Re: Re: Getting a vintage tram system going in Melbourne
IS Edit
Monday, December 10, 2001 11:03 PM
It only applies to emergency braking on the cars in Melbourne because of the
way the track brake is wired in.
But it's not the track brake per se that is rough, but only the fact that it
comes on after the dynamic brakes are full on. In other words when maximum
wheel brakes aren't doing enough stopping they kick in.
Tram operators try to avoid using track brakes because they wear the head of
the rail down. There were several passenger stops on steep hills in San
Francisco where the track brakes came on automatically on every car and the
track wore away rather rapidly.
So, once again, track brakes are only applied after full dynamics on most
cars, thus their use is connected with emergency stops.
But that's the way they are used, not the technology per se.
I don't know how they will be wired in on the W class cars. It would be
easy, now that those cars have low voltage systems, to wire in an air
pressure sensitive switch that would bring in the track brake when a lot of
air is used in a brake application. The pressure at which it kicks in would
be critical for its effectiveness. High enough so it doesn't come on in
normal service stops, low enough so you don't get flat wheels.
My personal preference would be pressure switch activation with a manual
override for those slippery autumn afternoons with the plane tree leaves on
Collins Street tracks as you sliiiiiiiddddddde gracefully down to Swanston
Street in a cloud of fine dust and your wheels grinding nice little flats to
keep you from falling asleep later in the shift. Clack, clack, clack, clack.
But that set up could well be too simple for them. They'll probably find a
complicated way to do it.
Bob Murphy
----- Original Message -----
From: "Michael Walker" <[email protected]>
To: <[email protected]>
Sent: Tuesday, December 11, 2001 8:56 AM
Subject: Re: [TramsDownUnder] Re: Getting a vintage tram system going in
Melbourne
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way the track brake is wired in.
But it's not the track brake per se that is rough, but only the fact that it
comes on after the dynamic brakes are full on. In other words when maximum
wheel brakes aren't doing enough stopping they kick in.
Tram operators try to avoid using track brakes because they wear the head of
the rail down. There were several passenger stops on steep hills in San
Francisco where the track brakes came on automatically on every car and the
track wore away rather rapidly.
So, once again, track brakes are only applied after full dynamics on most
cars, thus their use is connected with emergency stops.
But that's the way they are used, not the technology per se.
I don't know how they will be wired in on the W class cars. It would be
easy, now that those cars have low voltage systems, to wire in an air
pressure sensitive switch that would bring in the track brake when a lot of
air is used in a brake application. The pressure at which it kicks in would
be critical for its effectiveness. High enough so it doesn't come on in
normal service stops, low enough so you don't get flat wheels.
My personal preference would be pressure switch activation with a manual
override for those slippery autumn afternoons with the plane tree leaves on
Collins Street tracks as you sliiiiiiiddddddde gracefully down to Swanston
Street in a cloud of fine dust and your wheels grinding nice little flats to
keep you from falling asleep later in the shift. Clack, clack, clack, clack.
But that set up could well be too simple for them. They'll probably find a
complicated way to do it.
Bob Murphy
----- Original Message -----
From: "Michael Walker" <[email protected]>
To: <[email protected]>
Sent: Tuesday, December 11, 2001 8:56 AM
Subject: Re: [TramsDownUnder] Re: Getting a vintage tram system going in
Melbourne
theActually, acceleration is quite important so you can get out into the
intersection before the light turns red.
Good point I hadn't thought of!The main advantage of a track brake, whether it be mechanical (like cable
cars) or electromagnetic is that it increases the contact area and that
increased area is made up of a higher friction coefficient surface (in
thecase of a pine block track brake a la cable trams, they can get slick in
effectively.wet when they absorb water so then need sand under them to work
wasThey actually can cause the wheels to skid because they take some of the
tram's weight off them.).
But this only applies to emergency braking doesn't it? My understanding
(probably showing my ignorance here - always a dangerous thing in someemergency
circles) that track brakes on modern cars were only applied in an
as the braking is rather good and therefore significantly uncomfortablefor
commuters when it is used...-+-+
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