05-29-2016, 06:56 AM
Can I nerd out and talk about fixed-bogie articulation for a moment? 
This is a bogie, or "truck" from Toronto's new fleet of FLEXITY Outlook LRV's - substantially similar enough to our trains (FLEXITY Freedom) for sake of discussion. It's the frame that holds the wheels and motors - one motor per axle. You can see the motor and gear reducer on the left for the axle in the foreground; the motor for the rear axle is on the right, rotated 180 degrees. The disc brake assembly is on the far side of the near axle.
I was very happy to finally get to see a bogie out on its own like this, because I finally answered some of my own questions about how exactly the articulation is accomplished between modules on the FLEXITY series of trams.
These trains are a configuration known as "fixed bogie". Unlike the older Toronto fleet (called CLRV and ALRV's), where each bogie can turn under the car, these bogies are "fixed" with respect to the car (or module) that they are attached to. On the 5-module trains, modules A, C and E have bogies, and modules B and D are suspended between them.
So, the orientation in free space of module A, C and E is defined by the position of the bogie, which is tangent to the line drawn between the two axles on each bogie (ok, ever so slightly inboard, if you want to get picky!). The modules in between fall in line since they have an articulation point (hinge) fore and aft.
So that's fine for horizontal curves, and everything works great - but, in real life, you also have to deal with vertical curves, and even compound curves with twisting (roll), too. Think of the transition of Southbound track through Charles/Benton - this is a particularly aggressive section of track.
I have learned through watching the operation of the new TTC LRV's that the train is actually configured as such: Module A-B-C have only yaw between them, and module D-E can yaw, and then there's a full 3-axis articulation between C and D. So it's as if they've taken a 3-module train and put a 2-module trailer on it.
Again, this is all great... But any roll has to be taken up - and that's where my discovery yesterday was made. The modules sit on the bogies on four coil springs, which you can see in this photo. Just outside of them are four metal discs with a urethane element behind them - In the automation industry, we'd call this configuration a moment compensator. Essentially, it allows the module to bounce up and down, roll left and right, pitch forward and back... But inhibits yaw, which is exactly what we need - since yaw is what we need to fully define the orientation of each module relative to the track!
As a kinematic system, it all works out. This has been bothering me for 2+ years and I've never been able to get a straight answer out of anyone on how exactly is set up, so I was overjoyed to be able to finally crack the nut, so to speak!
This is a bogie, or "truck" from Toronto's new fleet of FLEXITY Outlook LRV's - substantially similar enough to our trains (FLEXITY Freedom) for sake of discussion. It's the frame that holds the wheels and motors - one motor per axle. You can see the motor and gear reducer on the left for the axle in the foreground; the motor for the rear axle is on the right, rotated 180 degrees. The disc brake assembly is on the far side of the near axle.
I was very happy to finally get to see a bogie out on its own like this, because I finally answered some of my own questions about how exactly the articulation is accomplished between modules on the FLEXITY series of trams.
These trains are a configuration known as "fixed bogie". Unlike the older Toronto fleet (called CLRV and ALRV's), where each bogie can turn under the car, these bogies are "fixed" with respect to the car (or module) that they are attached to. On the 5-module trains, modules A, C and E have bogies, and modules B and D are suspended between them.
So, the orientation in free space of module A, C and E is defined by the position of the bogie, which is tangent to the line drawn between the two axles on each bogie (ok, ever so slightly inboard, if you want to get picky!). The modules in between fall in line since they have an articulation point (hinge) fore and aft.
So that's fine for horizontal curves, and everything works great - but, in real life, you also have to deal with vertical curves, and even compound curves with twisting (roll), too. Think of the transition of Southbound track through Charles/Benton - this is a particularly aggressive section of track.
I have learned through watching the operation of the new TTC LRV's that the train is actually configured as such: Module A-B-C have only yaw between them, and module D-E can yaw, and then there's a full 3-axis articulation between C and D. So it's as if they've taken a 3-module train and put a 2-module trailer on it.
Again, this is all great... But any roll has to be taken up - and that's where my discovery yesterday was made. The modules sit on the bogies on four coil springs, which you can see in this photo. Just outside of them are four metal discs with a urethane element behind them - In the automation industry, we'd call this configuration a moment compensator. Essentially, it allows the module to bounce up and down, roll left and right, pitch forward and back... But inhibits yaw, which is exactly what we need - since yaw is what we need to fully define the orientation of each module relative to the track!
As a kinematic system, it all works out. This has been bothering me for 2+ years and I've never been able to get a straight answer out of anyone on how exactly is set up, so I was overjoyed to be able to finally crack the nut, so to speak!