[timmuir]

Paul's new General Electric 32 ton steeplecab is a neat little engine, one I heartily endorse for light-duty interurban or street railway freight service and yard work. These were used by numerous electric railroads for many years.

One thing that needs tweaking is the bounding box, which needs to be pulled back:

ESD_Bounding_Box ( -1.569720 0.037676 -3.7 1.569720 5.935963 3.7 )

Thanks Paul. This fills a much needed gap in the line of electric locos.

[charland]

Hi Tim,

The C&C was just up the road from the Springfield Terminal and dieselized about two years before the STRy. When I started the route I contacted Scott Whitney to see if he had any shots of the Springfield Terminal that would help me and within a week a CD arrived with over 400 shots plus a track chart and complete track diagrams. Scott's been a life long Claremont and Concord fan and asked if I had time could I do C&C 18 for him.. it was the least I could do for the help he's been providing.

Now, not sure where you get you Bounding Box information, but would like to know. When I was finished drawing the model I opened the shape file in sView, used their Bounding Box information to get the following with 1 meter removed from the length as I recall reading this somewhere.

InertiaTensor ( Box ( 3.139m 5.898m 7.673m )

I then set up a small activity in the Dogbone Route to stop and lift a car, checked the coupler spacing and it looked fine to me. Are you getting you're information through another program and where would you put this in your enging file?

Thanks for the help... still learning at this end!

Paul :-)

[charlie]

 charland, on Oct 24 2008, 07:11 AM, said:

When I was finished drawing the model I opened the shape file in sView, used their Bounding Box information to get the following with 1 meter removed from the length as I recall reading this somewhere.

InertiaTensor ( Box ( 3.139m 5.898m 7.673m ) )

I then set up a small activity in the Dogbone Route to stop and lift a car, checked the coupler spacing and it looked fine to me. Are you getting you're information through another program and where would you put this in your enging file?

Paul,

The InertiaTensor statement has nothing to do with the coupler spacing and how things look and hook up. The Size statement does it, and based on your visual experiment and the screenies above, that looks OK.

Imagine that the Box statement buried in the InertiaTensor instruction defines just that, a rectangular parallelapiped in the shape of a brick. The quantity specified in the Mass statement is homogenously distributed throughout the brick. The brick is given the ability to rotate about all three (x,y,z) axes with the center of rotation being at the centroid (center of mass). You can determine where the centroid actually is by examining the ESD_Bounding_Box statement in the *.sd file.

The InertiaTensor defines how the brick responds to changes in angular (rotational) momentum or inertia. Remembering Newton's First Law of Motion: "Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it." This is also known as the "Law of Inertia" and applies to both linear and angular inertia.

Imagine that the brick is moving along a tangent; angular momentum is zero. A curve is encountered, and the brick's response is to resist. Think of the wheel flanges as being at the ends of levers which apply the force needed to get the brick rotating. Once rotating, the brick has angular momentum and wants to continue to rotate. The whole process operates in reverse when the next tangent is reached and angular momentum must be reduced to zero again.

Based on some exp'ts I did with large changes to the InertiaTensor statement a number of years ago, I bet that the small change you made will produce no observable effect on train handling. In theory, the reduction you made has concentrated the homogenous mass closer to the centroid and should make it easier to change the rotational inertia. However, it isn't as if we're trying to modify the angular momentum of a high performance jet aircraft in a dogfight in a combat sim. :lol: It's best, as the TechDocs suggest, just to leave it the same as your final result for the Size entry.

If you google InertiaTensor, the wikipedia page appears to be OK. The better-known *.edu sites certainly are. This one's entertaining in style at least:
http://baba.astro.co...ertiatensor.pdf
If you wish, just ignore the math/physics bits and read the words. :o

You'll hafta excuse me for this post, but I've been doing this for 42 years. In any event, I have grave doubts about the proper implementation of the InertiaTensor in this sim...

regards,
charlie

[charland]

Hi Charlie,

Thank... I think! Might take me a minute to absorb all that!

So, the figures that Tim came up with that go into the SD file are the actual x, y, z, measurements that I might take from the center of my drawing but... I see the y measurement is different from the first and second groups... a little confusing. The second "y" appears to be to the top of the trolley wheel, and the first "y" to the top of the railhead maybe (I do raise my drawings .2m to appear to be on the top of the railhead in the sim).

Maybe for a switching layout with tight tight curves having it handle curves a little better isn't a bad thing but in the future I'll leave this the same as the overall dimensions given by sView's bounding box data.

Thanks for the help!

Paul :-)

[timmuir]

 charland, on Oct 24 2008, 10:04 AM, said:

...Maybe for a switching layout with tight tight curves having it handle curves a little better isn't a bad thing but in the future I'll leave this the same as the overall dimensions given by sView's bounding box data.

Thanks for the help!

Paul :-)

No! NO, Paul, you always have the Z-dimensions in the .sd ESD_Bounding_Box shorter than the actual size of the car to allow for trouble-free coupling. A good standard is to have the Bounding Box set at or near the car's end sill:


the overall dimensions given by sView's bounding box data is only that data taken from your model's .sd file which TSM generates from the outside dimensions. We have to edit the .sd file's Bbox values ourselves and you can get the measurements from the model while in TSM.

[charland]

Hi Tim,

OK, let me see, C&C 18 measures 28' between pulling surfaces and that is 8.15m, half of that would be 4.075m and you ended up with 3.7m each way. I was looking for some magic formula to achieve this figure but in the end there isn't one other then exposing the end of the pilot, testing the unit and making sure it works... does that sum it up?

Paul :-)

[timmuir]

 charland, on Oct 24 2008, 03:33 PM, said:

Hi Tim,

OK, let me see, C&C 18 measures 28' between pulling surfaces and that is 8.15m, half of that would be 4.075m and you ended up with 3.7m each way. I was looking for some magic formula to achieve this figure but in the end there isn't one other then exposing the end of the pilot, testing the unit and making sure it works... does that sum it up?

Paul :-)

Hi Paul,

No magic formula, just make a measurement while in TSM from the origin to the car's end sill and go with that. After awhile you'll get the hang of getting a feel for the measurements, an eye for it. I've been guess-timating it lately and checking the Bbox in Shape Viewer's Ctrl+D function.

[charland]

Hi Tim,

Thanks, I'm sure I have plenty of time before I start anymore rolling stock to forget this!

Paul :-)

[timmuir]

 charland, on Oct 24 2008, 05:20 PM, said:

Hi Tim,

Thanks, I'm sure I have plenty of time before I start anymore rolling stock to forget this!

Paul :-)

Well, it's an easy fix :lol: And at any rate, the little motor is a sweet model and I appreciate it very much.