1-String Test Setup

[sleepingdog]

I've got my 1-string test setup put together and it seems to be working. Everything is mounted on a piece of 3/4" plywood. The first time I tightened up a string on it the plywood bowed. I guess I should have predicted that I now have a couple of piece of 2x4 on the bottom to keep it stiff.

I intend to mount each string and take some measurements such as how much the finger rotates and how much the rods have to move for full and half raises. I've mounted a piece of wire to the finger to use as a pointer to measure finger rotation angles. I'm still trying to figure out a nifty way to measure the rod pull distances. They are a lot shorter than I was expecting. I was thinking of somehow attaching a digital caliper. Any suggestions or ideas would be greatly appreciated.

Here are some pics of the test setup. I will post my results later.

Dave

TestSetupSm.jpg (27.19 KiB) Viewed 1706 times

TestSetupChangerSm.jpg (58.35 KiB) Viewed 1706 times

TestSetupTunerSm.jpg (27.48 KiB) Viewed 1706 times

[sleepingdog]

I got through my first round of testing. I broke both of the smallest strings - 1 & 3. Not sure why. Both broke right at the tuner and they broke before even getting one semitone above the open tuning.

The results of the tests can be seen here: https://docs.google.com/spreadsheets/d/ ... sp=sharing

I am surprised at how short the pull distances were in general, and a few of them in particular. Too small? I'm not sure what to expect so would appreciate any feedback. One thing I thought of doing is to change the angle part that the lower bearing rides on to something less than the current 45 degrees to increase the mechanical advantage while at the same time increasing the pull distance a bit. I could also reduce the diameter of the finger where the string rests to have a similar effect. I think most use 3/4" but I used 1". Perhaps a mistake.

I ended up using a dial indicator to measure pull distances as seen in the following photo. I just used double sided tape to attach it.

Dave

[maxi19]

Hi Dave,

The length between the lower finger pivot and the bearing looks a bit on the long side making for a harder pull.
The leverage on the knee levers are too long to give an accurate test, and the pivot point on the knee levers don't lie on the same datum as the changer axle in reality.

http://www.pedalsteel.fr/index.php/173- ... ll-changer

Short string lengths tend to break very easily.

[Jason Lynch]

And if anybody on here would know, Ron would. I thought the beating should be further forward than it is? Anybody else? Or am I wrong!

[sleepingdog]

The length between the lower finger pivot and the bearing looks a bit on the long side making for a harder pull.

I see what you're saying, Ron. Mine is definitely longer than what you showed on your drawing. I'll rework that and see what difference it makes.

The leverage on the knee levers are too long to give an accurate test, and the pivot point on the knee levers don't lie on the same datum as the changer axle in reality.

The levers on the test jig were not intended to mimic or prototype actual knee levers. They are just something I threw together quickly in order to be able to test the changer.

Thanks very much for your feedback.

Dave

[maxi19]

Thank you Jason for your confidence in me. I arrived at these dimensions, whether they be the correct ones, by experimentation and help and advice from members of this forum.
Especially from Richard Burton who has a wealth of knowledge regarding the mechanics of the pedalsteel.

Best Regards to all

Ron Mc

[sleepingdog]

Well, after finding problems with the finger design I've been working on, and after having an offline chat with Ron, I've decided for my first PSG it will be more wise to use a tried and true finger design. Ron has kindly allowed me to use his design, so I am now putting together a prototype based upon that.

Thanks Ron!

Dave

[maxi19]

Your most welcome Dave.

[sleepingdog]

I've made a finger assembly based upon Ron's design (a few slight mods of my own, the biggest being the "hidden" lower plate (as viewed from above the guitar). I've got it installed in my test jig and I've taken pull distance and finger rotation measurements for all 10 strings. This finger is working very nicely. The amount of force required to raise and lower by 2 semitones is significantly less than with my previous one, and the pull distances are not so minute. Measurement results can be found here:
https://docs.google.com/spreadsheets/d/ ... sp=sharing

[b0b]

What is your scale length? That could be the cause of the string breakage.