I happened on to a number of N scale Bachman engines. Most run poorly. This group is the 1981 version as defined in Spookshow.com. Actually three different motor variations. This discussion is a subset of the larger examination on improving the performance of N scale Bachmann engines. I know why bother. Well they are usually strong runners for a low cost. Clearly the engine performance starts with the motor. Here the focus is on the motor no load test results. The process is to compare the performance of a number of test motors with a reference motor that is considered to be a typical healthy motor. All the motors that I get my hands on are used & abused to some extent. The reference motor achieves an engine performance that is typical of the “best” performing Bachmann engines. All of the test motors were from poor performing engines. Additionally, steps will be taken on the noticeably poor motors to attempt to quantify how close to the reference motor can be achieved with appropriate measures. The best version of each motor will be rerun in its drive to define how this improvement translates to the engine performance
The elements of this discussion are: Definition of the test motors. Test plan for each motor Analysis techniques. Initial test results discussion Speculation of why the performance is down & the techniques to bring the motors back to viability Results of these improvements Conclusions Test motors At this writing there are ten viable test motors to compare with the reference. These test motors come from engines that either did not run or have a very narrow range of operation. The motors all operate when voltage is applied & have no broken parts. The test motors are shown in the following charts. As indicated earlier there are three variations in these motors. Two major, motor 4, 6 & 10 have a white plastic brush assembly shell with a brass hex bolt for contact. The others have metal outer shells. Here motor ref,2,3, 5, 7, 8 & 9 have a plastic sleeve that loosely fits around the motor. The rest have insulation material permanently attached to the top and bottom of the metal outer shell. These are variations to prevent the motor shell from shorting the opposite polarity engine mounts(weights) At least two of the motors (8&10) were fouled so they would not run. The both ran with a little nudge. What ever was on the commutator burned off and they appear to run now. That may be worked later. Motor 2 ran when selected, however when it was set up to test it will not turn at any voltage, will work some more. May have to give up on it. More to come
Please be certain to inspect their gear trains. Bachmann has seen issues in the past with failing (splitting on the axles) gears.
I agree & understand that issue. I intend to deal with that on a different thread. This one is definitely related, but is focused on the motors only. Thanks for your interest.
The one motor that does not run may still be an issue of a dirty commutator if you can't see any broken winding wires. No matter what I'd take the time to thoroughly clean each motor while they are out using some isopropyl alcohol and either an acid brush with shortened bristles or a tightly wound cleaning swab like what tamiya makes for modelers - you don't want to leave fibers in the motor which can happen with the typical cotton swabs. I've revived many motors just cleaning that part up. My memories of an ozone smell while running Bachmann locos makes me think those areas get dirty more so than with other brands.
My long term plan for this task is a clean & lightly lubricate. I find that the commutators are dirty & most tend to have some sort of liquid, like some one decided to put some kind of oil on them. At this juncture a light clean to get them to run is all that I have done. Once they start running the material tends to burn off. There is a residue left. My thought is to identify the results in this condition. Then take two or three of the interesting motors & run in the reference engine. That will identify if the differences translate to the engine. At that point it will be appropriate to do the clean & tune on the motors & retest both as the motor alone & in the reference engine. Again looking to see how much improvement shows up in both tests. At that point the motor activity will be finished and I will focus on the dead or poor running drives. That is the subject of another thread. Thanks for your interest. More details will be included in this location:https://www.llxlocomotives.com/?p=3362
2. Test plan for each motor The specific plan is to measure no external load current draw & motor speed, rpm at various supply voltage settings. The voltage levels to be tested start at the minimum to achieve rotation moving up from zero. Additional data will be taken at 2, 4, 6, 8, 10 & 12 volts. Data will be taken after 30 seconds of operation at each setting. Finally at the measuring voltages, the stall current will be measured. This will be momentarily current readings. The tools to be used to collect this data are a lab power supply. Here you set the prescribed DC voltage. This is a square wave DC signal with no PWM. The supply also measures the current draw by the motor. The the motor rotational speed will be measured with a Tachometer. It is a hand held laser device. The motor shaft has to be darkened with black tape. A sliver of reflective tape is glued to the black tape surface. The tape adhesive alone was not sufficient to hold in place at high speed. Super glueing the sliver in place proved successful. 3 Analysis techniques The data measured for the reference & the ten test engines are shown in the following two charts. The first shows the current draw results, both the no load operating current and the motor stall current as they vary with voltage. For each motor, the difference between these represents the maximum power capacity of the motor. There is an error in the chart. The reference motor is show on black not green. The second chart shows the no load motor speed as it varies with the supply voltage. In both charts, the reference motor is shown as a black line. The initial visual assessment indicates that it is common with the other motors of the same model. These. are the five that are the same shape no matter the insulation technique. The motors with the white plastic brush assembly shell have higher stall current. The speed characteristics are also high relative to the other motors. These charts show variation between the motors, but do not readily indicate which are better or poorer.
The operational qualities of the motor will always translate to the operational qualities of the entire locomotive. It is, similar to the diesel engine in the prototype, the prime mover. Doug
4 Initial test results discussion To better understand the motor capabilities the normalized values of Torque capacity & speed need to be examined. Here the reference engine is used to normalize the test motors. This will help show which motors should be better than the reference and which should be poorer. This includes how they compare over the voltage range. A magnitude of this difference is also described in this process. . The following two charts show these results. The first shows the normalized Torque variation with Voltage (Power). The second shows the normalized speed with Voltage. The Torque data is the most revealing. Probably not surprising, this indicates that the amount that the capacity excess & short fall varies with voltage. Why this matters is that once the load exceeds the capacity of the motor it stalls. Once it stalls, it is unlikely to recover without a load reduction & a voltage reset. Keep in mind, these curves are ratios. The Torque curves are sensitive to small measurement errors, particularly at low voltage (power). Interestingly, the reference motor appears to be on the low torque side. The red curves (rectangular plastic brush assembly) have the highest Torque capacity. Three of these have the hex bolt brush cover if that matters. Motor 10 is a monster relative to the others. Based on this chart, it would be interesting to run three motors in the reference drive. 1- motor 5 because of a low inferred Torque over the entire range. 2- motor 6 because it takes the highest voltage to initiate rotation. 3- motor 10 because it has the largest Torque capacity. The speed data is indicative but can be misleading. There is a speed change with load. As load increases, the speed goes down. However, if there is indicated to be a significant speed change most of that will show up in the loaded application. The resulting speed curves have more peculiar variations than expected. Especially at low voltage/speed. All of motor types show a wide variation with other motors of that type. This implies different level of degradation, but could be typical of these low cost motors. As shown previously, the reference motor seems to be on the low speed side of these results. This is interesting, because it did well in its drive. Motors 1, 4, 5 & 8 all are slow at low voltage (power). Because of this, motor 1 should be added to the list of motors to be tested in the reference drive. The next steps will be two fold, 1- run the four motors defined above in the reference drive. 2- for all the other motors the clean & lube will be done & the motors retested to assess the improvements.
In Z scale, this guy came up with a cleaning procedure for Marklin chassis that involves running the whole thing in parafin oils/odorless kerosene to clean and dissolve hardened oils. https://www.trainboard.com/highball/index.php?threads/cleaning-märklin-locos.122508/ Now that you have the motors benchmarked, I will be interested to see how a basic cleaning/lube improves the motors. If there is limited improvement, it would be interesting to see if this method has any impact. Or even any alternative method, like a sonicator bath cleaning, or I have seen brushed motors run in DI water to clean them.
