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A tangential tracking pivoting tonearm
A tangential tracking pivoting tonearm
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Old 10th June 2021, 08:29 PM   #71
johnmath is offline johnmath  Australia
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Originally Posted by georgehifi View Post
This was a beauty.
This one wasn't:

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Old 10th June 2021, 10:54 PM   #72
georgehifi is offline georgehifi  Australia
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No that was was a good place to start, (an idea giver).

Cheers George
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Old 11th June 2021, 05:22 AM   #73
Bon is offline Bon  Australia
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Default Now I see it.

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Originally Posted by Bon View Post

Friction is not the only force at play here. If you do a force analysis of the tonearm at equilibrium, there will be a stylus frictional force in the forward tonearm direction. Assume that the sliding pivot is frictionless, for the sake of demonstration, as are the rear strut pivots. There will be a reaction force at the rear tonearm pivot, with a component directed towards the rear (the strut will be in compression).

There will also be a reaction component at right angles to the tonearm rear. This will be in opposition to the horizontal reaction force at the frictionless sliding pivot.
I should have taken more attention to my own observation

Quote:
Originally Posted by Straight Tracker View Post
Hello Bon,

Any tone arm that incorporates cams, links and levers to the LEFT of its pivot, will be subject to the inward force.

Ralf
I agree now.

Thanks to everyone who tried to put me straight with this design. The tonearm is tangential tracking but there will be sideforce.
I made a relevant observation early on but did not follow through on the consequences.

Assume the stylus tracking tangentially in a circular locked groove.
If the stylus does not move, the linear forces and torques must balance.
Assuming frictionless bearings, resolving forces along the tonearm, the stylus frictional drag on the tonearm must be balanced by the component in the tonearm direction of the reaction at the rear pivot.
This means the rear strut must be in compression. Then the component at 90 degrees must impart a clockwise torque about the stationary frictionless pivot at the origin.
This torque can only be balanced by a counter torque at the stylus. The groove must be pushing on the stylus at 90 degrees to the cantilever. There is sidethrust.

I now see where the complexity arises in other tangential tracking pivoting designs.
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File Type: jpg Tonearm sidethrust#2.jpg (38.7 KB, 17 views)
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Old Yesterday, 12:40 AM   #74
Bon is offline Bon  Australia
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Default Where to now?

Not totally ready to give up yet.

The geometry does give tangential tracking and the obvious measure to counter antiskating force is to provide a counter torque. My goal is a passive solution, so I will investigate an articulated tonearm strut connecting in front of the sliding pivot. I have added the linkage to my previous diagram. For purely reasons of aesthetics and simpler analysis, the new strut is attached to the tonearm mid point, to form a parallelogram. This reduces the number of variables substantially compared to an arbitrary linkage arrangement.

Firstly I intend to model and analyse the skating force for the original configuration, to have an idea of the varying nature of the sideforce. Then I will investigate the effect of the antiskating linkage. Even with the simplifying parallelogram arrangement, there are a number of parameters that can be adjusted to see if there is any possibility of (close to) perfect antiskate or a "sweet spot". The adjustable parameters include the tonearm original effective length and the subsequent attachment point for the linkage.

My original intention was to investigate whether tangential tracking can be achieved by a passive tonearm which does not resemble a Rube Goldberg machine. It is now looking increasingly unlikely. However, I am up for the challenge to see how close I can get, even if only as a concept. The increasing number of low-friction dependent linkage points is an obvious issue.

I did own 2 Garrard Zero 100 turntables for a short time in around 1970. They were purchased new, and at the time I was very excited with my first one. I was in college at the time and had a very modest system. Why did I have 2? Well the first one had such bad rumble I thought it must be faulty. I bought a second one, which was just as bad. A fancy tonearm could not compensate for typical cheap idler drive system.
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File Type: jpg Tonearm+antiskate.jpg (114.2 KB, 63 views)
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Old Yesterday, 01:25 AM   #75
directdriver is offline directdriver  United States
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Quote:
Originally Posted by Bon View Post
My goal is a passive solution, so I will investigate an articulated tonearm strut connecting in front of the sliding pivot. I have added the linkage to my previous diagram. For purely reasons of aesthetics and simpler analysis, the new strut is attached to the tonearm mid point, to form a parallelogram. This reduces the number of variables substantially compared to an arbitrary linkage arrangement.

A tangential tracking pivoting tonearm-tonearm-antiskate-jpg
Reminds me of the Thiele TA01 tonearm.

Click the image to open in full size.
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Old Yesterday, 12:20 PM   #76
Bfpca is offline Bfpca  Canada
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A tangential tracking pivoting tonearm
Hi folks. Great thread here and when reading it over I had a thought on the tone arm length changing in order to find tangency.
If you are playing a record that is off centre, an all to common occurrence, it appears that the tone arm and stylus would be oscillating in and out as the stylus is also moving side to side with each revolution. Would this cause additional pitch change as the stylus velocity is changing with the changes in tone arm length? Sort of a Doppler effect? If so, would this add to the pitch change we are already getting from the left to right movement of a conventional arm, or compensate for it? What would be the degree of this change in comparison to the existing side to side changes?
Thank you. I am really enjoying this respectful discussion where the magic of math is shown for use in solving a practical problem.
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Old Yesterday, 07:11 PM   #77
dtut is offline dtut  United States
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Bon,

The added arm is a good idea, but it will need to be pivoted something like the arrow added to your drawing in order to accommodate the arm movement across the record and the resulting side forces. It needs to be able to collapse forward.

One way to solve the Eff Length, Eff Mass, VTF problem would be to split two functions. Pivot a rail from the horizontal bearing that will carry the linear slider and mount the vertical bearings and the rest of the arm on the slider, either above or below. The new stub you added can be used to keep the vertical bearing housing vertical.

Unfortunately, bearings, mass and complication are added.

You and 2wice have come at PLT design from highly mathematical directions and, from a couple of his recent posts over at Angling For 90 degrees, he has developed a working design. I hope your attempt is successful, too.
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File Type: jpg Tonearm+antiskate.jpg (118.7 KB, 8 views)
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Old Yesterday, 08:11 PM   #78
georgehifi is offline georgehifi  Australia
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Lets face it though, get the angles perfect all the way across the record, thumbs up for that.
But you still got the big problem on at best channel separation of 30-40db at 1khz, 20db in the highs and almost 0db in the bass.
The one to figure that one out will make a fortune, then it will sound like the master tape being played, it's in the record grove, but the cartridge stuffs it up separating it and getting it out.

Cheers George
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Last edited by georgehifi; Yesterday at 08:13 PM.
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Old Yesterday, 10:05 PM   #79
Bon is offline Bon  Australia
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Quote:
Originally Posted by dtut View Post
Bon,

The added arm is a good idea, but it will need to be pivoted something like the arrow added to your drawing in order to accommodate the arm movement across the record and the resulting side forces. It needs to be able to collapse forward.

One way to solve the Eff Length, Eff Mass, VTF problem would be to split two functions. Pivot a rail from the horizontal bearing that will carry the linear slider and mount the vertical bearings and the rest of the arm on the slider, either above or below. The new stub you added can be used to keep the vertical bearing housing vertical.

Unfortunately, bearings, mass and complication are added.

You and 2wice have come at PLT design from highly mathematical directions and, from a couple of his recent posts over at Angling For 90 degrees, he has developed a working design. I hope your attempt is successful, too.
Thanks for the encouragement Doug.
I had come to all the same conclusions as you. The sidethrust cancelling strut needs to always have a forward component along the tonearm as well as the outward component for sidethrust cancelling. Aesthetics should not come into consideration until the full picture is known.

I intend to present all of my results in such a way that others can check them if they choose. First task is to model the side thrust for the uncorrected tonearm.

Then analyse the effect of an articulated strut with arbitrary lengths and location on the tonearm. A many variable optimisation may reveal appropriate set of parameters. That's the program anyway.
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Old Yesterday, 10:59 PM   #80
johnmath is offline johnmath  Australia
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Quote:
Originally Posted by Bfpca View Post
If you are playing a record that is off centre, an all to common occurrence, it appears that the tone arm and stylus would be oscillating in and out as the stylus is also moving side to side with each revolution. Would this cause additional pitch change as the stylus velocity is changing with the changes in tone arm length?
Warped records, platters with horizontal or vertical runout and eccentric records all cause significant pitch variations with both linear tracking and pivoting tonearms. Doppler effect is a good way of describing the resultant sound as it seems to 'come and go'. The main way of mitigating pitch variations is lengthening the tonearm; linear tracking arms are at a disadvantage here.
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