Rebuilt SD70MACH orders

C+C trucks seemed to work out on the Milwaukee Road F40Cs.

This made the Metra Facesomething Page:
Sharp looking locomotive...

512 running as a mid DPU NB through Cordele, GA:

Unlikely it was a DPU, more likely dead-in-tow.

Surprised no one has posted here, but EIS on the north side happened 11/29 and solo runs commenced 12/5.
https://www.youtube.com/watch?v=G_vpt_yFvr4
https://www.youtube.com/watch?v=oqH7RzlMXgY
https://www.youtube.com/watch?v=PI7yX7tATYY
https://www.youtube.com/watch?v=hbNoqWvz1ls
https://www.youtube.com/watch?v=4s0g9R3QX1c

Nice videos. Thanks. I'm not a big fan of hooded units pulling passenger trains, but it sure seems to step out quite lively. In my opinion, the livery is a step in the right direction.

Gilbert B Norman wrote: ↑Wed Oct 12, 2022 6:11 pm
The usual configuration for the non-powered idler axle for six wheel passenger engines' trucks is the center axle resulting in an A-1-A designation.

Wonder what prompted the change away from that traditional arrangement.

The FP-45. CMStP&P bought a few of them. The SD-70 fleet, like the FP-45, is C-C.

Also, non EMD passenger units with three axles were not necessarily A-1-A/A-1-A.

While A-1-A has been used around the world by EMD on E units and some exports, those were done with trucks that were designed from the rail up as A-1-A or were created from a C truck by removing the middle motor on the SD Flexicoil, as on the FP-45, or it's littler sibling the GC truck used on the SDL39's on the MILW and many EMD export locos. Those trucks have the end motors facing the truck center.

GE on their recent C4 units also removed the middle motor while adding a mechanism to take some of the weight, not all of it, off that axle when higher tractive effort is needed. They could not remove one of the end motors and have their weight shiffing mechanism work.

EMD first tackled the conversion of a three powered axle truck to a two powered axle truck with idler axle on the GT46PAC built for India in 2000 using a high traction (low weight shift) truck as a starting point. All EMD three axle trucks designed starting with the GLC then GHC then HTC truck have a low weight shift motor arrangement where all motors on are the same side of the axle within the truck. Combined with a relatively stiff rubber secondary suspension between the underframe (or bolster) and truck frame. This limits the flexibility of the truck in pitch which is why it allows relatively little weight shift under high tractive effort conditions. When faced with the decision of which motor to remove on the India GT46PAC, I advocated for the B-1 arrangement to preserve having one motor between each pair of adjacent axles, removing the motor that hangs from the inner end transom. For a two motor/three axle truck with the motors aligned on one side of the axle, analysis shows this arrangement yields the lowest weight shift under traction and braking. The same rational applied when the SD70ACe-P4 was later developed and applies to the METRA units since they were built with the same HTCR trucks.

On the SD70ACe-P4, the idler is purposely permanently carrying less weight, about 15Klbs less than the powered axles, to generate the highest tractive effort and make the locomotives perform similarly to the GE C4's without resorting to the patented clap-trap on the middle axle. I've been retired for a while now so I don't know if there is any biasing of static weight from the idler axles on the METRA units but suspect there is.

This has nothing to do with inverters but the P4 and the METRA units do have one inverter per axle.

Dave

FP45, SDP40/45, SDP40F and F40C models were all C-C. MILW's SDL39s were C-C as well, despite the lightweight truck design. Santa Fe converted one of the 1936 Super Chief B-B boxcabs by adding an idler axle to each truck, resulting in a 1B-1B configuration. From what I remember, the trucks were replaced at different times.

John_Perkowski wrote: ↑Tue Dec 12, 2023 2:17 pm The FP-45. CMStP&P bought a few of them. The SD-70 fleet, like the FP-45, is C-C.

There were six MILW FP-45's.

Colonel, you indeed located a rare photo of those engines; namely in color and on the lead of likely #105 or 6 "City of Portland". TRAINS had a photo as well of those engines leading, but it is B&W.

But as I've noted in the past they were not long in the lead. The truck hunting on MILW's "stellar" track, soon became an issue and they were restricted to trailing units.

They were not offered to Amtrak, converted for freight service, and reliveried accordingly.

Allouette wrote: ↑Fri Dec 15, 2023 1:13 pm FP45, SDP40/45, SDP40F and F40C models were all C-C. MILW's SDL39s were C-C as well, despite the lightweight truck design. Santa Fe converted one of the 1936 Super Chief B-B boxcabs by adding an idler axle to each truck, resulting in a 1B-1B configuration. From what I remember, the trucks were replaced at different times.

I did not intend in my first paragraph to indicate that the FP45 and SDL39 were A-1-A motor arrangement, merely saying they used the SD Flexicoil and GC trucks, respectively, which are not the same motor arrangement as the HTC and HTCR trucks. On those earlier trucks, A-1-A is the better arrangement if a motor is removed. Those trucks have a soft coil spring secondary suspension that allows for relative softness in truck pitch, which is the desired arrangement for best weight shift when the motors face inward symmetrically about the middle axle.

Dave

Has anymore of these SD70s been delivered to METRA recently? Last one one I heard coming was 512.

I understand the SD 70 MACHs are not B1+1B because some of the power from the prime mover that would have been for all six motors in a C+C unit was diverted for HEP. While Alaska Railroad's HEP-equipped units also draw power from the prime mover, that can be switched to allow all 6 axles to be used for tractive effort when in freight service. Since METRA doesn't run freight trains, there is no advantage for METRA to have the complexity of the power switching or the two extra motors.

RandallW wrote: ↑Sat Dec 16, 2023 6:04 am I understand the SD 70 MACHs are not B1+1B because some of the power from the prime mover that would have been for all six motors in a C+C unit was diverted for HEP. While Alaska Railroad's HEP-equipped units also draw power from the prime mover, that can be switched to allow all 6 axles to be used for tractive effort when in freight service. Since METRA doesn't run freight trains, there is no advantage for METRA to have the complexity of the power switching or the two extra motors.

The Alaska SD70MAC's have just two inverters, each powering three motors on a single truck. When HEP is required, the inverters supplying the motors in the rear truck are disconnected from those motors and redirected to a transformer that lowers the inverter output voltage to 480 VAC for the cars. These locomotives use Siemens GTO inverters. So when in HEP mode, the loco traction power is only available on the lead truck, which is sufficient for their operation.

On the METRA units, which use IBGT inverters supplied by Mitsubishi, there is one inverter for each of the 4 motors and a separate inverter for HEP, so all four motors are powered at all times with available traction HP reduced by whatever the HEP system draws.

Dave

I seem to recall six inverters on these beasts. One per powered axle, one for HEP and one as a hot spare.