|
|
| Re: Real 11-car Train April Fools Joke (766512) | |||
 |
|||
| Home > SubChat | |||
|
[ Read Responses | Post a New Response | Return to the Index ] |
|
||
|
Re: Real 11-car Train April Fools Joke |
|
|
Posted by JPC on Sat Apr 4 15:54:10 2009, in response to Re: Real 11-car Train April Fools Joke, posted by David on Sat Apr 4 12:29:42 2009. This is no problem at all. In fact this is a problem that no half-decent electrical engineering undergrad should have a problem with._Basic statement of the engineering problem_ I haven't seen specifications (and I imagine they vary from one car type to another), but the system must operate in a manner similar to this: Each door has a motor (or set of motors) which control that door (and only that door). These motors draw a fair amount of power, which means they probably draw power from the third rail (via shoes on that particular car; this power is mostly used to drive the traction system, but also powers A/C, heat, lights, and the doors, among other things). These motors are "dumb" - they need to be told what to do (i.e. driven with an appropriate level of current). At each door, therefore, there is a "controller circuit," which accepts input from one of several sources, and has as its output the drive current for the motor (presumably using a transistor-based amplifier in the final stage). This circuitry also controls the detailed operation of the motor - for example, stopping the motor when an object blocks the door, making repeat attempts at closing when the door is blocked from closing completely, etc. The only additional input needed is one which "initiates" the door opening or closing, and can come from one of several places: (a) a key inserted into the keyhole adjacent to the door (which opens/closes only that one door), or (b) remotely via a signal cable coming from the C/R's position, which can control whichever doors' controller circuits are connected to that system and accept the signal sent over that cable. There is a bundle of wires emanating from the C/R's position. These wires control the settings of the traction motors, A/C, heat, lighting, and door opening/closing, among other things. (There are also cables carrying back notification signals - such as the "all doors closed" signal - but these are independent.) The wires carrying the door signals must use some system to encode the C/R's instructions. The simplest example would be a switchboard-telephone-style system. The controller circuit reads the voltage between two wires: if the voltage is zero (or some other nominal value), nothing happens and no output is sent; if the voltage is "high" this is the signal to initiate door opening, and if "low" this is the signal to initiate door closing. Of course they could use some more complex system, but that doesn't change the basic idea. All you have to do is modify the controller circuits on each of the "special" doors so that they will not respond to the "usual" C/R/ open and close signals (i.e. by requiring different voltage levels to initiate opening and closing, or using an AC signal instead of a DC voltage level). Then, put a new button in the C/R's cab which sends a different signal, one which the new doors *do* respond to. That way those "special" doors only open when the new button is pressed; if the old button is pressed only the "non-special" doors open because the decoder circuits for the "special" doors do not respond to the signal sent by pressing that button. Keep in mind that when I refer to these "decoder circuits," what I'm actually talking about is likely a small PC board with some basic components (resistors, capacitors, transistors) soldered on. These are items which, if made in bulk, should cost *at*absolute*most* a few dollars each. Then the new controllers would have to be installed, presumably through an access panel located adjacent to each door. Depending on the current circuitry, it might be as simple as "plugging" in a new PC board, or severing a wire or soldering a new wire onto the existing board. Alternately, one can wire up a "second" signal system connected to that same "new" button in the C/R's cab, and connect the "special" doors to the "second" signal system (while the "non-special" doors connect to the regular signal system). This, however, requires running new wiring through the entire train, which would not be necessary for the first option. This is a simple engineering problem. |
|
(There are no responses to this message.)
|
|