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Duck
Guest
That's correct - thanks, Nfitz!
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TOareaFan
Superstar
This is the confusion causing the delays.....one group in TB keeps insisting on gauges and tires and the other group keeps thing them off
W. K. Lis
Superstar
Both streetcars and subway cars do, however, get "flats". That results in some noise, which needs to be corrected. See link.
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Duck
Guest
It seems like the modern solution would be to install a tachometer/encoder on each axle and modulate the dynamic braking to each axle's drive motor accordingly. In essence, train ABS.
Probably lots of technical reasons why they don't, however.
Probably lots of technical reasons why they don't, however.
Admiral Beez
Superstar
My 1969 Triumph motorcycle has no gauge. Instead there's a two stage fuel petcock, turn one way you get the first part of the tank, turn the other way and you get the reserve portion. So, you run until the first part is exhausted and then switch to reserve as a warning to get gas.
crs1026
Superstar
Duck, the technology exists for locomotives. Whether it is installed on Flexities, I don't know.
For locomotives, maximum adhesion is achieved when there is a small amount of slippage. So the units are actually noisier when the adhesion control is operating than when it isn't.
- Paul
For locomotives, maximum adhesion is achieved when there is a small amount of slippage. So the units are actually noisier when the adhesion control is operating than when it isn't.
- Paul
nfitz
Superstar
I'm well aware of this. I'm a couple of houses from Gerrard ... but sitting in my basement, I can feel when one of those go past!
Catenary
Active Member
I'd be interested to know more about this, as it runs contrary to the more basic concept of static friction being greater than kinetic friction.
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Duck
Guest
I was wondering the same thing, but held my thought. Static friction is greater for a given load and contact area than kinetic friction... Perhaps the belief is more generated on observation, that "we get the most traction right as our wheels start to slip" - since that's the "observable edge". You can't hit max traction without going a little too far (slipping) then backing off.
crs1026
Superstar
I'm not an engineer and don't pretend to understand the fine points.
What I gather is that with AC motors, it is possible to detect the point where adhesion is lost much more effectively, and reduce torque much faster than with DC motors, which will run away into true wheel slip. I believe that with AC, controlling the frequency of the power circuit does this inherently. So the traction control system is basically 'pushing the envelope' all the time, powering up until adhesion is lost, then cycling back quickly when wheel slip is detected. I gather the result of these micro-slips is that the wheels turn faster than the locomotive is actually moving. The units have a radar unit that measures speed over ground and compares to tread speed, and this controls how the power is modulated to the motors.
This system was first introduced with EMD's SD70MAC model. If you have ever heard this technology at work, you know the sound. It works in dynamic braking mode also.
- Paul
What I gather is that with AC motors, it is possible to detect the point where adhesion is lost much more effectively, and reduce torque much faster than with DC motors, which will run away into true wheel slip. I believe that with AC, controlling the frequency of the power circuit does this inherently. So the traction control system is basically 'pushing the envelope' all the time, powering up until adhesion is lost, then cycling back quickly when wheel slip is detected. I gather the result of these micro-slips is that the wheels turn faster than the locomotive is actually moving. The units have a radar unit that measures speed over ground and compares to tread speed, and this controls how the power is modulated to the motors.
This system was first introduced with EMD's SD70MAC model. If you have ever heard this technology at work, you know the sound. It works in dynamic braking mode also.
- Paul
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Duck
Guest
It sounds like you understand the fine points quite well! Thanks for the explanation. Sounds like it's doing just what we thought - riding the edge. That's all I meant when I said it's probably just perceived by the industry that maximum adhesion is actually "a little slip" - the reality is that's just when the feedback loop scales back real quick and it all happens so fast, that visually, it appears as though a little slip is best.
With regard to the new streetcars; where exactly are the Leslie Barns? I found a system map, but I can't seem to find one that shows where the barn is relative to the network layout. This goes back to my question of trying to understand why a couple of the new LFLRV's were showing up on a route other than 510.
With regard to the new streetcars; where exactly are the Leslie Barns? I found a system map, but I can't seem to find one that shows where the barn is relative to the network layout. This goes back to my question of trying to understand why a couple of the new LFLRV's were showing up on a route other than 510.
crs1026
Superstar
South of Queen, between Broadview and Coxwell. All LFLRV's make the trip across Queen to get to their runs, so they are effectively 501 or 504 short turn cars.
- Paul
Attachments
Catenary
Active Member
This makes sense, as it's essentially ABS for acceleration. As Duck says, if it happens fast enough, it would look like continuous slip.
smallspy
Senior Member
Modern DC traction systems do this as well, although they are not able to do it quite as well as the thermal capacity of an AC traction motor is enormous when compared to that of a DC traction motor.
Anyways, going back to the topic at hand - yes, the Flexities have wheelslip control, both for acceleration and braking. For that matter, the CLRVs do, as well. I'm not clear how exactly the system works in the Flexities, but in the CLRVs it measures the speed of the axles of the front truck versus those of the rear truck, and will reduce traction power or braking force momentarily and automatically apply sand to the rail.
Dan
Toronto, Ont.
SaugeenJunction
Senior Member
This isn't about the new Flexities and I wasn't sure where to post - but it looks like Nike is turning a TTC ALRV into a mobile shoe store dubbed "SNKRS XPRESS" for the NBA All-Star Game this weekend. Article here.
Interestingly, the rendering of inside the car looks like major modifications were made. I wonder if the TTC just sold Nike an old ALRV that wasn't being refurbished for them to use, then to be disposed of after. Insights on this?
Interestingly, the rendering of inside the car looks like major modifications were made. I wonder if the TTC just sold Nike an old ALRV that wasn't being refurbished for them to use, then to be disposed of after. Insights on this?