Basic question about component identification and purpose

Other Hardware General Electronics
1

Hi,

I am starting a project involving adding wireless control to model trains by fitting them with Arduinos and Xbee modules. I've bought a dodgy old second hand locomotive to play around with, but I'm a bit unsure about the simple circuitry that it has on board; I want to make sure I understand what's already there before I go adding things!

Here's a photo of the chassis of the thing, with the motor removed (it goes on top of the components and gets its power from the two contacts at the top):

And here's my sketch of how it's wired up:

Unfortunately I'm not very experienced when it comes to analogue electronics, so I have a couple of questions:

  1. What is the component in the middle? It looks to me like a capacitor, but I can't find any capacitor labelling schemes that match what's shown. The locomotive is quite old I think, and German, so perhaps it's an unusual code?

  2. What is the purpose of the circuit as a whole? From my limited experience, and assuming the mystery component is a capacitor, my guess is that it's used along with the inductors for noise filtering... but is this likely to be removing noise from the signal coming in off the tracks, or preventing noise from the motor making its way onto the tracks, or both? I can understand why this might be important for me, because I want to power a digital circuit from the lines, but why is it important for when the train is just driven directly by the track voltage?

Thanks!

Edit: OK, I had the bright idea of looking this up on some model railway forums and found a nice explanation here. Seems it almost certainly is a capacitor, and its purpose (along with the inductors) is to suppress the noise of the motor, since a loop of track can make quite a good antenna. I'm still curious what the markings mean though!

2

I'd say it's an ancient capacitor. It's common to put those (well, capacitors in general) across a motor to reduce the motor's tendency to generate electrical noise (both on the power line and EM radiation). I suspect the inductors are in an effort to achieve same.

3

If I had the space I would be experimenting with putting rechargeable lipo batteries in the locos and rolling stock (tractive power would still all be in the loco), controlling speed by RC and having a dead track, like a real RR. Wonder if anyone has done anything like this.

4

Not a bad idea. It is a real pain when the train stutters and carries on when it hits a bit of track that has a bad connection.

5

That would definitely be neat way of doing things, although it introduces the risk of a derailed train crashing into the scenery or going over the edge of the table, which would be fun but expensive! However, I'm working in N-scale, which means everything is tiny - an Arduino Pro Mini is just about narrow enough to get away with. My gut feeling (but I should look into it) is that I wouldn't be able to get enough batteries on-board to run for any significant length of time.

My plan was to put a few supercaps across the track inputs, to hopefully get the train over any small patches of bad connectivity. Is that reasonable?

6

It's possible. That's exactly how a ESU PowerPack works. It's a super cap with a DC-DC converter.

But why not use the world standard DCC? A lot easier then fitting a Xbee receiver...

7

merribob:
My plan was to put a few supercaps across the track inputs, to hopefully get the train over any small patches of bad connectivity. Is that reasonable?

Wouldn't that make it not stop at stations? Or are they sized small enough to only get you over a few mm of track?

8

He talked about controlling it with Xbee so the rail power isn't controlling the train.

9

septillion:
It's possible. That's exactly how a ESU PowerPack works. It's a super cap with a DC-DC converter.

But why not use the world standard DCC? A lot easier then fitting a Xbee receiver...

Because I'm keen to play around with Xbee and this seems like a fun project :wink: I made reasonable progress on something similar a few years ago with bigger trains (OO scale) and lower level 802.15.4 tranceivers, but didn't have the space for a decent layout. Coming back to it now, I'm happy to see that there are now boards that are (just about) small / cheap enough to make it feasible in N-gauge!

Also I'd like to experiment with decentralised control, where the trains form a mesh network together (with the switches/points, under-track proximity sensors, etc) and can negotiate blocks safely just by talking to each other, without any central computer in charge. I'm not sure I could do that with DCC.