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Built in scale speed display for DCC?

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  • Member since
    March, 2018
  • 236 posts
Built in scale speed display for DCC?
Posted by BNSF UP and others modeler on Thursday, June 07, 2018 8:09 PM

So, you know how there are speed steps in DCC? Well, I was wondering, is there an easy way to program your locomotive to accelarate in step with the speed steps (e.g. one speed step= 1 scale mph in 128 speed steps, etc)? Or, if your loco can't go that fast, have every 2 speed steps be 1 scale mph, or some other ratio. This would make it incredibly easy to move at prototypical speeds and not exceed the prototype's top speed. I have JMRI and an NCE powercab. What can I do with these to try this?

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  • From: perogie flats
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Posted by wvg_ca on Thursday, June 07, 2018 8:18 PM

jmri / dcc set the speed in percentage / portions of voltage applied, not scale mph ...

there is no direct correlation, sorry

PED
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Posted by PED on Thursday, June 07, 2018 8:59 PM

Not directly but there is a way to come close. I do N scale and I have a device (RollBy Speedometer) that I can use to measure scale MPH (SMPH) while it is hooked to my loco. Using Decoder Pro, I can play with the speed tables to adjust the tables value along with trim values (while loco is in motion and showing me the SMPH) such that I can make my throttle setting match very close to SMPH. This works well with my Kato locos but not very well with the Atlas slow motors. With the slow Atlas motors, I dial them into a 2:1 scale. A 60 on my throttle is about 30 SMPH.

A lot of work but it works for me.

Paul

Washita and Santa Fe Railroad
Circa 1970's in south central Oklahoma

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  • From: Reading, PA
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Posted by rrinker on Friday, June 08, 2018 7:01 AM

 ABsolutely doable. You just need a speedometer or speed trap, and patience. Adjust the speed table values until you achieve the results you want.

                                       --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 BNSF UP and others modeler on Friday, June 08, 2018 10:29 AM

Is there a calculation you can use if you find out what the maximum and minimum speeds are for a certian loco?

PED
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Posted by PED on Friday, June 08, 2018 12:16 PM

Not that I know of. I can take 10 loco's, same model, same mfg, same everything and then run them with my speedometer and they will all come out different. Some run slower/faster when cold but level out when warmed up. That is why you need to adjust their speeds with the speed tables and trim values in Decoder Pro. With that, you can tweek each one to all operate nearly the same at a given trottle setting. I let them run a few minutes to warm up before I make any adjustments.

Paul

Washita and Santa Fe Railroad
Circa 1970's in south central Oklahoma

  • Member since
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  • From: Reading, PA
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Posted by rrinker on Friday, June 08, 2018 5:56 PM

BNSF UP and others modeler

Is there a calculation you can use if you find out what the maximum and minimum speeds are for a certian loco?

 

 You'd need to know the motor RPM at various voltages, the total gear ratio, and the wheel diameter. Some of that will be impossible to find, especially the motor performance chart. Easier to just get a speedometer and measure 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.

  • Member since
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  • 2,190 posts
Posted by NWP SWP on Friday, June 08, 2018 6:33 PM

Also something I've noticed is when certain locomotives are are cold they don't run as well (or better, depends on the unit) than when warmed up.

Steven

Crooner, Imagineer, High School Graduate, living with Aspergers, President of the Republica Pacifica micronation,  President of the NWP-SWP System.

Hook'em Longhorns! 

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Posted by gregc on Friday, June 08, 2018 6:35 PM

BNSF UP and others modeler
(e.g. one speed step= 1 scale mph in 128 speed steps, etc)?

would you like the speed step to be the scale mph?

if at max voltage, the speed is 51 smph, you could program speed step 51 to be max voltage and all others between 0 and 51 a proportional amount.   speed steps above 51 wouldn't be used, would be set to max voltage.

of course a heavy train might run slower

greg - Philadelphia & Reading / Reading

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Posted by BNSF UP and others modeler on Friday, June 08, 2018 8:26 PM

That is an idea too. That way, it would make it physically impossible to exceed the prototypes top speed.

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  • From: Massachusetts
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Posted by Paul3 on Saturday, June 09, 2018 5:15 PM

MTH, with their DCS system, actually sets all their locos to run at 1 mph increments up to 120mph using an optical sensor reading the speed of the flywheel.  Every engine they make, from an 0-6-0 to the fastest diesel all run the same way: 1% = 1mph.  This is patented by MTH and so no one else can do it.

So for the rest of us that use DCC, we make do.  You can use a speedometer and set your locos to run so that 25% throttle is 25mph, 80% is 80mph, etc.  Provided, of course, that your loco can go that fast.

The problem is that locos vary so widely in use.  A loco that starts out running 60mph cold will speed up to 75mph when warm.  A brand new loco will run slow, and then as the gears mesh better with wear, will speed up later.  All your careful setting up of a loco when it was brand new can go right out the window after an hour or two of running.

Personally, I think it's a waste of time to try and get DCC locos to run in mph increments, especially for speed matching.  You're better off speed matching your locos to each other rather than to an arbitrary standard of speeds.  This only applies to locos that you'll run together, of course.  No need to speed match a SW-1 to a N&W J-class 4-8-4.

PED
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Posted by PED on Saturday, June 09, 2018 8:02 PM

All true. That is why I do not try to speed match my locos until they have been broke in and then warmed up for speed trials. Another factor not highlighted here is that you need to do your speed testing with a load on the loco. Initially I set mine up with no load and then when I tried to run them with a load, they ran noticeable slower. As a result, I set all my speeds while the loco is pulling a car load of about 6 oz.

I know some people think it is a waste of time but it is important to me to know that the locos in my consist will play nice with each other. 

Paul

Washita and Santa Fe Railroad
Circa 1970's in south central Oklahoma

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