Rebuilding the drive train

As originally built the MT-2 had a very good quality Sagami can motor coupled to a terrible gearbox.  The motor was coupled to the gearbox using the standard piece of rubber tubing.   To improve the drive train the gearbox and rubber tubing would have to go.


I decided to replace the original trashy gearbox with a quality NWSL 0.4 mod 28:1 idler gearbox.  As the overall height of the new gearbox was different from the original, I also needed to make a new motor mount.  As with my earlier MT-4 project I decided to use a torque arm and universals to interconnect the motor to the gearbox.


I milled a motor cradle out of a piece of 3/8” x 1/2" brass bar stock using a 3/4" (19mm) ball end mill.  The bottom of the motor cradle was fly cut at an angle to position the motor correctly.  On the bottom of the motor cradle I drilled and tapped two 1.4mm holes that aligned with the original holes in the frame.  RTV adhesive was used to secure the motor to the cradle.  The silicon rubber will damp out some of the motor’s vibration, and the screw mounting allows the motor to be easily removed if servicing is needed.


I replaced the rubber tubing with a set of NWSL universals.  I drilled and tapped a couple of 1.4 mm holes along the gearbox top to secure one end of the torque arm.  The torque arm is made from .016” brass sheet stock, and is .2” wide.  The motor was positioned in the motor cradle so that the 2 mm mounting holes were facing up.  I attached the motor end of the torque arm to the front motor mounting hole using a shouldered screw.  This secured the torque arm, but still allowed the joint on the motor end to rotate so that the gearbox could freely shift to the right or left as the locomotive goes around curves.


Here are a couple of pictures of the rebuilt drive train:





While I had everything apart I also checked the quartering of all the wheels.  The quartering was fine so I just replaced the axle gear and re-quartered the main driver set.  I also replaced the original driver springs with NWSL light springs.   The original plating on the drivers was worn off from use, so I cleaned up the drivers and re-plated them with a silver electro-plating kit.


Here are the before and after pictures of the drivers:




For reference here is a list of parts used in the drive train:


*     Sagami 2032     20mm x 32mm motor  (original)

*     NWSL 240-6      0.4 mod 28:1 idler gearbox

*     NWSL 482-6      U-joints

*     NWSL 21142-5   1.4mm x 2mm x .3 screws

*     NWSL 1401-1     Light driver springs

*     3/8” x 1/2" brass bar stock  (motor cradle)

*     16 mil brass sheet stock (torque arm)

*     2 mm x 0.4 shouldered screw (custom turned)


Page 6 - Last updated April 19, 2004


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