Looking at the picture below (not mine) makes me wonder:
http://www.flickr.com/photos/metra600/3435328094/in/set-72157605631165746/
Why did the trucks on these locos appear to have the 2 axles toward the ends of the trucks on these locos spaced closer together? A guess would have something to do with weight distribution. Obviously this isn’t happening on “modern” C trucked power. That leads me to deduce that any advantage(s) were minimal or it made things worse.
Any insight?
It has to do with the position of the traction motors. They face each other wide spacing and away from each other on the close spacing. The equalizer bars are sized so that there is equal loading on the axles.
All modern 3 axle trucks have the motors facing the same way in the truck frame. I can’t imagine a how you would have to wriggle between two motors to try and break the leads on that style of truck. The new ones are bad enough All EMD’s have had this style of arrangement. Not sure about old Toasters, but all the modern (dash 8’s and up) are this way too
Most early “C” truck locomotives had one motor reversed, it was only with the emphasis on increasing tractive effort that it was realized that having the torque of the motors in the same direction was beneficial. EMD Flexicoil trucks also were the same although less pronounced. With the introduction of the HTC truck EMD had all the traction motors facing the same direction.
Was the TM reversed to make maintenance easier?
No. Not really. It was to keep the package small and to keep the torque reaction force on the truck frame smaller. The smaller package allowed decent fuel tank size without having an overly long locomotive. The smaller torque reaction meant that the primary springs could be stiffer and the secondaries softer, which made for a better ride. Also, the center plate could be smaller.
So at some point someone, somewhere said “bigger is better” regarding loco size and made it work? Or was/is that a case of “to achieve a X hp/TE you need something of X size”? You also mention a better ride. I presume that’s versus locomotives “of the day” versus “modern” power, correct?
Actually, “bigger is cheaper” would be the saying…It’s a matter of evolution of locomotive design. To sell new locomotives, you have to reduce fleet size to get the savings to make it pay. So, as HP went up, TE had to keep pace. You can increase it by increasing the weight and/or increasing the adhesion. Doing the traction motor orientation thing was just one of the pieces of the puzzle.
So if “bigger is cheaper” would that explain the demise of the 4k HP “B” trucked motor?
The “C” truck center axle is offset to allow room for its traction motor, mounted ‘back-to-back’ with the traction motor on the axle farthest from it. On the early diesels, it’s the easiest way to differentiate between a three-motor “C” truck and an “A-1-A” truck, which has an idler center axle with no traction motor (such as that on an RSC-2 Alco locomotive).
M. Prater, Bailey, CO.
No if anything it would make the maintenance much much harder it would be very difficult to get the TM nose springs and the “dog bone” much much harder to get in position. As is stated earlier; the only possible upside would be to allow for a shorter truck.
Sort of. The killer of the GP60s, B40s, was a combination of things. The C version could do everything the B could do and have a greater range between fueling, so it was easier to manage the fleet. The cost was relatively small - a little bit of fuel for lugging around the extra weight and a little bit more motor maintenance.
Two other reasons of note.
Great info Nick. Any idea what the HP/axle “limit” you mentioned for AC is?
The limit for AC traction is about 1,000 HP per axle. But North American companies seem to have settled on 730 HP/axle for both their DC and AC units.
Nick
Those new ‘experimental’ BNSF AC locomotives with the A-1-A trucks - I believe they are 4,400 HP on 4 axles, for 1,100 HP per axle. But they are ‘one-of’s’ - otherwise, Nick’s figures are about right - unless you consider the AEM-7 electric types with 7,000 HP on B-B trucks = 1,750 HP per axle, with only about 50,500 lbs., even.