March 2013 Monthly Status
31 March 2013 23:13 Filed in: Administrivia,Monthly Status
I’m going to change how I do the end-of-month status posts, and just do them separately. This probably won’t get pushed out until the next real post, simply because I’m lazy (and my software makes changing one page in these musings far more work than it needs to be).
March, as you may have noticed, consisted mainly of me demonstrating how little electrical knowledge I really have, much to my chagrin. I set out to construct a model of how PWM works in a DC motor, so I could better understand how my motors worked, and I managed to get it wrong pretty nearly at every step.
That all being true, I still learned quite a lot, and I have a better handle on just what PWM does now than I did before, and what kind of trade-offs are being made. At some point I’ll go fix my last couple of errors and do another, hopefully final, post to summarize all that. But I’m going to let this cook in the back of my head for a while, both to spare my readers (assuming any are left) and my own sanity. Read More...
Modeling Subways
I realized that my subway material was scattered over several pages, and I didn’t really have anything that tied them all together. Also, some of the pages were a bit out of date. The main page is the Subway Line page. I’ve updated the outdated material, and here’s a post to describe what I was trying to do, how I went about it, and what I’d do differently next time. I’ll link to other pages in the text below.
A subway isn’t something you find on a lot of model railroads, but then most model railroads are focused on freight operations. Even ordinary railroads back in the steam era had underground stations (New York’s Grand Central Terminal has 44 platforms, all underground). Property costs in modern cities make it even more likely for structures to be built above the tracks, partially or wholly covering the station. Boston’s Back Bay station used to be above ground, largely in a cutting, but today is mostly out of sight below ground except for the entrance building and ventilation stacks.
Despite the high property values in Tōkyō today, most of the stations are surprisingly at or above ground level. In part that’s because the rail lines’ growth came after dense urbanization, so elevated lines were a more practical solution for expanding them. The city does have subways, and most of them use the same gauge track and same voltage power supply as the above-ground commuter lines, so some of these subways provide access to the city center for suburban commuter trains. Several subway lines have underground stations below or near surface line stations, to allow transfers.
I’ve used that as an important aspect of my modeling to capture the “layered” feel of urban railroading. Cities rarely exist on a single level, even ignoring multi-story buildings. There are often below-ground open plazas and hidden shopping arcades, and highways and rail lines exist and cross on multiple levels. Cities aren’t flat, and models of cities shouldn’t be flat either.
Read More...
A subway isn’t something you find on a lot of model railroads, but then most model railroads are focused on freight operations. Even ordinary railroads back in the steam era had underground stations (New York’s Grand Central Terminal has 44 platforms, all underground). Property costs in modern cities make it even more likely for structures to be built above the tracks, partially or wholly covering the station. Boston’s Back Bay station used to be above ground, largely in a cutting, but today is mostly out of sight below ground except for the entrance building and ventilation stacks.
Despite the high property values in Tōkyō today, most of the stations are surprisingly at or above ground level. In part that’s because the rail lines’ growth came after dense urbanization, so elevated lines were a more practical solution for expanding them. The city does have subways, and most of them use the same gauge track and same voltage power supply as the above-ground commuter lines, so some of these subways provide access to the city center for suburban commuter trains. Several subway lines have underground stations below or near surface line stations, to allow transfers.
I’ve used that as an important aspect of my modeling to capture the “layered” feel of urban railroading. Cities rarely exist on a single level, even ignoring multi-story buildings. There are often below-ground open plazas and hidden shopping arcades, and highways and rail lines exist and cross on multiple levels. Cities aren’t flat, and models of cities shouldn’t be flat either.
Read More...
Corrected PWM
Update (3/29/13): The “percent of maximum” numbers are all wrong. I’m never going to get this right. I need to go back and recalculate those, but that’s not happened yet. When it does, I’ll correct this post (and maybe make another one).
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I really thought I was going to be done with PWM and back to working on decoders this week. But, as is now noted on the last post, I got it wrong. As I mentioned then: “I’m not an electrical engineer. I think I know what I’m talking about, and my conclusions appear to line up with observed reality. But I could have fallen down the rabbit hole and just not noticed. Take it all with due caution and a grain of salt.” Yep, down the rabbit hole I went.
So, as Bullwinkle used to say, “this time for sure!”. Well, sort of. I’ve fixed my problems, but my model isn’t an exact one. For the details of that, and what conclusions I can draw from what I have, read on.
Read More...
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I really thought I was going to be done with PWM and back to working on decoders this week. But, as is now noted on the last post, I got it wrong. As I mentioned then: “I’m not an electrical engineer. I think I know what I’m talking about, and my conclusions appear to line up with observed reality. But I could have fallen down the rabbit hole and just not noticed. Take it all with due caution and a grain of salt.” Yep, down the rabbit hole I went.
So, as Bullwinkle used to say, “this time for sure!”. Well, sort of. I’ve fixed my problems, but my model isn’t an exact one. For the details of that, and what conclusions I can draw from what I have, read on.
Read More...
More About PWM
Update 3/16/13: Ok, my graphs (and some conclusions drawn from them) had a serious flaw. I’d modeled both the growth and decay curves incorrectly, and this caused current to drop to zero in a lot of situations where it wouldn’t have. Don provided an interesting simulator model, which led me to do some more reading and correct my model. It’s still not complete, but rather than re-do this post, I’m adding a new one that is the correction. I’ll leave this one here for history’s sake, but please see the new one.
Read More...
