@Ted S posted:
One challenge is that the Legacy electronics themselves (including the flywheel encoder ring and tach sensor) are not marketed as an upgrade kit. You have to order specific parts, or cannibalize them from a donor locomotive. In some cases Lionel restricts part availability for warranty purposes. A few 3-rail Legacy products eschewed the optical tach sensor in favor of using back-EMF for closed-loop speed control. The results weren't as good and some customers complained.
If you broaden your considerations from Legacy to Lionel's TMCC command environment, you could use the Electric Railroad (ERR) Cruise Commander decoder, which also uses back-EMF for speed control but is well-liked. It's still a proprietary solution (Electric Railroad closed about 18 months ago and 3-railers held their breath until production was taken up by Sunset/3rd Rail.)
Not really sure what you stand to gain with this approach. If you invite friends over or take your locos to another layout, you would have to bring your command gear and hope it's inter-operable with whatever system they have. Personally if I were in 2-rail, I would use one of the established DCC systems, or make the leap to direct R/C with a system like Airwire* or RailPro. (*Not necessarily battery power, but R/C direct to the loco, should be compatible with any existing system.) My $.02.
Hi Ted, thanks for the "heads up" on the conversion to Legacy. I do have some ERR kits in my stock and will probably start with one of them on an old Williams brass 2 rail camelback and ease my way into Legacy if I can. I do have a number of actual 2 rail DCC equipped locomotives that I can always use if need be but I have always liked the MTH DCS stuff because I am a little clumsy at times and having a "close to scale" locomotive is ok with me rather than a super fragile brass or plastic loco that I manage to bend due to my meat cleavers. I live out in the sticks and work in healthcare so at this time "friends" and "visiting other people" are kind of foreign since everyone seems to think I will give them the 'rona. Since my pike is only 4 X 12, I do not have a huge roster nor do I have anything larger than a 4-6-0 with blind center drivers. The MTH 3-2 stuff runs great on vintage Atlas 24" turnouts and track and I had the DCS set up and 3 lovely MTH steamers from my last pike, a three rail affair. I am one of those guys with very limited space that did not want to model only "traction" in 2 rail and with 24" radius, my options were limited so the whole MTH/TMCC set up was attractive. I appreciate your great advice, it is always nice to have a professional opinion before I butcher up a perfectly good specimen. Why make hamburger out of a T-bone steak....👍