Large Scale Central

Scaling speed question

General Discussion
#1

The oval track section we have in the backyard is very close to 52.8 feet long, so a train will need to traverse it 100 times to complete one mile. If a train can negotiate each loop in 20 seconds, it will take a bit over half an hour to travel a mile, at a speed just under 2 mph.

My question is: how best can we scale the speed of a G scale train to the real thing? Assuming a nominal 1:29 scale, is it as simple as multiplying the speed in mph by 29 (i.e., approximately 50 - 55 mph)?

Please note that this is a search for a valid methodology to use for estimation, not precision. There are too many variables impinging on the question to allow a high degree of accuracy.

This question was prompted by a clip:
http://www.dailymotion.com/video/189260

#2
Dave Healy said:
Assuming a nominal 1:29 scale, is it as simple as multiplying the speed in mph by 29 (i.e., approximately 50 - 55 mph)?
Dave:

Correct.

Speed is defined as distance over time. Distance (and length) scales directly as in 1:29. The time you are observing and measuring in is 1:1.

As you already calculated, 52.8 feet / 20 seconds equals ~1.8 miles / hour.

Just multiply by 29 to get 52.2 scale MPH.

On edit: Just a thought, but in deference to your statements about the precision of the measurements, you can safely round the result to 52 scale MPH. :slight_smile: :slight_smile: :slight_smile:

Happy RRing,

Jerry

#3

Thanks for the sanity check, Jerry.

I was expecting Hans to bog in with something like 52.29476538476532, plus the specification (in both English and German) for an optical device that would let ordinary mortals perceive the difference between the float and the integer. That would be followed by Warren’s detailed annotated history of the speed of scale model sugar cane trains, complete with time-lapse photographs. We’d finish with Dennis asking, “But can it run?!!”

Maybe I should be careful about publicising my expectations . . . .

#4

Dave,

A mile in 1/29 is 182’… You would lap your 53’ oval 3.4 times to make a mile…

Jerry,

Did I flunk math!!
52.8 / 20 is 2.64… 2.64 X 29 is 77 mph…

#5

Dave,

#6
Dave Healy said:
Thanks for the sanity check, Jerry.

I was expecting Hans to bog in with something like 52.29476538476532, plus the specification (in both English and German) for an optical device that would let ordinary mortals perceive the difference between the float and the integer. That would be followed by Warren’s detailed annotated history of the speed of scale model sugar cane trains, complete with time-lapse photographs. We’d finish with Dennis asking, “But can it run?!!”

Maybe I should be careful about publicising my expectations . . . .


Sheesh Dave,

Sorry that I didn’t live up to your expectations! :lol: :stuck_out_tongue: :lol:

But I could add one thing to the mix: Fast Clock. That allows you to designate smiles (scale miles) by setting a ratio that is suitable to the distances between the stations.
On the HOm RhB it was 4:1; that permitted using an existing proto timetable (with minor adjustments) and protoypical scale speeds to adhere to the timetable.
Quite neat or “what a pain” depending on what you were running and what mood you were in that day. I hope that isn’t too much additional info. :stuck_out_tongue: :confused: :smiley:

#7
Bob Burton said:
Dave,

A mile in 1/29 is 182’… You would lap your 53’ oval 3.4 times to make a mile…

Jerry,

Did I flunk math!!
52.8 / 20 is 2.64… 2.64 X 29 is 77 mph…


Bob:

Not quite: You need to carry / convert the time units as well as the distance:

Reworking your calculation with the units attached:
(52.8 feet) / 20 seconds = (2.64 feet / second)

Multiplying that times 29:
(2.64 feet / second) x 29 = (76.56 scale feet / second) (Not scale miles / hour.)

There are 3600 seconds in an hour, therefore:
(76.56 scale feet / second) x (3600 seconds / hour) = (275,616 scale feet / hour)

There are 5280 feet in a mile, therefore:
(275,616 scale feet / hour) / (5280 feet / mile) = (52.2 scale miles / hour)

Here is my solution for Dave’s question:

First, I calculated the 1:1 speed in miles per hour:
(52.8 feet) / (20 feet per second) = (2.64 feet per second)

There are 3600 seconds in an hour, therefore:
(2.64 feet / second) x (3600 seconds / hour) = (9504 feet per hour)

There are 5280 feet in a mile, therefore:
(9504 feet / hour) / (5280 feet per mile) = (1.8 miles / hour)

Now calculate the scale speed for 1:29 scale:
(1.8 miles / hour) x 29 = (52.2 scale miles / hour)

Exact same result, just two slightly different ways of getting there.

I truly hate doing engineering problems in public. Too much chance of small public error(s) before the thinking and accuracy checking is complete!! :slight_smile: :slight_smile: :slight_smile:

Happy RRing,

Jerry Bowers

#8

Hey Jerry,

How deep was that snow? :lol: :lol:

#9
Hans-Joerg Mueller said:
Hey Jerry,

How deep was that snow? :lol: :lol:


HJ:
Actually 3.937007874 inches (rounded), but there were a couple of atoms that were slightly out of position, so the real answer is somewhere between 1/2" and a foot. Probably not 52.2 miles / hour!

I’m a pilot and aviation enthusiast, so have been closely following the search for Steve Fossett. While I was writing the above, the news channel announced that the search has now been expanded to “. . . 18,000 acres . . .”! If that is a square, it would be 5.3 miles x 5.3 miles. The airplane Steve was flying has a cruise speed of ~120 mph and could cover that distance in less than 3 minutes. Once again, the media picks a number that sounds good (usually LARGE) and goes with it, not giving any thought to “. . . how big is that really?”

Details at 11:00.

Happy RRing,

Jerry

#10

Guess I’m old school… in college, we were also taught convenient conversion ratios.

88 ft/sec = 60 mi/hr … simple to remember and saves a bunch of step if you want to go from one to the other quickly.

Take your feet/sec… multiply by 60, divide by 88… .scale to 1:29 by dividing by 29…

I will state that I no longer do all the math in my head. Don’t know why because there seems to be a lot of empty space there lately.

Regards, Greg

#11
Greg Elmassian said:
Guess I'm old school... in college, we were also taught convenient conversion ratios.

88 ft/sec = 60 mi/hr … simple to remember and saves a bunch of step if you want to go from one to the other quickly.

Take your feet/sec… multiply by 60, divide by 88… .scale to 1:29 by dividing by 29…

I will state that I no longer do all the math in my head. Don’t know why because there seems to be a lot of empty space there lately.

Regards, Greg


Greg:

Yep, another way of doing it that gives the exact same 52.2 MPH result!

I do hundreds or even thousands of calculations every week. Many conversions between metric and inch dimensions with lots of sub-micron area and volume values. Really easy to have a 1/x error or to miss a decimal point. I always use an engineering calculator, then apply the “. . . does this look right . . .” filter. Still produces an occasional error, but the errors usually have a short life!

Happy RRing,

Jerry

#12

I agree Jerry.

One thing I was taught was to carry the units with the conversion factors… .then if the units “cancel out” properly, you have not inverted something somewhere… a good double check that hasn’t failed me in 35 years.

(The does it look right test is another good one, as well as doing an approximation/ballpark in the beginning)

Regards, Greg

#13

Somebody pass the aspirin…:frowning:

#14
Warren Mumpower said:
Somebody pass the aspirin....:(
How about a Xtra Strength Ibuprofen?? ;) :) See, and Dave thought we were going to confuse the issue :lol: :lol:

Oooops that reminds me, I have to determine the precise distance on that test loop in the office to calibrate my various engines.

#15

Hans, I’m interested in how you arrived at a 4:1 ratio for timetable scaling. Can you post? If you do, make sure you post an aspirin for Warren!

Greg, do you recall a thread where we discussed applying ArmorAll to plastic to protect it from sunlight? Did you spray it on, or apply by hand?

#16

Be sure to measure both the inner and outer rail lengths and average them.

Of course, then your speed calculation is only good for the exact center of the locomotive. If the engineer is sitting on one side, you need to calculate the offset precisely, and of course it depends on the direction of rotation.

Don’t want you to miss anything. (We may have to issue something stronger than aspirin for Warren!!)

Regards, Greg

#17

Dave,

That was highly scientific. :wink:

First I figured out the relative scale speed for the different engines. Typically 55, 65 and 75kmh top speed. Next was running one of each type of train, (Wayfreight, Fastfreight, Local and Express Passenger) between the different stations; at scale speed. Compare the time to the proto and BINGO if it took the proto four times longer, then the fastclock had to run at 4:1.

The other wrinkle is to limit max speed and acceleration to the engine typical values. Very easy to do with DCC, but with the DC EMM throttles I would assign specific throttles for specific jobs. No jackrabbit starts and no rocketing out on the main. :wink:

Keep them honest and drive them nuts. :lol: :lol:

#18

Better make that two aspirin for Warren, Hans - one for each direction of rotation!

Thanks for the post - I was curious to see if you’d factored in acceleration/deceleration and, if so, how.

#19

I took all three semesters of The Calculus in college. I think that the last semester took me, but we won’t go there. It convinced me that I needed to be a History major if I expected to graduate… :smiley:

Anyway, if I ever got an answer that was greater than plus or minus 3 units, I knew that I had done something wrong. It didn’t guarantee that I had done it right if the answer was less than three, but if it was greater than three, I had to do it over…

I used to be able to do a lot of calculations in my head, until they invented the electronic calculator, then my brain got lazy. Now I am lucky if I can add 2 + 2 and get 5. That is the right answer, isn’t it? I’m never sure, anymore.

I understand that if I am in the Southern Hemisphere, I have to work the problems backwards. It tends to make me dizzy.

#20

Dave, I spray it on from about a foot away. It does not seem to harm anything else, and does not appear to damage plants that get the occasional overspray.

Steve, not trying to one-up you, but took 4 YEARS of calculus in college, and haven’t used very much of it since then. Oh well, required for my major. But I learned habits like you have of “bounding” the problem and “bounding” the answer. Elliptical integrals was about the point where I really lost interest. Of course I took harder classes, one class was so hard, the professor could not do all the problems in each chapter! (although in a funny twist, my math professor stood in for him for 2 weeks, and he COULD… our lives were hell… this guy expected us to also know the entire greek alphabet)…

Boy am I glad I don’t have to do that anymore!

Regards, Greg

p.s. We used slide rules… calculators were not invented until after I graduated… at least not ones a student could afford…