Drive Evolution--The End of the Beginning

After years of building T scale locomotive models that looked good but were mostly dummies due to the limitations of the available powered chassis, last fall I decided it was time for the development of a CCE Models powered chassis.  Below is a summary of where I've gotten over the past few months. 

The original T-gauge models from K.K. Eishindo were all car-body designs, as have been the vast majority of subsequent models.  They were EMU's like the KIHA-40, and later TGauge.com came out with their beautiful Class 67 diesel.  Common among these designs is that they allow space for the 4mm diameter motors within the shell.  The only exception has been a toy-like "GP8" which is quite out-of-scale because they widened the model to accommodate the motor. 

Pulling power isn't very good--most trains need a ratio of about one powered unit to every 2-3 pieces of rolling stock. All trains benefit from having two powered units regardless--two help smooth out power pick-up issues on track and wheels that become dirty rather quickly.  

In addition, with the available stock chassis there are limited arrangements of truck bolster spacing, and the trucks themselves are based loosely on the Japanese EMU prototype--not applicable to modelers of the US or Canada in the 1980s, or Colorado in the 50s!  Over time, several longer chassis have come from China, the motors have gotten better, and pulse controllers have made the slow speed performance better.  But there's still room for improvement.  

I wanted to design a powered chassis to fit my models properly with regard to truck bolster spacing as well as having prototypical truck appearance.  The coup-de-grace would be one narrow enough to fit in hood diesels.  I also wanted it to be a good running design.  So here were my design criteria:

• Could fit in American designs--both hood and car-body locomotives.
  
• Flexible design to fit different truck spacing.
• Prototypical looking trucks.
• Good running.
  
• Relatively easy to produce.

Groundwork:  3D design and printing of chassis was clearly a great option for this project, offering the ability to print small quantities at reasonable cost, and adjust designs on-demand.  Having gained considerable experience over the course of making scores of 3D printed models, I felt up to the challenge.  So in the fall of 2020 I took an old chassis, my trusty vernier caliper and ruler and drafted a basic copy of the existing T-gauge chassis in my 3D design software.  I became very familiar with the stock drive arrangement, which uses a crown gear at a right angle to the motor shaft drive gear, and multiple reduction gears to transmit power the drive wheels.   

Frame Fundamentals:  The chassis frame is the main adjustable component in the exercise, and moreover the one I could most easily fabricate.  I needed to be sure the 3D printed materials would be sufficient to withstand regular use but precise enough for micron-size adjustments in gear alignment.  I reasoned the motor and drive gears could be easily scavenged from donor chassis for the time being; they were readily available and proven.  In addition, if needed, other gears could be sourced through various suppliers of micro-airplane and RC car models.  I made a test print of the chassis using Shapeways Smoothest Fine Detail Plastic and it was definitely robust enough to handle plenty of use.  In fact, the acrylic material seems to have a self-lubricating quality to it.   

Shortened Chassis Development:  To meet one of the key design criteria--that of fitting different length carbody units--I needed to be able to shorten the chassis.  Lengthening shouldn't be an issue: just move the power plant/drive train.  I adjusted the chassis design using the principle developed by the modeler David K. Smith, who about a decade ago kit-bashed an Eishindo chassis to make it short enough to fit in a T-scale EMD F7 or F3 carbody.  Using the text of his original article (the pictures were lost when his computer crashed!) I modified the 3D design accordingly and after a couple adjustments found it worked... rather nicely actually.  

As of this writing (2/17) this is where the "proven" technology stands.  The printed chassis is shorter than stock, and utilizes the gears and motor from a donor chassis, and it runs well.  The test chassis has truck bolster centers of 19.5mm, or 29 ft. in 1:450--so in theory any carbody diesel greater than that is possible.  Here's a list of truck bolster centers for reference.

Truck Development:  While working on the shorter chassis I also designed a set of Blomberg trucks that will accept the stock contact strips that would be a one-for-one replacement to the old Japanese prototype trucks in either the printed or stock chassis.  It stands to reason that if these models can be validated, so could CCE Models' AAR-B trucks, or others--even 3 axle.  Beta models of the Blomberg trucks are currently being printed so I should be testing these within the next few weeks.

Hood Width/Worm Drive Chassis Experiments:  As noted, the shorter chassis design above is confined to use with carbody/cab locomotives that have the needed scale width for the mechanism.  The limiting factor is primarily the 4mm diameter motor which sits above the frame.  The width of the standard powered chassis is 5mm (or nearly 7.5ft in scale).  A hood diesel like the GP40 has a long hood width of around 6 ft in scale (4.6mm) or about 0.5mm wider than the standard chassis itself.  

How to configure the chassis to fit in a hood diesel is a real challenge, and several ideas came up.  Use etched brass for hood sides?  I ruled out etching for the time being because it would be complicated and would be difficult to assemble well.  Source a motor with a smaller diameter and narrow the chassis?  It sure would be nice if there were affordable motors less than 4mm diameter but for now they don't exist. 

However, I might have come up with a solution utilizing a worm drive and a different motor configuration.  If my worm drive concept works it should also allow for further reduction in length of the chassis, perhaps even allowing switchers such as the SW1200 to be powered.  Another potential advantage of the worm drive is it may be more powerful and/or smoother-running.  That remains to be seen, however..  I have also speculated on using a flywheel or "keep alive" circuit, although pulse power might make the latter impossible.  A worm drive certainly has potential use in steam power..

There are sure to be additional developments and ups-and-downs, but I'm determined to get this done.  And rest assured all of these designs will be available from CCE Models as soon as I'm confident they are reliable and of value to other T-scale modelers.  

Until next time,

-- Jesse