Sarum Bridge

[Ozrail]

http://www.youtube.com/watch?v=WHo1ivW21Pc
http://www.youtube.com/watch?v=SqNyCNwYy7g

Maybe these videos might help with your inertial acceleration and braking request.
I knew someone has done it before, you'd just need to tweak to your requirements.

[martink]

I agree that acceleration & deceleration is quite doable in T. The problem is getting it to work reliably and repeatably on an automatic layout, since this is critically dependent on good electrical pickup with clean wheels and track. Longer term, I will be rigging up all my trains to have two power units permanently coupled and wired together so as to have four bogies of pickup on each "loco". I might be able to avoid that with my HST (and its three power cars), but may still end up having to swap the bodies of the buffet and a first class coach.

The traditional way to do slowdown in larger scales is for external hardware to attenuate the controller output voltage to slow down and speed up again. This works poorly in T, where you need to maintain the full voltage but just vary the PWM width. This is easy enough to do if you have designed your own PWM controller with this in mind, but is a bit trickier as an add-on. It is also a lot simpler with one train than with three or four. I am actually a bit surprised that Eishindo didn't do something like what you see in those videos with its current PWM controller's optical detector functions - it should just be a simple software feature.

[tjejojyj]

Another piece of automation I thought would be nice if I build the layout into a coffee table would be automatic operation if someone is looking at it using ultrasonic transducers as detectors.

My inspiration is a bookshelf layout I found online that does this http://scottpages.net/Newbury.html.
(This site has a whole swathe of small layouts with various forms of automation. No t-gauge though. There's also an interesting discussion of model railway controllers http://scottpages.net/ReviewOfControllers.html)

Tim J.

[NeilM]

Any controller (PWM or anolgue but with electronics) can be designed to have an accelarate/decelarate feature, ofter refered to as simulated momentum. When operated in this mode the locomotive will accelarate and decelarate smoothly even if the controller is switched immediately from off to full on or vice versa.

If such a controller could be used then the automation could become simpler, as the automation hardware will not need to worry about slow down and speed up, but can just supply the signal to the controller in an on/off fashion.

[martink]

Any controller (PWM or anolgue but with electronics) can be designed to have an accelarate/decelarate feature, ofter refered to as simulated momentum. ...

Yes... but... a critical issue is exactly how that feature modifies the voltage going to the train. With T, we cannot really afford to use anything that just reduces the voltage and so loses the PWM effect - we need to maintain the full pulse voltage and reduce the pulse width. This effectively means a lot of published slowdown circuits for larger scales simply aren't appropriate - they are not so much slowdown circuits as stall-and-stop circuits. Even when sticking with the full PWM, the slowest speeds reached just before or after stopping can still be problematic and cause the loco to stall. That is why I chose to use a stepped approach, so I can manually set the lowest speed to suit how the trains are behaving on the day.

Another issue is how long the train has to run at the lowest speeds. Very quick deceleration to an immediate stop after overrunning the sensor is one thing, but maintaining that low speed while the train crawls forward to a specified stop point is something else entirely.

[martink]

A bit more progress - the viaduct has its stone facade, and the scenery is nearly ready for plastering...

[peterg]

That is going to look stunning when finished mate.
Wish i had that kind of space.

[martink]

That is going to look stunning when finished mate.
Wish i had that kind of space.

Thanks, Peter. I'm hoping to exhibit it later this year. As for space, I just rechecked your posts on Borderline, and isn't that 48" x 18"? Sarum is only 57" x 20" - not much bigger.

[peterg]

That is going to look stunning when finished mate.
Wish i had that kind of space.

Thanks, Peter. I'm hoping to exhibit it later this year. As for space, I just rechecked your posts on Borderline, and isn't that 48" x 18"? Sarum is only 57" x 20" - not much bigger.

That is incredible! It looks so much bigger on your pic's....i would have guessed twice as big.

[martink]

The pieces are really starting to come together now. The basic scenery is in, at least to the painted plaster stage. I've still got to tidy up and finalize the three little automation projects (signals, roads and level crossing), give everything a good clean, and get the trains running again (the following pics are posed). I'll do another full video then, then it will have to be put away for a few months while I catch up on other stuff.

[Jmyrick]

NICE!

[martink]

The level crossing is now working. Four el-cheapo $3.00 servos controlled by a dedicated computer equivalent to the new Peco Smart Switch. The gates are clear plastic with the framework scribed on by a screwdriver, painted white then wiped clean. A bit rough, but easily replaced in the future.

A quick video... http://youtu.be/nD_m1co-QWg


The circuit board and ultra-sophisticated mountings for the servos...


The business end being tested with pieces of sticky tape instead of gates. This gets pushed up through 4 holes in the baseboard, then the real gates are super glued into position....


The first attempt at proper gates. As usual with T, they look better at a distance.

[mattd10]

Wow! That level crossing is absolutely fantastic!
Are you going to include them in the automation so they open when no trains are coming?

Sent from mobile device

[martink]

Are you going to include them in the automation so they open when no trains are coming?

Yep. Already done. The crossing is on the quietest spot on the line, behind the viaduct. It isn't as visible there as I would have liked, but that is the only place where the trains are far enough apart to give it time to open and close again.

[Ozrail]

That Level crossing is super impressive.
Don't worry about it being in place you would like, think of it as a layout easter egg.
Most layouts have something people ovelook, but a few do notice, even on mine.

[martink]

That's finally the end of this batch of changes. No more work on the layout for a couple of months. And this time I really mean it. Really! Well, except for another couple of locos... And some fixes to the speed control logic... And some more buildings ...

So, here's a slightly-more-polished-than-my-usual video of the whole kit and kaboodle...

http://youtu.be/dfCoFVD2H_U

[mattd10]

WOW! I could sit and watch that all day! The automation is fantastic, changing signals, level crossing...all such great little extras! You don't see details like that on larger scale layouts, let alone in T!

I love the HST whizzing over the viaduct and the mix of trains! The speed changes seem a lot more noticeable with the HST (maybe something to do with the way it was filmed, or the fact it has 3 power cars whereas the freights don't?) but still looks absolutely amazing!

Cannot wait to see it finished and at an exhibition one day!

[tjejojyj]

I agree although I'm not sure I could watch it ALL day. (I have looked at it three times & I didn't notice the subtitles the first two times as I was so absorbed in the action and the details even as they stand.)
On one of the early shots the freight train crossing the bridge seems to be noticeably surging. Is that right? And is that just a byproduct of the PWM controller?

[martink]

Glad you both like the video - it was fun to make and gave the layout its first really good workout. It added up to at least two hours of running, and after some initial problems with wagon couplers, swapping coaches around a bit on the HST, etc., it all ran remarkably well. I consider this a (successful) dry run for a possible exhibition showing later this year.

I haven't tracked down the cause(s) of the speed fluctuations yet. I think I might still have a software problem here, and there also seems to be a hardware one with the controllers. I believe that one is tied up with the overload protection part of the circuit - all the power feeds through a current sense resistor, so as trains (particularly the HST with its three motors and lights) are switched on to and off from that controller the output voltage will vary for the other trains running on that unit. I can see a couple of possible remedies, but I'll leave that for the next stage. I should also be able to reliably run the trains much more slowly when I get around to double-heading all the trains with the locos wired together to give them 4-bogie pickup. Anyway, all of the issues look manageable.

I didn't think to get any shots of what happens when the level crossing didn't trigger properly or one time when my sleeve tripped the cancel sensor prematurely and the gates closed on a goods train passing through! These were the usual minor hiccups that only show up when you run something for real.

BTW, you might not have noticed the subtitles at first because I only added them a couple of hours after initially posting the video on youtube.

[tjejojyj]

I'm glad to hear the sub-titles were added later (I didn't think I was that unobservant). They are a nice touch.

You many know of this already but my only suggestion on the video would be to put more light on the layout when filming. Your camera should "stop-down" in response and give better depth of field. (Personally I wouldn't mind some closeups of the signal going to green and a train departing. )