Landon,
I don't see why you need to have both axles coupled to the expansion link, if
they're also coupled by connecting rods on the wheels.
What you show looks very much like Stephenson's link, though of course the
omission of the cylinders and the valve rod make that conjectural. The main
difference is that the slot in the expansion link is an arc in Stephenson's gear,
but you can show that the error is negligible in scale models. For cylinders
inside the frame, a direct valve rod should work, but for outside cylinders, you
have to have a rocker arm and time the eccentrics 180 degrees from a direct
link.
I suggest keeping an eye open for a copy of Martin Evans' "Model
Locomotive Valve Gears". It's a bit hard to find (unless it's been reprinted
again recently) but well worth some effort to locate it.
regards,
-vance-
Vance Bass
Albuquerque, New Mexico, USA
Small-scale live steam resources: http://www.nmia.com/~vrbass
