Jim Exler, Nampa, ID June 22, 2022
When I first set up a decoder, I determine the momentum rates (CV3 &4) by trial and error. Once I have the settings I like, they are stored and recorded. The time for each setting would be 0.896 x the momentum number.
After determining the preferred braking rate and recording that, I multiply it by a factor (3 for a small layout but 4 works nicely also) for coasting and use that result for the value in CV4.
For Soundtraxx Tsunami 2
This will set the braking rate for the Dynamic (CV116), Independent (CV117) and Train Brake (CV118). For locomotives that don't have dynamic brakes, set CV116 = 0.
Get the numbers as above and set CV4 to the coast number. I use the same values for the Independent and Train Brake. Independent Brake is shown. We now need to calculate a value for CV117.
CV117 = CV4 (coast value) - CV4 (original value before multiplier) + 128 .
[ CV117 = ( 75 - 25 ) + 128 = 178 ] higher value = more braking, a lower value = less.
Note: The 128 portion is only used by the decoder to make the value a negative number so it is subtracted from the coast value. It sets bit 7 of CV117 (sign) to a negative value. If you are using Decoder Pro, insert the value calculated in CV117 under the "CV" tab and then check the advanced tab. You will see the value is entered properly with the subtraction message displayed.
Important: Disable the automatic brake release function for braking to work, set CV1.403 = 0.
For the Dynamic Brake, I use the original value of CV4 + 128 for CV116. [ CV116 = 25 + 128 = 153 ]
Once these values are set, each CV (116-118) can be easily adjusted to suit with Program on the Main.
| Coast Factor | CV3 (accel) | CV4 (decel) | CV116 (dyn brake) | CV117-118 (ind/train brake) |
|---|---|---|---|---|
| 3 | 25 | 75 | 153 | 178 |
| 3 | 30 | 90 | 158 | 188 |
| 4 | 25 | 100 | 153 | 203 |
| 4 | 30 | 120 | 158 | 218 |
On the Loksound V5 DCC decoders (USA & Australia), the braking rates for Brake 1,2 and 3 can be calculated using the following method. Brake 1 is shown.
We need to calculate a value for CV179 to provide a braking rate that will get us back to our original number with braking for CV4.
The Loksound Manual provides a formula: CV4 x (255 - CV179) / 255 = the value for time. I think it is really the value of the momentum factor.
Simplifying this, we get CV179 = (1 - (1 / 3)) / 0.0039 . Either the ratio of the braking to coasting for CV4 or the actual numbers will both work.
e.g., CV179 = (1 - ( 1 / 3 )) / 0.0039 = 171 CV179 = (1 - ( 1 / 4 )) / 0.0039 = 192
CV179 represents the percentage reduction of CV4 to provide a braking rate. CV179 / 255 = reduction factor. Using the formula above to calculate CV179 and then dividing the answer by 255, we get a reduction factor to multiply the CV4 value by. Subtract this from the CV4 coast value and you have the original CV4 value before the coast factor was applied.
For 3x coast: (CV179 / 255) = 0.67 * CV4 = reduction value. Subtract this from the coast value.
To find the times involved, these CVs will need to be multiplied by 0.896 .
CV179 is labeled in Decoder Pro as "Brake Function 1 time reduction"
Loksound V4 Select
The momentum values use a time variable of 0.25 seconds per unit (European standard) instead of the NMRA standard of 0.896. This results in larger values for CV3 and CV4 but the function is the same.
CV179 is not documented in any v4 literature I can find but it is referenced in the v5 manuals. In Decoder Pro and Lok Programmer, CV179 is listed as the Brake Reduction setting. The value entered represents the time to stop from full speed. Each unit is 0.25 second so for 7 seconds to stop, enter 28.
(28 x 0.25 = 7)
I set CV4 and CV179 and remap the dynamic brake function to my independent brake function key. This brake will only work if the throttle is reduced and will only stop the train with the throttle at zero.