Friday, July 8, 2011

The 2 EPB power bogie

The Bachmann 2 EPB has now been partially converted to P4; the TMBS is now re-wheeled with a Black Beetle and plain 18.83mm coach wheels. Initial running trials of the motor bogie with the Bachmann side frames added was not very encouraging - very rough and hesitant. I couldn't work out what was wrong at first, but after removing the outside frame assembly I discovered the cause - the brake shoes were rubbing the wheel treads (at least they were in line!). So some careful work with a sharp craft knife and very fine wet and dry soon sorted that out and the unit ran smoothly. I then temporarily assembled the whole chassis and this also ran very sweetly and true up and down my P4 test track. 

Today I've been assembling the working third rail pick ups, having made up the parts yesterday.  The description below is rather rudimentary just giving an idea of how this tricky "experiment" was achieved.
I opted for a very thin strip of plastic sheet that has a nice light spring to it for the main cross beam and very thin nickel silver strip for the pick up shoes. The plastic cross beam is super glued to a small square of plywood strip; then two very fine wires (removed from stripped layout wire) were also super glued to the ply strip leaving four free ends. The nickel silver strip pick ups were fashioned into shape by observing a No Nonsense kits 2 EPB whitemetal pick up; it is as close to scale as possible (1.3mm wide is the correct scale for 4mm). These were then soldered to two of the fine wires and the pick ups then superglued onto the ends of the plastic cross beam. The other two fine wire ends are connected to two flying leads coming off the motor. The resulting assembly is very fragile and fiddly and has to be handled extremely carefully! It was super glued to the base of the Black Beetle making sure the pick ups were in line with the shoe beams. It looks very good and is not far off the prototype 2 EPB pick up. The spring of the pick ups is light but quite positive.

I then turned my attention to setting up a third rail test track using some spare C and L flexi track and a piece of Scalefour Society conductor rail (this has the correct scale prototypical profile). As this was just to assess whether my third rail pick up experiment worked or not I glued the conductor rail, at the approximate contact height, onto some small bits of ply strip which had been super glued to the sleepers of the flexi track. I then wired it all up (two positive leads and one negative lead). The moment of truth had arrived...  I gave the motor bogie a spin...   and off it went, smoothly and quietly! The pick ups worked a treat and just to test that they were picking up current I removed a positive lead from the track; the motor bogie still worked well! I was very happy indeed. I also put a test ramp into the conductor rail to see how the pick ups entered and left the third rail; the springing action was realistic and positive, and when the third rail was providing the only positive current, the bogie would stop as it left the ramp. Excellent stuff and most satisfying. I will now go ahead and build the layout with a working third rail system as planned using Scalefour Society insulator pots and conductor rail. The photos below show the system in "action" just after the first few test runs. The pick ups themselves will be refined and tidied up and then weathered.

The remaining work on the Bachmann 2 EPB will now continue to finish off the P4 conversion and super detail the unit, with suitable weathering applied.

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