OK, I went back over what you said and talked to a buddy.
You have some conceptual missteps.
1. if you have a battery as you say, it goes into pins 4 and 2.... the battery directly to 4 and 2, as in the schematic above.
2. if your battery is over 12 volts, then you need to reduce it, again as in the schematic above, U1 is the regulator to drop the voltage.
3. you indicate you are feeding the circuit with the Revolution motor outputs WRONG!!!!
4. you indicate you are feeding the Revolution motor outputs to a buck converter WRONG!!! you cannot feed a DC regulator PWM!!!!
Battery >> buck converter (output 12v or less) >>> pins 4 (positive) and pin 2 (negative)
chuff contacts to pins 11 and 12
Change anything and it won't work... if you use autochuff you need the opto isolator
Read my page on the chuff contacts in the shay, they are crap.
Sierra page:
Greg Elmassian web site on large scale trains and garden railroads, cigars, and computers
elmassian.com
Shay page:
Greg Elmassian web site on large scale trains and garden railroads, cigars, and computers
elmassian.com
Greg