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Re: Sarum Bridge

Postby Ozrail » Wed Mar 26, 2014 2:26 am

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.
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Re: Sarum Bridge

Postby martink » Wed Mar 26, 2014 3:19 am

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.
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Re: Sarum Bridge

Postby tjejojyj » Wed Mar 26, 2014 5:50 am

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)

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Re: Sarum Bridge

Postby NeilM » Wed Mar 26, 2014 8:43 am

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.
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Re: Sarum Bridge

Postby martink » Wed Mar 26, 2014 4:04 pm

NeilM wrote: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.
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Re: Sarum Bridge

Postby martink » Sat Apr 05, 2014 5:27 pm

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

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Re: Sarum Bridge

Postby peterg » Sat Apr 05, 2014 7:43 pm

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

Postby martink » Sat Apr 05, 2014 8:07 pm

peterg wrote: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.
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Re: Sarum Bridge

Postby peterg » Sat Apr 05, 2014 10:39 pm

martink wrote:
peterg wrote: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.
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Re: Sarum Bridge

Postby martink » Mon Apr 14, 2014 2:03 pm

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.

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