Crazy project #1: variable-pitch pullrods for JI tuned PSG.

[Georg]

Allan, I simply did not understand that one ... I'm a bit slow and/or have my mind working on something down a different (probably wrong) path. So could you run that by me one more time, a bit slower and more detailed, please..?

[Allan]

Georg, I am now wondering if I have got the thing into a negative gain situation.
Look at the pic in the light of the previous post... I think I may have made the situation worse with this.

geared.jpg (40.63 KiB) Viewed 919 times

However, by dropping the pull rod in the area of axle 'C' and extending arm 'C' to suit, leverage could be added.

Am I making any sense now?

Allan.....

[Georg]

Am I making any sense now?

Yes, but it looks like you've found a new way to turn the (yin/yang) axle. Am I right?

I want to move the (yin/yang) axle towards or away from the changer by making the "C" arm pivot on a screw above the axle. The pivot screw can of course be below the axle if I want the moving action to be in reverse.

My "leverage" problem is that the "C" arm is only slightly longer than the arms on the "A", "B" and "D" axles that controls the move - has to be in order to avoid bending the pull/push rod to much while playing, and I'm not sure if this short "C" arm will give me enough leverage and precise enough control of the "C" axle move without placing quite a bit of extra load on the "A", "B" and "D" control pedals/levers.

Guess I will have to do some testing...

[Allan]

Yeah, as I said above, I thought I had it the wrong way around. Why am I putting stuff into this thread after saying I wasn't going to?

Last try its late.jpg (8.19 KiB) Viewed 918 times

Here is another crazy idea - and my last one EVER! (I think - or not...)
I was gonna animate it to see how much swing it gave but it's just way too late. (yawn)

Allan.....

[Georg]

Why am I putting stuff into this thread after saying I wasn't going to?

Hmmm, maybe you kind of like crazy ideas?
After all: if on the outset an idea isn't best suited for a "Dnt Undrstnd" section, there's no use in taking it any further.

Now the drawing makes perfect sense and should solve the leverage problem, but, as you know, the practicality of it is more like: "poor pull/push rod"


However, after having given it some thought: a more solid piece to keep the push/pull rod straight and rigid is all that's needed, and such a piece can also be angled sideways to let several push/pull control rods pass along side of each other while keeping the "C" arms on several pitched axles where they belong - fastened to the body frame.

Yes, I think that simple "bended rod" may actually be a near-perfect solution for the leverage problem, and easy to install too

Many thanks Allan.

[Allan]

Georg, Some math will be needed to see if this is really any kind of answer.
The quick/sloppy animation is to illustrate a point. Movement of 6mm in the pull rod only gives 1mm at the 'moving axle'.
The gain ratio is thus 1:6. Some attention is therefor needed to the positioning (relative) of the arm pivot and the center point of 'axle C'...

Animation.gif (4.19 KiB) Viewed 909 times

The drawing is rough but the numbers were measured from the full scale version in my CAD program.

Allan.....

[Georg]

Allan, yes, I had all those variables and relative measurements in my head already - who said "mutual pedal pitch tuning" was going to be easy I just needed to see the light about how to increase the leverage a bit, and your "bended rod" lit the candle.

Instead of a bended rod I'll use a triangular shaped thin steel plate with a wide edge curled around and fastened to a straight rod and the opposite "point" attached to the bottom of the "C" lever. A simple guide-wheel on the "C" axle itself will be enough to keep the push/pull rod running straight and stable, and I'll be able to use tunable bellcranks of a type I'm familiar with on the controlling axles to pull/push the rod precisely.

This means I only have to design/manufacture the pivoting "C" arm(s) from scratch, and - as you said - get the distance between pivot-point and axle on the "C" arm(s) within range for fine-tuning the push/pull rods where it is connected to the controlling bellcranks, for correct travel-length for desired pitch-change.

Thanks again Allan

BTW: I disable animation by default in my browser, as I'm not fond of "live emoticons" and other moving objects on web sites. I enabled animation for this site only, long enough so I could check your illustration.

[Georg]

Me just thinking out loud here ... it's a habit of mine

I'm looking at various ways in which pedal/lever stoppers can be "displaced" on-the-fly, as another way for introducing mutually controlled JI tunable variable-pitch pedal action in PSGs. Although the movable bellcrank axle is likely to work just fine, quite a few parts have to be redesigned to make it work. I'd like to reduce the complexity and number of parts, while keeping the advantage of JI tunable pedals.

A few positive points:

• There's only one stopper pr. pedal/lever to control, while, obviously, there are two bellcrank axle ends that must be controlled simultaneously. This means I only need half the number of tunable push/pull rods to "displace" stoppers compared to "displacing" bellcrank axles. Fewer parts means simpler assembling and lower weight. Good.

• I already have two "displaced" stoppers on my steel, and they have worked fine for over 22 years. So although I'm looking at ways to upgrade the existing ones, at least I know such "displacement" really works after it has left the drawing board. Good.

• A small stopper "displacement" goes a long way, so the leverage problem is easier to solve. My variant of Allan's "bent control rod" will on my Dekley give me something like 2 to 4 times the leverage for the same pitch-shift when used to "displace" stoppers compared to "displacing" bellcrank axles, which obviously is a good thing.

I will probably come up with more positive points later...


Some negative points:

• Although all foot pedal stoppers are arranged along the front side of the body frame on most PSGs and therefore are relative easy to design a solution for, levers are, or can be, "everywhere". So new "variable-pitch stop" lever mechanisms must be designed.

• Spring-loaded control rods can only hold back so much even if leverage is increased, so it will be technically possible to push a 2 position pedal/lever stopper to its ultimate position by using extreme force on the pedal/lever that "displaced" stopper is on. Since by "extreme force" I mean really extreme, I'm not sure if this is such a bad thing.

• Along the same line: the effect of a "displaced" stopper will be felt in the relevant pedal/lever, so may take a short while getting used to. I've listed this as a negative point, but I'll probably see this "action-feel" as an advantage while playing.

• The regular pullrods for several strings changed by same bellcrank axle must be timed well, since there will be only one variable-pitch control for each bellcrank axle. Not much of a problem on most PSGs, IMO.

I will probably come up with more negative points later...


I hope to be back with sketches for "displaced" stoppers later, presumably after Bent and I have turned a couple of Dekley and BenRom steels upside down and looked at options. Sometime next week, maybe.

In the mean time: shoot! I do need some resistance in order to perform optimally

[Allan]

Well, I am probably at the end, or close to the end, of my ability to provide resistance. I don't have a PSG to turn over and look at! Just a very quick observation which I hope is WAY off track. I see a lot of mention of that dreaded word, springs! And, also, the dreaded 'extreme force'! This brings the even more dreaded thing into my head - cabinet drop. I know, and I know that you know, it is very possible to design a steel with zero cabinet drop. We also know that the easiest approach is to design it so that it would need a fork lift to get it on to a stage at a gig.
Hey, I believe that it is very possible to design a steel with zero cabinet drop and a light weight body - a little bit of structural analysis could go a long way. Just stirring the pot here.

Regards, Allan.....

[mac639]

A little off this thread....but, remember that I'm still working on my new design PSG. Having a bit of a problem with the knee lever design but what I wanted to say here was that it has ZERO cabinet drop with all the three floor pedals. There was no great engineering in the design, it just seems to be happening that way. A & B pedals down, the 4th string E doesn't move at all on my Seiko meter. And with the A pedal only, the 6th string G# doesn't drop either....better than anything I've built so far in my life! It's got to be the changer that's making it that way. I've never took much stock in the cabinet flexing anyway. I never could imagine a 2" piece of maple on edge on the front and a 1-1/2" piece on edge on the back ever bending. Heck you could pull a car with a body built that way and it wouldn't bend I don't think.
There....that's my .02

Mac