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  • Origin of "Roller Blades" truck design

  • Discussion of General Electric locomotive technology. Current official information can be found here: www.getransportation.com.
Discussion of General Electric locomotive technology. Current official information can be found here: www.getransportation.com.

Moderators: MEC407, AMTK84

 #584663  by Allen Hazen
 
Starting with the Dash-9 (introduced late 1993), many GE six-axle locomotives have used a truck dubbed "Roller Blade" style by railfans. (This is the NON-radial truck used on C44-9, ES44DC, and some but not all AC44 and ES44AC: for primary suspension each journal is flanked by a pair of prominent springs in a "Napoleon Hat" bracket.) I vaguely recall reading, when it was new, that the design was partly due to Krupp, the German manufacturer which has at times been a GE partner in the export locomotive market.

I just noticed a drawing "Jane's World Railways" 28th edition (1986-1987), page 121, of a double cab locomotive with an FDL-12 engine: caption doesn't identify the exact locomotive portrayed, but of the units with photos in the same article (a one-and-ahalf page Krupp entry in the "Manufacturers: locomotive and rolling stock" section of the book) it most resembles a UM22C for Botswana Railways: a 96 tonne (ca. 212,000 lb) unit built for 3'6" gauge.

The truck LOOKS very similar to the "Roller Blades" design: similar spring arrangement (and, like the "Roller Blades" truck, with all three traction motors on the same side of their axles).
 #607078  by Engineer Spike
 
I read something about the traction motors all facing the same direction. This is supposed to increase tractive effort. Spuuosedly the MLW/DOFOSCO truck did this too. They were thinking about using this, but the short wheelbase would concentrate too much weight in one place. I don't know if this is rumor or true.
 #607110  by Allen Hazen
 
Engineer Spike--
Yes, having the motors face the same way is supposed to improve traction: it reduces the degree to which motor torque alters the weight distribution. (On starting, the weight transfer can partially unload one axle, promotiv wheelslip.) The "Dofasco" truck (Dofasco was the foundry that cast the frames, but I don't think the design originated with their engineering staff or that they owned the patents) had this feature, as well as very short wheelbase. I have read that Canadian National urged MLW to improve its truck design, and may even have put some of its own money into the engineering studies that led to the Dofasco truck. (The weight concentration of the short wheelbase didn't bother them, apparently, and on a non-radial truck the axles will be closer to perpendifular to the rail going around a curve on a short whellbase truck than a long one.) Introduced on the C630M in (I think) 1968.

EMD saw the advantage of having the axles all face the same way and introduced a C-truck with this feature on the six-axle Dash-2 models in 1972. (The Dash-2 C truck is called the HTC: I think that stands for "High Traction C.")

GE stuck with the FB-3 truck through the 1970s and 1980s (for its domestic locomotive line: many GE export locomotives have what looks very mjuch like the Dofasco truck, often in narrow-gauge versions), evidently not believing that the advantage of the newer truck design was very great. In about 1990 they got to play with M630 locomotives being traded in by CN (and/orBCR) and fitted Dofasco trucks to the C40-8M (cowl carbody) units built for CN and BCR. Whether or not it was this experience that convinced them of the virtues of a truck with all the motors facing the same way, they adopted such a truck for the Dash-9 three years later.
 #622443  by trainiac
 
I have also noticed that a common theme of high-traction C trucks, aside from having the traction motors oriented in the same direction, is to have taller springs for the primary suspension. I believe that's why the GE Hi-Ad "Roller blade" truck has the springs below the level of the axle--because there is not enough room for taller springs within the truck sideframe above the wheel bearing. This would also be why the springs are supported at axle level on the GE radial-steering truck and the EMD HTCR. Taller springs were also incorporated into the earlier EMD HT-B and HT-C by using a notably taller truck casting than the Blomberg or Flexicoil. My understanding is that this maintains a more even axle load over rough track, reducing the likelihood that the axle in a "dip" will slip.
 #629003  by bogieman
 
It is correct that modern 3 axle trucks orient the motors to face the same direction to minimize the weight shifting between axles during high adhesion operation. A 3 axle truck such as the EMD SD Flexicoil or GE Floating Bolster suffer from significant weight shift caused in large part by their motor arrangements. At 25% adhesion, these earlier designs result in the lightest loaded axle being about 78% of it's static weight whereas on an HTC, HTCR, or Hi-Ad the lightest axle is about 92% of it's static weight with most of that weight shift due to the offset between the coupler height and the rail which shifts load from the lead to the trailing truck. If you study a free body diagram of an axle with traction motor you will see that the torque produced by the motor results in a reaction that pulls up or down on the motor nose suspension, which simultaneously causes the wheel load to increase or decrease by the same amount to balance the forces. The resultant wheel load is the sum of the load thru the coil springs of the primary suspension and the force at the motor nose. By positioning the motors on the same sides of the axles, the net force of the motor noses on the truck frame lifts or pulls down on the frame adding to or reducing the primary spring load depending on the direction of travel. Coupled with the moments created by the tractive effort in the horizontal direction and the means of transfer of that load to the underframe, the total of the forces causes the truck frame to lift or lower and pitch affecting the primary spring forces. With all motors on the same axle side, it is desired to prevent truck frame pitching to keep the spring loads equal accross the truck since the motor nose forces are equal and the same direction. That is why all Hi Adhesion 3 axle trucks have relative stiff secondary suspensions made of rubber compression pads - the desire to resist truck frame pitching. To get good ride quality and attempt to equalize wheel loads on rough track, the primary suspension is much softer than the secondary, hence tall coil springs. If you observe a 6-axle unit with high adhesion trucks starting a train generating 25%+ adhesion you can see one truck frame rise over an inch re the journal boxes while the other truck will squat a similar amount.

Re Dofasco, they did have a design department and produced many truck designs including the Hi-Ad used by MLW and the trucks for the LRC locomotive. The Hi-Ad design was purchased by Atchison Castings when Dofasco went bankrupt and is available today. The HTC truck at EMD was not the first truck there to feature the high adhesion characteristics. The export GLC truck first used in Angola in 1963 had that arrangement as did the export GHC. The GLC was for very light axle loads with the GHC for loads between the GLC and the HTC, which was first used in 1969 on the SD45X demonstrators before becoming standard on the -2 series.

Dave
 #630160  by DASH9DAD
 
Dave,

That is an excellent explanation of the "goings" on in a truck to turn the rotational forces into pulling forces.

One additional item worthy of mention in regard to your statement:

"Coupled with the moments created by the tractive effort in the horizontal direction and the means of transfer of that load to the underframe, the total of the forces causes the truck frame to lift or lower and pitch affecting the primary spring forces".

Both the EMD HTC and GE Hi Ad truck transfer the pulling forces from the truck to the underframe, platform in GE speak, through the center pin which is a round machined casting that only extends about 4 inches below the bottom of the platform. The GE platform/truck interface is through a traction pin that extends down into the truck frame to a much greater depth, to a point were it is close to being inline with the coupler. This decreases the moment arm you talk about, which in turn reduces the weight transfer.

I have a uploadable picture of this pin that some may find of interest.

Being a new contributor some quick pointers on how to do this, (I looked at the rules), I would appreciate any information on what is the best way to accomplish this would be.
 #630167  by MEC407
 
DASH9DAD wrote:Being a new contributor some quick pointers on how to do this, (I looked at the rules), I would appreciate any information on what is the best way to accomplish this would be.
To post a photo:

You will need a photo storage account at a site such as PhotoBucket -- http://www.photobucket.com/

Once you establish a free account there, you can upload your photos and they will be stored on the PhotoBucket site. After you've done that, PhotoBucket gives you several different ways to share your photos, such as Direct Link, HTML Code, and IMG Code. IMG Code is the one you would use here at RAILROAD.NET. All you have to do is copy the IMG Code for the particular photo you want to share, and then paste it into the message window.

Let me know if I can be of further assistance, and welcome to the forum! :-D
 #630776  by D.Carleton
 
First off, welcome aboard DASH9DAD; subject matter experts are always welcome.

Your above references to the longer traction pin were explained to me by a CN/IC mechanic. But he also added that, due to pin's length, it is not over the center axle. And, due to the off-center position, the trucks were experiencing severely unequal wheel wear leading to increased wheel lathe time. Would you know if this has been remedied?