# Rookie Question on running 2 DC locos together



## spacomp92653 (Jul 5, 2018)

Dumb question maybe but if I get 2 of the same N scale Kato F7A, DC only, and I want

to run them connected together, can they have the rear of each connected, with the

noses facing opposite directions? I have zero experience running 2 locos on a DC track.

Or am I better off buying one A unit and one B unit? What I do not know is on a typical oval

track where let's say the outer rail is positive, and inner rail is negative, do all locos placed

on the track all travel the same direction?


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## MichaelE (Mar 7, 2018)

"...do all locos placed on the track all travel the same direction?"

Yes.


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## spacomp92653 (Jul 5, 2018)

thank you.


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## DonR (Oct 18, 2012)

I understand that your question is...can I run a consist of 2 F7As back to back
on a DC track. Yes you can. When you set the rear loco on the track, backwards,
you are effectively reversing the polarity going to the motor...therefore...both
will go together in the same direction. One thing to consider...determine which
runs fastest at a set speed...that one should be the 'lead' loco.

Don


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## spacomp92653 (Jul 5, 2018)

fastest as lead, got it thanks!


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## 65446 (Sep 22, 2018)

That might be incorrect...Lead going faster could break the couplers between them..If faster one is in rear that can not happen, rear pushing the slower front..


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## DonR (Oct 18, 2012)

I agree, there are two sides to this question...all that pushing
could also lead to uncoupling...but it has been my experience
that when there is a mismatch, the trailing loco as the slowest
stayed coupled. I had 3 consists of this type and hever
had a problem.

Donj


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## Gramps (Feb 28, 2016)

FWIW, A few years ago this discussion came up in a G scale forum I was involved in and both points of view were discussed at length and there was no real conclusion.


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## mesenteria (Oct 29, 2015)

I can see both sides of this, but unless one has third rate couplers between them, it probably shouldn't matter a great deal. If neither engine scrubs its tires, thus prematurely wearing the sintering, or just filing a groove, and also prematurely wearing the rails you've spent a lot of time making look prototypical, everything else is relative; pushing or pulling, it's what the prototype does as well.


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## 65446 (Sep 22, 2018)

Here's the way I go about it in DCC, double-heading steam:
I prefer running each engine separately, not consisted/MUed in the throttle, same as 1:1 had/has to do..
What I do is this:
I toot the whistle on the second loco and begin rolling 1 MPH..This bunches the couplers..
Front/lead engine then begins to roll. Then by volleying back and forth I'll get rear engine's address up again and speed her up to again slacken the couplers.. Back to lead's address and speed her up to match rear....on and on until we're at speed on the main..
Then, to begin stopping, it's the opposite; lead slows a bit, rear then slows a bit, volleying until we're stopped..I go back and forth as if I'm two different engine crews.. This guarantees no knuckles are broken...
Whether or not the 1:1 scale did/does this I don't know..But when I had my last layout I really loved doing all that with steam,..at least 'thinking' the big guys do/did it that way...


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## 65446 (Sep 22, 2018)

*Sorry*. I nearly forgot the aim of the thread here...
So, for the *OPe*r, I merely am casting my vote you run slower loco in front...But as the others imply, there is no proof positive over this being an absolute...You must make up your own mind as how to go about it...
For fear of insulting your intelligence, in DCC this can be corrected with speed matching programming; making one loco's motor a different RPM for the same given speed step on the throttle; the 2 locos in 'consist' (well, sumpin' like dat)...


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## Gramps (Feb 28, 2016)

Is it a possibility that the two locos would speed match each other no matter which way they were coupled, the slower one decreasing the speed of the faster one and vice versa?


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## Jscullans (Jul 8, 2019)

Aaaaaaaaaaaaand Pandora’s box has opened! My opinion is I would put the faster in front but it really doesn’t matter if you have good couplers hahahaha


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## Old_Hobo (Feb 20, 2014)

I’ve always run the fastest one first, and have never had a problem with broken couplers….


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## mesenteria (Oct 29, 2015)

Gramps said:


> Is it a possibility that the two locos would speed match each other no matter which way they were coupled, the slower one decreasing the speed of the faster one and vice versa?


Yes. It would be somewhat deleterious for the drives and the sintered coverings of the drivers if the two mechanisms, or three, are widely disparate in terms of gearing. Say a PCM/BLI Y6b and an ATSF 4-8-4 (with its scale 80" drivers), but also from BLI. I know for a fact that the two gear towers are roughly equivalent, as are the motors, but the driver diameter disparity means the Y will want to move considerably slower at the same DC voltage as the Northern. It also being the much heavier locomotive, and with the geared mechanical advantage over the smaller drivers, it will tend to drag the Northern, or resist the Northern's inclination to move more quickly. It doesn't take much imagination to understand what will happen over the long term. 

Generally, the slower locomotive should be placed up front to get the couplers bunched some. This reduces stringlining on long consists of, say, coal hoppers as one sees in the video on youtube called Pillars of Smoke in the Sky. However, in those videos, the Y is often a helper at the bottom of the Blue Ridge and shoves, from the rear, a much faster Class A 2-6-6-4. In that real world, the Class A uses shorter cutoff and less throttle, and lets the Y produce most of the horsepower and tractive effort from the rear.


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## 65446 (Sep 22, 2018)

The first sentence of the second paragraph of replier in post #15 is what I said in posts #10 and #11; put slower loco in front to bunch (not stretch) the couplers between the two. 
It may not be an issue to begin with..But better to err on the side of caution...No ?


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## Gramps (Feb 28, 2016)

mesenteria said:


> Yes. It would be somewhat deleterious for the drives and the sintered coverings of the drivers if the two mechanisms, or three, are widely disparate in terms of gearing. Say a PCM/BLI Y6b and an ATSF 4-8-4 (with its scale 80" drivers), but also from BLI. I know for a fact that the two gear towers are roughly equivalent, as are the motors, but the driver diameter disparity means the Y will want to move considerably slower at the same DC voltage as the Northern. It also being the much heavier locomotive, and with the geared mechanical advantage over the smaller drivers, it will tend to drag the Northern, or resist the Northern's inclination to move more quickly. It doesn't take much imagination to understand what will happen over the long term.
> 
> Generally, the slower locomotive should be placed up front to get the couplers bunched some. This reduces stringlining on long consists of, say, coal hoppers as one sees in the video on youtube called Pillars of Smoke in the Sky. However, in those videos, the Y is often a helper at the bottom of the Blue Ridge and shoves, from the rear, a much faster Class A 2-6-6-4. In that real world, the Class A uses shorter cutoff and less throttle, and lets the Y produce most of the horsepower and tractive effort from the rear.


The OP was asking about F7 locos so my post was referring to diesel hookups.


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## 65446 (Sep 22, 2018)

*Gramps*
Yes, you are correct...
But I too told a tale (hee hee) about *my* steam control; how I do it as if 2 separate crews,..since 1:1 scale steam can't be MUed...(I.E. I purposely don't put steam in DCC 'consist' when double heading)...
The gist of it is only that my vote, whether it's steam/diesel/traction, the slower goes in front to prevent over tugging couplers with possibility to snap the knuckles between the two if lead were to roll faster.
Once again though, I accept there's no proof positive of this being an advantage..


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## Bonz85 (Sep 16, 2019)

I run HO dc and have found it works best to run the slower locomotive in the lead. There are a few reasons for this. If the faster loco is in the lead it is going to be pulling the second loco and tend to get a bit of wheel slip. If the faster loco is in the rear the weight of the cars slow it down to where it closer matches the speed of the slower loco. In my experience you can pull a few more cars when the slower loco is in the lead since you're not wasting as much energy since the faster loco isn't basically dragging the slower on. If you put the slower loco in the rear it's going to further increase the speed difference. 
 I have found this to be more critical when running 6 axle units. If I were to run the faster unit in the lead the rear truck would often times jump the track. I'm think the reason for this is since the lead loco wheels are going slightly faster the truck walks up the rail and derails. Any time this issue happened and I rotated the loco's the problem went away. I've tried it with multiple locos and always came to the same conclusion. 
The most stressed coupler should be the one between the rear loco and first car. However if the slower loco is in the rear I can see the couplers between the two locos being the most stressed. It certainly makes a difference on how many cars your pulling and the speed difference in the locos. But I can see several reasons to run the slower unit first and don't think there are any advantages to running the faster first in most situations.


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## Bonz85 (Sep 16, 2019)

I've already been long winded but had to add something. When I've ran locomotives with horn hook couplers the faster unit needed to be in the lead or they would usually come uncoupled. However with kadee there shouldn't be any issues no matter how you run them.


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