From the DIYCorner: Increasing B-Pedal Travel and a Problem

Fay Reid · From: Orono, Ontario, Canada

You are sitting at someone else's guitar and notice that the B-pedal has a relatively long, smooth feel while the one on your machine is short, jerky, and stiff. You want to match it with the feel of the A-pedal since the two are used together, constantly. Some guitars allow for minimal adjustments in attempting to increase pedal travel associated with the G# to A change. Described is a method for making the needed adjustment when others listed will not.

I had thought about making this change for a few years and had the workable remedy in mind. One day, I had the fortune of observing the underside of the guitar owned by Al Brisco and saw what was recognizable as the change for the desired effect. Originally, not knowing whether or not the change was worth it, I now had my immediate answer. I could hardly wait to get home to begin the modification.

There are about 5 methods of changing the amount of travel on a pedal:
1) Change the string; its gauge or whether it is wound or unwound
2) Change the location of the pull rod at the changer to a more desirable one (experimentation may be required here unless your are knowledgeable concerning the physics of the changer)
3) Change the location of the pull rod at the bell crank
4) Change the angle of the bell crank on its cross shaft (unfortunately, not generally available for square shafts) (the photo reveals many such on my machine)
5) Add an intermediate cross shaft with associated bell cranks, etc.

I shall be dealing with method 5) above.

Labeled Photo Parts
A - bell crank connection on B for connection to D
B - intermediate cross shaft
C - B-pedal rod
D - connection on B-pedal cross shaft
E - B-pedal cross shaft
F - connecting rod between B-pedal cross shaft and intermediate cross shaft
G - three G# to A bell crank pulls (the 12-string guitar has 3 of these)

We are applying the "law of the lever" on both the intermediate cross shaft, B (in photo), and the driving or B-pedal cross shaft, E. Pulleys and sprockets, essentially, obey this same law. I tend to think of a pulley as an "endless" lever.

As long as there is a greater distance between the cross shaft centre, B, and the connection point of the connecting rod, F, on this shaft compared to the distance correspondingly on the B-pedal cross shaft, we have increased the pedal travel required to pull the G#'s to A's. All three G# to A bell cranks are located on the intermediate cross shaft on my guitar. You need only place those pulls requiring more travel (than is possible on the B-pedal cross shaft) onto the intermediate shaft.

Without the intermediate cross shaft, we are left with adjusting from 1 to 4 above. Steps 1 to 4 above should be done prior to step 5 since they are relatively quick and easy modifications. If you have done steps 1 to 4 and still can't get enough desired pedal travel in their extreme conditions, step 5 offers almost unlimited access to more pedal travel. Also, increasing pedal travel reduces the force of the foot needed for activation.

Note, from the photo, that the intermediate cross shaft is a half shaft making room for the 20-degree pedal discussed under the heading, "The Comfortable LKL", on the Forum. I have discussed bell crank construction in one of the articles, if you wish to attempt making your own. You'll likely need some brass wristpin connectors as well. Start with the required diameter stock, drill a suitable hole crosswise for accepting the pull rod, drill out the centre with a lathe and tap thread for a short setscrew, then and only then, cut it to length (about 1/4") to match the thickness of the bell crank. Otherwise, contact you local steel guitar technician for required parts. Suitable setscrews can be obtained at specialty shops in almost any city. Phone around. Pull rods can be cut from 1/8" drill rod, available at specialty shops, also. Coat hangers are about 3/32" and ideal for the likes of Carter guitars or those requiring the 1/8" rods.
Fay

Considerations before making this change:
1) Check to see that increased travel of the B-pedal still allows for the foot to clear the B-pedal when depressing the A-pedal and coincidentally activating the LKR lever. Likewise, make sure that the foot can activate the B-pedal while moving LKL without interfering with the A-pedal.
2) Increasing pedal travel will increase the time to activate the pedal. Are you sure that the change will not “cramp your style”?

Earnest Bovine · From: Los Angeles CA USA

There are 2 easier ways on old Sho-Buds:

Those old hillbillies weren't as dumb as I look!

richard burton · From: Britain

I found an even simpler way of increasing the pedal movement when I had a ShoBud:

If you look at Earnest's steel, you can see that the bellcranks are held on to the cross-shaft by set screws.
I simply loosened the set screw on the B pedal bellcrank, which allowed the bellcrank to rotate slightly on the cross-shaft, and this 'slippage' gave me the increased pedal movement that I desired.

Just kidding ya.... Very Happy

Nic du Toit · From: Milnerton, Cape, South Africa

Fay, could you please elaborate on the effects described in your point 4?

Bent Romnes · From: London,Ontario, Canada

Fay,
I still don't get why a different angle on the bell crank would make for a different length of pedal travel.

Eddie's Fulawka guitars seem to have combined all the attributes you're looking for ... I recommend that you take a look/try out his products and he uses a square shaft, as do most other manufacturers (some use hex shafts. In all of them, without exception, you see the bell cranks standing upright.

On my home built, they are standing upright. I was unhappy with the amount of pressure needed to depress the pedals, and the travel and feel. The old ShoBud pedals I used had 2 holes. I drilled a 3rd one very close to the pedal bar...about like the one in your picture. Now the pedals are to my liking: Nice and soft, the right amount of travel and when mashed, the end of the pedal ends up about a 1/4 inch above the floor.

richard burton · From: Britain

Bent,
When a bellcrank is set at the usual 90 degrees to the steel guitar body, it has maximum LINEAR travel (when it is rotated).
Imagine that same bellcrank is positioned parallel to the body, it has less LINEAR travel for the same amount of rotation

Fay Reid · From: Orono, Ontario, Canada

Thanks Richard.

Another Example:
It is quite advantageous to be able to rotate the bell crank very close to the 9 o'clock position for compensators such as you might have on the first string, F#.(At 9 o'clock, most of the rotational component is in the vertical direction which isn't moving the pull rod very far horizontally as it would if the bell crank were set at the 12 o'clock position.) A compensator makes a very slight adjustment to keep a string in tune when a particular pedal, producing a different chord, is activated. The slight adjustment requires a very short string-stretch/pedal-pull, but does require the same initial force as if it were being pulled to, say, G. If it's bell crank is set at 12 o'clock, the stretch on the F# string does not start until the other strings on this pedal have been pulled nearly to pitch. To lessen the effect of having to "start" the F# with low mechanical advantage near the end of rotation, turn the bell crank very close to 9 o'clock so the "start" must be much sooner on this string. Ideally, it would be best to start it with the other strings on the pedal. So, now the force on the F# is applied over a longer rotation of the bell crank, so you feel much less resisting force on your foot. Also, the whole pedal travel will feel smoother. Of course, this is true of all strings associated with a pedal.

The extra force at the end of pedal travel may cause your foot to stop early, leaving all associated strings out of tune.
Fay

Bobby Bowman · From: Cypress, Texas, USA, R.I.P.

I don't see where you have addressed the pedal stop adjustment. Until you adjust the stop to where the pedal can travel more distance, you don't have more pedal travel. If you move the pull rod closer to the cross rod in the bell crank and/or farther away from the axle at the changer you can achieve more travel as well as easier pedal action. But, in most cases you will usually have to open the stop adjustment up some.
On some brands such as older Sho-Buds and a few others, it's just as Earnest points out, you have additional adjustments at the pedal itself and also at the pedal pull crank. Closer to the axle on the pedal and farther away at the pedal pull crank.
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Nic du Toit · From: Milnerton, Cape, South Africa

Fay Reid · From: Orono, Ontario, Canada

Nic: This problem could likely be solved mathematically. But, we don't have the string stretch coeficient, even 'though we could make an assumption concerning the diameters, and this problem deals with stretch. I don't have the answer for this. Trial and error is your easiest bet here. Others will already know from T + E or because they've studied the subject.

I have a thought problem:
Neglecting friction of all kinds, imagine two identical strings except for their diameters suspended as pendulums in a clock, and allowed to swing freely. They will swing at the same frquency. Gravity is acting on all sections of the strings. Even two strings tied together (all other parameters being the same as in the case above) and these two will swing with the frequency of the two above. We could even vary the materials and all would "keep the same time". So, in the swinging pendulum case, a large pendulum can be thought of as many small pendulums tied together.

However, if the ends are secured, as in the case of vibrating strings on a musical instrument, the same is not true (or is it?). Take two differing-in-diameter strings and place them under the same tension, with all other parameters being the same. The lighter gauged string would vibrate at a faster rate. So in the case of the vibrating string, we can't think of a larger string as being made up of many smaller ones as in the case of the "string pendulums", above.

1. What have I neglected to take into consideration here?
2. Do the "laws of vibrating strings", in your explanation, lead you to the conclusion that we can treat vibrating strings as as we did the pendulums? Give the mathematical relationship that proves it.

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