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Snubbers? B36-7

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Snubbers? B36-7
Posted by BigDaddy on Wednesday, November 13, 2019 6:54 AM

Rapido's latest video on the B36-7 says the factory put new many snubbers on the SP model to be prototypical.  I know what DCC snubbers are, but they must mean something else.

Henry

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Posted by rrinker on Wednesday, November 13, 2019 7:29 AM

 Effectively rubber bushings in the springing of the trucks to keep them from being too free moving. The truck needs to be able to flex to keep the wheels in contact, expecially on a locomotive since otherwise you lose tractive effort, but too much freedom of motion can make things sway and oscillate. Possibly with bad outcomes, like picking points or just climbing the outside rail.

 Patented, it seems, back in 1944: http://www.freepatentsonline.com/2389840.html

Electronically, a snubber does the same thing as a mechanical snubber on a spring. Dampens unwanted oscillations.

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Posted by BigDaddy on Wednesday, November 13, 2019 8:11 AM

Thanks Randy

Henry

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Posted by mvlandsw on Friday, November 15, 2019 11:16 PM

I think they are talking about the shock absorber type things on the ends of the axles.

Mark

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Posted by BigDaddy on Saturday, November 16, 2019 9:04 AM

mvlandsw
I think they are talking about the shock absorber type things on the ends of the axles.

I don't think it's ethical for me to take a screen shot of Jason's video, nor am I beating up on Rapido.  They are going to issue replacement side frames, so it's not even an issue for rivet counters.

If you look at this pic, there is indeed a shock absorber-snubber on the front axle but not the second.  

http://www.rrpicturearchives.net/showPicture.aspx?id=4503039

On the Rapido there is also one on the rear, below the brake cylinder(?)  That can be seen @4:55 in the video.

https://youtu.be/5NJ_DUtIbcg

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Posted by Overmod on Saturday, December 7, 2019 11:48 AM

BigDaddy
If you look at this pic, there is indeed a shock absorber-snubber on the front axle but not the second.  

This reminds me a bit about the construction joke about the nails with the heads on the 'wrong end'.  As with practice on the dash-2s, the 'missing' shock is on the other side of the locomotive; there's only one per axle but they 'alternate' sides.

GE floating-bolster trucks of that era used an almost astounding number of rubber pads at various angles in the truck construction, which function in the sense of 'rateless springs' to give compliance with little if any resonance.  This is different from damping with either friction or hydraulic means.

'Snubbing' on three-piece freight trucks, and GG1 electrics as built, refers to a very different thing: the use of spring nests with intentionally mismatched internal spring rates to 'break' any critical resonance in suspension - this is essential for any modern high-speed design of freight car and accounts for why the hydraulic damping on some of the '50s 3-piece designs, like Chrysler's, aren't seen in much practice.  Interestingly, the GG1 was judged not to need the additional spring complexity in service, and the arrangement was rather quickly removed (rather than allowed to continue in service) which indicates to me it had active problems, not just a lack of intended damping effectiveness.  (Personally I suspect the transverse effect of the quill drive arrangement from spider to wheel did any required snubbing quite effectively at any practical speed...). The prospective high-speed rebuild in the Seventies involved chevron primary springing (with much better rubber for the composite construction than Fabreeka had in the older days for pedestal tenders or N&W lead trucks) and hydraulic supplemental damping, but of course those were 'not proceeded with' in no small part because of the emergent tire-heating issue... but I digress.

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Posted by BMMECNYC on Monday, December 30, 2019 9:10 PM

A Snubber is a mechanical shock arrestor. 

 

Apparently the following description is different from a locomotive snubber:  They absorb movement by rotating an inertial mass, the mass has a big spring that tightens against a fixed shaft that also supports the axially moving shaft.  

Here is a company that makes big ones.

http://basicpsa.com/

Cutaway view:

http://basicpsa.com/products/psa-mechanical-snubber/cutaway-view/

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Posted by Overmod on Wednesday, January 1, 2020 7:00 AM

The PSA mechanical arrestors are worthless for any transportation application.  They are intended for things like piping runs, and lock solid on any movement (like seismic movement) but permit long-term accommodation of thermal expansion or other factors.  

A more appropriate technology is that in the BE series (hydraulic) from PSA, but again, these are designed for relatively long-period accommodation, which is not what any type of 'snubber' relevant to the OP does.

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Posted by BMMECNYC on Wednesday, January 1, 2020 11:54 AM

I was wondering if they were that much different.  I also wonder if the people complaining about the incorrect placement of snubbers on their models properly place models of snubbers on their piping runs?

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Posted by Overmod on Wednesday, January 1, 2020 10:34 PM

BMMECNYC
I also wonder if the people complaining about the incorrect placement of snubbers on their models properly place models of snubbers on their piping runs?

Probably not; I suspect that most layouts have a tremendous dearth of 'prototype detail' on their piping.  I know I'd have to do hours of research to be sure I had many of the details right; snubbing is just one part of the superdetail that would have to be provided.  (This begs the question of how many model railroaders would appreciate the accuracy of the work done ... I know I would greatly appreciate it if someone recounted in depth what the details were, and why the prototype involves them.

Too many snubbers on the Rapido models was just a kind of rookie mistake -- not that Jason & Co. are actual rookies, just not looking carefully at both sides of the prototype when assessing the model details for production, perhaps.

think there have been articles in MR about the use of hydraulic damping in postwar passenger-car trucks (together with rubber isolators in three-strut locating rods) and at least some discussion about more modern low-unsprung-mass truck designs.  There have been some discussions over on the Trains side about how damping and compliance are implemented on modern locomotive trucks -- some approaches, for example the original snubbing arrangement on the GG1, have actually been discussed in some detail.  With search disabled, these might as well be on the Moon unless someone remembers them firsthand and can locate references.

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Posted by Randy Stahl on Saturday, January 4, 2020 7:34 PM

many locomotives have both snubbers and dampners. The snubbers you can't easily see, the dampners are usually large shock absorbers. Without dampners a locomotive will not stop rocking once started especially on jointed rail.

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