the arm. (I am of course ignoring the sideways force due to groove modulation as this occurs at a frequency above that at which the arm moves)
As you are aware force = mass x acceleration.
The mass in this case is the effective mass of the arm.
With a perfectly centred record the arm tracks sideways at a near constant speed so there is zero acceleration.
Any mass x zero acceleration = zero force.
In reality there is always some bearing friction plus the flexibility of the wires so the side force is never going to be absolutely zero.
With a record that is not perfectly centred the arm has to be accelerated back and forth. A basic formula for determining the peek magnitude of this force is
Force = effective mass x angular velocity squared x twice the eccentricity.
All unit have to be SI. So effective mass is in kg , angular velocity in radians per second, and the eccentricity in metres. (Twice the eccentricity is equal to the amount you see the arm move from side to side) The resultant force is in Newtons.
As an example :
If we have a typical cartridge with a 15um/mN compliance mounted on an arm so total effective mass is 17g. The record revolves at 33 1/3 rpm (3.49 rad/s) and the eccentricity is 0.2mm. This is pretty typical/average.
The peek sideways force will be. 0.08mN.
(The average sideways force is this force divided by root 2. Which is 0.058mN.)
0.08mN is tiny. With our 15um/mN cartridge this would result in a stylus displacement of only 1.24um.
If the cantilever of our cartridge is 5mm long we can easily calculate the angular deflection using simple trigonometry. The deflection would be 0.014°.
There are more comprehensive formulas that take damping and resonance into account. I thought including them here would over-complicate this description and they give very similar results at this frequency, 33 1/3rpm.
So yes, there are side forces required to track the arm across the record but these are absolutely miniscule and do not cause any significant lateral tracking error. The tracking error due to friction is going to be much more significant.
I hope that this clarifies things.
Niffy
Hi Carlo,
You are doing very valuable research, and I hope it will work eventually as you imagined. Doesn't cause the modulation of "Danger of Explosion!" (title of Hungarian heavy metal album that you are experimenting on) too much stylus drag ?
Just joking.
Was that ever patented?
I went through my file of patents on pivoted tangential arms that I’ve been collecting since starting to read this thread and thought I’d post the links here. Some were already posted earlier in this thread but I think I found a few you haven’t seen before. Newcomers to the thread might find these an interesting read on what the thread topic is all about. My favorite is US1386892 issued in 1921 for a pivoted tangential acoustical phonograph with a diaphragm soundbox instead of a cartridge. Were any of you around when that one came out?
CA582660 [year?] Burne-Jones:
Patent 582660 Summary - Canadian Patents Database
CH694567 [2005] Thales:
https://www.google.com/url?sa=t&rct...CH694567.pdf&usg=AOvVaw0Agb3HDE1aq5z46CvJ0xRQ
DE202013102003U1 [2013] Schuch:
Patent DE202013102003U1 - Drehtonarm fur Plattenspieler, Plattenspieler mit Drehtonarm und ... - Google Patents
Schuchtronic:
http://www.schuchtronic.de/Images/GebrauchsmusterSchuchtronic.pdf
US1386892 [1921] Acoustic Player!!!:
https://www.google.com/patents/US1386892
US1933400 [1933] Synchronized phonograph for movie sound (note disc plays vertically):
https://www.google.com/patents/US1933400
US1963673 [1934]
https://www.google.com/patents/US1963673
US2516565 [1950]
https://www.google.com/patents/US2516565
US2522997 [1950]
https://www.google.com/patents/US2522997
US2585396 [1952]
https://www.google.com/patents/US2585396
US2966360 [1960]
https://www.google.com/patents/US2966360
US2837339 [1958]
https://www.google.com/patents/US2837339
US2977126 [1961]
https://www.google.com/patents/US2977126
US2983517 [1961]
https://www.google.com/patents/US2983517
US3005059 [1961] Raabe
https://www.google.com/patents/US3005059
US3232625 [1966] Van Eps
https://www.google.com/patents/US3232625
US3476394 [1969] Birch
https://www.google.com/patents/US3476394
US3502339 [1970]
https://www.google.com/patents/US3502339
US3826505 [1974] Birch
https://www.google.com/patents/US3826505
US3920249 [1975] Birch
https://www.google.ch/patents/US3920249
US4111433 [1978] Raabe
https://www.google.com/patents/US4111433
US4153256 [1979]
https://www.google.com/patents/US4153256
US4344168 [1982]
https://www.google.com/patents/US4344168
US4497053A [1985] Wolff
https://www.google.com/patents/US4497053
US4722080 [1987] Dieckmann
http://www.google.ch/patents/US4722080
Chasing down a patent’s documented 'reference patents' and 'citing patents' leads to more and more patents on the topic, but now I have to quit for the evening. The ingenuity displayed in pursuing pivoted tangential arms makes my head spin. Hope I’ve dug up some fun reading for everyone.
Ray K
I went through my file of patents on pivoted tangential arms that I’ve been collecting since starting to read this thread and thought I’d post the links here. Some were already posted earlier in this thread but I think I found a few you haven’t seen before. Newcomers to the thread might find these an interesting read on what the thread topic is all about. My favorite is US1386892 issued in 1921 for a pivoted tangential acoustical phonograph with a diaphragm soundbox instead of a cartridge. Were any of you around when that one came out?
CA582660 [year?] Burne-Jones:
Patent 582660 Summary - Canadian Patents Database
CH694567 [2005] Thales:
https://www.google.com/url?sa=t&rct...CH694567.pdf&usg=AOvVaw0Agb3HDE1aq5z46CvJ0xRQ
DE202013102003U1 [2013] Schuch:
Patent DE202013102003U1 - Drehtonarm fur Plattenspieler, Plattenspieler mit Drehtonarm und ... - Google Patents
Schuchtronic:
http://www.schuchtronic.de/Images/GebrauchsmusterSchuchtronic.pdf
US1386892 [1921] Acoustic Player!!!:
https://www.google.com/patents/US1386892
US1933400 [1933] Synchronized phonograph for movie sound (note disc plays vertically):
https://www.google.com/patents/US1933400
US1963673 [1934]
https://www.google.com/patents/US1963673
US2516565 [1950]
https://www.google.com/patents/US2516565
US2522997 [1950]
https://www.google.com/patents/US2522997
US2585396 [1952]
https://www.google.com/patents/US2585396
US2966360 [1960]
https://www.google.com/patents/US2966360
US2837339 [1958]
https://www.google.com/patents/US2837339
US2977126 [1961]
https://www.google.com/patents/US2977126
US2983517 [1961]
https://www.google.com/patents/US2983517
US3005059 [1961] Raabe
https://www.google.com/patents/US3005059
US3232625 [1966] Van Eps
https://www.google.com/patents/US3232625
US3476394 [1969] Birch
https://www.google.com/patents/US3476394
US3502339 [1970]
https://www.google.com/patents/US3502339
US3826505 [1974] Birch
https://www.google.com/patents/US3826505
US3920249 [1975] Birch
https://www.google.ch/patents/US3920249
US4111433 [1978] Raabe
https://www.google.com/patents/US4111433
US4153256 [1979]
https://www.google.com/patents/US4153256
US4344168 [1982]
https://www.google.com/patents/US4344168
US4497053A [1985] Wolff
https://www.google.com/patents/US4497053
US4722080 [1987] Dieckmann
http://www.google.ch/patents/US4722080
Chasing down a patent’s documented 'reference patents' and 'citing patents' leads to more and more patents on the topic, but now I have to quit for the evening. The ingenuity displayed in pursuing pivoted tangential arms makes my head spin. Hope I’ve dug up some fun reading for everyone.
Ray K
I agree with your posts, Niffy.
However, I think much of the potential benefit from tangential arms isn't just because of improved geometric lateral tracking angle error per se. IMO there are two further, and often more significant effects: (a) that the line of stylus drag force is applied tangentially rather than at an offset angle (eg 20deg) which reduces a torque causing mistracing/mistracking by stylus preferentially riding up the inner groove wall. Effectively there's then non-symmetry to groove shape such that angles are effectively steeper if the groove turns toward the outer edge of the disk in an offset angle arm; and (b) smaller lateral tracking angle error can improve stylus attitude and reduce stylus-groove friction for some stylus profiles.
It's one of those picture's worth 1000 words, so hope this makes sense without. a) is an expansion of skate force in a dynamic situation - the average result is skate force, of course, but the dynamic result is momentary mistracing or mistracking.
Just my 2p worth.
LD
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Maybe we diyers are still believing to flat earth (flat like an LP): we see the sun rising up and we think it's running around us, we see the tonearm rotating on the platter and we think that a mysterious influence (the Side side of the Force) drives it to move and sound for us.
Well, Science clearly demonstrates (thanks Niffy) that there is only the stylus drag (vtf x friction's coeff. = 0,5> 2gr) and not the side force (zero acceleration = zero force - elementary, Watson) that appears only with eccentric disks taken from garbage, and so small (6 milligrams, homeopathic dose) that it is not the case to worry about. The stylus drag instead is so healty that it's enough for everything, and even more (skating as bonus)
Clear: so evident that with foggy memories of half a century ago I had almost got the same ideas #1536. Just thought of being crazy. You've convinced me: no more doubts, even in front of deviant behaviours of tonearms. (that's the science, baby, the Science ).
But please, convince also my poor Syrinx arm: because if pulled in axis with 1 or 2 g it rotates smoothly (Ray will be glad) but when put on a record it's nailed there like a mule.
carlo
just kidding, Niffy. Thanks instead for detailed and rigorous explanation: seems perfect on tangency, with uniform motion. But this motion is circular not linear (with centripetal acceleration ac= v2/r = 1,84 m/s2 for external groove, not zero - so there is always side force, and less stylus drag, since vtf generates both). Unfortunately Newton's laws are three, not two
Well, Science clearly demonstrates (thanks Niffy) that there is only the stylus drag (vtf x friction's coeff. = 0,5> 2gr) and not the side force (zero acceleration = zero force - elementary, Watson) that appears only with eccentric disks taken from garbage, and so small (6 milligrams, homeopathic dose) that it is not the case to worry about. The stylus drag instead is so healty that it's enough for everything, and even more (skating as bonus)
Clear: so evident that with foggy memories of half a century ago I had almost got the same ideas #1536. Just thought of being crazy. You've convinced me: no more doubts, even in front of deviant behaviours of tonearms. (that's the science, baby, the Science ).
But please, convince also my poor Syrinx arm: because if pulled in axis with 1 or 2 g it rotates smoothly (Ray will be glad) but when put on a record it's nailed there like a mule.
carlo
just kidding, Niffy. Thanks instead for detailed and rigorous explanation: seems perfect on tangency, with uniform motion. But this motion is circular not linear (with centripetal acceleration ac= v2/r = 1,84 m/s2 for external groove, not zero - so there is always side force, and less stylus drag, since vtf generates both). Unfortunately Newton's laws are three, not two
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Hi LD,
I'm not sure that I follow your last post. Are you saying:
Constant changing stylus drag results in what is essentially modulation of skating force. This would result in cartridge movement and hence a lateral signal, probably at low frequency, and made worse if it coincided with the lateral compliance resonance. Definitely an intriguing possibility.
As pivoted tangential arms also have skating force this would effect this type of arm as well.
If I have missed the point could you elucidate?
Niffy
I'm not sure that I follow your last post. Are you saying:
Constant changing stylus drag results in what is essentially modulation of skating force. This would result in cartridge movement and hence a lateral signal, probably at low frequency, and made worse if it coincided with the lateral compliance resonance. Definitely an intriguing possibility.
As pivoted tangential arms also have skating force this would effect this type of arm as well.
If I have missed the point could you elucidate?
Niffy
Circular motion and centripetal acceleration
Hi Carlo,
It's funny that you mention the flat Earth. Many people believe that the Earth is flat because locally it looks flat. This is because the Earth is very big and we are very small. Likewise, to the very small stylus contact point the large diameter curve of the groove looks locally straight.
With an unmodulated groove (for instance the lead-in groove) the groove walls are parallel to the motion of the record. There is no side force acting on the stylus and thus no stylus movement. (ok there is the small force and movement due to the pitch of the groove)
With the run-out groove the groove is angled relative to the motion of the record. This causes a force acting from the right that moves the stylus to the left.
With a modulated groove the angle of the groove changes constantly causing the stylus to move back and forth.
The curve of the groove has no effect other than that the right hand wall of the groove moves slightly faster than the left. Even at the very innermost groove (where the difference is greatest) the difference in speed is less than 0.01%. You may think that this will result in a very slightly different drag on the two sides of the stylus. However stylus drag is calculated as VTF multiplied by the coefficient of friction. The drag is independent of velocity so it will be even. When groove modulation is added into the mix the rapidly changing forces and speed completely swamps the small velocity difference.
Although the motion of the record is circular the instantaneous motion of the small section of the groove in contact with the stylus is, to all intents and purpose, linear. When I say linear I mean it. At the outside of the record the curvature of the groove over the contact width of the stylus is about the same as the curvature of the earth over 300m.
Centripetal acceleration.
A particle sitting on the outer edge of a record and revolving with it will indeed experience a radial acceleration of about 1.83m/s^ 2. The outer groove of the record will also see this acceleration. As the record is a robust solid it will stay in one piece and there will be no outwards movement and thus no outwards force. Unlike the particle the stylus does not revolve with the record but instead remains stationary above it and so it does not experience any radial acceleration.
Centripetal acceleration will have absolutely no effect on the stylus/groove interface or any other aspects of record replay.
Mr. Newton is still happy.
Niffy
Hi Carlo,
It's funny that you mention the flat Earth. Many people believe that the Earth is flat because locally it looks flat. This is because the Earth is very big and we are very small. Likewise, to the very small stylus contact point the large diameter curve of the groove looks locally straight.
With an unmodulated groove (for instance the lead-in groove) the groove walls are parallel to the motion of the record. There is no side force acting on the stylus and thus no stylus movement. (ok there is the small force and movement due to the pitch of the groove)
With the run-out groove the groove is angled relative to the motion of the record. This causes a force acting from the right that moves the stylus to the left.
With a modulated groove the angle of the groove changes constantly causing the stylus to move back and forth.
The curve of the groove has no effect other than that the right hand wall of the groove moves slightly faster than the left. Even at the very innermost groove (where the difference is greatest) the difference in speed is less than 0.01%. You may think that this will result in a very slightly different drag on the two sides of the stylus. However stylus drag is calculated as VTF multiplied by the coefficient of friction. The drag is independent of velocity so it will be even. When groove modulation is added into the mix the rapidly changing forces and speed completely swamps the small velocity difference.
Although the motion of the record is circular the instantaneous motion of the small section of the groove in contact with the stylus is, to all intents and purpose, linear. When I say linear I mean it. At the outside of the record the curvature of the groove over the contact width of the stylus is about the same as the curvature of the earth over 300m.
Centripetal acceleration.
A particle sitting on the outer edge of a record and revolving with it will indeed experience a radial acceleration of about 1.83m/s^ 2. The outer groove of the record will also see this acceleration. As the record is a robust solid it will stay in one piece and there will be no outwards movement and thus no outwards force. Unlike the particle the stylus does not revolve with the record but instead remains stationary above it and so it does not experience any radial acceleration.
Centripetal acceleration will have absolutely no effect on the stylus/groove interface or any other aspects of record replay.
Mr. Newton is still happy.
Niffy
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Drag force acting on the stylus is always tangential. This force vector can be decomposited to two vectors: one in direction stylus-arm pivot, and one in direction stylus-record spindle. For linear tracking arms the second is zero. For offset angle arms the second is causing skating force (pressure to the inner wall of the record).