Will we see clearly?

Expected Results
The results will take the form of the tractive effort to speed function shown in the basic physics post. The maximum velocities at any tractive effort will correspond to the maximum voltage to be tested. Per the NMRA edict, this will be 16 volts. The following figure depicts this curve and other potentially possible lines of lower voltage.
f16

At the maximum tractive effort, the velocity will be at or near zero. This maximum tractive force should be an output of the activity.
This point may not actually be attainable with a particular locomotive. Depending on the engine weight, drive wheel diameter and wheel roughness, the adhesion line may dominate the maximum Tractive Effort. The shape of this adhesion line is also a desired output of the activity.
Below the maximum attainable Tractive Effort the velocity will increase as the Tractive Effort decreases. The maximum velocity will be for the loco only configuration.

This loco only maximum velocity will be an output of this activity.

The shape of this constant voltage TE to velocity characteristic is one of unknowns for each engine. This shape is dependent on the motor electric power to horsepower transfer, the gear ratio and a few other factors. Each of these will be different from loco to loco depending on the design of each element. With proper care in the testing, this shape will be and output of the activity.

As discussed earlier, this loco only curve will follow a resistance curve as the power is reduced until it intersects the zero velocity axis. For real systems this operation near zero is possible. It takes some effort to just get the system rolling.

This loco only (no load) initial tractive force will be a desired output of the activity.

This initial tractive effort has to be associated with a minimum electric power to the motor. For model locomotives, because the gear boxes are simple and there is no variability in the gear ratio through a “transmission” Then this initial tractive effort will also be associated with the minimum power to rotate the motor. This will occur at an electric voltage somewhat greater than zero.

This loco only minimum voltage will be an output of the activity.

There will be a finite velocity associated with this loco only minimum motor rotation voltage (power).

This loco only velocity at the minimum motor rotation will be an output of this activity.

Critical to the description of the results are the shapes of the resistance curves. As described earlier, the resistance of a given load takes the form of the quadratic equation:
f11

The higher order terms will be ignored in these controlled tests. To define this curve for each of the possible loads to be tested, the zero velocity Tractive Effort will be required.

This loco zero velocity tractive force for a given load will be an output of the activity.

2 thoughts on “Will we see clearly?

  1. Jani

    Good day! This is my 1st comment here so I just wanted to give a
    quick shout out and tell you I really enjoy reading
    through your blog posts. Can you recommend any other blogs/websites/forums
    that go over the same subjects? Thanks for your time!

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