I too am following this post, and I am actively looking at collecting the components to give it a go.
The reasons that I have been looking at trying to get an Electronic Flywheel to work is directed firstly at the cost of Motors in O'gauge these days. The suppliers want to charge us £25 odd quid for a double ended motor that can supply enough power and take a flywheel, when some high quality, and highly suitable, single ended Mabuchi's can be found for around £5 each. This makes a terrific difference to the cost of an O'gauge diesel with twin motor bogies.
Secondly, there has always been a problem with twin worm drive loco's in that they have the capacity to eat their brass gear wheels. This is not just due to the low ratios used to try to get an irrelevant maximum speed from the loco (with the commensurate increase in friction between the worm and the Gear, as the torque required to just move the loco has been doubled, or the fight that occurs between the two bogies all the time, as one bogey will always want to go a fraction quicker than the other, but it's also due to the added stresses and strains on the gears caused by sudden losses of power stopping the motors, and therefore damaging the gear wheels as the worm stops rotating and the gearwheel is now locked in a battle to the death with a worm that will not move. You would probably only be able to see the damage under a microscope, but it's there and the dents in the gear wheel will increase wear at that spot when the power is reconnected. Do not underestimate the effect of 4 kilograms of rolling stock travelling at a scale 40 mph (40 cm / s - &etc.) upon a worm drive that has lost all it's electric impetus.
This version of a UPS has some very interesting features which I believe will be of interest to many other railway modellers.
By using a latching relay you are reducing the wastage of volts through the diodes and transistors of other circuits, shame about the rectifier.
By using a battery as the power source you can change the Amp-age available for different scales, in N gauge I do not know what you would use, but in O'gauge we could even use one of the micro Lead Acid batteries being used as backup batteries to alarm systems - just remove the sheet lead from your loco and put one of these in !
By keeping the motors rotating we are reducing the wear and tear on the worm drives of our loco's, as we remove the hammer action on the gear wheel caused by a loss of power.
And that sum's up what I've always wanted from an 'Electronic Flywheel'. Something which just keeps the motor rotating. In O'gauge we don't need to worry about the loco keeping moving over the dirt, the weight of a passenger train alone will get the loco past the dirt, but I've always thought that if we can keep the motors turning then we should be able to reduce the damage to the mechanisms when the power does drop off, for whatever reason.
I'll let you know how I get on. It'll take a month or 2, but I'm building my next chassis at the moment and I'm looking for a nice little Lead Acid battery to put into it, and I don't think a TIP41C is 'excessive', I think 3A is 'required' !