MU Problem

[ronp]

Morning all,

I'm having a problem MUing two engines.  The engines are both G scale USAT GP38's.  At low speeds I noticed the rear engine was hunting and bumping the front engine.  I separated the engines but still kept them MUed.  While the front engine ran smoothly the rear engine darted up and down in speed.  Both engines when not MUed and run separately run very smoothly at low speeds.  It appears that the rear engine is getting erroneous speed commands when MUed.  I'm new to RailPro and today was my first attempt at MUing, of course I may have set up something incorrectly.  Any help would be appreciated. 

Thank you
Ron 

[nodcc4me]

I would try reversing the position of the engines, then MU them again. If the front engine is still hunting, check its maximum current setting.

[ronp]

I'll reverse the order and see what happens.  When you say "check it's maximum current setting" do you mean redo the initial current load procedure?

[nodcc4me]

Yes, check the full current load setting.  You can run the auto setting again and see if it is the same. Sometimes the setting needs to be tweaked manually when MUing the locomotive.

[ronp]

OK, that makes sense.  Because when the engines are run individually, they run smoothly at about the same speed at the same power setting. 

I just reversed positions, now the rear engine runs considerably slower and jerky.  Again hinting at an error in my load settings.  I will redo both.  It will be a while, for safety, they should be outside for this test.  And presently it's raining.

I will report back.  Thanx for the help.

[nodcc4me]

Hope that works. Let us know.

[KPack]

Ron, if you are running the two engines light (no cars), you might see the rear one "hunt" a little.  This is most likely because the lead locomotive is experiencing no load, therefore it's trying to figure out what to tell the rear locomotive to do.  Lead experiences no load = rear locomotive slows down.  When the rear locomotive slows down = lead locomotive senses a load and tells the rear to speed up.  When running a train, there is a constant load on the lead locomotive due to the weight of the train behind it.  Any adjustments that the rear locomotive makes are minor and not noticeable because the load is never fully taken away from the lead locomotive. 

When you get a chance, run both with some cars behind and let us know what you find.

-Kevin

[ronp]

Kpac, thanx for the reply.  I'll try that very thing.  Again, it will be a bit.  Having an outdoor layout allows the weather to exclude some days from operation. 

[G8B4Life]

I can only echo what Kevin has said, though I'm not entirely sure that's exactly how it works; it is interesting that Rings own video shows and claims that two loco's running MU'd but not coupled run at the same speed with no train attached, even if one of them is significantly faster than the other one when run by itself. For an experiment try running them MU'd but not coupled together and see what they do.

The only thing I can really offer further than re-running the full load current test for each loco is that the lurching your experiencing (hunting is a different train phenomena) may be exacerbated by the couplers you use; if there is a lot of slack between the coupler faces then there is more distance for the loco's to lurch before any load is transferred and compensated for.

- Tim

[ronp]

Good weather today so was able to get the trains outside on the main.  Both of the recommendations I received helped solve the problem.  First I redid the load tests on both locomotives.  It took me a few tries to get valid tests.  Just doing this greatly reduced the hunting problem of the second loco.  I ran them linked both coupled and uncoupled.  I then drove the locos outside with about 30 cars; everything seemed to smooth out.  I ran the train back and forth, up and down a 2% grade at speeds from a crawl to moderate.  All went well.  I would like to thank both Al and Kevin for their help.  Frankly I was somewhat lost.

[nodcc4me]

Glad to hear that, Ron. Now, have some fun with RailPro.

[ronp]

Tim, I may be using the wrong terminology.  In fact, lurching sounds more descriptive.  And the point about sloppy couplers fits.  The couplers are pretty much what came w the cars.  They need to be exchanged but that mod seems to be a bit down the list, but the conversion will happen.  Good points and thanx for the reply.

Ron

[ronp]

Will do.  I had a good time today running the engines and building the train.  Perfect day after a rain storm.

Ron

[William Brillinger]

Suggestions:
1. make sure your software is all up to date on the HC and the LM's
2. if the units are not broken in yet, do the current load test again. (a few times as the units get broken in)

[ON28]

I got some advice here (apologies, forget who) to tweak the starting voltage/speed of (HO) locos so they are moving steadily at 1% throttle (not zero), then adjust accel/decel to about 10%. It was good advice and virtually eliminated any buff or drag in MU consists.