(05-22-2019, 07:44 AM)ijmorlan Wrote:(05-21-2019, 09:08 PM)trainspotter139 Wrote: Wheel flats are quite common during the testing, training and commissioning phase of a new system.
That’s probably it then. I wouldn’t be surprised to find they use the emergency brake more during testing than in the following century of normal operation.
Per the radio traffic, E-stops are part of both the operator training and certification programs. They'll definitely have been doing a lot of them in the past several months.
(05-22-2019, 10:06 AM)danbrotherston Wrote: It would be unfortunate if emergency stops resulted in flats. I've been on a TTC streetcar during an emergency stop, it seems like it isn't an infrequent thing in Toronto.
There's different levels of 'emergency' stop used at the operator's discretion, some are just stronger levels of service brake application (with ABS), full service brake (with ABS), force brake under ATP (not sure if that uses ABS or not), and an actual emergency stop button that locks the wheels and drops electromagnetic track brakes. Not all will result in wheel flats. Note that once you have even the slightest wheel flat it will tend to grow even under regular service brake applications, as that's the spot where the wheel is most likely to start slipping the next time. Even with ABS, an axle will lock briefly before the system detects it and lets up on the brake pressure to start the wheel spinning again. This is much more of an issue with steel wheels versus rubber tires because the contact patch of steel wheels is so small due to their total lack of elastic deformation. I suspect that one e-stop won't cause a noticeable flat spot on a good wheel, but plants the seeds for one that will develop over time. Multiple e-stops will hasten its development into the clunk clunk clunk that we've been hearing.
...K