Swing Link Talk

This forum is dedicated to the Live Steam Hobbyist Community.

Moderators: Harold_V, WJH, cbrew

User avatar
ccvstmr
Posts: 1646
Joined: Sat Jan 04, 2003 10:37 am
Location: New Lenox, IL

Swing Link Talk

Post by ccvstmr » Sun Nov 06, 2016 9:13 am

Been having discussions with a few local hobbyists about proper swing link orientation. Shouldn't matter if the application is for a steam loco front end or swing bolster equipped rolling stock. Seems as though there are more opinions than possibilities. So, thought I'd turn to the board for additional comments, insight and explanation.

The following drwg was put together to help describe the different configurations:
swing link config.JPG
Three different configurations shown: 1) links parallel, 2) links angled in at the top, and 3) links angled in at the bottom. Dimensions are shown for reference only and to help show the pivot points and swing link movement. Based on the link motion shown in the diagram, the wheels set would be entering a left hand curve which results in the links and swing bolster moving to the right.

If the purpose of the swing links is to transfer load as the loco or car enters a curve, it seems the "links angled in at the top" is the proper orientation as the load is transferred (more) to the inside wheel(s) as the link straightens while preventing those wheels from lifting. Another benefit is the swing bolster elevates the the piece of equipment to pitch inward on that curve. The "links angled in at the bottom" does just the opposite...would reduce the load on the inside wheels and have a tendency to pitch the loco or car outward (not good). Parallel links...does not offer proper load transfer.

So, I put it to the board contributors to offer their opinions and experience. Thanking all in advance. Carl B.
Life is like a sewer...what you get out of it depends on what you put into it!
I don't walk on water...I just learned where some of the stepping stones are!
I love mankind...it's some of the people I can't stand!

User avatar
BigDumbDinosaur
Posts: 832
Joined: Tue Jun 28, 2011 9:19 pm
Location: Midwestern United States

Re: Swing Link Talk

Post by BigDumbDinosaur » Sun Nov 06, 2016 1:13 pm

ccvstmr wrote:If the purpose of the swing links is to transfer load as the loco or car enters a curve, it seems the "links angled in at the top" is the proper orientation as the load is transferred (more) to the inside wheel(s) as the link straightens while preventing those wheels from lifting.
Your supposition is correct, and what you describe follows typical automobile suspension geometry. In all cases, the intention is to make the centrifugal force acting outward on the locomotive or car to work against itself. A similar principle was used in the days of fully independent automobile front suspension to reduce the tendency for the front end of the car to nose down during braking. This so-called anti-dive feature is a byproduct of the unequal length A-arm suspension system that dominated in the days before the introduction of the (technically inferior but cheaper) MacPherson strut. The same principle is present in the rear suspension of rear wheel drive cars, except there it is called anti-squat.

Aside from maintaining stability in a curve, the lateral equalization effect of a negative trapezoidal linkage has a tendency to produce more even wheel wear on equipment running mostly in one direction on a circular track.
—————————————————————————————————
I'm an old guy. What's your excuse? ☻

User avatar
FLSTEAM
Posts: 1498
Joined: Sun Jan 05, 2003 10:55 am
Location: Central Florida
Contact:

Re: Swing Link Talk

Post by FLSTEAM » Sun Nov 06, 2016 1:53 pm

swing link.pdf
(10.18 KiB) Downloaded 206 times
Here is the pilot swing link I used on my Mogul. Copied from a full size engine.

Jb
http://www.ngshay.com/
Shay drawings and castings

jscarmozza
Posts: 312
Joined: Mon Mar 03, 2014 5:09 pm

Re: Swing Link Talk

Post by jscarmozza » Mon Nov 07, 2016 8:45 am

I'm building a 1" scale GG1, according to what I found on line regarding their trucks, they had a rocker system instead of links; so that's what I made. It seemed to work fine on a couple on trial runs made with the incomplete chassis, I since added lateral coil springs to dampen the motion, I haven't tried to run it with the springs so I'm not sure if that was a good idea. Originally I was going to copy the cardioid swing links used on my LE Atlantic, but they're difficult to machine and don't seem to swing freely. John

User avatar
Bill Shields
Posts: 5510
Joined: Fri Dec 21, 2007 4:57 am
Location: Somewhere in the World
Contact:

Re: Swing Link Talk

Post by Bill Shields » Mon Nov 07, 2016 5:53 pm

rockers do one thing very well...they fall out....

had rockers on my 3/4" Hudson for about 2 months...

1 month to realize they were a PITA
1 month to make captive roller replacements that have been in for 30 years.
Too many things going on to bother listing them.

jscarmozza
Posts: 312
Joined: Mon Mar 03, 2014 5:09 pm

Re: Swing Link Talk

Post by jscarmozza » Mon Nov 07, 2016 6:35 pm

I never had them fall out, but when I moved the chassis around or took the load off the trucks the rockers would flop around. I corrected the problem by adding a coil spring between the pivot plate and truck frame on each side. That kept the pivot plate centered and the rockers aligned in their seats, now I can handle the trucks without any problem. The rocker bottoms are hinged to the frame, the tops have seats in the bottom of the pivot plate and are connected to the plate and each other with a bar. The bar keeps the rockers parallel and has a slightly oversized slotted hole at the plate connection to facilitate freedom of movement. It works well.

jscarmozza
Posts: 312
Joined: Mon Mar 03, 2014 5:09 pm

Re: Swing Link Talk

Post by jscarmozza » Wed Nov 09, 2016 5:17 pm

I was looking at my rocker system today, it's a parallel system. I understand the benefits of the trapezoidal configuration and I'm looking at how I can modify the pivot plate to toe in the rockers at the tops. Thanks Carl and Dino for describing how a swing link is supposed to work. John

Smokey N Steamer
Posts: 49
Joined: Sun Jul 29, 2012 4:09 pm
Location: Seattle, WA

Re: Swing Link Talk

Post by Smokey N Steamer » Thu Nov 10, 2016 1:30 pm

Looking at photos of EMD's Blomberg truck, with its swing hangers angled at the bottom, is that a flawed design based on your study?

Image

I'm confused. By "angled at the bottom" are you referring to the middle or bottom row in your original illustration? Also, you describe the illustration as the truck is entering a left-hand curve, but the illustration says "on right curve." Can you clarify this?

User avatar
ccvstmr
Posts: 1646
Joined: Sat Jan 04, 2003 10:37 am
Location: New Lenox, IL

Re: Swing Link Talk

Post by ccvstmr » Thu Nov 10, 2016 9:41 pm

Well guys, 1st...thanks for the responses. 2nd...tried to find mention of swing links in other publications lurking around the library. Didn't find anything in my Kalmbach Car Builder's Cyclopedias. However, I found something in Mayers Locomotive Construction book. Several examples were illustrated. All but one showed the swing links angled in at the top. The only case described where the links were angled out at the top (similar to John B's example)...was for a single axle loco pilot truck that was equalized. Still, no explanation of the benefits of one configuration over another.

Smokey...the EMD Blomberg truck example is interesting. That too would behave similar to the bottom example in my initial drawing. Using the diagram of the Blomberg truck...and lets' assume we're facing front...as the loco nosed into a right hand curve...the bolster swings to the left. This (in my mind) shortens the vertical distance on the left side of the truck (as shown), but increases the vertical distance on the right side of the truck as that swing link approaches a true vertical orientation. To me...that's backwards as that would tend to pitch the loco body to the outside of the curve. Mind you...I realize that loco bolster is not moving much laterally. Still trying to understand why swing links would be configured differently (inclined inward vs inclined outward), and the benefits of each. Anybody else have ideas, examples, comments...other? Carl B.
Life is like a sewer...what you get out of it depends on what you put into it!
I don't walk on water...I just learned where some of the stepping stones are!
I love mankind...it's some of the people I can't stand!

User avatar
Steamin
Posts: 224
Joined: Wed Jan 22, 2003 9:56 pm
Location: St. Louis, MO, USA
Contact:

Re: Swing Link Talk

Post by Steamin » Fri Nov 11, 2016 1:15 pm

One conclusion from previous discussions was to make the links parallel. The parallel design imparts a vertical force as the truck moves under the frame, which is desired, whereas If you have a parallelogram design, it also imparts a tilting force onto the frame (undesired).

See link for discussion: http://www.chaski.org/homemachinist/vie ... 88#p295188

jscarmozza
Posts: 312
Joined: Mon Mar 03, 2014 5:09 pm

Re: Swing Link Talk

Post by jscarmozza » Fri Nov 11, 2016 6:35 pm

Well now that I have taken my trucks apart, should I leave them as a parallel system or adjust the rockers to tilt in at the tops? Is it possible that locomotive trucks function differently than car trucks, one staying flat and the other leaning into the curve? Just asking because I don't know. John

User avatar
Fender
Posts: 2720
Joined: Wed May 02, 2007 8:33 pm
Location: Chattanooga TN

Re: Swing Link Talk

Post by Fender » Fri Nov 11, 2016 10:21 pm

jscarmozza wrote:Well now that I have taken my trucks apart, should I leave them as a parallel system or adjust the rockers to tilt in at the tops? Is it possible that locomotive trucks function differently than car trucks, one staying flat and the other leaning into the curve? Just asking because I don't know. John
I would be cautious about making changes to an existing setup, if it works well now. A friend, who is building a pacific, took his loco to the track for the first time, and discovered that his angled links were causing the wheels on one side of the lead truck to lift off the rails, derailing the engine. He determined that the angles were causing the problem.
Another thing, does your truck have swing links, heart links, or rockers? The heart links have two pivot points at the top, and are generally parallel to each other. (heart links have a heart-shaped cutout at the top that hang from double pins, while swing links just have a single pin at the top and bottom).
Dan Watson

Post Reply