Over the engine testing several steam engines from various manufacturer have been examined. Some of these engines are from my collection. Others are from the series of engines that I tuned up for clients or part of a buy-fix-sell activity that I have been doing since 1999. During that time there were dozens of these steam engines that brought back to life and were run through a limited test run that was not recorded. Since the 2014, virtually all engines have been put through the formal test series that is documented else where in these blog pages. In every case, the data presented here is from engines that have been tuned up and lubricated as appropriate. Where needed, the engine traction tires were changed to yield the best result for the model.
For these engines the standard test activity has been performed and the results compared and will be discussed in this write-up. The intention is to examine these steam engines in a consistent manner. Implicit to this examination will be a ranking of the engines that have been tested. It is not intended to say that every engine of the type or by the manufacturer would show the same results. The sample size is not large enough to make that kind of statement and be statistically valid.
The steam engines included are listed in following figure:
Note that there are several types, manufacturers and eras for model train technology included in this set of engines. The motors range from very early open frame to an Athearn Genesis can. There are plastic and die cast boilers and an entirely brass engine. The driver arrangement varies and some are articulated. Unfortunately, this is due to the limited sample size that occurred in the more recent engine activities. More steam engine variations were worked on in the early 2000’s then in the 2015 activities. All of these had and were tested with a tender as part of the test unit. These tenders were consistent with the model and not intended to be the same for load purposes. The presentation is for interest rather for scientific examination. Even with that caveat some interesting results are described.
This discussion will focus on the performance measurements of each of the steam engines. The basic test requirements are as follows:
1.) Powered with DC voltage with no external pulse wave modulation
2.) Running on a level surface (measured and adjusted as required weekly).
3.) The same 8-foot segment of track is used for all the basic tests.
4.) The track is cleaned before each test.
5.) The unit runs without external load (except for the tender) for all but the max draw bar force tests.
6.) Each, track running, data point is the average of three measurements.
These discussions do not deal with accuracy of the shell, the location and nature of the details or the lettering.
To appreciate the results, the question of relative to what always comes to mind. For this reason, the data is compared with the results from the full set of nearly 350 engines tested in the database.
Basic function results are presented in the following charts. The data in each category is compared to the total set of engines.
Some of the steam engines tested on this series are shown in the following figures.
1- Scale velocity vs. voltage of the engine running alone on straight and level track. There is no external load in this test.
This data is shown from 4 to 16 volts. The color code is maintained throughout these charts. The grey lines are from the data base of engines tested in this manner.
These include all the engines in the data base with no attempt to segregate by some feature or era. The black lines on the chart are the maximum, average and the minimum of all of the steam engines recorded in this series. For this chart, the blue reference line would be a goal speed function. For this case it goes through 60 SMPH at 12 volts from the power supply. Interestingly, the average result is close to this goal line. The solid lines of color are from several of the engines examined and labeled appropriately.
These results are typical of a DC no pulse signature. There is a finite voltage when sustained velocity is achieved. Below this voltage, the unit may start to move, but will stop because the resistance is greater than the motor torque can handle.
Notice a significant number of engines from the database run slower than the goal level. The steam engines for the group were selected by interest based on the overall performance criteria. It is interesting that these are all below the goal and average characteristics. The slowest of all, and probably intentionally so, is the PFM 2-8-8-0 engine. The actual engine of this type was a strong puller but slow machine.
The range from maximum to minimum is large for this set of data. It spans vertically all of the experience. Only some very fast unit are outside these results.
2- Current draw vs. voltage for the engine only operating on straight and level track.
The current draw demonstrated for these steam engines are shown to span a large part of the range of all of the testing experience. The selected engines from the previous chart are show on this chart. Of the five that were highlighted, the latest versions have the lowest current draw.
The PFM brass unit is a current hog. Clearly not suited for the digital age where a current budget dominates operation. The Mantua 0-4-0 is also having a significant current draw. This in the final assessment was because of a bad motor. However, current draw alone is not the total indicator of a worn out motor.
3- Starting velocity.
This is the minimum velocity that will sustain movement. This occurs at a discreet input voltage. This voltage varies from motor to motor and drive to drive. It seems to be a function of engine weight and motor capacity. For these charts it is shown as a function of weight.
The background data on this chart has been segregated by era, pre 2000 and post 2000 approximated release date.
For this chart and others that follow, the Average, maximum and minimum are shown with a black symbol. All of the steam engine results are shown with a green circle. Note that the maximum and minimum data have both the black and green symbol. For these charts, a few of the best engines are identified and the worst engine is also identified. The PFM 2-8-8-0 has the lowest starting velocity in this group while the Marx 0-4-0 has by far the highest starting velocity. While the lowest starting velocity units are competitive with the history, the average and maximum starting velocity for these steam engines are both considerably higher than what the data base would suggest was likely.
4- The voltage that is required for the sustained velocity is shown in the following chart:
For the best low speed capabilities, the starting velocity and voltage levels need to be as low as possible. The experience shows several examples that start a lower voltage levels than these steam engines.
The unit with the lowest starting voltage is the Athearn Genesis 2-8-2 unit. It is followed by a Rivarossi Heisler and two Bachmann pancake motor engines. While generally not good pullers, the old pancake motors would start at low voltage and current levels. Their speeds were usually fast. The unit that required the highest level of starting voltage was a classic Mantua 0-4-0 with a Pittman type motor. This is another indicator that the motor may have been bad and the results were not typical for this type unit. A similar motor Mantua 2-8-2 unit started with a voltage below the average on this chart.
5- Starting velocity variation, implied torque wobble
In every case, the data is repeated three times. Running over the same distance. The velocity and current levels are measured digitally. Differences in these readings are an implication of the potential torque wobble of the motor. This also can be a measure of the pulsing level of a PWM impact on the motor, if there is one.
Here some older low end units hold there own with any tested units. Two more recent units do as well. As has been seen before, the average and the maximum levels for these steam engines are higher than the experience would have suggested. This particularly the case for the very old Marx 0-4-0 unit.
6- Starting current draw
The initial current draw follows the trend indicated in the earlier current draw chart. The lowest levels are for the fairly recent Walthers P2K and Athearn Genesis units. These are followed by a Bachmann 2-8-0 and the AHM Rivarossi Heisler engines. once again the Mantua 0-4-0 unit falls on the high(bad) side of the data. The John English 0-4-0 is very close in high current draw. When these units were designed, power was the most important consideration, so high current draw by it self may not be indicating a bad motor.
7- The maximum pull force of the engine is shown in the following figure.
These data are taken at 12 volts, when the engine will no longer pull the weight off the floor. Thus it is zero velocity. This may actually be just above the maximum pull force.
Here there is a large variation in the engines examined in this series. Of the top four pullers, three have traction tires. The tires add friction coefficient to the engine which will enhance the pulling capability at a given engine weight. The AHM Rivarossi Heisler is clearly the best puller. The engines seem to fall in four pull to weight categories. The Heisler stands by itself. The Rivarossi 2-8-8-2, the Mantua 0-8-0 and three others fall at a second level of Pull to weight. The Mantua 4-6-2 defines a third level that five of the other engines are at. A fourth level is indicated by the John English 0-4-0. There are three engines at this level of pull to weight, the Mantua 0-4-0 is one of them as well. The best at any pull to weight level is the heaviest engine in the group. At the end of the day, the highest pull force is the goal for the best train puller.
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9- Current draw at max pull force.
This is the more meaningful current draw level. In every case, the wheels are slipping. Therefore, there has been some current relaxation.
Here we are looking at the current draw at the highest load point. The engine is not moving and the wheels may or may not be slipping. In the case of engines with traction tires, the wheels are likely not slipping and this is likely very near the stall current. Case in point is the Rivarossi 2-8-8-2 engine. The highest current draw on these steam engines. However, the two lowest max load current draw engine also have traction tires. These are Bachmann pancake motors that do not achieve the level of power that the Rivarossi engine does. All but four of these steam engine exceeds ½ amp at maximum load. Definitely high by todays standards.
10- Based on the work of others, the maximum pull force can be translated into the number of 4-ounce cars that can be pulled up a 2.5 percent grade.
This assumes that the entire train is seeing an integral grade of 2.5 percent. This is a fairly sever assumption.
In this case, the force curve is mimicked by the translation constant. The beauty of this is that one can see how many cars are implied by the differences in pull force.
Now we can see that the Heisler appears to be capable of pulling a 39 car train. Here the John English can only pull a 10 car train. Interestingly the real engines would be expected to pull 2 times the number of drive axles. The Heisler has six drive axles so would expect to pull 12 cars where this model can pull 39. The Rivarossi 2-8-8-2 should pull 32 cars where this model can pull 29. The John English would only be expected to pull 8 cars where this model pulled 10. Your desire and perspective is critical to this assessment.
11-Taking all of these results into account through the performance criteria as defined on www.llxlocomotives.com, these motors are compared in the following figure.
As a gage, a PC2 value of 10 or more is considered acceptable. Greater than 50 would be very good to excellent.
This parameter AHM Rivarossi to be the best on this parameter followed by the two recent vintage units, the Athearn Genesis 2-8-2 and the Walthers 0-8-0. Only six of these engines would be considered acceptable. Interestingly the other three in the acceptable range are the low end Mehano and Bachmann units. The Bachmann units have pancake motors. This assessment will be up dated in the future when additional steam engine results become available. While I am not buying, refurbishing and selling units like I once did. I am still fixing clients units and have and will have additional units that are part of my collection. Come back and see how the perspective changes.
