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I agree with Lawrence. There is simply not enough mass on the drivers on most HOn3 2-8-0’s for the springs to have any effect!
There is another item that needs to be addressed with the driver springs on the second run of Key C-18’s.
The connecting rods were not articulated! They are one solid piece with four holes in them for the crank pins. In order for an equalized driver suspension system to be even marginally effective. The drivers all must have independent vertical movement and the connecting rods must be articulated so that they can follow their respective drivers up and down. Like the way the HOn3 PFM and Westside K-27’s we’re sprung.
Very few fully equalized models were ever commercially produced. Off of the top of my head only the On3 Kodoma K-27’s and the PSC Ma & Pa O scale 2-8-0 come to mind. It is interesting to note that neither of these models had driver springs! Just rocker arms and connecting legs.
I did away with the driver springs on my second run C-18’s too. I think the main thing that made this mechanism run so smoothly was not the springing at all. It was the twin independent sintered bronze bearings on each axle. They give the axles a smooth ride and have just enough horizontal and lateral play to handle any rotational oddities they may encounter in a wheel revolution.
Another negative thing that the springs did on these models is that they tended to torque the thin photo-etched frame members during disassembly and reassembly. Not a good thing at all.
By the way, these C-18’s were derived from the PBL Sn3 research information. Bill shared it with Dan.
Hi Mark. I think there's a world of difference between the two C-18 runs in terms of overall quality. The first run came about during Key's initial attempt to make a presence for itself among HOn3 modelers. Like the C-17 before it, the basic ideas were good, but the execution by the builder, Samsamoga (sp), was really not too impressive. Bill Peter over in Sn3 was also getting involved with the Sammy's at the time and made several critical comments about their performance on his Sn3 items. As we all know, Sammy embarked on a very serious period of course correction, and eventually became one of the premier builders. This was a very good thing for us and the second run C-18 locomotives reflect this evolution. Given the variability of handmade brass, even fabulous runs have some individual members that should have not gotten past quality control, but did. Comparing engine runs widely separated in time for various features requires a very large sample size to support any conclusions about which is superior from an engineering or QC point of view. Electric pick up may be a good point of comparison or not, depending on the number of other variables that influence pick up. Over the years I've really been amazed by the number of hidden gremlins that have to be checked out. The same thing applies today whether you are looking at recent Blackstone or the last few runs of PSC locos. I've got several examples of Blackstone C-19's and I can see variability in performance in spite of all the electronic devices now used to hone performance. Jim Vail's reviews of the various PSC runs revealed problems I've never seen and I've dealt with glitches he never mentioned. With steam locomotives I think we are looking at a piece of machinery that really can drive us nuts. The comment about physics I offered goes way back to the 1980's. The author of that piece was commenting on the premise that sprung drivers should improve tracking due to equalizing the loco's weight on rough track and allowing all drivers to maintain contact with the railhead. He pointed out why this works on a 25 ton locomotive but not so good on one that weighs in at less than a pound. I have never seen any visual evidence of equalized driver motion on any quality track from any locomotive with sprung drivers I have ever watched go by, and I have (or more accurately did have) a pretty good eye. It seems that if the springs are strong enough to support the loco in an upright level position, they are too strong for the light weight of the loco to allow the drivers to match the track contours. On the other extreme, if weak springs are substituted, the loco can't maintain an even keel as it's weight distribution changes. top heaviness comes into play and other disruptions in pulling power begin to appear. It's really a can of worms. As far as good results after doing modifications goes, you need to be careful in drawing conclusions because the simple act of loosening and removing the coverplate can provoke beneficial or detrimental changes in the relationships of parts that make up a rod driven drive train. Small changes in the torque used to retighten screws can influence how a driver interacts with its bearings and rods, leading to alterations in how the driver responds to minor differences in quartering or concentricity. Weak frames can be accidentally bent during handling. Years ago I was taught that a lot of scientific investigations are later found to be flawed simply because the design of the experiment didn't completely isolate the tested element's variables. Trying to isolate the performance of steam loco components is really a very difficult thing to do. Substition of stock springs with whimpy's can give smoother running, but it's hard to rule out other changes that can occur as the result of opening up a mechanism to work on it. Tuning brass is a very empirical activity and it helps to have a secret chant and a bonafied rabbit's foot on hand too. The fact that one loco has a sprung suspension and the other, poorer performing one doesn't could turn out to be a red herring. Good running to you.
I ---Original Message-----
From: Mark Kasprowicz <marowicz@...
Sent: Wed, May 13, 2020 10:36 am
Subject: Re: [HOn3] coreless motors again
I'm not sure I agree with the sentiment that springs do not make a difference in model locomotives because they lack the mass to make them effective. I have a number of these C-18's (those who know me will know why!) including the sprung version of the 318 as well as the unsprung one with the wrong tender. The difference in running between them is quite noticeable which I put down to better electrical pickup up. Many sprung locos have had the originals replaced with NWSL 'Wimpy' springs and I believe that makes for a smoother running model as well.
As for holding spring in place, I use a tiny amount of grease though I ws recently put onto Conductive grease which contains copper.