CV 181

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CV 181
BEMF Critical Speed Step
Range of Values3-126
Accepted Values3-126
Default ValueVaries

NMRA CV 181 - BEMF Critical Speed Step

CV 181 controls at what speed step "inertia takes over" and the BEMF algorithm can change how fast it reacts. The speed/RPM at which this transition occurs will vary based on the type of motor, gear ratio, etc. Usually this speed step is 7 (of 128) or below. This CV is used to set a speed step at which the behaviour of the BEMF changes. Through the use of CV's 178 and 179, you can set up two different levels of "responsiveness" for the BEMF above and below this speed. This feature is most useful with 3-pole and "coreless" motors which tend to have dramatically different BEMF swings depending on the RPM. You may want to have a less sensitive response at slow speeds (below Speed Step 7 for example), but a faster response at higher speeds above 7, or vice-versa.

!!!WARNING!!! This CV should not be modified unless you are trying to correct a significant issue with slow speed motor control. We do not suggest modifying this CV unless absolutely necessary.

This "responsiveness" refers to the motor control itself, not necessarily the sound functions such as chuff intensity or prime mover RPM. Refer to our section on Prototype Throttle Mode for guidance on BEMF calibration for sound function.

NOTE: This CV was introduced at different times in different decoders. This CV will not do anything if programmed with a value on a decoder which does not support the feature.

Only current-generation decoders (V4.5 Diesel, V4.6 Steam, V90+ Mobile) support this CV and featureset.