I've been playing around with a Weaver 4-6-0 chassis I got from Ed Rappe last year. I modified an old MTH 2-8-0 boiler by extending it to fit the chassis. At the same time I was building a Vanderbilt tender for future use for a Seaboard Q3 Mike. I finished up what I wanted to do to them this past week, only thing is all I have installed is the original DC motor and the 4-pin connector. I have the QSI F/N/R unit, but didn't want to use it and go back to strictly old-style conventional operation. I've even been thinking of going battery-operated RC.
The 4-pin connector on the back of the engine has 2 pins that go to the motor, the other 2 pins are connected to the drive wheels and center rollers and when the QSI module is hooked up it works like any other 3-rail engine.
I decided to try running it with just the DC motor (and my old Troller Transamp 1 DC power supply from my HO days) so I scrounged around and found 2 of those jumpers you see on the back of computer hard drives. I inserted them in the connector on the back of the engine (to connect one side of the motor to the drive wheels and the other side to the center rollers) and presto...when I turned on the power and cranked up the knob the engine started down the tracks!!!
THEN I had a brainstorm, I also have an old Aristo-Craft Train Engineer (TE) from my HO days. I pulled it out of storage, re-read the instructions (hasn't been hooked up in 15 years), put some fresh batteries in the transmitter and started running the engine. I couldn't believe it still worked, and with an O scale engine no less.
Right now I have 6 pieces of rolling stock and a caboose hooked up behind the engine and it seems to be running fine. Has some decent slow speed, but a little jerky towards the bottom and when reversing direction.
The TE receiver has a switch for Linear or Pulse Width Control (Modulation), but I didn't see any difference when I moved the switch. The transmitter has 5 buttons to press if you want to change the momentum times for reaching top speed and full stop (5 to 30 seconds). The receiver is good for up to 10 amps.
Funny, I don't miss the sounds of the engine as much as I thought. The sound of the train going down the track is plenty fine.
With what I have now, I can run an engine with only a DC motor in it on my 3-rail layout, no TMCC, no DCS, no F-N-R to worry about.
PLUS, to go 2-rail, all I would need to do is to insulated one side of all the wheels, do away with the center rollers, and get some 2-rail track. Then when the time comes install a true, battery-operated RC system.
Will this line of thinking get me banned or are there more folks out there who are risk takers 
The mere fact that it could possibly free up more room inside our locos should be incentive enough.
