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NovaBus

Drum Switches

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Hey all,

 

What is a drum switch and what it do exactly? Googling the name's image led me to this: 8516_1.JPG

 

Is that what a drum switch is? I'm not 100% sure so I figure I'd float it by here. I was also told that it is called a "master control"? And it controls acceleration? Correct me if I'm wrong?

 

Thanks.

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That's not a master controller. Seems like it's just a directional switch.

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Y2Julio, it was just an image pulled from a site as an example, I wasn't asking about that particular switch because even though you use a term somewhere, it's different elsewhere.

 

No problem...

Well, directional is more possible...

 

I assumed it, but you know what they always say about assumption. Just wanted to be sure about it.

 

Thanks for the replies anyway.

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OK what you're asking goes into some hard core electrical stuff, I'm familiar with the equipment but not so much the science behind it so you'll forgive me if I'm a bit hazy on the details, perhaps Ducman or another car inspector can help "fill in the blanks"...and this is relevant to DC traction as AC is not something I am familiar with and also way more complicated from what I've gathered.

 

So on the train, as has been said, the master controller unit is what controls the acceleration of the train - if it were a car you could think of it as your "gas pedal". In simplest form it controls the flow and direction of the current to the traction motors that move the train through "contacts" inside it. This is what the Master Controller "MC" would look like if you took the cover off:

 

dqoccx.jpg

 

The picture of the drum switch YOU posted above looks most like the reverser on the master controller. The reverser sets the direction of the current to the motors (whether the train will move in forward or reverse...or if the reverser is centered, not at all). Then, once the reverser is set, motion is possible. The contacts are set up so that each notch on the MC has progressively less resistance than the previous until the third "point" where the train is at full acceleration.

 

The beauty of a MC instead of a manual acceleration type controller like a "K" controller is that acceleration is automatic, and limit switches and field shunts make it progressive, so that to accelerate to full speed, an operator need only set the reverser and move the MC to the fastest position, where as on the manual acceleration type equipment, they would have to notch gradually up to avoid jolting the train.

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In NYCT, drum switches set operating positions (T/O or C'r). On R38 and older, they were key slots under the cab window and had to be manually set whenever a position was being established. Later cars, they were relocated under the car, and only Car Equipment had access to them (which were now set automatically by activating the position with our operating tools or keys), except for the NTT's, where they are visible under the side fof the car, and we can set them if for some reason they are not activated from above.

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