Their have been several posts about the Underground Ernie "Inspection Vehicle" like this one:
Bogie Wheelbase: 25mm
Wheel Diameter: 10.5mm
I don't think I have seen anything about the Underground Ernie "Two Car Set", 1 motorized car + 1 non-motorized car. A friend in the UK sent me several of both types to play with. They are made by Bachmann and all ran very good out of the box. Both models show up on British ebay and can still be found in some stores in the UK. MSRP for these are about 20 "UK" Pounds but like everything they can be found cheaper.
What scale are you working with? Do you just want to use the power truck from Ernie as a donor for another loco or convert the Ernie to three rail? What scale is your three rail? Are you planning to re-gauge the Ernie?
It would seem you could add the center rail roller system to the Ernie model and convert it to three rail but I don't know how that would work using 16.5mm track.
The three rail thing came about when I discovered three rail automation whereby a following machine acts as the switch for the one in front. It is popular with model tram enthusiasts who realistically collect from the overhead.
Doing my own thing I decided to model the 'wireless' tram using a third rail in lieu of the overhead. Methods used in the past have included studs that switch on as the tram passes over, and a live rail in a slot. The latter was quite extensive in London at one time.
Current systems include a variation on the stud from Ansoldo. Basically a segmented centre rail with segments only live under the tram. There is also a high frequency induction system from Bombardier.
I have acquired Hornby and Trix three rail track. Hornby track is lovely stuff but is no good for three rail automation as the running rails are not insulated from each other. Trix twin however has insulated running rails. So far my early three rail conversions run on both types of track.
I am working on a layout which will be three rail using Peco track. Peco supply a third rail and fittings to be used on the edge or centre as required.
I am working to OO 1/76 scale which means 16.5 mm represents nearer 4' than standard gauge. As the local long defunct tram system was to 4' gauge my whatif layout has a certain local realism.
However, before this occurs I really need to make a decent centre collector for the UE chassis. Still work in progress but I have a few more ideas to try out yet.
One day I might finish something................. find out if I do at my own paid for site (under construction) http://www.picsntech.co.uk
This is like the carnival ride where the ticket buyers stand around the inside of a large drum, which starts rotating. When a certain speed is reached, the drum floor drops, leaving the people (hopefully) plastered up against the drum wall by centrifugal force.
Except what happens on the straights?
____________________ Fix it again, Mr Gates--it still works!"