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Easements over a 42 in radius curve

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Easements over a 42 in radius curve
Posted by MikeN8FWD on Monday, October 4, 2021 2:02 PM

I am adding a 42" radius curve to my corner module on my modular 4'x4' module. The 2'x4' straight module from the out side of the module in to the first track is 5". Acording to my easement calculations for a 42" radius my offset should be 5/8ths of an inch and the length of the easement is 25". So between my tangent and curved track is one inch. Instead of using 5/8ths of an inch for my offset would it hurt to use the 1"? Can i use bigger offsets and longer easements on any curve I use? 
Thanks,

Big Mike 

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Posted by 7j43k on Monday, October 4, 2021 2:28 PM

I'm not following your explanation, probably because I do my easements in my own way.

 

But.

A 25" easement is a thumping nice one.  You certainly don't HAVE to have a longer one.  But there is no reason not to, IF it suits you.

FWIW, I have two modules (22 degree) with 60" radius, and easements of 18".  Works great!

 

Ed

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Posted by Lastspikemike on Monday, October 4, 2021 2:29 PM

Yes.

Shorter and tighter easements would not be ideal but longer and wider ones are beneficial assuming you have the space. 

Alyth Yard

Canada

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Posted by selector on Monday, October 4, 2021 8:08 PM

MikeN8FWD

... Can i use bigger offsets and longer easements on any curve I use? 
Thanks,

Big Mike 

 

  Probably, but at some point for any given radius, you'll end up with something more like the original radius the longer the easement and the wider the offset. 

The whole point of an easement is to horse the forward end of the car into a fixed radius, but gently, and thence to reverse that process as the curve widens and becomes tangent once more.  With more offset and a longer easement, you might as well dispense with the effort because as you increase the two, you encroach on a closer and closer version of the very curve radius you're attempting to 'ease'.

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Posted by kasskaboose on Monday, October 4, 2021 9:38 PM

Is that necessary for what you're trying to achieve?  Not sure if you want to go through the hassle if there is an easier alternative.

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Posted by 7j43k on Monday, October 4, 2021 10:25 PM

kasskaboose

Is that necessary for what you're trying to achieve?  Not sure if you want to go through the hassle if there is an easier alternative.

 

 

I don't think it's any more difficult when you change the dimensions.

Which seemed to be what OP is considering about doing.

 

Ed

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Posted by Lastspikemike on Tuesday, October 5, 2021 8:00 AM

The more you initially offset the tangent from the constant radius the longer you should make the easement. But you don't have to make either number larger. Making the offset wider will give more easement and so will lengthening the easement without changing the offset. Increasing both is a better solution if you have space. 

You can easily see the relative effect of offset and length by bending a piece of flex track or a thin piece of wood like doorstop or window moulding. A spline in other words. 

Alyth Yard

Canada

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Posted by Overmod on Tuesday, October 5, 2021 10:22 AM

Keep in mind that one purpose of an easement, whether true spiral or not, is to produce progressive angular acceleration from 'zero' (in the tangent with correct tread guiding) to the constant value observed traversing the fixed-radius part of the curve.  At typical model speeds, the required transition can be very short; the advantages of longer spirals are largely visual.  NOTE that since you're still using the portion of the transition from tangent to fixed-radius, there is no mysterious 'reduction' of any part of the curve to less than the fixed radius; you can think of it as 'spreading' the sharp angular change from straight to curved over whatever distance you choose.

I'd at least look at using transitions equal to a couple of your maximum 'rigid wheelbase' dimensions.

The 'offset' is only to get the fixed-radius portion lined up with the transition at both ends.  Think of it as the last step after the transitions are in, as if measured across the transition ends and then cut to length...

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Posted by 7j43k on Tuesday, October 5, 2021 11:12 AM

Overmod

Keep in mind that one purpose of an easement, whether true spiral or not, is to produce progressive angular acceleration from 'zero' (in the tangent with correct tread guiding) to the constant value observed traversing the fixed-radius part of the curve.  At typical model speeds, the required transition can be very short; the advantages of longer spirals are largely visual.

 

 

The purpose of an easement in MODEL form is to:

Look good

Gradually introduce the offset to car ends as the curve is entered.  We use very sharp curves, which introduces some very large offsets to the end of cars.  This is particularly true of passenger cars closely coupled and with diaphragms.  From experiment, I and others have found such passenger cars work better and more reliably through eased curves.  And longer easements make them "happier".  The benefits aren't lost on other long cars.

 

Ed

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Posted by Doughless on Tuesday, October 5, 2021 11:16 AM

Yes, gradually reduce the radius from tangent to a chosen place along the curve where the radius remains constant, in a manner that suits your visual tastes.  Doesn't matter what the radius actually is, as long as it fits in the space and is broad enough for equipment. 

- Douglas

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