Category Archives: Motor impact testing

Motor test bed #8- Athearn BB Seaboard U30B with six motors

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 has been 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 GP38-2 engine with the following characteristics:
1. Athearn BB Drive Parts
2. Athearn BB U30B BB 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

* (except as noted)

This engine is a stock configuration showing the performance impact of adding various motors including a stock Athearn blue box rectangular motor.
In this series there were five variations tested. These configurations are:
1. Sagami Round Can motor
2. Athearn BB Rectangular motor #4
3. Mashima 1833 can motor #2
4. Mashima 1824 can motor #1
5. Stock P2K open frame motor #4
6. Athearn RTR High Performance #2
There are no electronic modules in place for these six variations.

This test engine is shown in the following figures:

This discussion will focus on the performance measurements of the unit with each motor. 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 DCC modules 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 database run slower than this goal level.
This series while not complete currently has six motor data sets. Of special interest is that there are two Athearn motors and two Mashima motors in these six. This allows an assessment of the impact of these motor variants by the same manufacturer. In the case of the Athearn motor, we are looking at a rectangular blue box motor compared to a recently released Ready to Run High Performance motor. The Blue box motor has been used. The RTR motor was new right out of the package. This was the first running on the motor.
Except at low voltage, five of the motors have velocity levels that are higher than this notional goal value. The sixth, the Mashima 1833 can hovers close to the line just below 12 volts. The resulting slope changes above this voltage creating a significant short fall at 16 volts.
The two Athearn motors run well above the goal. The high performance is closer, but still above the other four.
The Mashima 1824 can motor runs faster than then its sister motor over the entire range of voltage.

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

As shown in the chart, there are three distinct levels of current draw for these motors, except at 16 volts. In this case, a variation changes the position on five of the motors. At low power, the two Mashima motors are the lowest (best). These are followed by the Sagami & stock P2K motors. At high Power, the Mashima 1824 and the Stock P2K motors increase rapidly showing a higher than desired current draw.
The Athearn High Performance motor is much improved relative to the Stock Blue box, but it is still second highest at low power. It appears to have a relatively flat current function with voltage. At high power, it is second from the lowest. This is good for loaded trains. As has been seen in other tests in this series, the Athearn blue box motor tends to be a current hog.

Keep in mind that the input voltage times this current is the input power to the system. If the efficiency of the motors 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. Normally, this no load draw is indicative of the relative operation position when in a loaded operation. In this case, that changes as will be seen in the later maximum load discussions.

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 stock P2K motor achieves the lowest initial sustained velocity.
The drive and trucks likely dominate these results compared to the database. While the parts were cleaned and lubricated. Five are pre dog bone designs. The Athearn High Performance motor has hex/ dog bone shafts. In this case, the tower worm gear was changed. All of the variations used the original trucks. In five configurations, the drive shafts varied in length using the standard blue box couplings.

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. These motors all are below the pre 2000 expectation. Four of these motors are at or above the post 2000 average.

The unit with the lowest starting voltage is the Stock PK open frame motor. It is on the current expectation line. The two Athearn motors have the highest initial starting velocity. The High performance version is improved relative to the Blue Box motor, but still higher than the rest. The two Mashima motors are next lowest with the 1824 version showing a slightly lower level. As in most of the parameters examined so far, the Sagami can motor hovers near the best, in this case fourth.

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 the Sagami motor shows the least variation. It does show very little variation over the entire range of tested voltage. The other five motors all fall between the two eras in the data base The Athearn high performance open frame motor happens to yield the most variation, followed closely by the Mashima 1833 can motor and the stock P2K open frame motor. These all show a very respectable result. One might infer ht can motors have less variation than open frame motors, but the difference is small.

6- Starting current draw

The initial current draw follows the trend indicated in the earlier current draw chart. The Mashima 1824 can motor sets the standard for these six motors. It is better (lower) than the current expectation results. The Athearn Blue box open frame motor is clearly the highest in the set.
As indicated earlier, the Athearn High Performance motor is the second highest initial current draw.

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. Interestingly, here the Athearn blue box motor is the weakest puller. In other examinations in this series, it was the best. The best is the Sagami can motor by a big margin. The other three all fall just above the current expectation average. Here the Athearn High Performance motor shows its worth, coming in second in this parameter. Considering that very little has changed on in most these configurations, beyond the motor, this is an interesting result.

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.

When looked at this way, the difference between the Sagami can motor and the Athearn High performance open frame motor is primarily the base engine weight. At a common weight, their pulling capacity is much closer together. The Sagami motor shows a weaker slope with weight such that the Athearn high performance motor is the better puller at the higher weights.
A similar pattern is shown between the Mashima 1824 can and the Athearn Blue box motors. The Mashima can is the stronger puller at the base weight, but they are nearly equal at the high weight.

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 draws a lot of current.
The second highest is the Athearn High performance motor. When looking at common engine weight, the can motors show the lowest current draw at the maximum pull force. Over this range, the Mashima motors are the lowest. The Sagami is looking better as weight is added.
Therefore, if current budget is the biggest criteria, then a can moor is likely going to be the right choice.

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.

The Sagami round can motor and the Athearn high performance open frame are exceptional train motors. This comes with a current draw difference as indicated in the last section. Over most of the weight variation, the Athearn Blue box open frame motor lags in last.

Keep in mind in the tested engine weight range, all of the motors can pull well over eight cars up the grade. The real engines would be expected to pull 2 times the number of drive axles, or 2 X 4 = 8 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 Stock P2K open frame, Mashima 1824 and the Sagami round motors to be substantially better than the other three in the series. The best at it base weight is the Sagami round can motor. The best at a given weight is the Stock P2K motor. Clearly as of this writing, these would be the motors of choice. The actual selection would depend on train size and current budget requirements.

The two Athearn motors show to be least desirable in this assessment.

At the base weight, the Athearn blue box motor is very marginal. The Athearn high performance motor is much improved, but still falls short of the other options here. Both improve with added weight, but do not change their overall position.

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.