To make use of as "normal" parts and solutions as possible, I've worked out an alternative way of moving/offsetting a bellcrank axle for tuning of pedal-pitch. Here's a rudimentary sketch...
Since I only want to move the axle over "C" in a 2 millimeter range, I think a push/pull rod will do.
Since there's a limit to how many pedal-changes that can be operated together with "C" and create "corny" chords if engaged "C" stays in fixed pitch, only a limited number of pedals need to push or pull it to a different pitch.
I described the "sliding rod" in another thread, so I haven't included it in this sketch. May need it to control pitch for certain pedal combinations.
Action can be reversed by using one of the solutions for making right-going knee-levers pull the right way, so I have left out those too. May need such "reversers" if pitch for "C" has to be lowered instead of raised in certain pedal combinations.
Since the basic (only this pedal activated) pitch for a pedal should be the same as on a non-compensated pedal, I think it will be enough to be able to either raise or lower the pitch along with other pedals - not both raise and lower. So the axle will rest in one extreme-position when activated alone, and the rest is a matter of sorting out and mapping which pedals that need to be pitched either way.
The hollow adjustment screw
can be an adjusting screw for brake wire on bicycles - or something of that nature. I have used a "brake screw" to couple "B" string pulls for pedal "A" and "C" onto one pullrod on my steel for 22 years, and it works perfectly.
To reduce the load from the short lever on axle "C" onto other pedals it should pitch along with, I think a spring at the end of the pull/push rod will do. That spring will also be used to assure that if the "C" needs to be pitched down, its resting position will remain stable in "high pitch" when activated alone.
1 to 2 millimeter offset doesn't sound like much, but I think it will provide more than 25 cent pitch adjustment if/when needed. From what I have measured on my own steel that should be enough to tune out all but the strangest "unusable" pedal combinations and make them "perfectly usable."
It is of course important that a tiny amount of extra freeplay is provided on pullrods coming from the variable pitch bellcranks, so neutral - no-pedal - tuning of those strings doesn't get messed up.
A sensitive player
may be able to feel that an activated pedal/lever gets pitch-adjusted when another pedal gets pushed into a combination, but apart from that the slight adjustments needed shouldn't disturb mechanically. It is only the actual chords that will
sound purer.
Again,
please twist, break and crush the logic and practicality in the above, so I can improve the idea as much as possible before actually designing and building anything.
