Configuring an Athearn GP40-2/Tsunami2 for the ProtoThrottle

This post will take you through the steps to configure an Athearn Genesis GP40-2 with Tsunami2 decoder for use with the ProtoThrottle.  Special features of this GP40-2 locomotive include flashing warning strobes on the cab roof which we can control using the ProtoThrottle.  DecoderPro was used in the example below, but individual CVs can also be set manually – refer to the Tsunami2 Diesel Technical Reference (available from Soundtraxx.com) for details.  A CSV file containing all the CV settings for this locomotive is available below.

Locomotive: Athearn Genesis GP40-2
Decoder: Soundtraxx Tsunami2 v1.2
Settings: UP-1390-PT.csv

UP-1390

Getting Started

The first thing to do is to set the locomotive address.  In this case, we will make it match the locomotive number, 1390.  Select the Long (two byte) address and enter “1390” for the Extended Address.

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The next thing to do is to increase the acceleration and deceleration values in CV3 and CV4, respectively (Motor tab).  These will result in much more realistic operation of the locomotive when used with the ProtoThrottle.  An acceleration value near mid-scale (128) is a good place to start.  This can be adjusted up or down, depending on the intended use of the locomotive and your operating preferences.  The deceleration value should typically be set very high, often at the maximum of 255, to provide a coasting effect when you let off the throttle, thus requiring use of the brake to bring the locomotive to a stop.

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Prime Mover Tweaks

The Tsunami2 decoder provides a number of options to tweak the behavior of the primer mover with respect to the throttle settings and when power is applied to the locomotive.  First, we will enable True Idle (Sound tab, CV112).  This feature was introduced in v1.2 of the Tsunami2 decoder.  On the prototype, notch 1 simply applies the field to the traction motors and does not increase the speed of the prime mover.  With True Idle enabled, the decoder will mimic this behavior – the locomotive will move in notch 1, but the prime mover will not change speed until notch 2.

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Next, we will prevent the Prime Mover from starting automatically when power is applied and instead wait until the decoder receives a speed step greater than zero or an RPM+ function.  To do this, set the Engine Auto Start (Sound tab, CV114) to Disable.  Also, set the Engine RPM Interlock (Sound tab, CV114) to Manual Control.  This prevents movement of the locomotive until the prime mover sound has been started.

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Prototype locomotives do not start moving immediately when the throttle is notched up.  To simulate this behavior, increase the Motor Speed Step Deadband value (Motor tab, CV216).  A value of 2 is good for a light engine.  For a heavier train, you might want to use something like 3 or 4.  This value delays movement of the motor until the decoder has internally reached the programmed speed step.  Combined with high momentum, this provides a time delay on the start of movement until after the prime mover sound has notched up.

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The number of speed steps that corresponds to each prime mover sound notch can be configured on the Tsunami2 decoder.  Higher values require using more speed steps to reach Notch 8 with a correspondingly higher top speed, while lower values have fewer speed steps per notch, less speed resolution between notches, and a lower top speed.  This value also has consequences when setting the braking rate below.  For this Athearn GP40-2, we are going to set the Engine Notch Rate (Sound tab, CV114) to 7.

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Finally, since we control the notches manually using the ProtoThrottle, we don’t want the decoder automatically shifting to other notches based on load.  Disable Dynamic Digital Exhaust by setting Throttle Sensitivity (DDE tab, CV2.511) to zero.

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Braking

Braking can take several forms in the Tsunami2 decoder: independent brake, train brake, and dynamic brake.  For this GP40-2, we are only going to configure the independent and train brakes.  The ProtoThrottle will be set up later to allow us to switch between the two on the fly.  Both brake settings are configured in the same way.  The braking rate is a value between 0 and 127.  This value is then either added or subtracted from the CV4 deceleration rate.  For our purposes, since we want the train to stop faster when using the brakes, as opposed to just coasting, we want to subtract the value from CV4.

For this example, we will configure the independent brake to provide a faster braking action than the train brake.  The idea is that you’d be using the independent brake when switching short cuts of cars, thus being able to stop faster, and the train brake when operating full trains which will take longer to stop.  Set the Independent Brake Rate (Advanced tab, CV117) to the maximum of 127 and the Train Brake Rate (Advanced tab, CV118) to a value of 25.  In both cases, select Subtract for the Brake Rate Sign.

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One final change is required to make the brake work when the brake function is activated.  On the Function Map tab (CV1.403), deselect the Forward Standing and Reverse Standing options.  This will allow the brake function, when activated, to slow the train and bring it to a stop.

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Note: Unfortunately, the most CV4 can be reduced when braking is 127.  In order to get the maximal coasting effect by setting CV4 to 255, the maximum braking effect is therefore limited.  By compressing the speed curve using the Engine Notch Rate above, braking is also more effective since there are fewer speed steps to decrement.  However, that is at the cost of a reduced top speed, but in many cases this is an acceptable trade-off.

Lighting

By default, the headlights are set up for automatic directional operation.  Since the ProtoThrottle has independent knobs for the headlights, we need to remove the automatic operation and put the rear headlight on a new function.  First, enable both the front and rear (backup) headlights in both the forward and reverse directions (Lights tab, CV57 and CV58).

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Next, leave the front headlight on function F0 and assign the rear (backup) headlight to a different function number (Function Map tab, CV1.258).  On this Athearn locomotive, F19 is unused so we’ll use that.

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ProtoThrottle Setup

The last step is to configure the ProtoThrottle.  To begin, select the locomotive number (1390) using the SET LOCO menu.  Then, enter the CONFIG FUNC menu.  Set each function to the corresponding DCC function number shown in the table below.  Finally, the speed step sent in each notch of the throttle should be adjusted to match the decoder settings.  See this article for details on finding the correct notch settings and apply those values in the NOTCH CFG menu.

Recommended ProtoThrottle Settings

MenuSettingValueComments
CONFIG FUNCHORNF02
CONFIG FUNCBELLF01
CONFIG FUNCBRAKEF11
CONFIG FUNCBRK OFFF--
CONFIG FUNCAUXF12Brake Select
CONFIG FUNCENG ONF26RPM+
CONFIG FUNCENG STOPF27RPM-
CONFIG FUNCTHR UNLKF11
CONFIG FUNCREV SWAPF--
CONFIG FUNCF.HEADF00
CONFIG FUNCF.DITCHF05
CONFIG FUNCF.DIM #1F00
CONFIG FUNCF.DIM #2F07
CONFIG FUNCR.HEADF19
CONFIG FUNCR.DITCHF--No rear ditch lights
CONFIG FUNCR.DIM #1F19
CONFIG FUNCR.DIM #2F07
CONFIG FUNCUP BTNF--
CONFIG FUNCDOWN BTNF06 LATStrobe lights
NOTCH CFGNOTCH 15
NOTCH CFGNOTCH 210
NOTCH CFGNOTCH 316
NOTCH CFGNOTCH 424
NOTCH CFGNOTCH 531
NOTCH CFGNOTCH 638
NOTCH CFGNOTCH 745
NOTCH CFGNOTCH 850
OPTIONSVAR BRKOFF

Summary

By now, you should have a working locomotive and ProtoThrottle combination.  Some function mappings might differ, so consult the manual (or your own installation notes) when applying these instructions to other locomotive models.  Additional tweaking may also be needed to suit your operating requirements and style, but these instructions have hopefully given you a good starting point.  Happy railroading!

Comments

  1. Michael, using the CV3 value of 128 yields an acceleration rate that is too slow for most anyone that is trying to use a locomotive for switching during an operating session. Real engineers have locally settled on a CV3 value of 25 – 35 as being a relatively reasonable representation of the real world but still acceptable in the model operating environment.
    The CV4 value of 255 and the maximum CV117 value of 255 yields a net deceleration rate of 127, which I believe is not a useful braking rate. I recommend setting CV4 to a value of 128 and the setting CV117 to somewhere from 200 to 240. Using CV117 at 240 yields a deceleration rate of 12 which most of my prototype engineer friends find to be very realistic.

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