The availability of the RR Speeds for TMCC control is useful for synching TMCC lashups (assuming one is careful about picking TMCC engines to MU wrt to gear ratio, driver size and Odyssey board version). It's also just cool, and the Legacy remote was the first device to properly use TMCC absolute speed commands. Up until then, the first couple firmware revs of DCS tried using them, and the only other way to use them was by hooking up a pc with something like the old Railman software (which also had a really cool port reader from what I remember). A lot of this stuff was discovered and played with a very long time ago, like from 2000-2001.
The velocity knob has to at least inject relative speed commands, otherwise you'd never trigger RS4 and RS5 chuffing and diesel RPM changes in relation to controlling speed. This is easy to observe/hear/prove with RS4 diesels. If you skip to the RR Speed menu and punch in a speed, the engine will proceed to that speed setting without affecting RPMs. Hopefully everyone is starting their old RS4 TMCC diesels with the AUX-1 key and not just rolling them out with the knob. This was an old RS4 bug from way back pointed out by Clyde Coil.
Careful when talking about PWM to Lionel motor drivers, I believe this went away with Odyssey 2, the on/off version. I think that used direct serial comm or a combo of PWM for open loop and serial for closed. At least that's what I'm thinking.
