Subscriber & Member Login

Login, or register today to interact in our online community, comment on articles, receive our newsletter, manage your account online and more!

Will Using a Pusher Loco in My Train Consists Likely Mean Derailments?

1369 views
15 replies
1 rating 2 rating 3 rating 4 rating 5 rating
  • Member since
    January, 2010
  • 1,829 posts
Will Using a Pusher Loco in My Train Consists Likely Mean Derailments?
Posted by peahrens on Saturday, March 18, 2017 3:58 PM

I just got a HO UP 2-8-8-2 converted to DCC and sound and I read that, while not very helpful (too slow) for UP they might have been used as pushers for Big Boy or Challenger led freights.  I know I could just try it, but if I get the locos reasonably speed matched (the Big Boy and Challenger are Tsunami's and the 2-8-8-2 is a LokSound) will I tend to get derailments?  Even though the Tsunami has no CC5 nor CV6 I imagine I could match the 2-8-8-2 to the Tsunami.

If after matching, the 2-8-8-2 is just a tad faster, I imagine it would be pushing the last few cars, which should be no worse than it pushing a few cars by itself in terms of derailments?  (I presume that pushed cars are more likely to derail than pulled cars but don't know this for a fact.)

If the 2-8-8-2 were a tad slower, that would seem like adding just a bit more drag to the train, somewhat like adding more cars.  If the 2-8-8-2 were significantly slower, would it add enough drag to stringline the train and derail some of the middle cars.  I have not weighted my cars to NMRA specs religiously.  Most are kits, so I often add a bit of weight inside if they are pretty light, but some for sure are on the light side.

Any insight is welcome as I'm considering taking a shot at this with these locos as well as my diesels.  

Paul

Modeling HO with a transition era UP bent

  • Member since
    March, 2017
  • 205 posts
Posted by Track fiddler on Saturday, March 18, 2017 5:01 PM

Wow Paul that's a heck of a matzo ball of physics you have going there. And I may not be the one to answer it as I've never tried it. I had to read your description and the analogy twice. Everything you said made perfect good sense like you hit all the nails on the heads. Seems to me if the pusher was a tad slower it would be better than a tad faster. It would cause drag like more cars. But all that would do is make the drive train wheels of the lead engine slip a little bit while The Pusher was still helping. If the helper was a tad bit faster. Jackknife time. I think this would be prone to pushing the cars out on the outside of a curve because of the weight of the front engine is resisting the help. This is only an opinion but that as well as the analogies you made makes perfect sense to me.                            Al                                                                     PS  I am very curious on the outcome of this one I've had a little more time to think and I'm already second-guessing myself.  This is a good one Paul                                                                    

  • Member since
    December, 2001
  • From: Northern CA Bay Area
  • 3,478 posts
Posted by cuyama on Saturday, March 18, 2017 5:10 PM

Everyone I know regularly using pushers with DCC has a second operator running the pusher independently. This reflects real life and allows the pusher operator to recreate prototype functions such as gently shoving to bunch the slack for the lead engine to start. Not sure how one would accomplish that with the pusher engine(s) consisted to the head-end engine(s) – which is what I think you are wishing to do. No DCC programming needed, just some operator practice at the throttle.

Edit: Of course, one person could try this with two throttles (or a double-control throttle as on some Digitrax throttles, the NCE Twin, etc.), but it would be tricky

  • Member since
    February, 2008
  • 5,693 posts
Posted by maxman on Saturday, March 18, 2017 5:24 PM

peahrens
If after matching, the 2-8-8-2 is just a tad faster, I imagine it would be pushing the last few cars, which should be no worse than it pushing a few cars by itself in terms of derailments? (I presume that pushed cars are more likely to derail than pulled cars but don't know this for a fact.)

The question is can the 2-8-8-2 push all the cars by itself?  If it can push all the cars itself it will, given enough time, eventually have all the slack bunched up behind the lead engine.  At that point either the pusher will slip its wheels;  the pusher will push the entire train as well as the lead locomotive which will have its wheels spinning and not actually be doing anything;  or something somewhere in the train will derail if the lead engine prevents the pusher from pushing the entire mess.

There was recently an article, I believe in MR, where pushers were discussed.  One of the things it mentioned was that the lead locomotive should not be able to pull the train by itself.  If it can, then there is no need for a pusher in the first place.  I don't remember the exact number of cars each engine should be able to pull/push, but I think it was said that the lead engine should actually be able to pull 2/3 of the cars in the train.  That way the pusher actually had something to do.  And then the pusher had a separate engineer who had to watch where the slack was in the train to make sure he was pushing his alloted share.

  • Member since
    January, 2010
  • 1,829 posts
Posted by peahrens on Saturday, March 18, 2017 7:47 PM

The idea only occurred to me as I completed the 2-8-8-2 and, as well, yesterday took the grandkids to the local train museum and they announced a train coming by and we all went outside to observe. It had two diesels in front and one in the rear, which was working.  I did not observe if there was an operator or if there is a remote way of it being controlled up front.

I have a rather small layout so it's just for interest I want to pursue this.  I have a 3-unit Geep consist (all LokSound Selects) set up currently where I may try it.  I like the idea of adding cars so that the lead two can't quite get the train up my 2.4% grade.  Then add the 3rd unit at the end so I know it's making the difference on the grade, pushing a few car uphill.  Of course on the flat the rear unit will push more or even all the cars, unless the speeds are ideally matched.  Since the locos run together ok as a threesome, without cars behind, I'd guess they will do ok on the flat; i.e., the very slightly faster or slower ones will only slightly affect the load distribution.  On the downhill with a pusher, the cars will all push aginst the lead loco, unless the rear one is enough slower to pull back on everything ahead.  But, again, since the 3 locos run together ok, uphill, flat or downhill,I'm guessing it will work.  I suspect the biggest risk is if the rear loco pushes too much, likely on the flat or more likely downhill, in combo with too light cars, that I could see some pushing of light cars off the track.  But I'm guessing.  While interesting to analyze, I'm just going to have to try it out.  I thought some might have tried it and advise on whether it was rather likely or unlikely to work.

I'm only interested if I can do this with the front and rear locos consisted, using a single throttle.  I don't have other operators except occasional grandkids and I don't want to work two throttles at once. 

I'll see if I can find the related "pusher" article mentioned above.

Thanks for any comments or suggestions.

Paul

Modeling HO with a transition era UP bent

  • Member since
    February, 2002
  • From: Reading, PA
  • 22,399 posts
Posted by rrinker on Saturday, March 18, 2017 9:22 PM

 Yup, it should generally be pretty reliable if the lead loco can't pull the whole train, and the pusher can't push the whole train, either. That way should reduce the chances of the lead loco pulling too hard and stringlining the thing, or the pushed pushing too hard and shoving the cars off.

                                --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

  • Member since
    October, 2006
  • 25 posts
Posted by trevorsmith3489 on Sunday, March 19, 2017 5:44 AM

I have done this on my model railroad.

I have used three locos on the front end of a train and one loco acting as a DPU at the rear. (I have also tried with a loco acting as a DPU in the middle.) Locos are six axle modern locos with a twin stack train of 20 cars, some articulated as five car units and all weighted as per NMRA standards.

All four locos were speed matched - but not exactly - it would have taken me too long to do this accurately.

Track is Peco Code 83 and the grade in my helix is 3% with all other track level. Minimum radius is 27"

I have had no problems with stringlining or jackknifing caused by mismatched loco speeds.

The problems I have had are with stalling because of a lack of electrical connectivity. (The three locos at the front have never stalled, if an individual loco stalls on dirty track or frog the other two will pull/push the offender until it makes electrical connection again.)

Problems have occurred when the pusher loco looses electrical connection and the sudden dead weight of a loco at the end of a train has resulted in stringlining.

I guess this would not happen with a steam loco with multiple pickups on both loco and tender.

 

  • Member since
    January, 2010
  • 1,829 posts
Posted by peahrens on Sunday, March 19, 2017 4:00 PM

rrinker
Yup, it should generally be pretty reliable if the lead loco can't pull the whole train, and the pusher can't push the whole train, either. That way should reduce the chances of the lead loco pulling too hard and stringlining the thing, or the pushed pushing too hard and shoving the cars off.

I tried this out today.  In summary, as Randy and others noted, the key seems to be to ensure the locos at each end do not handle all the work.  

I used my 3 Geeps.  They are a P2K GP30 and a Genesis GP9 in the lead, with a Kato GP35 pushing.  All have LokSound Select decoders and are speed matched reasonably well with CVs 2, 5 & 6.  All were controlled together in a common consist; i.e., using one throttle. 

This was mostly for fun as my roughly 5' x 9' layout hardly needs long trains.  I started with 22 cars but increased it to 31 cars.  It was interesting to observe the couplers on the flat, uphill and downhill.  One thing is to recognize what the Kadees do as we run trains, doing the job well whether in tension or compression.  I only ran up to moderate speeds but tried all the mainline routes enough to feel derailments can be avoided. 

- The most stressful occasions I observed were some quick starts, jumping the throttle from 0 to 10 or more (of 126).  If the rear loco moved soonest, this briefly caused the rear loco to push the train quickly into compression.  Perhaps this happens because the locos behave a bit differently.  I have not turned off the BEMF and have not run the CV54 BEMF "training" for these locos.  (I will do that).  A contributing factor was that the lead locos and some cars were already on the hill whereas the pusher and cars near it wer still on the flat, easier for the pusher to get going.

- I was most nervous about light cars being pushed into derailment than about being stringlined under train tension.  I added two rather light hoppers (about 60% of NMRA recommendation), first separated somewhat and then together in the middle of the train.  They seemed to behave.  I think that such (light) cars would be the biggest weakness, perhaps the worst case being light cars with poor adjustment of the trucks. 

Oh, and if one has mainline permanent magnetic couplers (I have the 3-pair vertical magnets) this will doubtless increase the odds of undesired uncoupling at certain speeds as the couplers tension varies somewhat from steady state in the train.

Just another wrinkle of fun with the hobby.  I look forward to showing the grandkids.  In this case it was fun to hear the front loco sounds, 4 Soundcars in the train, plus the pusher loco working.

  

Paul

Modeling HO with a transition era UP bent

  • Member since
    March, 2017
  • 205 posts
Posted by Track fiddler on Sunday, March 19, 2017 5:06 PM

Nice.   I'm glad that worked out for you. Grandkids eyes will light up. Good-looking layout I enjoyed your post

                                  Al

  • Member since
    January, 2004
  • From: Canada, eh?
  • 7,342 posts
Posted by doctorwayne on Thursday, March 23, 2017 10:54 PM

cuyama
Everyone I know regularly using pushers with DCC has a second operator running the pusher independently. This reflects real life and allows the pusher operator to recreate prototype functions such as gently shoving to bunch the slack for the lead engine to start....

When DCC first became popular, I always wondered why nobody ever talked about operating in that very prototypical manner.  Pretty-well everybody appeared to be "consisting" all of the locos and missing out on a good opportunity to replicate the prototype.

I run DC, and often use pushers, even with multiple locos on the head end.  I've found that, when using DC, if extra locos are actually needed to move the train, they generally behave quite well together, even when their individual running characteristics are dissimilar.
However, if the train doesn't actually require a pusher and one is used anyway, it generally leads to problems.  
With DCC and a lone operator, consisting may lessen that if you can get the starting currents and speeds well matched.

Wayne 

  • Member since
    October, 2006
  • From: Western, MA
  • 7,298 posts
Posted by richg1998 on Thursday, March 23, 2017 11:20 PM

I did this about maybe twelve years ago with a MRC2K DCC controller that would operate one DC only loco. The 2K had five throttles. Throttle #1 only for a DC loco.

A DCC HO tender drive with DCC would pull a freight. A kit bashed 0-8-0 Winans Camel DC loco would come up and push. Had to watch the coupler slack. The 0-8-0 did buzz. Uncouple at the top of the hill and the pusher would back down. Park it on a siding and turn off power for that siding.

Rich

N

  • Member since
    February, 2002
  • From: Mpls/St.Paul
  • 9,982 posts
Posted by wjstix on Friday, March 24, 2017 7:43 AM

If you take the time, you should be able to speed match the engines so they start, run, and stop the same. CV2 is important to get them to start together, but using CV 3 and 4 to set momentum is also important to getting them to start and stop together.

If one engine's decoder doesn't support CV 5 and 6, you can still slow it down by setting up a straight-line speed curve (which is usually the default anyway), then use CV 66 and 95 to reduce speed.

Stix
  • Member since
    March, 2014
  • 142 posts
Posted by TheWizard on Friday, March 24, 2017 7:49 AM

I was just doing this last weekend at the club. We had a something-10-something pulling about 31 cars up the 2.5% grade when it started to slip. I came in with a BLI class A to push, and there were no issues. I went slower than the lead engine, usually, so the worst that ever happened was some wheel slip up front.

  • Member since
    December, 2004
  • From: Bedford, MA, USA
  • 17,256 posts
Posted by MisterBeasley on Friday, March 24, 2017 2:34 PM

I would try using a separate throttle for the pusher, and watch the coupler slack somewhere near the middle of the train.  Once the slack is gone, the pusher needs to speed up a bit, and likewise when there's more slack it needs to slow down.

Here's a question for DCC users:  If you have BEMF on the pusher engine, will that compensate for the changes in load and actually keep the engine moving at the right speed?

It takes an iron man to play with a toy iron horse. 

  • Member since
    February, 2002
  • From: Reading, PA
  • 22,399 posts
Posted by rrinker on Friday, March 24, 2017 3:46 PM

 It should, up to the point where the load is more than the loco can handle. Thus the idea of using pushers and/or mid-train helpers not just because it looks neat but because the train is actually too heavy for one loco to pull it up the hill.

                 --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

  • Member since
    November, 2015
  • 825 posts
Posted by ATSFGuy on Friday, March 24, 2017 4:15 PM

It will work if you don't apply a lot of power to the throttle and keep the locomotive going slow.

Subscriber & Member Login

Login, or register today to interact in our online community, comment on articles, receive our newsletter, manage your account online and more!
Popular on ModelRailroader.com
Model Railroader Newsletter See all
Sign up for our FREE e-newsletter and get model railroad news in your inbox!
ADVERTISEMENT
ADVERTISEMENT

Search the Community

ADVERTISEMENT
Find us on Facebook