Help Ressurecting an Odyssey - geometry and effective mass?

[AndrewL]

Hi to all

the bending point should be at 226.9 mm from the center of the little dome and the angle is as Andrew says, 30°.

Seb

The length is less of an issue, I think, as a slightly oversize tube could be bent, and then trimmed to length accordingly.

Then bend seems to be the critical bit.

the best thing to do is may be a table indicating the perpendicular distance between the stylus point and the axe of the tube + the distance between E and the stylus point.

Yes, very good idea, a table of different possible effective lengths and associated measurements, I think 10.5" might be a good compromise, the issues seems to be that all the mass and the bearings are on the left hand side of the arm, this may pull thing inwards towards the spindle, if we're not careful.

Perhaps, 10.5" is also a nice compromise between alignment and friction/stiction?

I shall have a think.

-- Andrew

[AndrewL]

Just to give some rough ideas...

I'm not sure how Seb got 226.9 (not saying its wrong) these are just based upon my rough calcs/drawings which uses AE (222.93) in Seb's diagram as the point of the bend.

Anyway, 10.75" we need an extra ~47mm (plus headshell) on the end of the old arm, at 12" we need an extra ~73mm (plus headshell).

Please note, these are just to give a rough idea of how much extra metal the pillar has to support.

Seb's table should give us more accurate dimensions...

-- Andrew

[AndrewL]

Lateral balance...

I notice there's a good lump of the counter weight that is positioned to the other side of the main pillar (horizontal pivot). See page 20 of the Source-Odyssey Catalogue in the Library for the engineering drawing.)

I wonder, does the presence of this mass have some lateral balancing effect?

-- Andrew

[Seb]

I wonder, does the presence of this mass have some lateral balancing effect?

-- Andrew

yes, it certainly help to have a lateral balance.

so, here's the table for various effective length



if interested by the excel file, just ask

a new drawing is proposed (in fact, I made a little mistake on the first one (why didn't you tell me!!) about the FE distance).

whatever the effective length, AE (what we could call the arm tube) is constant and equal to 226.89 mm - if the arm is too long, the bending point will be in E. AE is constant because the linear offset (BD) is constant.

second drawing

so ?

best regards

Seb

[AndrewL]

Ah, thanks Seb (or should I say merci beaucoup).

The first penny has dropped! The 226.89 is the arm tube length for Loefgren, whereas 223 was the arm tube length for the original null points.

I now see why the bend should be at 226.89mm

I hoping j7 can manufacture the bend, that is the next big hurdle!

Although the headshell becomes much simpler to make with the bend than with a straight arm as we had originally discussed.

With a straight arm the tube must enter the headshell at a strange angle which is more difficult to drill. Then bend eliminates this and the tube enters on axis so the drill is at right angles to the back face of the headshell; drilling at an angle, is, of course, more difficult.

Tell me now, if this were your project what length etc would you choose?

best regards and thanks again,

-- Andrew

[AndrewL]

I'm drawing up two versions one at ~12" and one at ~10.5" for comparison, I will post as soon as I'm happy with the sketches.

Then its onto effective mass

cheers,

-- Andrew

[Seb]

well, effective mass...

take a look at the stevenson paper, the way to calculate the effective mass of a tonearm is explained. Now, the technique is for a straight arm, not for your strange one....

http://www.vinylengine.com/phpBB2/viewtopic.php?t=11568

prepare yourself for a heavy arm...

best regards

Seb

[AndrewL]

Seb to the rescue again..

I was going to do it from first principles using this stuff...

http://en.wikipedia.org/wiki/List_of_moments_of_inertia

I will read up on the paper.

I use a 103R so somewhere between 16-20gms would be fine, in fact, the more mass the 103 sees the better it seems to work.

-- Andrew

[AndrewL]

prepare yourself for a heavy arm...

Seb

Might be another good reason for a 10.5". I wonder what Odeay wants to do now we have made some reasonable progress?

Odeay, are you still up for this?

-- Andrew

[odaey]

I've been following you closely but i'm really embarassed that I can't keep up with you guys.

You have to understand that my brain cells are NOS and would need years of break-in before I can understand any of this.

In any event 10.5 is still fine with me though we may still need to fabricate heavier counterweights to balance things off.

[AndrewL]

Hi Odeay,

Well I was thinking 10.5" may minimize the counter balance problem, and reduce any lateral balance issues. It is also a nice compromise between friction and stiction, as a frfiend of mine put it.

Also, we can engineer the tube to be slightly thinner walled than the existing arm so as to reduce the impact of the extra 50mm or so length right at the end where it matters and still have slightly more effective mass than we have now.

I will post basic some images for comparison soon between 10.5" and 12" and then work on the effective mass.

-- Andrew

[natty_dredd]

Andrew, as an aside - trying not to distract all your trains of thought here! - what marks this out as being a prototype arm as I have one exactly the same in black and gold with the wires not going back into the arm, a rough looking rectangular base plate and separate arm rest, much like yours.. Can I also ask if you need extra flexible armwire for this to move freely (mine has them cut short)?

I also have John Gordons home telephone number! ... from the 80's, written on the odyssey info sheet. I've googled the number and it is a record market in Paisley...

CDs, DVDs ,Vinyl and Tapes Company: Record Market
Telephone: 0141-840 2474
Address: 3 Broomlands St, Paisley, PA1 2LS

Who wants to find out if there's any conection? (err, wasn't sure about posting up the number but as it is a business I hope it is ok)

Some little sketches on it too, perhaps demonstrating the differences between the one I have and the production model? Worth scanning and putting in the library? How do I do that?

Cheers,

Nat

[odaey]

Hi Odeay,

Well I was thinking 10.5" may minimize the counter balance problem, and reduce any lateral balance issues. It is also a nice compromise between friction and stiction, as a frfiend of mine put it.

Also, we can engineer the tube to be slightly thinner walled than the existing arm so as to reduce the impact of the extra 50mm or so length right at the end where it matters and still have slightly more effective mass than we have now.

I will post basic some images for comparison soon between 10.5" and 12" and then work on the effective mass.

-- Andrew

WOW!, you guys really have things figured out.

I'm thinking with a 10.5 , We even have a more comfortable mounting distance away from the garrard metal base compared from the 9.

[odaey]

Natty_dredd,

Those scans would be really interesting.

some Tips on posting images by our Boss Jas

http://www.vinylengine.com/phpBB2/posti ... ly&t=13623