I just came across images of these for the first time at that great photo site http://www.railpictures.net/.
What is the background to to these types of motive power? For what purposes are they made? Are they all converted from other locos? Are they restricted to yards? (I see some pictures of some on rail lines, but perhaps just being moved). What unusal features or control systems do they have?
‘SLUGS’ are switching diesels with just traction motors. Body is reduced. Weight is added. They get power from the lead locomotive, which means they’re permanently coupled.
General application is Hump Yard engine (pushing a longer string of cars ‘up the hill’).
To model, all that is needed is a cut down ‘dummy’.
Here is a nice conrail Slug lash up. Most stay in yards.
Tjsingle
One of the Indiana Regionals uses them in road service. There was an artcle in an RMC about making an RS3 into a road slug.
In addition to powering trains up humps, they were also useful in trying to make sure that the engines don’t go down the other side, and tear up the switches and retarders. SP had specailly designed ones called Brake Sleds, but I believe that slugs can do the same thing.
Sorry but the link did not take me to a specifc picture.
The CPR had slugs as early as January 1951. These (B-100 and B-101) where custom made by MLW for hump service with S-2 switchers.
Addressing the question of how they originated, I really don’t know - but here is one possible scenario.
Some railroad, somewhere, had a diesel switcher with a catastrophically failed prime mover. Rather than replace the diesel engine, they rigged that unit and another with power jumpers, then assigned the Siamese twins for use where there was a need for high tractive effort at walking speed. Once the concept proved workable, the wrecked prime mover and cab were removed and replaced with a simple housing and a concrete weight.
The traction motor blowers had to be retained, along with the headlight and class/marker lights on the end away from the mother unit. All else was surplus, and salvaged or scrapped as appropriate.
Then, like any good idea, it was copied and expanded on.
If anyone has a more authoritative answer, please post it.
Chuck (modeling Central Japan in September, 1964 - with diesel-hydraulics that can’t be ‘slugged’)
O:
Here’s why a slug works (Ed: And now I see SFRR already said this, but I expanded on it a little. 
).
A diesel-electric locomotive, put simply, is a constant power machine. Power is proportionate to force x speed. At low speeds, more pulling force can be produced from that constant power source. Theoretically, infinite force would be available at zero speed…
…but in reality, there are several limits, including:
-the traction of the wheels. This is determined by friction, and friction can be calculated by multiplying the loco weight by the coefficient of friction of steel on steel (something like 0.2, but very variable depending on conditions). In fact, while it doesn’t seem to make sense, the area in contact does not really matter - an SD80 would have just as much traction with four wheels, but the axleload would be huge. Heavy drag engines have lots of wheels, not because the greater area gives better traction, but because the greater weight gives better traction, and the many wheels allow it to be carried.
-the current-carrying capacity of the motors, which always dissipate some power, but will overheat if run above the blowers’ ability to carry off this excess power (as heat) for too long.
SO at low speeds, locomotives are capable of generating more power than they can use.
Slugs allow this power to be used by putting more loco weight on top the driving wheels, increasing potential tractive force. They also put more motors into the loop, so the engine output can be used by a larger number of motors at reasonable power levels in each motor.
At one time KCS had slugs for yard and road use. Most of the road units were converted F units. The yard units were mostly SW7’s and NW2’s.
I have a couple surplus rs-3 in the box of parts. Do you have that article from rmc for making that rs-3 slug
Two part article for a CNW RS unit. RMC Mar and April 08.
As mentioned, slugs can be for yard or road to increase tractive effort at low speeds. CR, SP and I believe N&W used chopped units for yard work. UP also uses older GE four axles for yard slugs in El Paso and Houston, but they aren’t chopped. CNW used an RS3 for road work. CSX uses Roadmates from GP30s/35s. St Lawrence and Atlantic also has Roadmates from GP38s/40s paired with GP40-3 mother units (a couple of which used to be GP40Xs). Both the CSX and SLR units have operational cabs, so the consist can be operated from either slug or mom. The mother units don’t have to be permanently coupled as mentioned above, but do have to be configured with cables to provide power to the slugs in addition to the standard MU connections. Road slugs provide some additional flexibility, offering extra tractive effort at low speed for high HP four axle units to start a train or climb a grade, but the fuel savings is there when they don’t need the extra unit.
Dan
While attending Teletype school in the 70’s I used to go to the Southern yards in Atlanta. Their hump swtichers were two SW1500’s with a chopped down RS? slug between. The slugs had a large speaker mounted on top broadcasting Southern RR radio traffic.
Always thought it would make a neat model.
Rob
Let’s do it!
(I think this may be the trio you mean.)
If you go back, I believe I first read about slugs or as the then SCL line wanted to call them MATE’s (M ? Additional Tractive Effort) in a railway trade magazine here in Australia circa 1971. They were intended to be road units of sorts as I recall and to my knowledge built from scratch rather than recycled road units which they now morph from.
Whether the SCL units were actually built new as road units or from recycled trucks and motors I cannot tell you… sorry I’m here and you are there…
Hope this is of help!
Regards from Down Under
Trevor www.xdford.digitalzones.com
CSX has road slugs (old GP30 and 35’s). They use them here between Hagerstown, Md and Gettysburg, Pa over the Cotoctin mountians. How are these rigged diferently from yard slugs since they run at over 25 MPH?
The Indiana Southern Railroad , uses an old RS-3 as a slug , but it is cabless . The article that was referred to from RMC is a different slug .
The one from Indiana Southern is sililar to ones built by the L&N RR.
I built one many years ago , but traded it to a friend years ago so I don’t have any photos , but it was an easy project .
I took an old AHM RS-2 and removed the cab and used some Styrene to fill in the hole where the cab was . I redid the hand rails and added grab irons and number boards . It was a fast fun project that I plan too try again some day .
If anybody that lives around Oshawa Ontario wants to see one up close go down to the Oshawa GM car plant. For the last couple weeks I’ve noticed CN has been doing some switching at the car plant with one. You may have to look around for it.
Otis, you got it. The Atlanta slugs had the speaker mounted on a triangular metal frame centered on the hood and about a foot or so above it.
Rob
I used to see road slugs on the SCL N. FL during the 70’s but never around Miami/Ft Lauderdale.
Rob