# How to Measure Scale MPH?



## gc53dfgc (Apr 13, 2010)

I have a few QSI sound installed engines from Atlas and they all have an automatic Sacle MPH readout that tells me how fast i am going. My question is how exactly do they figure that out automatically and also how does one view that in real time, so say I am running an engine and I want to lower the max voltage so it runs more to prototypical speed. This is more a question for NIMT but does anyone know what CV is used to program the Scale MPH readout on QSI engines say if the max speed and low speed is adjustaded and it becomes out of scale or does it self correct somehow?


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## NIMT (Jan 6, 2011)

GC,
You will need to give me the Decoder model # for me to tell you if I can!


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## Massey (Apr 16, 2011)

Which CV it is, is going to depend on which mode you have your speed table in. Once you know that then you can find out what CV you need. I can look at my Atlas engine on JMRI for you tomorrow if you want. I already know I use a speed table and not the Vlow, Mid and Hi.

As for the speed, the decoder can do this in a couple of ways. The easiest is for it to calculate the freq of the motor pulses with a referance to the current draw. (I dont know the exact math) The other way is to use a photo or magnetic sensor on some type of flywheel or gear. 

Massey


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## gc53dfgc (Apr 13, 2010)

Right Massey but how do I measure it without having a decoder readout. Is there like a radar gun thing for it? The only decoders that have the readout and sound are the QSI ones which I am planning on getting and would like to be able to set the voltages/speed tables right so it will run prototypically. I can figure out the CV with the manual that comes with it when I am ready to do the programming but my main problem is figuring out how to monitor it myself and program accordingly.


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## Massey (Apr 16, 2011)

Time divided by distance = speed

You also need to count for scale as well.

Just set up a known distance and between 2 points and time how long it takes to cross said distance and then do the math.

If you time a train taking 15 seconds to go between 36" you are traveling at 11.9 MPH

Check out this site for the math.

http://www.mcr5.org/NMRA/articals/speed.htm

Massey


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## gc53dfgc (Apr 13, 2010)

Okay. I was just trying to figure out if there was a handheld type device that I could just point at the engine when it is at a certain speed step so I would not need a special track to measure and label as well as a stop watch and a calulator.


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## Massey (Apr 16, 2011)

How about something like this then

http://www.trainelectronics.com/speedometer/speedometer_manual.htm

Massey


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## gc53dfgc (Apr 13, 2010)

yes! that is perfect, I can just set it over my layout and run the engines at their max and min speed steps to get their sale MPH so I can do the proper programming with more ease then needing to recalulate all the time. Thank you Massey!


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## raleets (Jan 2, 2011)

OK, that gizmo looks pretty cool :thumbsup:
How many bushels of $100 bills do I need to buy one? Didn't see a price anywhere or did I miss it?
Bob


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## gunrunnerjohn (Nov 10, 2010)

raleets said:


> OK, that gizmo looks pretty cool :thumbsup:
> How many bushels of $100 bills do I need to buy one? Didn't see a price anywhere or did I miss it?
> Bob


Bottom of the page:

*NOW AVAILABLE - $169 + $9 shipping (lower 48)*


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## bradimous1 (Mar 3, 2010)

what you need is the readout to be at 1:87 scale so that you can make it look like a construction sign next to the track


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## raleets (Jan 2, 2011)

grjohn,
Story of my life.....had to leave before the end of the movie and never did find out who did it 
Bob


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## gunrunnerjohn (Nov 10, 2010)

raleets said:


> grjohn,
> Story of my life.....had to leave before the end of the movie and never did find out who did it
> Bob


You need to find the *Cliffs Notes* version.


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## trainguru (Jun 28, 2011)

I'd like to make a case for the February 1950 issue of Model Ralroader's article on "Mouse Power" for all of us HO modeler's, because of all this scale mph talk! A mouse is a good measure to horse power on all of our big counterparts. If you can get a copy, then it's a good standard (per say), but I think were a little past that now (not by much!). What do you think?  -  - :laugh: -


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## tjcruiser (Jan 10, 2010)

Yeah, but _which_ mouse sets the standard? Mighty Mouse? Mickey Mouse? Minnie Mouse? All mice are not equal, you know ...


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## trainguru (Jun 28, 2011)

A lab mouse, and the variable that effects the measured drawbar power, is your fuel (cheese!), get a copy of Model Railroader in question and figure it out! -


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## raleets (Jan 2, 2011)

I am so totally SOL ......my cat kills all the mice around here! :thumbsup: 
Bob


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## Evan (Sep 1, 2010)

Buy a police speed radar, then stand next to your layout and aim at your trains! Lol, just kidding. I think Massey's idea was good.


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## mr_x_ite_ment (Jun 22, 2009)

I once tried to mathematically figure out how fast my trains were moving. If I am correct, I realized that 1 MPH in the real world was equal to about 1 foot per minute in the HO world. I timed how far the train went in one minute. That distance is roughly the mph you are going. If your train travels 40 feet in one minute, then you are going about 40 MPH. Shoot, it would be easier to just get the device that measures it for you...that was pretty cool!

Chad


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## trainguru (Jun 28, 2011)

*Another one for math!*



mr_x_ite_ment said:


> I once tried to mathematically figure out how fast my trains were moving. If I am correct, I realized that 1 MPH in the real world was equal to about 1 foot per minute in the HO world. I timed how far the train went in one minute. That distance is roughly the mph you are going. If your train travels 40 feet in one minute, then you are going about 40 MPH. Shoot, it would be easier to just get the device that measures it for you...that was pretty cool!
> 
> Chad


Could you please post your formula? The Bonati Grand Central is using a formula I gave on the "Made in America" thread a few months back for scaling HO trains.


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## gunrunnerjohn (Nov 10, 2010)

Actually, that formula isn't all that close.

1 mile an hour is 5280 / 3600 = 1.4666 ft/sec.

If you divide that by 87 for HO scale, it's 0.0168582375478927 ft/sec = 1 MPH.

So, if your train is going a foot a second, it's cooking right along.

1 / 0.0168582375478927 = 59.32 MPH.


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## tjcruiser (Jan 10, 2010)

I think you guys are missing the fact that time has to scale, too.

In the marine world, we model test at equivalent "Froude Numbers" ... essentially, the speed of the craft divided by the square root of its length. The Froude value for a model is matched to that of its counterpart ship. Equivalently, the model speed is equal to the ship speed times the squareroot of the scale factor. Additionally, we know that any speed is simply distance divided by time. And, if you go through a little math, you see that the model "time" is proportional to the square-root of the ship's time. In short, time itself scales, too.

TJ


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## gunrunnerjohn (Nov 10, 2010)

Are you saying the previous calculations are wrong for determine scale speed? Or are you saying that the scale speed isn't simply a scaling of the prototype size vs. the model size?

Why don't you go through that math that you're talking about if we're way off base?


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## tjcruiser (Jan 10, 2010)

gunrunnerjohn said:


> Are you saying the previous calculations are wrong for determine scale speed?


Essentially, yes. I agree that the steady-state speed of any object is determined by dividing distance by time. But when you're comparing (or calculating) the speed of a scaled (small) object in contrast to its full-size counterpart, one needs to consider that time itself scales.

My simple example here is Hollywood. When they film action scenes in model scale, they need to be played back in slow motion in order to "look right" as a full scale scene.



gunrunnerjohn said:


> Or are you saying that the scale speed isn't simply a scaling of the prototype size vs. the model size?


Yes.



gunrunnerjohn said:


> Why don't you go through that math that you're talking about if we're way off base?


I'll try to do that Mon or Tues.

Cheers,

TJ


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## xrunner (Jul 29, 2011)

tjcruiser said:


> I think you guys are missing the fact that time has to scale, too... In short, time itself scales, too.


You mean in N scale, time would scale by 1/160?


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## tjcruiser (Jan 10, 2010)

Runner,

I think it's via the _square root _ of 160, but I'll need to delve into the math more.

TJ


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## tjcruiser (Jan 10, 2010)

A couple of links ... I haven't read through these myself in any detail ...

http://annarborrcfalcons.com/scale_model_speed.htm

See Rule #5 and Rule #6 in this link ... (they talk about model planes, but the same is true for model anything) ...

http://www.astroflight.com/pdfs/ScaleSpeed.pdf

Cheers,

TJ


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## mr_x_ite_ment (Jun 22, 2009)

To gunrunnerjohn...I was claiming that 1 MPH in the real world was very close to 1 foot per MINUTE (not second) in HO land. My math was supported by the train speed calculations link that someone brought up earlier (I think it was Massey). I am not sure how to make time scale like TJ said...I always thought time was time.

Chad


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## xrunner (Jul 29, 2011)

tjcruiser said:


> I think it's via the _square root _ of 160, but I'll need to delve into the math more.


OK, but I'm not sure I believe it yet. If time can be measured by, say, an atomic clock, which measures oscillations of atoms, and I got shrunk by 160, the atoms wouldn't change their oscillations just because I was smaller. So I don't see why time would change for me. I would still see the atomic clock and it would still measure time the same way, because atoms wouldn't change the way they work just because I got shrunk. 

Atoms are atoms - time is time. As far as I was aware time only changes in relation to how fast I am going with respect to the speed of light (Einstein's relativity theory), but now were getting into some really deep stuff.


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## mr_x_ite_ment (Jun 22, 2009)

Yes, the conversation is getting into deep stuff. I did not take time to scale, but then neither did the link Massey sent because my calculations were dead on with the formula in that link.

Chad


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## tjcruiser (Jan 10, 2010)

I'm not saying that time is distored in an Einstein relativity sense, but rather that time (or more specifically distance traveled divided by speed) must be scaled (or slowed down) when correlating the motion of a model to it's full-scale counterpart.


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## mr_x_ite_ment (Jun 22, 2009)

I hear what you are saying, TJ. I read through that link you sent. It was fun to see all the different calculations they went through with model airplanes. Some of it was a little over my head. I admit that I am not quite sure how to factor time into the HO world. I should check out other scale speed calculators (I think Massey sent a second one). The first one he sent didn't seem to take time into consideration, because it matched with what I thought.

Chad


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## Massey (Apr 16, 2011)

I dont think that time needs to be scaled as far as we are concerned. For the camera yes time will need to be scaled but that is due to the frame rate of the camera. I think. 

To think about it, for us to walk at the average 2.5 to 3mph that humans walk at we take on average a 3 foot step, and it takes about 2-3 seconds per pace at a normal walking distance. Now if you were 3/4 of an inch tall you would be stepping about 1/4-1/2 inche per step which at the same speed we are walking would only take 1/4 to 1/2 of a second. In this case time would have to be scaled back to make the figure not look like the Flash.

Massey


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## mr_x_ite_ment (Jun 22, 2009)

I am just going to go out on a limb a little bit. Time to me seems like it should be the same for both scales (HO and real world). Obviously the speeds are different, because different distances are covered in the same time frame. Our little HO trains are actually going at a certain MPH speed. I would be willing to guess that the link Massey sent about the SMPH measuring device (which I thought was for another speed table) is probably measuring the HO train in feet per second, and just simply converting everything to MPH. Whether you are talking MPH, feet/min, or feet/second, they are all just rates. A simple conversion changes one into another. Obviously, we have to factor in the 1/87 ratio as well.

Unless there is something I am missing, I will stand behind what I said earlier. 1 MPH in the real world is about 1 foot/minute in HO world. If the HO train travels 40 feet in a minute, then you are going about 40 MPH (factoring in the 1/87 ratio).

Chad


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## gunrunnerjohn (Nov 10, 2010)

I'd like to see some reference where this is applied to model trains.


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## Artieiii (Apr 25, 2011)

I found this link to App store scale MPH calculator. It says to accruately measure part of your layout (like a bridge) then you click when a train gets to the bridge and click again when it passes the other end of the bridge. The 
App calculates scale MPH. I found it in Model RR hobbyist magazine latest issue.
-Art
http://www.mynabay.com/


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## raleets (Jan 2, 2011)

Got a new neighbor last week. Invited him over to see my trains in action.
He asked "how fast they goin' in real life?".......I said "67 mph" (with straight face).......he said "wow!"
End of story. 
P.S. P.T. Barnum was right!!


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## Artieiii (Apr 25, 2011)

raleets said:


> Got a new neighbor last week. Invited him over to see my trains in action.
> He asked "how fast they goin' in real life?".......I said "67 mph" (with straight face).......he said "wow!"
> End of story.
> P.S. P.T. Barnum was right!!


Nice raleets. Baffle them with Bull$#%*
-Art


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## deboardfam (Oct 8, 2010)

What about this?

http://www.eurorailhobbies.com/erh_detail.asp?ca=60&stock=72600

LOL if you can figure out what the german means on the buttons...


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## trainguru (Jun 28, 2011)

*Enstine and Trains*



tjcruiser said:


> I'm not saying that time is distored in an Einstein relativity sense, but rather that time (or more specifically distance traveled divided by speed) must be scaled (or slowed down) when correlating the motion of a model to it's full-scale counterpart.


Funny you mention that, he described how that we could never get past the speed of light with a train analogy! We can go bump up against the speed of light, but no matter how much fuel you put into the firebox, or firemen stoking we can't surpass the speed of light. We just can't! Enstine's analogy will be somehow be proven right or wrong someday, but in the mean time try creating an algabraic formula for this, and I still want to make a case for "mouse power" equivelent to horsepower for HO trains, if you don't get this, get the February 1950 Model Railroader issue for further reference! 

To think I learned about Enstine, the man, the theory, and this analogy in Elementary School!!! -


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## Massey (Apr 16, 2011)

It was once said that we could not break the sound barrier. The X-1 failed 2x before Chuck Yeager finally took the stick and made it happen. Now today breaking the sound barrier is not difficult at all. In the future some one may figure out how to break the light barrier. Until then it is just sci fi. 

I still don't see how time is scaled, time is time no matter how you look at it. When it comes to film then you have to worry about the timing of the film (frame rate) and the model so in that case you would need to sync them both up and that would mean speeding up the film or slowing the motion on the model which ever is easier for the project you are working on.

Massey


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## mr_x_ite_ment (Jun 22, 2009)

Now "mousepower" would be an interesting way to measure the strength of HO trains! I imagine the Kato gives you more "mice" under the hood than the entry-level ones!

Chad


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