Author Topic: Surging on grades when DPU  (Read 1218 times)

Alan

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Surging on grades when DPU
« on: December 05, 2017, 07:26:20 PM »
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I have noticed some "surging" on downhill trains. The longer the train, the more apparent it becomes.

I've noticed the same on occasion, but it's intermittent.  I ran a rather long train on a friend's layout with grades the other week, specifically to test this.  On the first run it started to surge slightly when the locomotives reached the bottom of the hill and the entire train was pushing downhill against them.  However, a second time on a longer grade had no surging.  Same locomotives, same train.  No DPU on this train....I wonder if that would've made a difference?  A separate thread with some test results would be great.

-Kevin

Starting Kevin's thread...

I have not experienced surging although I have seen repetitive coupler bunch and slack. Not enough effect to affect the loco speeds. My layout has but a single grade on it. It is fairly long (est. 30 ft) with vertical easements. At its steepest it is 2.0% for about 8 ft which is partly on tangent and partly on 32"R curve. A fairly mild grade which is I believe the reason I do not see surging.
Alan

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When I was a kid... no wait, I still do that. HO, 28x32, double deck, 1969, RailPro

MRL Trains

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Re: Surging on grades when DPU
« Reply #1 on: December 05, 2017, 07:41:49 PM »
The grade I experienced it on is about 50' of 1.6% leading to a helix of 2.2% with 29"R.   The problem shows up when I slow down the train before entering the helix. Once I'm running slow in the helix I continue to have the problem. I'll add this to my list of things to test and report back on. 

Chris

Modeling the Mullan Pass in 1995

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Re: Surging on grades when DPU
« Reply #2 on: December 05, 2017, 10:27:43 PM »
Ran some tests tonight and could not replicate the surging.  I was hoping to get some video.  Apparently RP is camera shy.  :)
If it happens again I'll try to catch it.  I did video how nice and smooth it ran tonight.  I'll post it as soon as it gets done loading to YouTube.

Chris
Modeling the Mullan Pass in 1995

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Re: Surging on grades when DPU
« Reply #3 on: December 05, 2017, 11:03:40 PM »

Video of DPU'd grainer down my 2.2% helix.   What looks like surging is just the video frames.  It running nice and smooth as you tell by listening to the sound of the wheels.


Chris
Modeling the Mullan Pass in 1995

TwinStar

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Re: Surging on grades when DPU
« Reply #4 on: December 06, 2017, 03:42:39 PM »
On the 1:1 railroad there was a 10,000' limit between the Harris boxes on the lead and DPU's without a repeater in the middle. Our Harris boxes are RP modules. Does anyone know how far apart two LM's can be and still communicate?

Jacob Damron
Modeling late 1950's Dallas Union Terminal in Free-mo+ modules

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KPack

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Re: Surging on grades when DPU
« Reply #5 on: December 06, 2017, 05:26:05 PM »
On the 1:1 railroad there was a 10,000' limit between the Harris boxes on the lead and DPU's without a repeater in the middle. Our Harris boxes are RP modules. Does anyone know how far apart two LM's can be and still communicate?

No idea, but I imagine that it is the same distance between the HC and LM, which can depend on environmental variables (physical obstructions like walls or tunnels, airwaves crowded, etc).  I don't think that most of us will run into a situation where we are running a train so long that the front and rear can't communicate.  I know there are people who run 100+ car trains but normally that would occur on a Freemo-type setup, where there are almost no physical obstructions.  Besides, Railpro is designed as a repeater system so there will be multiple pathways for any signal to get communicated.

-Kevin