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Exhaust Chuff Rate Off: Wheel Base Too Large/Small

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  • Member since
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  • From: Berwyn, PA
  • 409 posts
Exhaust Chuff Rate Off: Wheel Base Too Large/Small
Posted by Trainman440 on Friday, April 20, 2018 10:54 AM

Hello!
I've had this problem once too often: When I installed a sound decoder on to a steam locomotive into a Bachmann 2-10-0 decapod, the chuff rate was off sync as the loco sped up, because the wheelbase of the engine was really small. 

Similarly, when I installed a decoder into my PRR k4 with a huge wheelbase, as the loco sped up, chuffs became off sync. 

Without using a cam, is there any adjustments I can make?

Adjusting the speed curve dosen't help, because the chuff sound is also adjusted. 

I've seen this is a problem for all TSU1000 decoders, and TCS WOW decoders(I dont own any other decoder brands)

Charles

 

---------------------------------------------------------------------------------------------------------------

Charles L.

Modeling the Santa Fe & Pennsylvania in HO!

Youtube Channel: https://www.youtube.com/channel/UCLb3FRqukolAtnD1khrb6lQ

  • Member since
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  • From: Vancouver Island, BC
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Posted by selector on Friday, April 20, 2018 11:28 AM

This is a problem with all sound decoders with which I have experience, and mine ends with the Paragon II, and also with the QSI Titan series introduced about six years ago or so.  I haven't purchased a Tsunami in about eights years.  

The wisdom may have crept left or right in the past few years, but it used to run that one should set the chuff rate about 1/2 the way through the scale speed the loco would reasonably be expect to run most of the time.  For a decapod, that would be in the 10-15 scale mph. Also, as one uses a given locomotive for a bit, the innards warm up and the motor takes less amperage/voltage to keep things moving apace as per the throttle setting at that time.  This will affect the BEMF and what the decoder decides is a commensurately appropriate chuff rate.

Bottom line: suspend disbelief even more when ya gotta.  Get it good enough at a defined lowish speed, and then conveniently forget to count chuffs with each revolution of the main crank.  Enjoy an illusion that should be good enough.

  • Member since
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  • From: Pa.
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Posted by DigitalGriffin on Friday, April 20, 2018 12:29 PM

QSI has the best chuff compensation system.  You program in the driver size, and gear ratios.  Every time a 5 pole motor crosses a pole, it creates a little break in the voltage/current.  So the QSI decoder can count the number of pulses as a pole is crossed.  5 crosses = 1 revolution.  If you know the final drive ratio you can sync your chuff up to 1/10th of a motor revolution.  Considering drive ratios are quite high, that's only a small offset.

But programming it is a pain in the duckass.  It's like 500 indexed parameters.  I recommend the QSI programmer.

Don - Specializing in layout DC->DCC conversions

Modeling C&O transition era and steel industries There's Nothing Like Big Steam!

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  • From: Reading, PA
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Posted by rrinker on Friday, April 20, 2018 1:34 PM

 There is a CV that adjust the chuff rate relative to speed. Best bet is to tune it for slower speed, because that's when you can see it. Once the loco is turning above a certain speed you aren't going to see the rods to count it.

                              --Randy


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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Posted by greendiamond on Friday, April 20, 2018 2:10 PM

Charles:

 

The TCS WOW steam decoders can be programmed to autosync with the drivers.  It works very well.  Simple programming in voice mode. It will run your loco back and forth a bit on the track to get it in sync. Then it's correct at all speeds.  You need to check their website for directions on how to do it. 

 

Michael Tyl

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  • From: Mpls/St.Paul
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Posted by wjstix on Friday, April 20, 2018 4:55 PM

One thing I've noticed without having a cam is the chuff rate is different for a light engine compared to an engine with a train. It takes a little more power to pull the train at say 20 scale MPH than to just run light at 20 MPH, so the chuffs are off because the decoder is going by the amount of power being sent to the motor. I end up splitting the difference, getting the chuffs right when the engine has about 1/2 the cars it would normally pull in a train, so it's "tempered", a little off running light or pulling a train, but not too much.

Stix
  • Member since
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  • From: Huntsville, AR
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Posted by oldline1 on Saturday, April 21, 2018 8:15 PM

All my decoders are old Tsunami's and they had the brown wire to be used with a cam or wiper. They reproduced the correct chffs no matter what speed you were running.

I talked to the Soundtrax guys about the new Tsunami2 and they said there was no provision for the this way of doing it and it needed to be adjusted with CV's. They said it would get "close enough".

I may be one of the few modelers who remember steam and I find the chuffs not in sync with the drivers to be toy like. That's something American Flyer had and I just find it offensive. I want my amazing $800 brass engine, $300 paint job and $150 worth of sound system to be accurate and not "close enough". I don't always run my stuff at the same speed so I need it to be in sync.

If it was done before why can't it be done with the newer decoder? Apparently I'm not alone.

oldline1

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  • From: Reading, PA
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Posted by rrinker on Saturday, April 21, 2018 9:36 PM

Loksounds still have the chuff cam connection. Modern ones work on either a contact or a hall effect magnetic sensor, so it can be done without pulling a wheel to install a cam and a wiper.

                         --Randy


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

  • Member since
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  • From: Huntsville, AR
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Posted by oldline1 on Saturday, April 21, 2018 10:12 PM

I'm not at all familiar with Loksound stuff. I've only used the original Tsunamis. I understood the TCS decoders can use a cam too.

I was fortunate enough to find about 8 Cantara cams on feebay though. They are great products. Brass 2 piece items that get soldered to the axle and each other then micarta pices glued into the 4 gaps and sanded smooth. They work great!

oldline1

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  • From: Berwyn, PA
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Posted by Trainman440 on Saturday, April 21, 2018 11:43 PM

Okay, so basically, I can't do anything unless I invest in QSI decoders(which I personally don't like their sound)

All other replies are in one way or another saying no.

Thanks,

Charles

---------------------------------------------------------------------------------------------------------------

Charles L.

Modeling the Santa Fe & Pennsylvania in HO!

Youtube Channel: https://www.youtube.com/channel/UCLb3FRqukolAtnD1khrb6lQ

  • Member since
    February, 2002
  • From: Reading, PA
  • 24,647 posts
Posted by rrinker on Sunday, April 22, 2018 10:06 AM

Or ESU or TCS.

                 --Randy


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

  • Member since
    February, 2002
  • From: Mpls/St.Paul
  • 10,632 posts
Posted by wjstix on Friday, April 27, 2018 4:45 PM

Trainman440

Okay, so basically, I can't do anything unless I invest in QSI decoders(which I personally don't like their sound)

All other replies are in one way or another saying no.

Thanks,

Charles

 
Or you could adjust the CV that controls chuff rate until it synchs up. I have a Spectrum 2-10-0 with the "Sound Value" Soundtraxx decoder, and I can get it synched up to the drivers. Changing the speed of the engine or the speed curve doesn't do it, you have to adjust the chuff rate. It's usually a bit of trial and error, but some manufacturers instructions have a formula for what number to calculate based on how many chuffs you want per revolution (4 normally, but some three-cylinder engines would use 6) and the drive wheel diameter.
Stix
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  • From: US
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Posted by greendiamond on Thursday, May 03, 2018 5:04 PM

Charles.

 

Michael again responding. Did you check out TCS's website for the video on how to set the chuff rate for the WOW Steam decoders.

 

Here's a link for you.

http://www.tcsdcc.com/Customer_Content/Web_Tools/Videos/WOWSound.php

 

 

  • Member since
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  • From: Sweden
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Posted by Graffen on Friday, May 04, 2018 12:37 PM

So many replies without answering the question...

Soundtraxx Tsunamis are easy to adjust the chuff ratio on.

Just download the steam users manual from their website, look up the right chaptet and program it after instructions.

It's one! CV value....

Swedish Custom painter and model maker. My Website:

My Railroad

My Youtube:

Graff´s channel

  • Member since
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  • From: Sweden
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Posted by Graffen on Friday, May 04, 2018 12:47 PM

Chuffs are computed as:

 

                                    SPD

CV Value = 115.9 X ——— X Gear Ratio 

                                     DIA

where SPD is the locomotive’s top speed in scale miles-per-hour at full throttle and DIA is the locomotive’s driver wheel diameter in scale inches, and Gear Ratio is the gear ratio for shays and other geared engines.

For conventional steam engines, use a Gear Ratio = 1.

The driver diameter can be easily measured with a scale ruler but remember to convert the measurement to scale inches.

If you don’t know your locomotive’s top speed, you can also estimate it and still get pretty good results. A good rule of thumb is to use 45 MPH for freight locomotives and 70 MPH for passenger engines.

Hints for Setting Engine Exhaust Chuff Rate

Because most locomotives do not respond linearly (i.e., straight line) to the throttle settings, it can sometimes be difficult finding the magic auto-exhaust chuff rate setting that works across the locomotive’s full speed range.

We have two procedures for setting the chuff rate that have worked well. The first method is easy to implement and produces good results that should satisfy all but the stodgiest of nitpickers.

The second method takes more effort but produces more accurate results.

Method 1

Begin by setting the starting voltage (CV 2) such that the engine begins to barely move at speed step 1. Then increase the throttle setting until the engine is moving at 10-15 scale MPH.

Then adjust CV 116 up or down until the chuff rate corresponds to approximately four chuffs per wheel revolution.

Method 2

This procedure uses the loadable speed curve to compensate for the locomotive’s non-linearities. Begin by setting CV 25 = 16, CV 29 = 18 (50 if you are using a long address- see Table A) and CV 116 to the value calculated from the formula above. Set your command station to use 28 speed-step mode.

Set the throttle to speed step 1 and adjust the first entry in the speed table, CV 67 until the locomotive speed matches the chuff rate. 

Increase the throttle to speed step 2 and adjust the second entry in the speed table, CV 68 until the locomotive speed once again matches the chuff rate. 

Repeat this process until you have adjusted the locomotive speed across all 28 speed steps using CVs 67-94.

Swedish Custom painter and model maker. My Website:

My Railroad

My Youtube:

Graff´s channel

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