EMD F7 in SCALE

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BigDumbDinosaur
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Re: EMD F7 in SCALE

Post by BigDumbDinosaur » Sat Nov 14, 2015 5:32 pm

Andrew Pugh wrote:EMD 645 locomotive diesel engine RPM vs throttle position:

Low idle: (I saw this figure posted in several places while searching for rpm by notch, of course now I can't find it...but will post it when I do)
Idle: 307
N1: 307
N2: 360
N3: 490
N4: 546
N5: 627
N6: 728
N7: 812
N8: 900

These may not jive with published technical specs (possibly contained in maintenance literature I could not access for free from the internet...), rather these were observed speeds noted during emissions testing of an SD40.

Not the nice even 75rpm steps for the 567 from 275 to 800.
It's been many years since I last read up on the turbocharged engines' detailed behavior. However, I seem to recall that the speed steps from notch to notch were around 85 RPM. If so, that would produce the theoretical progression:

Code: Select all

LI	185 (low idle)
 I	300 (normal idle)
 1	300
 2	385
 3	470
 4	555
 5	640
 6	725
 7	810
 8	895
[/size]
Variances in governor calibration could account for what you were seeing during the emissions test.

Also of note is that there is a substantial change in BHP moving from notches 6 to 7 to 8, due to the effects of the turbocharger coming out of "blower mode." That in itself doesn't affect governed RPM, but does matter when the combination of engine and load is considered.

In my F-unit, the governor increases engine RPM by 200 per notch. Hence:

Code: Select all

I	1000 (idle)
1	1000
2	1200
3	1400
4	1600
5	1800
6	2000
7	2200
8	2400
[/size]
The RPM change from notch 1 to notch 2 has relatively little effect on the unit's behavior, primarily because of the square law characteristic of the hydrodynamic coupling. This has led me to consider an alternative throttle sequence:

Code: Select all

I	1000 (idle)
1	1000
2	1300
3	1500
4	1700
5	1900
6	2100
7	2250
8	2400
[/size]
As the V-twin's torque curve peaks around 2400 RPM, the 150 RPM change from notch 6 to 7 and from 7 to 8 would have more effect than one might think. In that RPM range, the V-twin's torque curve is almost flat, which means that BHP increases almost in direct proportion to RPM. Also, in that range hydrodynamic coupling slippage is reduced to about 17 percent of what it is at the same loading at idle RPM, producing a substantial increase in power transmission efficiency. Hence the perceived effect of throttle changes is greater than at the lower power settings.
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BigDumbDinosaur
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EMD F7 in SCALE

Post by BigDumbDinosaur » Sun Nov 15, 2015 4:20 pm

EMD F7 in SCALE
————————————————
As my design work progressed I reached a point where I needed a more complete drawing of the F7, a view that included the body and its supporting structure. After expending a few (!) hours in the CAD program, I had a view that looked like a reasonable facsimile of an F7.
emd_f7.gif
EMD F7 Phantom View
Actually, the body outline you see is that of an F3—it came from a scanned image that I carefully sized to be as close as possible to the scale of the rest of the drawing.

A key element of my design is that of being able to open the body by hinging it on the rear of the frame. As the body is made up of sheet metal panels with little innate rigidity, it was necessary to devise a structure ("skeleton") to support the body and keep things from getting out of alignment. In some ways, this skeleton resembles the truss inside the real F7's body, but does not act as a structural member of the locomotive en toto.

Here is a drawing of the skeleton.
skeleton.gif
Body Skeleton
Key elements in the structure are the roof arches, which support the roof sheet and tie the two sides of the skeleton together.

Here are some pictures of the skeleton as I was jigging and welding it.
skeleton01_reduced.gif
Building Body Skeleton #1
In the above, one of the skeleton's sides has been jigged. Note the thick aluminum tooling plate used as the work surface.

The framework is fabricated from 1/2 inch × 1 inch rectangular tubing and 1/2 inch square tubing. The particular type of tubing I use for this sort of work is called "light structural grade," which has good rigidity with reasonable weight and cost.
body_skeleton_jigged01_reduced.gif
Skeleton Jigged for Welding
In the above, the skeleton has been jigged so the two sides can be joined with the roof support arches. When it comes to building up weldments like this one can never have too many C-clamps. :D I also keep an ample supply of thick extruded aluminum bars around for spreading out clamping forces and keeping things in alignment. Some Pony pipe clamps are also handy in drawing things together.
body_skeleton_partial_reduced.gif
Partially Completed Skeleton
The above is the skeleton with the arches welded in. The arches were laser-cut from 3/8 inch thick hot rolled steel. My original plan was to bandsaw them from stock, but I couldn't get access to a saw with enough moxie to do the job. The thickness of the arches gives them immense rigidity, which is essential to keeping things in alignment, as well as resisting bending forces due to opening the body. The holes in the arches' ends are there to accept 1/2 inch diameter thin-wall tubing, through which electrical wiring will be passed.

All that was left to add to the skeleton was the number two end bulkhead assembly, which I separately built up. More pictures will follow in the next post.
Last edited by BigDumbDinosaur on Wed Nov 18, 2015 4:10 am, edited 1 time in total.
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BigDumbDinosaur
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EMD F7 in SCALE

Post by BigDumbDinosaur » Sun Nov 15, 2015 4:29 pm

EMD F7 in SCALE
————————————————
Continuing from the above post...
no2_bulkhead_frame_reduced.gif
Number Two End Bulkhead Frame
Above is the number two end bulkhead frame, which is the attachment for the body's vestibule end bulkhead and diaphragm assembly. This frame also supports the rear of the body—the tabs on the bottom are bolted to rod ends on the frame, thus acting as a hinge. Here again, I used light structural grade tubing.
jigging_no2_frame.gif
Jigging No. 2 Bulkhead Frame
In the above, the partially-completed skeleton has been jigged to the number two end bulkhead frame. It was convenient to lay the frame flat on the jigging plate and stand the skeleton on end. Some patience was required to get everything nice and square for welding. You can see the "precision adjustment tool" laying on the jigging plate in the background. :lol:
finished_skeleton02_reduced.gif
Finished Skeleton
Above is a fireman's side view of the almost-completed skeleton. The wiring tubes have been inserted into the roof arches but have not been cut to size or welded in place. The tubing stock is 1/2 inch diameter DOM mild steel, such as would be used for medium pressure hydraulic applications. This stuff is cheap, easy to work and has a smooth bore, which means it won't damage wire insulation.
finished_skeleton05_reduced.gif
Finished Skeleton Viewed From No. 2 End
Above is a view of the number two end of the skeleton. The holes in the bulkhead frame are to mount the vestibule bulkhead and diaphragm assembly. This will be covered in future postings.
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EMD F7 in SCALE

Post by BigDumbDinosaur » Sat Nov 21, 2015 9:28 pm

EMD F7 in SCALE
————————————————
The full-size F7 was fitted with Blomberg "B" trucks, so-named after their designer, Martin Blomberg. This truck is characterized by a springing system that utilizes packs of leafs that support the locomotive's weight through hinged hangers attached to the truck frame. This design imparts good riding qualities and takes advantage of gravity to dampen lateral movement when the locomotive enters or exits a curve. The locomotive carbody is able to laterally shift relative to the truck bolster center to compensate for changes in direction or when encountering "wavy" track, with gravity causing the carbody to return to center after movement. The result is a reduction in the lateral forces applied to the track and a truck that behaves well at high speeds—consider that the F7 with passenger gearing was rated for a maximum speed of 102 MPH, and could safely operate at that speed on the typical bolted joint mainline track of the early 1950s.

The wheelsets are independently sprung within the one-piece cast truck frame, further improving the truck's ability to negotiate uneven track. The traction motors are supported on one side by a clevis that is cast into the truck's bolster beam, and on the other side by the gear-case, which in turn, is supported on the axle by some plain bearings. This arrangement allows the relationship between the traction motor and axle to be accurately maintained, while imparting plenty of allowance for movement.

As my unit was going to be hydrostatically propelled, using one traction motor per truck, the prototype design could not be exactly modeled. The plan was to rigidly support the traction motor from the underside of the truck bolster and couple the motor to the axles via an opposing roller chain drive. "Opposing" in this sense means that a separate chain transfers power from the motor to each axle, which causes the radial loads generated from chain tension to be largely cancelled out and not applied directly to the motor's PTO end bearing. The end result would be reduced bearing and seal wear. The traction motor mounting bracket would be made so that some lateral movement of the motor was possible to achieve proper chain slack.

The trucks were the first major assembly I acquired when I embarked on this project and were produced by a well-known builder. The cast steel side frames were originally a Tom Bee product (still available, I believe), as were the bearing boxes. As this project progressed and I got to a point where I could mount the frame to the trucks I encountered quality control and design problems in them that ultimately lead to a substantial rework.

The principle problem was that the traction motor was mounted too low relative the the railhead and that the traction motor mounting bracket could in some cases strike a rail when passing through turnouts and diamonds. After careful consideration of what I was dealing with, I concluded that reworking the bolsters would consume at least as much time as making new ones, so I scrapped the old bolsters and fired up the CAD program to make some drawings for a new bolster assembly. As long as I was doing that, I decided to figure out how to add brakes. Furthermore, I decided that the truck side frames should be made into a one piece affair like the prototype, so I designed cross beams like those of the real Blomberg truck, which are what supports the outboard brake shoe hangers.

Brakes were an interesting design problem. The real Blomberg truck utilized a clasp brake arrangement that would press the brake shoes to the wheel treads. That arrangement can be scaled down, of course, but doesn't produce a whole lot of braking force. Also, duplicating the Blomberg brake rigging would mean making a lot of fiddly little parts that would be prone to bending and breaking. So I decided to take a different approach and instead adapted small pneumatically-actuated industrial disc brake calipers operating against cut-down go-cart rotors, one brake assembly per truck. Each caliper is supported on a floating bracket that allows automatic alignment with the rotor as the pads wear, and compensates for truck frame roll relative to the wheelset. Below is a picture of a wheelset with brake.
wheelset_w_disc_reduced.gif
Wheelset w/Brake
The caliper is a Tol-O-Matic product and its mounting bracket was machined from a piece of 3/4 inch thick extruded 6061-T6 aluminum. The bracket rides on a plain bearing on the axle (note the grease fitting) and engages a pin on the bolster to act as a reaction point. Below is the bracket drawing.
caliper_bracket_reduced.gif
Caliper Mounting Bracket
After rework, I finally had what I thought was a pretty decent truck, although initial operating experience would soon highlight more issues related to the wheelsets. So I bolted the mess together and what you see below is the result.
truck_assy01_reduced.gif
End View of Blomber 'B' Truck
truck_detail01_reduced.gif
Vertical View of Blomberg 'B' Truck
At the time these photos were taken, my camera was slowly dying, which accounted some of the poor picture clarity (I've since broken down and obtained a new camera). Also, I was undergoing heavy chemotherapy at the time, which had the annoying tendency to give me the shakes. :(

The roller chain is ANSI 40 and runs on stock Browning sprockets with case-hardened teeth. Gearing between the traction motor and axles is 1:1. ANSI 40 is the smallest roller chain in terms of pitch that can safely handle the expected loads. It would have been nice to use ANSI 35, which is somewhat more tolerant of centerline variations between sprockets, plus less prone to chordal vibration, a phenomenon that can in some cases cause a lightly-loaded chain to jump teeth. However, calculations proved that continuous loading on ANSI 35 chain during a hard drag would be approximately one-half its rated tensile strength, which was not acceptable. With ANSI 40, the loading was reduced to about 20 percent of tensile strength, which although higher than recommended, was still well within acceptable limits.

The spacing between the side frames is such that the wheelsets are able to laterally float in the bearing boxes about 1/4 inch. This produces a relationship between the truck and track that is analogous to that produced by the lateral springing and damping in the full size truck. Without lateral float, track conditions would have to be pristine to avoid derailment at any speed above a crawl.

In the second photo (above), you can see how the brake caliper bracket engages the bolster—I used a stripper bolt for a removable pin. The two large braided hoses extending to the right are how the hydraulic plumbing is connected to the traction motor—they engage bulkhead fittings on the underside of the frame's "tub." The hose and fittings are -10 size to mitigate the pumping losses that hoses insert into the system. This is the only place in the propulsion system's high pressure circuit in which hose is used.
truck_bearing detail.gif
Truck to Carbody Support Detail
The above picture is of the bearings used to support the locomotive's weight on the truck. The truck is physically attached to the frame via the flange bearing that is centrally attached to the bolster. This bearing is a 1/2 inch, self-aligning, industrial unit that is bolted to the underside of the frame. I'm taking advantage of the fact that being a self-aligning unit, the bearing cartridge can swivel in any direction inside the housing without binding or otherwise impeding movement. Hence it acts like a heavy duty spherical rod end, minus the threaded shank.

During assembly, the flange bearing for each truck is bolted to the underside of the frame. After the frame has been lowered onto the truck, the bearing's hub is secured to the truck bolster beam with a 1/2 inch socket head capscrew that is inserted through a hole in the frame and into a tapping plug in the bolster. The capscrew is torqued to around 120 lb/ft—if it were to come loose and work its way out, the truck and frame would part company and there'd be one heck of a wreck. :shock:

The two small ball bearings—lateral roll bearings—on the truck bolster make contact with wear pads on the underside of the frame. The center bearing is shimmed relative to the bolster so that a very small amount of contact between the lateral roll bearings and the frame is maintained at all times. Hence the truck is free to swivel and longitudinally roll relative to the frame, but cannot laterally roll. Any lateral roll that occurs with the unit is due to movement of the wheelsets in the truck frame pedestals, which is resisted by the springs. The result is that the truck can easily follow abrupt changes in track height, such as might be encountered when moving the unit from a transfer table to a lead track, yet maintain good lateral stability.

Each truck assembly weighs approximately 90 pounds and is handled with a cherry picker and a 1/2 inch lifting eye that threads into the bolster's center bearing hole. Additional pictures will be in the next post.
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BigDumbDinosaur
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EMD F7 in SCALE

Post by BigDumbDinosaur » Sat Nov 21, 2015 10:04 pm

EMD F7 in SCALE
————————————————
As noted in the previous post, the truck's center bearing is bolted to the frame and the bearing's hub (inner race) is secured to the bolster. The below picture was taken after the rear truck was attached to the frame.
truck_mtg_reduced.gif
Truck Mounting
As can be seen, the socket head capscrew that secures the center bearing to the truck protrudes through the frame, necessary so it can be removed to detach the truck from the locomotive. The clearance hole was sized so that the capscrew's head could act as a stop and limit how far out of plane the truck could tilt if the unit was lifted off the track or derailed. The tilt angle is about 15 degrees either side of center, well in excess of what is required to negotiate exceptionally uneven track.

The below picture is of the truck-to-frame interface.
truck_frame_interface_reduced.gif
Truck-to-Frame Interface
In this picture, the relationship of the lateral roll bearing to the frame is visible. Note the wear pad, which can be replaced by cutting the small welds that secure it to the frame.

The next picture is a (somewhat blurry—I was again undergoing chemo when I took this) closeup of the truck frame pedestal and bearing box detail. The linkage for the brake shoes had yet to be made at the time.
truck_bearing_box_reduced.gif
Truck Frame Pedestal & Bearing Box Detail
As each wheelset is fully sprung, the truck is able to maintain relatively equalized loading on all wheels despite undulations in track profile, which helps to reduce wheel wear, as well as maintain good adhesion.
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Andrew Pugh
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Re: EMD F7 in SCALE

Post by Andrew Pugh » Tue Dec 01, 2015 2:32 am

Not sure how I missed the posts on the trucks BDD, they look great!

Still waiting patiently for more details on the drive and control system :mrgreen:

AP

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BigDumbDinosaur
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Re: EMD F7 in SCALE

Post by BigDumbDinosaur » Tue Dec 01, 2015 12:14 pm

Andrew Pugh wrote:Not sure how I missed the posts on the trucks BDD, they look great!

Still waiting patiently for more details on the drive and control system :mrgreen:

AP
I'll get there eventually. Been busy with non-railroad work. :)
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Andrew Pugh
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Re: EMD F7 in SCALE

Post by Andrew Pugh » Tue Dec 22, 2015 2:10 am

I'm still checking back periodically for your next post BDD. :)

AP

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Re: EMD F7 in SCALE

Post by BigDumbDinosaur » Thu Dec 24, 2015 2:21 pm

Andrew Pugh wrote:I'm still checking back periodically for your next post BDD. :)
I'll get to it eventually. Recovering from major eye surgery right now.
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chooch
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Re: EMD F7 in SCALE

Post by chooch » Thu Dec 24, 2015 9:06 pm

Well gosh Darn. Wishing you a speedy recovery and a Merry Christmas.
L D
BigDumbDinosaur wrote:
Andrew Pugh wrote:I'm still checking back periodically for your next post BDD. :)
I'll get to it eventually. Recovering from major eye surgery right now.

tomc
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Re: EMD F7 in SCALE

Post by tomc » Fri Dec 25, 2015 11:26 am

Me too as I enjoy your wordsmith and craftsmanship!

Tom C.
tom_at_srclry_com
Lost somewhere in Michigan!

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Re: EMD F7 in SCALE

Post by BigDumbDinosaur » Sat Dec 26, 2015 1:10 am

I'm hoping to get back on to this series in a couple of weeks. It'll depend on to what extent and how soon I regain full eyesight. The problem was a pretty serious one. :cry:

Meanwhile, here's are some pictures of what the loco looked like about a year ago. I've only been able to intermittently work on it since then.
EMD_F7_reduced.gif
EMD F7 in the Rough
EMD_F7_fs_reduced.gif
EMD F7 in the Rough
EMD_F7_frv_reduced.gif
EMD F7 in the Rough
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