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ION - Waterloo Region's Light Rail Transit
Why can't they allow the LRV to twist, pitch, and yaw on every joint?
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(02-10-2018, 09:37 PM)jamincan Wrote: Why can't they allow the LRV to twist, pitch, and yaw on every joint?

The more types of flex you allow, the more complex the joint. Don't forget these are open gangways that have to allow people through.
My Twitter: @KevinLMaps
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(02-10-2018, 02:14 PM)Canard Wrote:
(02-10-2018, 02:10 PM)bgb_ca Wrote: At least these reworks are getting done now and only take a few weeks.

Fixed that for you

...and no, they should have been done 1+ year ago, when they were completed, instead of now where it is delaying testing (and opening).

But, no worries, someone will find a way to blame Bombardier, I'm sure.  Rolleyes

Was the uptown refit really several weeks? I thought they had that done a lot quicker than that.

And yes, it should have been done last year.
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(02-10-2018, 10:45 AM)Canard Wrote: From the sounds of things, the curve at Northfield and the Spur is the latest casualty for gauge rework. Unbelievable.

I drove past there around 3:30pm and there were several workers going at it with a tent and blowers, and a huge row of traffic cones restricting part of the right lane. On my way home at 10pm the equipment was all still there. Hopefully they will be done by Monday or the traffic won't be fun.
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(02-10-2018, 11:09 PM)bgb_ca Wrote:
(02-10-2018, 02:14 PM)Canard Wrote: Fixed that for you

...and no, they should have been done 1+ year ago, when they were completed, instead of now where it is delaying testing (and opening).

But, no worries, someone will find a way to blame Bombardier, I'm sure.  Rolleyes

Was the uptown refit really several weeks? I thought they had that done a lot quicker than that.

And yes, it should have been done last year.

The uptown refit was a week. The hoardings went up on the 1st and they tested with the vehicle on the refit section on the 8th.
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(02-10-2018, 07:40 PM)Canard Wrote: Module order is A-D-C-E-B, with bogies in modules A, B, and C.  Modules D and E are without wheels and supported by their neighbours.  It is worth noting that this nomenclature is only valid for the 5-module variant; not the 3 or 7.  In other words, you can't just benignly say "a C module is always a short, intermediate one with a bogie and no doors", because on the 3-module variant you'd have A-C-B, and C would be the same as a 5-module's D or E.

[....]

I don't think they will ever swap out a module on-site at Dutton.  If a train gets hit by a car, and the damage is more than superficial, it'll likely go back to Bombardier for them to swap it out.

Thanks for the detailed information and photos. Much appreciated!
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(02-10-2018, 09:18 PM)tomh009 Wrote: Are D and E modules interchangeable? How about A and B?

I don’t know the full answer, but there has to be at least some small difference between D and E (and between the two ends of the C) because the C-D and C-E joints are different as mentioned in Canard’s post.

In principle they could put most 1-per-train equipment in the C module (and indeed, that is where the pantograph is) and 2-per-train in the other modules, but I have no idea how this is actually laid out. In fact, I know almost nothing in detail about what equipment is present beyond vague notions that there must be traction components, power handling, climate control, etc.

To a question somebody else asked about why there are only limited motions at the joints, if all the joints allowed pitch (up/down rotation) then the joints would not have a single defined arrangement to match any given track profile. The way it’s done, the C module can only exist in one pitch when the train is sitting on any given piece of track. Essentially the A-D-C/B-E-C (we don’t know which) modules form a bridge between the trucks on the A/B and C modules; then to keep the wheels on the B/A module on the track, it bends between the A-D-C/B-E-C and E-B/D-A modules.

I don’t know exactly what would happen in practice if there were more pitch joints, but seems to be considered desirable that the positions of the modules follow deterministically from the shape of the track. I’m guessing the C module would rock backward and forward unpredictably but I don’t know. Actually now I want to know what that would feel like to ride in. Probably not as smooth as the actual ride.
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KevinL: that’s not why. Jamincan: The train would sag, and wouldn’t form a straight line on straight track. The system, kinematically, would be underconstrained. In other words, if you were a giant, you could reach down and twist and tip the train and it would stay in the pose you placed it in. That’s bad.

I have been trying on and off for a couple of years to make an animation for you guys (knowing this would come up and someone would ask eventually!) about why the trains are articulated the way they are. There is a bug in SolidWorks that prevents me from completing it (I have an SPR in...). I may just make a little model out of LEGO and a video for you instead. It’s immediately obvious why it’s configured the way it is if you can feel it with a model.
For daily ion construction updates, photos and general urban rail news, follow me on twitter! @Canardiain
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I guess I can see why you wouldn't want any twist between the sections, or at least only one point that allows twist between the bogies, but I don't really understand the issue with pitch and yaw as I would have thought sections A-C-B were essentially fixed points relative to the track (in orientation and pitch).
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That’s the thing - they’re not!  The bogies can pitch.  So, if they did what you suggest, the whole train could be a zig-zag if viewed from the side.

   

Even worse, even if the bogies truly were fixed axles directly mounted on the bogie frame, and we had pitch articulation between them, if the centre module were overloaded (say, by too many passengers), this would happen:

   

This configuration for fixed-bogie* trams is very obvious when viewing a 3-module LRV moving along track with a vertical curve, like the bridge in Kansas City right by Union Station. The whole LRV looks like a ridgid log when moving across it.

   

*- a little bit of a misnomer, because, as I’ve explained, the bogies can pitch relative to the module, and even yaw just a little bit, to take up shock/jerk loads, if spiral curves are not used (ie, Toronto’s legacy network).
For daily ion construction updates, photos and general urban rail news, follow me on twitter! @Canardiain
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Is the ability to pitch relative to the bogie simply an outcome of the suspension, or is it desirable for other reasons?
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It is a requirement, and achieved via the suspension springs. If not, and the axles were ridgidly affixed to the module frame, this would happen:

   

(Trains would lift the leading and trailing axles when navigating a convex vertical curve)
For daily ion construction updates, photos and general urban rail news, follow me on twitter! @Canardiain
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That wouldn't happen if they could pitch at the point of articulation, though.

With only two bogies, you might run into an issue where too much weight between the bogies could lead to the entire vehicle sagging and lifting the front/rear-most wheels off the track. I suppose they could balance the sections out to a degree to prevent this, but it might be possible that an uneven distribution of passengers could cause a problem.
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Jamincan, my 2nd drawing in my 2nd last post illustrates exactly what you’re saying in your first paragraph, and why it won’t work. If the axles were fixed, and the vehicles could pitch between modules, you’d have a scenario where overloading the centre module causes a derailment.

   
For daily ion construction updates, photos and general urban rail news, follow me on twitter! @Canardiain
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Love your drawings Iain!
...K
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