Motor test bed #6- Santa Fe Kodacrome SD40-2

This engine has been tested as part of a series of engines to extensively to evaluate the impact of various motors & electronics modules.

This is one of a series of tests being performed on various motors with and without electronic modules. The purpose in this series is to understand the performance differences with various motors. It is also looking at the impact when an electronic module is in the circuit. These electronics can take many forms. The most obvious is a DCC decoder. It can be as simple as a light card. It can be as complicated as a sound system added to a decoder or something else. It may be one of the new DC control modules.
This is by no means a complete examination of the motors. It is intended to understand how the addition of a different motor in the overall system affects the engine performance.

The standard test activity is to be performed on each variation and the results compared and discussed. The intention is to examine this over a series of engine, motor and electronic variations. It is important to verify and define the usual result and the anomaly. This will require several tests. Each of these reports will focus on a test series on one engine. The overall results will be examined as testing proceeds.
For this specific test series, the engine configuration is an Athearn Blue Box Santa Fe Kodachrome SD40-2 engine with the following characteristics:
1. Athearn BB Drive Parts
2. Athearn BB SD40-2 C-C trucks
3. Stock Athearn BB Wheels
4. New Axle Gears
5. No weight added
6. Motor & Trucks Cleaned & lightly lubed
7. Wheels polished with Kadee wire brush
8. 5-Wire connections

This engine is a stock configuration showing the peformance impact of adding various motors including a stock Athearn blue box rectangular motor.
In this test series there were five variations tested. These configurations are:

1. Athearn BB Rectangular Open Frame Motor #1, No electronic module
2. Mashima 1833 Can Motor #1, No electronic module
3. P2K Open Frame Motor #1, No electronic module
4. Helix Humper Can Motor #2, No electronic module
5. Roco Open Frame Motor, No electronic module

This test engine is shown in the following figure:

This discussion will focus on the performance measurements of the unit. 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 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. In fact, because it is a test bed, several details have been left off for expediency.

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 300 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.

1- Scale velocity vs. voltage of the engine running alone on straight and level track. There is no external load.

This data is shown from minimum to 16 volts. The actual minimum values are included here because they show how the motors are impacting the shape and position of the curves. 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.


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. The velocity level that is sustainable varies and is an interesting discriminator for the motors.
In this chart a reference line is shown (in black reference) that is intended to represent the goal of best speed voltage function. Basically, the desire is for the unit to crawl as slow as possible at low voltage and be able to replicate the full size unit at high-speed. For this purpose, 80 smph at 12 volts was chosen as the value. One could argue that it should be higher. True, but without any external load, why would it be lower? Notice a significant number of engines from the data base run slower than this goal level.
Except at low voltage, all the motors have velocity levels that are higher than this notional goal value. The motor that runs closest is the Mashima 1833 # 1. While still faster, it runs very close to the line. The Roco motor has a speed to voltage that is much higher than the other motors. Really not consistent for the use as a train motor.

2- Current draw vs voltage for the engine only operating on straight and level track.

As shown in the chart, there are two distinct levels of current draw for these motors. The Mashima and the P2K motors have a very good (low) current draw signature. The other three are drawing levels above the average of the database. From six volts up, the Helix Humper and the Roco are on a second level of these motors. The Athearn blue box motor tends to be a current hog, which is the typical experience for blue box motors.

Keep in mind that the input voltage times this current is the input power to the system. If the efficiency of the versions were the same, this would indicate how the output power would look. Fortunately, they do not have the same operating efficiency. That was indicated in the velocity chart and will show in other parameters as well.
This current draw is artificially low. There is no external load or resistance on the engine. These are the normal loads that would be introduced by a train. Later the max load current is also described. That is more representative of the requirements of the engine. This level does indicate a required current difference of the motors.

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.

All of these motors are starting higher than the average recent experience engines.
In this case, the lowest velocity is achieved by the stock P2K motor with the Helix Humper and Mashima motors slightly higher.
The drive and trucks likely dominate these results compared to the database. While the parts were cleaned and lubricated, they are pre dog bone designs. For these motor variation tests, the trucks and wheels are the same. The drive shaft varies in length with the standard blue box couplings. The exception in this set is the Roco motor. Here an early dog bone is required to match the flywheel coupling. This motor tends to be on the high side of the group in velocity.

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 low. These motors all are below the pre 2000 expectation. All but the Athearn blue box are close to the post 2000 average.
The unit with the lowest starting voltage is the stock P2K motor. The second is the Mashima can motor. These two tend to compete for the best spot on most of these parameters

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.


Interestingly, again the P2K open frame motor has the smallest starting velocity variation. All of these motors are very good in repeatability. The Mashima can motor happens to yield the most variation. This is one of the few cases where the Mashima motor is not near the best in the parameter

6- Starting current draw

The initial current draw follows the trend indicated in the earlier current draw chart. The Mashima and the P2K motors set a very low standard. Both are better than the post 2000 expectation for their weight. The other three exceed the pre 2000 averages. Definitely, at a higher level in this set.

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 five engines examined in this series. Interestingly the Athearn blue box motor is the strongest puller. Followed closely by the Mashima can motor. The P2K and Helix Humper motors are both excellent pullers, but much lower than the former two. The Roco motor falls well below the standard level of the other four engines. Interestingly it is near the expectation of a post 2000 result. Considering that very little has changed on these configurations, beyond the motor, this is a disappointing level.

8- Maximum Pull force weight function is shown in the following chart.

Here four weights increments have tested for each motor configuration. This is a relatively new test in the series, so the data base does not include as much history. The weight increments are roughly 150 grams. Totaling just over a pound of added weight. The base engine configuration is the left end of the curve.

In this case, the two can motors, Mashima and Helix Humper, show a larger pull increase with weight than the three open frame motors. The result is that at high weight, the Helix Humper is equitant to the Mashima motor. Both exceed the Athearn over the last half of the weight increase. This is one of the reasons that recent model have all the weight squeezed in that can be fit under the shell. The open frame motors all improve with weight, but their relationship to each other does not change. This is another positive for the Mashima motor.

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.

This shows that the Athearn blue box and the Helix Humper motors draw a lot of current. The Helix Humper goes from being close to the other three to distinctly higher by adding weight. The two can motors, Mashima and Helix Humper share this increased current trend with weight. Interestingly, the two lowest/ best current motors are the Mashima and the P2K open frame. They trade position with the added weight due to the Mashima current slope.

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.
Depending on the engine weight, the two can motors; Mashima and Helix Humper become exceptional train motors. This comes with a rise in current draw as indicated in the last section. Here the third place motor is the Athearn blue box motor. This shows that the P2K motor is a distant fourth and the Roco motor really lags in last.

Keep in mind, all of the motors can pull well over 12 cars up the grade. The real engines would be expected to pull 2 times the number of drive axles, or 2 X 6 = 12 cars.

11- Taking all of these results into account through the second performance criteria as defined on, 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 shows the Mashima and the P2K open frame to be substantially better than the other three motors in the series. Clearly as of this writing, these would be the motors of choice.

The Helix Humper fairs a distant third in this parameter. At the base weight, here is little reason to change from a stock Athearn motor to the Helix Humper. However, with added weight, the advantage grows considerably.

This engine is scheduled to be run with additional motor variations; these will be more recent production motors to see how they stack up with these.

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