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Discussion Starter #1
I have an NCE Powercab. I set up a consist with 2 locomotives.

I ran them individually on the same track and they were a good speed match. Started together at speed step 1 and stayed about the same distance as I went up through speed step 8. (28 step speed table)

Then I put them in a consist. The front locomotive, #40, is a Bachmann sound equipped. The rear locomotive, #17, is an MTH non sound with a digitrax DH165IP decoder. Both GP38-2s (not that that matters). I gave the consist ID 117.

When I ran the consist it was as if the rear #17 locomotive was not responding. The front locomotive #40, was dragging the rear locomotive. I thought I may have done something wrong so I cleared the consist and redid it. Same thing happened.

So I uncoupled the locomotives and ran the consist number. The front #40 started moving at speed step 1, but not the rear #17. The rear #17 didn't start moving until speed step 3 and then slowly. At speed step 3 the front #40 was moving ahead by quite a bit.

So run individually the speed matched nicely. In consist the #40 was moving out more quickly and gaining speed faster.

Neither one had been consisted before and the consist I set up with these 2 is the only consist I had.

I again cleared the consist and ran them individually on the same track and the speed match was good.

Any ideas what is going on?
 

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Ok no but I'm happy to guess. You've got two DC motors sharing the one track voltage and current. Because the motors are different, different draw etc. Because ho sound decoders use back EMF (bemf) to estimate motor rotations... And derive some speed... They aren't behaving the same. Of course mth in o sample motor speed using an ir mechanism and calculates scale speed. Maybe in ho since they own the patent anyway that's what they do. I don't own any mth ho engines and have never seen one apart.
 

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[You've got two DC motors sharing the one track voltage and current. Because the motors are different, different draw etc. Because ho sound decoders use back EMF (bemf) to estimate motor rotations... And derive some speed... They aren't behaving the same. /QUOTE]

Wouldn't that also be the case when I run the at the same time controlling each by it's individual address?
When I do that they speed match well.
 

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Ah. I didn't get that part. Well my guess then. Ok let's just say I'm dumb. You run them together but apart. They are ok. You hook them together...it's not so hot. It's the PID control then fighting each other.
 

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Car cruise control is a kind of pid controller.

In DCC decoders that implement it, and I think they all do in various ways... One can think about in various ways

For example if the engine is cruising at "10" and you stop it with your hand, and then let it go. It (should) quickly but smoothly resumes speed at 10.

Likewise one imagines something dragging it below 10 means it tries to compensate.

Given that one can imagine two engines linked together and their pidscontrol algorithms fighting each other.

Perhaps two sound decoders of the same make and model can be setup to work together more smoothly.

Well... It's a theory. I admit to never having tried it. But I do now have exactly two the same model by athearn. I could look in the hefty user guide to see what it says about consisting... If anything.
 

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Thank you brother
Boy sounds like an awful lot like what’s happening with me. What I don’t get is when I tether to the UR92 it works perfect.
very frustrating. Definitely gonna try another 4d
Veetz
 

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Just another random guess, but do either (or both) of your decoders have CVs to control the speed step in consist mode separately from the setting in individual mode? Since the rear loco is acting differently when consisted I would look at that one first, maybe there are some setting that only kick in when part of a consist? If that's true, getting them in sync may be as easy as matching the settings between consist and non-consist mode.
 

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Discussion Starter #10
Severn, great reference. Sure seems like advanced consisting can get a bit complicated.

Shdwdrgn - What you said sure seems to fit with what is in the reference Severn posted.
 

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Discussion Starter #11
The Bachmann sound locomotive uses cv 23 for consist acceleration and cv 24 for consist deceleration.

The decoder I put in the MTH is a non sound digitrax DH165PI. According to the Digitrax documentation, it looks like CVs 23 and 24 are not supported.
 
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