This weeks activity has been very productive on the weight and motor study. The four weight steps have been completed on the BB GP38. The first three steps have been completed on the BB SD9 and the Bowser C-636. The first two-step testing has been completed on the BB Trainmaster and the MTH Bi Polar engines. The F9B, the GP9 are ready for the first test. The E7A has some truck damage. This is actually the reason it was selected for the study. It will be repaired, if it can be, after the above engines have been through the first set of tests.
This activity has brought to the surface the weakness of the draw bar measurement. In order of confidence, it is the lowest of the four parameters critical to performance. Up to this point, the force had been measured with a Micro Mark gauge. This has been periodically compared using a trigger pull force tool. The comparison has always been good. A few anomalies have seemed to appear, so a comparison was made. Again good agreement. The biggest question has been level. In some cases the level just seems unlikely high.
So, now this activity is varying the weight with the expectation of an increased draw bar force among other changes. To test this measurement, a couple of options have been tried. First, a couple of engines were tested, one step at a time all data taken on different days. The GP38, the SD9 and the C-636 were tested that way. The force increments were inconsistent with the weight increments. The variations were unbelievable.
A first attempt to achieve a better set of force data was to take all four sets of forced data at the same test period. In this case, the same instrument was used to measure the data, the maximum force was measured at 16 volts, 12 volts and the maximum level. Three measurements taken at each point. The force was measured on the GP38 and the C-636. All seemed better. The trends seemed to make physical sense. Then the SD9 and Trainmaster were measured the same way. Some inconsistencies returned. The track was cleaned and measurements repeated. The result was improved but still strange.
All along, the intention was to make this measurement in a couple of ways. Both different from the gage technique. The first was to use a pulley and weight system. Here a weight of known quantity is strung around a pulley and connected to the engine coupler. The weight is hung down towards the floor. The current draw and engine velocity is measured at several voltage levels. The weight is successively increased until the engine no longer will pull the weight off the floor.
The second option was to actually have cars that can hold different amounts of weight. In this case the actual number of equivalent cars would be measured rather than a force.
Up to this point the gage method has seem to be adequate. It is less time-consuming, so that was the main factor. This activity has brought that to question.
Because of this, the force measurement has need made a third time on several of the engines. The pulley and weight method has been used. The intension was to measure the weight at several voltage levels. The GP38 was tested first. The resulting maximum force did not change above 10 volts. This was determined at the first two weight increments. So for now the data will be taken at 12 volts. This will be checked again over the next few days.
Three of the engine force measurements have been recorded this way. The recorded trends are possible. The rest of the engines will be examined this way. The GP38 will be repeated on one of the weight increments over the next few days to verify the repeatability of this process. The maximum force voltage will also be examined to understand the best or approximate voltage for these measurements.
The implications of this will require some testing reruns of a number of engines in the list. Until the full impact is better understood. The published list will remain the same. No new engines will be added to the list.
Relative to the testing at hand, the impact of adding weight has diminishing benefits in pull force. The Trainmaster shows no benefit beyond the second step. The down side is the starting voltage, velocity and current generally increase as the weight is increased. The first weight variation testing on all the engines will be documented as the data is available. The tuning and motor variation results will be reported separately.