Has anyone experienced a situation with Atlas engines where they alternately surge forward quickly and then slow down abruptly continuously as they’re descending a grade?
I have 8 Atlas HO engines, both Atlas Master and Trainman, all with either NCE, Digitrax, or the Atlas Dual-Mode decoder installed, and they all show a very noticeable and unrealistic surge when descending my 2% grade when pulling even short trains of 8 to 12 cars. Coupling them together in consist doesn’t minimize the situation, it amplifies it.
This only occurs in Atlas engines, not Athearn RTR, Athearn Genesis, Athearn blue box, or Proto 2000. Right now I’m trying to consist other make engines with Atlas to cancel out the surge with moderate success.
Would this be a gear issue in the chassis, or a decoder problem? Any thoughts are appreciated. I’ve never seen this issue addressed in the product reviews of locomotives in MR.
Atlas engines have excessive play in the worm and other gears in the truck gear tower. If your train is pushing the engine down hill the slack in the gear runs in and out causing them to bind. Adding small washers on the worm shaft may help. Double heading causes the engines to push and pull making the problem worse. It is a mechanical problem not DCC.
I would see if decoders have BEMF and if it is turned on in the decoder. NCE decoders don’t have BEMF so that would not be the problem with a loco with an NCE decoder.
If BEMF is causing the problem it could be worse in a consist of multiple locos.
It has to do with the decoders more than likely. Atlas engines are IMHO (and years of experience) the best running diesels you’re going to find.
Back-EMF is kind of a “cruise control”, you set your engine going level at say 20 scale MPH and the decoder gives the motor more power going uphill or less going downhill so it’s still going 20 sMPH no matter what.
The problem is when you put two engines with BEMF together. One engine’s decoder senses it’s speeding up (because it’s going downhill) and slows the engine a little. The other engine picks up that the other engine’s slowing down and assumes the train is going uphill, so adds more power. Then the first engine feels even more speed (due to the other engine speeding up) and cuts power even more. The two end up doing a tug-of-war back and forth.
I’d see if the engines have Back-EMF, and how each runs on it’s own. If the trouble comes when they run together you can either turn the BEMF off in all but one engine in a consist, or to dial down the BEMF’s affect so it doesn’t buck with the other engines. (You can turn down the amount of compensation from 100% down to say 75% and see how that works.)
That all being said, I find Atlas engines run so well I don’t think I’ve ever put a decoder with BEMF in one. They don’t really need it from my experience.
I’ve been crucified before for suggesting this, but I’ll do it again … because it works (for me anyway) !
I tighten the side-frames on all my rolling stock so the wheels aren’t free rolling - just enough drag that they still turn easily, but not free roll. This way, my engines are PULLING the train both upgrade AND down. This has also added an additional benefit in the fact cars won’t inadvertantly uncouple over magnetic uncoupling ramps because they are always being pulled tightly.
Lastly, after fourteen years of operating this way, I’ve seen NO resulting premature wear to the side frames.
Interesting. After reading the initial post on this subject, I took count and of the just over 200 diesels on my layout, over 100 are Atlas of various age and models, and I DO NOT HAVE THIS PROBLEM. So I am unable to add any help or thoughts, I can only say of my diesel fleet, the Atlas and Kato units are the most dependable. I am assuming HO in this instance. I also use the decoders that came with the first Atlas (no problem) and Digitrax, TCS, Lenz and NCE decoders with the rest.
So I cannot add to a solution, only testify that for me, it is not a problem.