Sunday, 30 June 2019

D/DA Loco with ViTrains Mechanism - Extra Instructions

As of June 2019, Marbelup Models has modified the design for the DA locomotive to suit the ViTrains mechanism, as used for the DB locomotive, due to the closure of Hollywood Foundry and unavailability of their mechanisms.

The changes made are:

  • ViTrains drive bogies and motor used, from their UK Class 47 model.
  • Coupler height changed to correct WAGR scale height, with option to fit Kadee #149 offset couplers to match Kadee HO scale coupler height (same as for DB loco).
  • Coupler draft gear boxes changed from Kadee #262 (narrow type) to #242, which are the type supplied with all Kadee whisker couplers.  The wider #242 box allows greater coupler swing on curves.
  • Provision made for brass strips (6 x 1 mm) to reinforce the underframe and support the weight of the motor and (weighted) fuel tank.
  • Extra thickness added to the attachment points for the fuel tank, to minimise the risk of stripping the screw threads in the underframe. 
  • An additional "parts sprue" which includes a rectangular frame to fix the motor in position, 2 drive shafts and packing pieces for adjusting coupler height (in 3 thicknesses).
  • A cutout is included in the rear cab wall to provide clearance for the ViTrains bogie gear tower.
Note that these changes also involve changes to the body, fuel tank and bogie sideframes, so it is not possible to retrofit the ViTrains mechanism to an existing model built for the Hollywood Foundry mechanism.


Underframe Preparation and Coupler installation 


Refer to DB Assembly Instructions, the only difference being the use of #242 coupler boxes.

ViTrains Mechanism Assembly


Refer to DB Loco ViTrains Instructions.  Note that the drive shafts supplied are slightly shorter than those for the DB and are not interchangeable.

Brass Reinforcing Strips


The reinforcing strips are cut from K&S item 9843, each pack containing 3 x 300 mm long strips, of which only 2 are required.

Location of Brass Reinforcing Strips
The strips should be cut to 180 mm long.  Recesses are provided in the speaker support enclosure (just behind the cab), and in the support "saddle" for the rear drive bogie.  The strips should fit neatly in the recesses, but shouldn't be a tight fit.  Don't force the strips into position if they are tight, as this could fracture the 3D printed underframe.  Instead, file the top of the strip slightly until if fits.

Position the strips so that the front end of the strip extends about 6.5 mm in front of the speaker support enclosure.  In the photo below, the strips can be seen through the unpainted body.  The strips are white in colour, as styrene strips were used to test the fit pending purchase of the brass material

Photo of Test Model (prior to fitting of correct bogie sideframes)
When the body is attached, the strips will be held in position but it may be useful to secure the strips to the underframe with glue (e.g. superglue or Pliobond) or thin double-sided tape, so they stay in position until final assembly.