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speed formula/voltage+ a shay

Started by bob kaplan, February 16, 2007, 05:47:35 PM

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bob kaplan

Using Hunt's formula from the "general discussion" area, i clock my 38 ton Shay to see at what speed she is running, when i feel she is running at a "good" speed or a specific voltage.

These are things i am taking for granted when i ask my final question.
    1.  all Bachmann 38 ton Shays run basically the same at the same
    2.  my volt meter works  (it is OLD) and a swing needle thing.
    3.  the length of the train won't affect the speed toooo much at a voltage
         once the motion is underway.
That being said, at approx. 10 volts, my shay ran a distance of five feet in 9.91 seconds.  IF i use the formual correctly, i get something like 6.9 miles per hour.

To me, it looks like it is MOVING faster than that speed.  But does this sound approximately correct or are there major mistakes on my part?

Thanks for your help.


You used the MPH formula correctly (6.98 rounded 7.0 MPH).

Too many variables to state all Bachmann Large-Scale 1:20.3 38 Ton Shays will be running 7.0 MPH at 10 Volts.

bob kaplan

Ok....thanks for the info and the formula.

Matthew (OV)

That sounds about right.  A 1:20.3 locomotive is moving a lot slower in scale than even a 1:29 locomotive travelling at the same actual speed would be going in scale....

And, if that doesn't twist your brain a bit ... nothing will.

This may be a bit easier to get your brain around....

For a 1:20.3 scale locomotive, take a section of (old) track and mark it with a dremel every 23 inches... this will simulate the rail joints every 39 feet that allowed railroads to put them into 40 foot cars ....   now run your locomotive at your scale 7 mph, and listen to the "click clack" as the wheels cross the joints.  You'll notice that it sounds like a train going between 5 and 10 mph....   

To achieve the same effect with a 1:29 scale train you'd have to put the marks closer together, about every 16 inches..... and then run the train proportionally slower to make the shorter distance give you the same "click clack" rhythm of the larger scale train travelling the longer distance.

Interestingly, I knew a locomotive engineer who used his musical background to set a tempo of 1 "click clack" per second to approximate 25 mph (actually 26.something but who's counting) when running a locomotive with no speedometer.

Back to your original question .... picture yourself in the cab of your shay, and watch the relative speed of the world going by. (If you have trouble doing this, a video camera on board can help) .... you'll see that it really does approximate the slow speed at which you'd run a Shay .... up around 15 miles per hour, small parts would likely start flying off!

Matthew (OV)


QuoteA 1:20.3 locomotive is moving a lot slower in scale than even a 1:29 locomotive travelling at the same actual speed would be going in scale....
Matthew (OV)
To cover the same distance in the same time
1:20.3 scale is 7 MPH
1:29 scale is 10 MPH