DCC Loco Conversions - 35 - Dublo Co-Bo (MetroVic)

The internal design of the Co-Bo is very similar to the Co-Co including the same mounting plate joining the two bogies (but different holes used for attaching the unpowered bogie) such that the conversion is similar. However I take a different approach with the Co-Bo to the two Co-Co locos which I think is a better solution which I would apply to any further Co-Co conversions.

Very Important - the power bogie was modified as in article 33, failure to do so can destroy a decoder.

https://platform1mrc.com/p1mrc/inde...dublo-ringfield-motor-bogie-co-co-co-bo.6156/

All original wiring and suppression components were removed, the wiring on my two Co-Bo locos were flimsy, frayed and badly soldered as seems to be the norm for most of my vintage locos.

Leaving the original wiring in place is asking for faulty running and possible decoder burning, if you want to retain the original suppression components, or wiring I strongly advise you dismantle, clean them up and re-solder them before continuing.

Both locos were already fitted with NEO magnets.

Ample space allows the use of 10/0.1 PVC insulated wire.

Mounting of Decoder

The RoS-218 decoder was chosen as there is plenty of space in the body shell, surplus wires were sprung from the supplied harness plug and the remaining wires extended as required with simple soldered hook joints protected with heat shrink sleeving.

The decoder is mounted on an offcut of laserboard to the metal plate that joins the bogies so the wires clear the retaining screw on top of the power bogie frame. It is also retained by lacing cord for security as there is very little surface of the wrapped decoder available for applying a double sided sticky pad.

These cords are also useful for routing the motor drive wires as shown in wiring stage 2.

Wiring - stage 1 - Track Power

Power pickup is solely from the 4 wheeled bogie, a tag on the frame for one rail and the collector wire for the other rail.

The red wire from the collector is sleeved black so as to be less obvious through the cab windows.

Wires are restrained with lacing cord with sufficient loops to allow free bogie swivel and the wires not to be damaged, especially the wire to the solder tag on the frame.





Wiring - stage 2 - Motor Drive

Motor drive wiring routed to avoid fouling on body reassembly especially as the body is live at track voltage and the motor drive outputs of a decoder must never connect to rail voltage.

These wires are routed and restrained such that they are kept away from being crushed when fitting the body shell and have sufficient free length to enable the power bogie to swivel freely without damaging the wires.

At the decoder.





Past the body mountings.



To the motor brushes.





Setting Up the Decoder

A nominal start voltage setting of 10 was required in both locos as backlash in the gear train caused some juddering by upsetting the BEMF response, however the lowest low speed running is acceptable and they run smoothly once rolling.

Summary

The completed locos ran well on track and layout testing, they rattle a little due to the slop between the mounting plate connecting the bogies and the retaining screw on the power bogie. The metal body shell amplifies the noise well.

Despite power pickup only from the unpowered bogie there was no hesitation at low speeds.

I would apply this approach to any further Co-Co locos too.

A closing note, avoid placing two NEO fitted Co-Bo locos next to each other if facing the same way, keep them at least 30 mm apart otherwise they may slam their bodies together, not good if you have pristine models!


Discussion always

Jim

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