Can I run Atlas and Kato engines together?



Swap motors between 5 locos and test each one multiple times? Interesting perhaps, but impractical in terms of time.

You can't remove the worms from these gearboxes without breaking the locos down to individual pieces. Again impractical.

None of the locos have any spring tension on the trailing trucks: they rely on the weight of the trucks themselves to keep them on the track, and it works fine in that they never derail. The leading trucks *are* all spring loaded, but only enough to keep them on the track; I.E. less than 1 oz each: an inconsiderable percentage of the loco's total weight on the drivers. (Roughly 26 oz.)

Southern Pacific GS-Class steam locomotives were all large 4-8-4s, and carrying the factory weights these all balance right between the center two pairs of drivers. Right where you want the CG to be located. The Balboa GS-2 that was poured full of lead balances slightly forward of that, but not as far forward as the second pair of drivers, and not enough to cause the front springs to sag measurably.
While I could -and probably will- easily test each loco's tractive effort for comparison purposes, it's the large speed differential between mechanically identical units that interests me the most.
I'm wondering if I could get consistent speeds out of them by switching to modern can motors -which would mean I could run any of them together while double-heading- but since they all run just fine right now I hesitate to swap motors only to find that they *still* run at different speeds!
Pete
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"P. Roehling" wrote:

Ok, so pick the fastest and the slowest. That would show if motor differences were the entire problem.

It's obviously going to depend on how much you want to solve your problem or if you prefer the problem. Exchanging motors might well eliminate the need to explore further problems.

It was a suggestion.

Agreed. That is presuming you've tested the weight taken by the bogies to a reasonable degree. You can get a fair impression just by picking up the front of the bogie (with say a screwdriver) and seeing how firmly it snaps back to the rails.

Sure, I suggested a common problem - you've got it covered.

If you're certain that they don't have disperate gear ratios the problem is clearly either motors or mechanical resistance.

From others comments it's clear that the motors are quite variable in qualities. A good beefy Sagami (NWSL) in each should give you reasonably consistant operating speeds. They're not perfect but they should be close enough in performance to operate together.
I'm not in favour of coreless motors but I have had excellent results from Sagami and Mashima motors. If you're running analogue then add a big flywheel, DCC, no flywheel.
Regards, Greg.P.
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uh.edu says...

Those open frame motors were a mess. I wonder if the magnets varied a lot in strength, or it's friction of the drivetrains just pulling them down. Did they pull the same loads?
BDK
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Never tried to find out, but one of our club members has a very accurate machinist's gauge that measures pressure in grams and fractions thereof.
Might be rewarding to test all five 4-8-4s for comparative tractive effort and then compare their weights to see what sort of correlation exists.
Pete
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uh.edu says...

Just using a home brewed "scale" that probably was inaccurate, we found that the two pairs of FA-1's (slower and faster ones) had widely varying pulling power. The slower ones, identical except for speed, pulled better than the faster ones. Others seemed very close in pulling power, but speed was totally different. I had another Rapido loco, I don't remember what it was, with as far as I could tell, an identical mechanism as the Geeps had, was much slower. It pulled almost identically, but the Geeps were just insanely fast. In a "drag race" on the longest straight track run I had, the Geeps would run away from any other loco, until it was loaded to the point the wheels spun, or spun when the throttle was increased too quickly. Those two Geeps could get a big train, if you slowly worked the throttle, moving to an insane speed, where a derailment was a 100% certainty. I had big radius curves, especially the outer main, and the Geeps would "fly" if I wanted them too. I had a hunk of foam rubber to catch them before they went off the bench and hit the floor. I removed my garage that I had built there too, as the Geeps nearly destroyed it when they hit it one day when they decided to fly.
BDK
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snipped-for-privacy@but.us.chickens says...

The only time I actually noticed wheelspin is if I put my Rapido Geeps on the front of a train with some of my slowest locos behind them. They would spin at the start, but after the train was moving at a decent speed, they stopped, or at least I couldn't hear them. The Geeps couldn't pull worth a damn out of the box, but after I added every bit of weight I could jam into them, they pulled ok. But they still were insanely fast. Even without a train on them, just "goosing" the throttle broke the wheels loose until I added weight.
BDK
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It's pretty common actually. And when it isn't bad enough to get slip, sometimes you get annoying groaning sounds from the motors laboring.

In a slow vs. fast moving motor that's geared like most trains are, it may not be all that tiny, and there's not lots of friction to spare. Unless you have tires on drive wheels, slippage is definitely an issue.
I'm not sure how much you could do about it on a DC layout - maybe toss in some diodes in series with the faster motor to lower the voltage? On DCC, you can tinker with CV settings to harmonize engines run together, but it's a bit of a black art requiring a lot of experimenting. *
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pv+ snipped-for-privacy@pobox.com (PV) wrote in
*snip*

Adding diodes in might work, to a point. However, all the diode would do is change the starting voltage. Your speed curves would still be the same, so as you sped up the locomotives would start moving at different speeds.
Do most decoders do anything on DC regarding speed curves? I'm guessing not. (I haven't played with speed settings on my DCC locos yet.)
Puckdropper
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I have never tried it. Given that the decoders want a fixed voltage to operate, I'm guessing the decoder is bypassed when on a DC system. *
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The reason they run slower when all the locos are together is because you have more locos drawing power from your transformer, therefore reducing the effective current available to each one.
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Oh, sorry about not clarifying, I meant with more box cars. So if I have one engine running by itself (not pulling any cars) it goes faster than when pulling 30 cars. Does this mean the wheels are spinning a little or are they actually slowing down due to the pull load? Note, just one engine in this case. The only difference is the number of cars it's pulling.
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