Based on the early results, a series of design of experiments was specified:
Using a Taguchi orthogonal L design which has four factors with 9 runs for each series.
The over all process was to run ten DOE’s using this technique. The four factors are as follows
- engine as X1,
- Delta Weight as X2,
- Wheel material as X3
- Motor as X4
The salient features for each variable are as follows:
- The delta weight variation is base weight, +154 grams & +306 grams. (The last should be +308 grams, but 306 is what I have)
- Weight has been shown to be a large driver of pulling capacity.
- Is it all good>
- What are the limitations?
- The wheel material variation is stock Athearn BB 42 in, NWSL 42 in NS & NWSL 40 in SS.
- NWSL is Northwest Short Line, NS is nickel silver & SS is Stainless steel
- A number of previous tests indicated that SS & NS perform considerably better than standard blue box.
- Looking to see if it holds here
- These last two factors are repeated on all ten DOE’s.
- The engine variable is made up of six diesel models that are split into two groups of three.
- The first group is made up of the six axle models.
- The second group was intended to be made up of four axle models.
- Because of limited supply, this group is actually 2 four axle & 1 six axle model
- The first group are used in DOE 1,3,5, 7 & 9.
- The second group are used in DOE 2,4,6, 8& 10.
- Embedded in the engines are several variables:
- All engines have different base weights.
- Drive shafts vary between stock BB splines, Athearn hex dog bones & conventional dog bones. By necessity these splines vary in length as required.
- The truck gear ratios & gear configurations vary from model to model.
- The Fifteen motors are divided into five groups of three.
- The first group of three are used in DOE’s 1 & 2. The second group of 3 are used in DOE’s 3 & 4, and so on.
- All motor- fly wheel sets are as received. Except the Bachmann engine. A single flywheel was added to one side of that motor.
- Athearn motors were mounted using four screws through the frame
- All other motors mounted with chalk on A-line saddles
The potential for variation in these test is real. Every effort was expended to minimize the differences where possible.
The total number of runs for the ten DOE sets is 90.
The engines used for these DOE’s are all Athearn blue box vintage:
These cover most of the possibilities to allow the DOE analysis to highlight the benefit of several aspects of these engines.
- The use of Athearn BB configurations allows for ease of configuration change for each run.
- The weights recorded above are without the motor, drive spline or tower gear.
- The engines are fundamentally minimal in detail and robust against damage that would bias the results.
- The internal torque losses should be consistent from engine to engine. However, the group are not likely to be the same as a current release engines.
- The results will be internally consistent to these engines, but may be better or worse than would result in a current release engine architecture.
The after a reexamination of the motors and getting some online help, fifteen were chosen to be run in the test bed engines. These motors are:
- Sagami 1836 #1
- Walthers ES44
The numbers (#x) are the version of that motor in the group. No number means it is the only sample of that motor
Of the list, Mashima, Kato, Atlas China, Bachmann & Sagami 1836 motors are 20-30 years old. The others were purchased new within the last five years. Most for this activity and are representative of recent release engine motors.
The study will track the impact on several measurable engine performance metrics:
- The train speed at several settings.
- Engine only at minimum sustained speed, 4,6,9,12 & 16 volts at level grade.
- Engine plus 2 times number of drive axle cars at 12 volts on a level grade
- For a 2.5% grade at 12 volts the speed is tracked from engine only. Plus train lengths from 2 times number of drive axle cars to the number of cars that can not be pulled up the grade.
- At all of these settings, the power supply current is measured.
- This describes the input power to the test at each point
- The engine max draw bar force and current draw are measured at 12 volts.
- The motor stall current is measured at 8 & 12 volts.
- Using several of these measurements a performance characteristics value is determined. This criteria is defined here:https://www.llxlocomotives.com/wp-admin/post.php?post=643
The operation of the four variables in the DOE set will show the impact on several combinations of these performance values:
- Maximum number of cars on a 2.5% grade
- 12 volt engine only velocity on level & 2.5% grade.
- Change in velocity for a nominal train length at level & 2.5% grade
- Power impact of nominal train lengths on level & 2.5% grades
- Minimum sustained velocity
- Minimum sustained velocity power ratio.
- Overall performance characteristics
Each DOE parameter will be rated on the impact on these performance parameters.
With limits, the winning inputs from the initial DOE sets will be compared in subsequent combinations using these same data to establish which DOE parameters have the largest impact on the measured performance.
