I have two identical ALCO RSD-15 mainline swtichers. (HO) If I run together,should the faster one be in front or does it make a difference?
Thanks
Harley,
Are you running them on DC or DCC?
Tom
DC
General rule of thumb is to run the faster one in front. That’s what the old timers tell me and having tried it both ways, faster in front seems smoother.
Lou
The force of each engine is unidirectional, so both drives should experience the same loading the same way regardless of which one is towing the other…both engines, if they run as well in either direction, should run the same way regardless of which is in front.
If engine A is in front, it pulls and the gear faces load on one side of them. When that engine is placed in the rear shoving the other, the same gear faces must develop the same load for the same voltage applied to the same motor. I don’t see how there could practically be a difference. With DCC and BEMF, yes, there could be problems with two different decoders, but in DC with the same drives, same voltage, either engine is going to be loading the same forward faces on its gearing.
Now that I think about it a bit more, you’d maybe want the faster motor in the rear. When the slow is towing, it would be forced to resist the faster motor, so there would be less force on the forward faces of the gearing, and there might be backlash…only on an engine that didn’t run as well backward. The trailing unit would still be front-loaded, so no change.
At least, that’s how I see it. Maybe I should stick to psychology…[%-)]
Crandell
Crandell, the theory is some what sound, but real world application has proven that two identical engines are almost never 100% identical. Though, admittedly a lot of the newer RTR and more expensive models seem to mesh much better than engines of 10+ years ago.
Almost certainly there will always be slight differences in gear quality (burs, run-out, etc), motor tolerance (for electrical and mechanical) between two identical engines and a myriad of other discrepancy’s that can cause one engine to run ever so slightly faster than the other one.
I grew up with the general rule of pulling the slower engine. Why? Well, think of it as taking up the slack in the cars of your train. Slack between cars will cause bucking and jerkiness. Same applies to the engines with slight running differences. If the faster one is pushing the slower, you have slack between the two; not good. Loading the gear faces (either the coast or drive side) is something to take into account, but assuming that the run characteristics should be the same between the two is lacking any consideration for the mechanical input to those gears from the characteristics of how the motor acts.
At high speeds (relatively, or say around 30smph) you probably won’t see the issue if the faster one is pushing the slower. It’s at crawl speeds where I’ve always seen the issue. Low speed is where you see the cogging effect of the motor, coupled with slight gear difference, causing the jerkiness of a slower engine in front. This is compounded by the fact that you have a slightly faster engine pushing from behind that is creating the change on what side of the gears are getting loaded, so the “slower” engine is accelerated for a brief moment by the other engine, then the gears mesh on the other side and it slows it. This contributes to the bucking/jerking problem. You would want to believe, as you theorize, that the f
I run DC and almost strictly steam, so when I double-head locos, I usually put the ‘faster’ of the two in front, let it ‘pull’ the slower one. Generally at a speed of about 25-30smph, the two locos seem to ‘even out’ pretty well, so there’s no real jerkiness.
I generally ‘test run’ double-headers to see which locos work best together, and then when I have an actual operating session, make sure to pair those PARTICULAR locos up. I have a fairly large steam roster, that also contains duplicates of the same wheel arrangement from the same manufacturer, so for instance, if I’m running a double-headed expedited heavy freight, I’ll choose two of my similar 4-8-2’s, which run in tandem well together without much ‘push-pull’.
If I’m running one of my articulateds as a road engine, I’ll usually choose a lighter loco either as forward helper or mid-train helper. Yes, it can be done on DC if you’re careful, and plan ahead, just like the prototype seemed to, LOL! I’ve even been able to hook up twot identical running 2-8-2’s as pushers on a long freight:
Tom [:D]
D94R wrote:Better gearing, material and/or quality control, and motors lately seem to help alleviate the issue that used to be inherent with products such as the Atheran BB models.
Actually I found the BB locomotives closer in speed then any brand even today I usually run 3 BB locomotives.
If you will note the GATX GP38-2 is a new RTR while the 2 C&HV units are 20 year old BB GP38-2s.
I too run DC and run lots of multi loco lashups with no problems.
3-4 diesel lashups with all units powered are the order of the day on most mainline trains. I never worry about “faster/slower” on units of the same brand and type - they all run fine together.
Like Tom I run lots of double headed steam, not always matched locos.
My Bachmann 2-6-6-2’s run just fine double headed with my Proto 2-8-8-2’s and the Bachmann 4-8-2’s run well with the Bachmann 2-8-4’s (which I have converted to 2-8-2’s). And both of those run fine with my Broadway 2-8-2’s (which no longer have sound or decoders, in fact they now have Bachmann tenders).
If they are close, I couple them up and go! Putting the faster loco in front does smooth out some of the less perfect matchups.
Sheldon
No doubt. I was using the BB models as personal experiences example vs higher end models from Stewart and Kato I had. You are right, most of the BB models ran just fine together, but a few had to be ran as second units depending on which other units I lashed them to. The few Stewart and Kato models I had didn’t have to be ran one way or another when together. Maybe my sample size wasn’t enough to encounter “problem” engines from the “better” models, or it does support the idea that “better” products aren’t usually as finicky… usually.
I believe Athearn uses the same gatio ratio in all their RTR BB locomotives as the former BB locos.I have mu’d a SW1500 with my BB GP38-2 with no difference in speed.
As a turn in events the upgraded SW1500 will not play well with my older BB SW1500 because the upgraded SW1500 runs much slower…
My SD38 won’t play well with my older BB locomotives but,will run with my new GP60s.
I am begining to wonder if I should remove the shells and take a peak at the motor in these units because none of them has the BB whine like the RTR GP38-2 s and GP40-2s I have.
This may be a silly question: Every time I try to MU two of my diesels, they either try to pull away from each other, or to push into each other. Orientation does not matter. Why is this?
Most of these attempts involve a Life-Like RI F40PH, a Tyco Santa Fe C430, and an unknown brand Conrail FA2. (All HO)
Actually very simple, one or more of them are wired “backwards”, that is to say that they are not all wired correctly to the motor. You will need to find out which ones are correct then take the odd unit and swap the leads on the motor.
Mark
Are these DCC or DC? If DCC, try switching off BEMF. If DC, it could be anything from cogging to dirty drives, worn gears, different gearing, sticky wheel bearings…
Like Tom and Sheldon, I also run doubleheaders and pushers using DC. I seldom worry about faster/slower, as most of my various locos run well together. I should note that multiple locos are usually used because they’re needed to move the train over the many grades, not simply for appearances sake. Even using locos with different pulling capabilities causes no problems, as long as the combined capabilities of the locos used are sufficient to move the train.
Problems can arise if one loco’s starting voltage is markedly higher than that of the others, though. On a doubleheader, the easy starter will drag, or attempt to drag, the entire train and the non-running slow starter, too, until the power is increased sufficiently to get things rolling. I have a couple of Moguls that respond in this manner - once underway and at track speed, they’re fairly closely matched.
However, using such a combination with either loco on the head end and the other as a pusher will usually result in disaster, and, as train length increases, so does the extent of the disaster. [banghead]
I have run relatively long trains (over 70 cars) using multiple locos both fore and aft - on my layout, different parts of the train are heading uphill and/or downhill, and/or are on curves in different directions all at the same time. It’s surprising how slack runs in or out in varying locations as such a train works its way around the room.
Wayne
Theoretically both locomotives should run evenly. By reading your post, I see that you have one that runs faster than the other. In this case I would suggest (and I practice this theory on my layout) you have the slower locomotive up front. Let the faster one haul the bulk of the train, and perhaps even slightly shove the slower unit. If you have any grades on your layout, then as the train enters the grade and gravity starts to act on the train, the slightly slower locomotive will be pulling against the drawbar and you will then have both locomotives pulling as even as possible. BTW, you don’t have to have any grades on the layout for the first locomotive to start working. If your train consist is more than one locomotive can pull, you will achieve the same effect as a layout with grades.
All of this gets to be fun when you want to doublehead with two or more different manufacturers and/or steam & diesel. That’s when advanced DCC would have an advantage.
In many cases, you’re correct, but, when I still owned lots of diesels, I often ran them (mostly re-motored Athearns) with my Bachmann and Athearn steamers in just about any combination: another reason why I chose to stay with DC. [swg]
Wayne
I run steam and diesel together on DC. True thay have to be somewhat close in speed/response but it does work fine.
And as previously noted, i run many different brands/wheel arrangemtns together with no problem.
Sure DCC will allow matching OR seperate control for double heading or pushers, but getting EVERY loco in a 120 loco fleet on the same speed curve would be a challenge. Much simpliar to just run together those that run together well.
Especially since in many/most cases, at least for my modeling period and loco choices, that seems to cover most all the logical matche ups anyway.
I spent my money on signals and CTC rather than DCC.
Sheldon
Sheldon;
I’m a DC man as well, and glad to be. I to, have better/other places to put my money. It took me a little while to find out who ran with who, and the results are just as satisfying. I want to enjoy the time I spend at the layout, not having to be concerned with all of the hassles of DCC. The more I learn about it, the less I like it.
I wasn’t going to add anything but I agree with DRWAYNE, for better than 50 years now I have been putting the slower engine on the front and let the faster engine absorb the lions share of the work which usually results in them running pretty evenly matched.
I also am in agreement about the DCC thing, my Dad and I built our own controllers back in the 1960s using “Variacs” which are infinitely smoother than any powerpack produced and not difficult at all to assemble. Total cost per unit is under $50 and control is very precise amd smooth.
Mark