Author Topic: Poor power pickup on Atlas RSD-4  (Read 5921 times)

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mmagliaro

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Re: Poor power pickup on Atlas RSD-4
« Reply #60 on: January 31, 2018, 09:41:03 PM »
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I spent some time tinkering on the RSD-4/5 my friend sent me today.

The long phosphor bronze contact strips that are pressed into the frame and ride on the little truck "thumbs" were one big problem with this one.  One of them was loose-fitting enough in the frame that even after pushing it back into the correct position, it would easily work its way out so that it could slide right off the truck thumb.  I was able to squeeze the little gap between the two frame parts where it presses in to correct this.

As for the diagonal wobbling...
I saw that on this engine too.  One thing I notice is that there is about zero side to side play allowed in the truck pivot in the frame.  Comparing this to a Kato F3 and Atlas/Kato RS-1, those engines have a little side-to-side slop and I think that is crucial.  The trucks on this RSD had fore/aft play, but not side to side.  This tends to lift a truck up on one corner when it goes around curves unless the track is 100% dead perfect.   I removed the trucks.  There are little plastic nubs near the center that bear on the frame.  I lightly sanded the tops of those, and then put the trucks back in.  You don't want to do this too much!  It can't be "sloppy".  It just has to have a little "breathing room" so the frame can rock on the trucks just a hair.

Finally, I loosened the frame halves (two screws), set the engine on the track, pressed gently but firmly so all wheels were seated, and then tightened the frame halves.  You need to do this on track, not on a flat surface.  You want the wheel treads to be the bearing surfaces, not the flanges.

All of this got the rocking to a minimum, and the pickup is excellent.

Having said all that, I'm still no fan of this engine.   There is really not much room to add weight in it, and the pulling power is terrible.   12 cars on a flat, but only 4 up a 1.7% grade!  I did manage to add 3g of tungsten, but did not help.
It weighs about 67g (70g with my added weight).  In contrast, my Atlas/Kato RS-1 can pull 12 over that grade with ease and it only weighs 56g.  So it's not all about weight.  I suspect the Kato wheels are made of a metal with a little more "grip".

Perhaps the RSD will do better after it runs a while and takes the "shine" off the new wheels. 

brokemoto

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Re: Poor power pickup on Atlas RSD-4
« Reply #61 on: February 01, 2018, 09:50:46 AM »
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Thank you for the word on the plastic nubs, Max.  While mine do not show the problems that Original Poster described Y-E-T, I will be sure to try your fix should mine show them.  I do not run mine much, any more.  In fact, I might  try to sell them on Fee Pay.

I suspect more the presence of the idler truck, which lowers the factor of adhesion, than I would the difference in the metal.  This is due to my experience with the RS-1 and RS-3, as well as the Kato RS-2 and RSC-2.  I find Atlas' B-1-1-B gearing arrangement curious, but  I am guessing that it was easier or cheaper to gear it in that manner rather than A-1-A, although there are plenty of A-1-A geared models out there.  In fact, I do wonder about the cost argument, since I recall paying the same for the Kato RS-2 as for the RSC-2, despite the RSC-2 model's being geared C-C (the prototype was, of course, A-1-A).  I did not pay list for any of the foregoing, so I do not know if the list prices between the four and six axle models were different.

My experience with the RSD-4 vs. either the RS-1 or RS-3 was not dissimilar from other posters to this topic.  The B-B geared models pulled better than did the
B-1-1-B geared model RSD-4.  One thing that I did note, though, was that when I ran a pair of Atlas RSD-4s, the pulling power difference between them and a pair of the B-B geared models was only one or two cars.  The paired B-B geared models did pull better, but only slightly. 

I had only one Atlas/Kato RSD-4, which did have the C-C geared trucks of the prototype.  I traded it away long past, so I never had the opportunity to try to put those trucks onto the Chinese frame.

The Kato RSC-2 does pull slightly better than does the RS-2.

As far as I know, Atlas has been silent on its reasons for gearing the model RSD-4 as it did.


mmagliaro

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Re: Poor power pickup on Atlas RSD-4
« Reply #62 on: February 01, 2018, 02:43:17 PM »
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If the idler wheel were not carrying much weight, it would not affect the pulling power.  If the truck is balanced right, it could mostly ride on the two geared axles, in which case, it should have just as much pull as if it were a 4-axle diesel.

But if you look at the trucks on this engine, the center column coming down from the frame land to the left of center on the cab end truck, which means the weight bears on the center axle and the IDLER axle.  The same is true on the long-hood truck. 

So I think you have a point about the idler axle, and it's even worse than if the weight were at least balanced over all 3 axles.  It's biased toward the "dead" axle on each truck.

While we're talking about the trucks, anyone else notice that this engine rides a mile in the air above the trucks?  What's up with that?  My RS-1 sits nice and low over the trucks.