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MOC: USRA 0-6-0 with Onboard Decoupler


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#1 zephyr1934

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Posted 03 December 2012 - 05:10 AM

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(full gallery)

This post is about my little 0-6-0 USRA switcher that I debuted at Brickworld 2010, but have not had time to write about until now (and really didn't get many good photographs of either). More on the prototype can be found here. My locomotive is actually part of a larger system, so let me start with the back story of the system.

For Brickworld 2009 I built up an automated switchyard controlled completely by two RCX's using a pair of 9V locomotives, remote controlled switches, a trackside decoupler, and a few isolated blocks. The four car train would come in to the yard, the sensor would position it to uncouple the caboose, then the train would pull forward and a shunter would push the caboose back on the main line. The train would back up, drop a car, the shunter pushes it to one siding, then repeat for the next car and a different siding, and so forth until the train has completely swapped two cars. The full circuit is split over two videos, part a and part b. These videos are the best overview of the components.

Here's an overview shot of the layout (without the motion of the videos it is unremarkable) and a detail shot while I was fine tuning the RCX program.
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While it was great fun to work out all of the quirks, a viewer had to stand there and watch it for five minutes to appreciate the nuances and from an operating standpoint... well, with an automated system all the fun work has already been done.

So for Brickworld 2010, I wanted to retain the remote control, but drop the automation. I kept the switch design functionally unchanged, updated a great modular 9V modular switching block to PF

2004 original by Philippe "Frogleap" Label
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My 2010 PF update
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I had originally intended to build my SP Pacific powered through the drivers, but I got side tracked with the insane power that a pair of XL motors could deliver through the tender trucks. So to experiment with a driver powered locomotive, I built up this 0-6-0 based on the USRA standard design that was used by many railroads in the US.

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Several folks watching the switcher working have asked me where I hid the motor, but it should be painfully evident in the above shot. I borrowed details from my earlier locomotives, like the vent doors on the cab roof. And I also borrowed great ideas from others, like the cab windows from Garret and I improved upon one of his cylinder designs. I also liked my use of the old technic connectors for the side rods (something I have since replaced with custom rods, but that's another story, grin) and my pilot design (see the photo at the top of this post).

The real magic is in the tender. Exploiting the fact that I had a second channel on the tender-mounted IR receiver, I used it to control a PF M motor at the back of the tender. While there had been a few earlier locomotives with an on-board uncoupler, e.g., this one, none of them seemed to retain the full freedom of a normal coupler and bogie truck. Ultimately I found my solution with the 12v uncoupling track (7862). The 12v couplers had a pin that hung down and would allow an uncoupling track to split the magnets. I wanted to do similar, but pull the magnet from onboard the train. I quickly discovered that this goal is far from trivial on a bogie that also has to rotate around curves when it is not uncoupling. You also need a lot of force to overcome the bond of the magnets. Ultimately my design snaked a fishing line tied to the coupler, to a toggle point on the side of the truck, then up through the hole in the bogie plate and to a spool driven by the M motor, all without modifying any of the parts. Here to, pictures cannot do it justice and I was having too much fun when playing with it at shows to shoot movies, which is part of the reason why it has taken me so long to post about it. I shot a couple of movies a few months back, right before I rebuilt the locomotive to address an operational problem with the XL motor (discussed below) and added the custom drive rods. The quickest movie is here, but more can be found here.

So here's the problem with an onboard uncoupler- you can pick up as many cars as you want, but all you can do is drop the entire string of cars. You cannot actually switch things around like this. You also need the ability to drop some cars while keeping some coupled to the locomotive. To this end, I rebuilt the trackside uncoupler to be capable of working between buffers. This shot shows the uncoupler along with two switches

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The white 1x1 rounds should be between the rails to show the "cut line" (which is not the case in the shot) and indicate that this unit has the white control switch. In the top right of this photo you can see the unit as installed.

That's the complete system. It worked well at Brickworld 2010, and then I came up with an ambitious yard for the World's Greatest Hobby show in 2011.
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The trouble was, I now could assemble a cut of 20+ boxcars. Pulling them through the curves, however, proved to be too much for my poor little bevel gears off of the XL motor.

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So as noted above, I have redesigned the powertrain and have hopefully solved the problem. I am hoping to build up the yard again at another show some time soon and take her for a spin (I'm packing spare gears from now on).

The kids love to work the switches while I drive the locomotive ("red away... white towards you," locomotive moves, "white away," etc.).

(full gallery)

#2 Legoroni

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Posted 03 December 2012 - 06:22 AM

Hiding the motor in plain sight was an interesting idea. You've given me a few ideas.

#3 eurotrash

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Posted 04 December 2012 - 12:42 AM

I looked at the first picture and thought that was an interesting color choice for the front of the engine.  Then I read the rest of the post and had to go back to that first picture.  What an ingenious positioning of the motor.

#4 Daedalus304

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Posted 04 December 2012 - 01:03 AM

I really love this engine, most notably the pistons and how you used the XL motor. (A trick I may just end up stealing in the future!!)

The fact that you've got such a large system for shunting and decoupling is amazing, too. Great work!
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#5 LEGO Guy Bri

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Posted 04 December 2012 - 05:08 AM

Excellent work zephyr1934! Using the motor as the smoke box is a great idea! The engine overall looks great, though I am trying to figure out your decoupling mech.  :classic:
-I don't tell you how to tell me what to do, so don't you tell me how to do what you told me to do... I know when to use finesse

#6 zephyr1934

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Posted 04 December 2012 - 06:24 AM

Thanks Legoroni, eurotrash, and Daedalus304 for the kind words. I believe the positioning of the XL motor is what caused the problems with the bevel gears (I think I was off by half a plate). Not a problem when pulling small loads, but with 20+ cars it could be fatal. Hopefully my redesigned drivetrain solved the problem, but I'll update this thread as I see how well it performs.

Meanwhile, if you haven't done so, definitely check out one of the videos of the engine uncoupling. The quickest movie is here, but more can be found here.

View PostLEGO Guy Bri, on 04 December 2012 - 05:08 AM, said:

though I am trying to figure out your decoupling mech.  :classic:

Hey, LEGO Guy Bri, you slipped in while I was responding to the earlier posts. Likewise, thank you for the kind words. In the top picture of my first post you can see the fishing line on the left side of the rear tender truck. That is tied around the near edge of the magnet holder. The fishing line goes in between the two wheels and up the hole in the center of the bogie plate. Inside the tender is a spool driven by a PF M motor. Driven one way, the fishing line has enough slack that the coupler can swing freely, driven the other way, it pulls the line taught and snaps the coupler to the side. There is a little delay as the fishing line initially stretches for a fraction of a second, e.g., as in the detail video. If the train is heavy occasionally I will have to back the locomotive up to give enough slack for the coupler to break the magnets.

To maximize power I did not build in a clutch. So the motor stalls whenever you uncouple or release. As long as I quickly hit the stop button on the remote it hasn't been a problem for me. Once or twice at a noisy display I did not hear that the M motor did not stop, it remained stalled and inadvertently wasted a lot of the battery power. I contemplated using an indicator light, but I couldn't come up with a version I like. Perhaps the new Servo motor will eliminate the need to be vigilant on the controls.

Edited by zephyr1934, 04 December 2012 - 07:07 AM.


#7 LEGO Guy Bri

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Posted 04 December 2012 - 07:21 AM

View Postzephyr1934, on 04 December 2012 - 06:24 AM, said:

In the top picture of my first post you can see the fishing line on the left side of the rear tender truck. That is tied around the near edge of the magnet holder.

Now that you pointed that out, I can see what you've done. I never would have noticed the fishing line. Seems that stuff comes in handy with LEGO (I use it to hang aircraft) That is a pretty neat and simple decoupling mech. Thanks for the clarification.  :classic:
-I don't tell you how to tell me what to do, so don't you tell me how to do what you told me to do... I know when to use finesse

#8 Hrw-Amen

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Posted 04 December 2012 - 09:09 PM

I like the way that the engine looks used and old in the first photograph, it seems to be a typical old workhorse, put through miles and miles of hard work up and down, without much attention paid to its paintwork and keeping up a good image that some of the mainline engines have. It has replicated that look well. Of course I also think it is a good idea with the XL Motor, I was trying to figure out what it was until I read your post I was thinking deodorant bottle top.

I have to admit I have no idea where you are coming from with the decoupler, I've read it a few times and watched the video. Glad it all works but seems way to technical for my mind to ponder. I expect if I could see it in action in person it would all make perfect sense but just reading it and watching a video I am afraid you have lost me.

Never mind, a great build nonetheless!

#9 zephyr1934

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Posted 05 December 2012 - 07:24 AM

View PostLEGO Guy Bri, on 04 December 2012 - 07:21 AM, said:

Now that you pointed that out, I can see what you've done. I never would have noticed the fishing line. Seems that stuff comes in handy with LEGO (I use it to hang aircraft) That is a pretty neat and simple decoupling mech. Thanks for the clarification.  :classic:

If I can fly an XL motor under the radar, imagine what I could do with fishing line (grin). In all seriousness though, it did take a bit of fine tuning to get it working right. As I said earlier, I'm hoping the servo motor will make it a lot simpler.

View PostHrw-Amen, on 04 December 2012 - 09:09 PM, said:

...Of course I also think it is a good idea with the XL Motor, I was trying to figure out what it was until I read your post I was thinking deodorant bottle top.

I have to admit I have no idea where you are coming from with the decoupler, I've read it a few times and watched the video. Glad it all works but seems way to technical for my mind to ponder. I expect if I could see it in action in person it would all make perfect sense but just reading it and watching a video I am afraid you have lost me.

Never mind, a great build nonetheless!

Oh, you are too kind, and yes, the XL motor does look like a detergent bottle cap, doesn't it (heh heh).

As for the uncoupler- I don't have any good shots of the back of the tender and she is on display for another month where I can't get to it. So imagine you were looking straight down on the tender. I have a pull-string on the coupler (or the magnet on the modern buffers). When the string is loose, the coupler can pivot freely left or right as the train goes around curves. When I pull the string perpendicular to the tracks, it will pull the magnet all the way to one side, breaking the coupling with the car behind.

If the string was not mounted on the truck I'd probably pull the tender off the tracks before breaking the coupling. Instead, the string has a few mounting points on the truck and I pull it through these. I just have to make sure the string still pulls the magnet perpendicular to the tracks.

#10 Locomotive Annie

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Posted 08 December 2012 - 10:36 AM

I love the XL motor in plain sight doing duty as the smokebox.  Back when I was much younger and my eyesight much sharper I built a tiny Manning Wardle 0-4-0 saddle tank to 4mm finescale standards (P4) and due to the tiny size of the boiler I simply used the miniature instrument motor that powered this very small loco as the boiler.  It was just about impossible to tell what I'd done and folk would always ask me how I'd got a motor to fit into something so small.
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#11 zephyr1934

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Posted 19 January 2013 - 08:18 AM

Doh! It would appear that I left out some very important information in my original post.

The instructions for the actual switches can be found in RailBricks 12

The original challenge for these switches was presented in issue 9, which provided a little more information about the switches themselves, "there is not much to look at, just a clean, efficient mechanism.... The red Technic connecter serves three purposes: a color code for the switch, an indicator for which way the switch is lined, and a manual override to throw the switch. The switch is un-modified and I have never had a failure with the six remote controlled units I have built." I've got to say that even with the motor attached this design is easier to throw than the normal lego switch lever since the light blay box provides a convenient spot to pull against.

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I haven't documented the remote control yet (I'm planning on including it as a short article in a forthcoming RailBricks), but if you scroll up to my original post, you'll see the pictures of the 2004 original by Philippe "Frogleap" Label and a link to more information. My design for the remote is very similar, except that I've updated it to the PF pole reverser.

#12 bricks n bolts

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Posted 19 January 2013 - 10:13 AM

Great work on the decoupler zephyr1934, looking forward to any more details!

I have the original 7862 12v decoupler set somewhere but it's not very good with all the limitations regarding exact train position and pins. One idea I had which I'm not sure if there is a solution for, so probably just a day dream, is finding a small put powerful enough elecro-magnet to pull the train magnets down if positioned under the track, ideally small enough to fit inside the space made by the original 7862 mecanism (see http://www.bricklink...m.asp?P=decbase - the round bit in the middle could easily be replaced) - you then power the magnet from the rails using the circular motion of the switch mechanism to turn it on or off.
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