DD1s? Why do the wheels have a driving rod in a electric loco?

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DD1s? Why do the wheels have a driving rod in a electric loco?
Posted by CandOforprogress2 on Friday, September 29, 2017 9:32 AM

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Posted by Firelock76 on Friday, September 29, 2017 3:36 PM

Back when those DD1's were built they hadn't figured out a way to put a powerful enough motor on the driver axles.  See where that connecting rod comes in at a 45 degree andle to the main rod?  It's connected to an electric motor up in the locomotive body.  Click on the picture to expand it and you'll see a counterbalance behind that connecting rod. 

The Virginian's jackshaft electrics were somewhat similar, however their electric motors were mounted on the frame.

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Posted by Overmod on Friday, September 29, 2017 3:39 PM

Quite a few early electrics were rod (and jack shaft) drive.  The DD1 is notable for employing it at precisely the time Westinghouse was looking at competing drives, including quill drive, for the 11kV  New Haven electrification.  There were several ‘odd D’ prototypes built for PRR to test competing drives.

A major issue then was that lateral force from heavy motors mounted low in truck frames caused bad riding and even track damage.  So  Unusual as this may seem, keeping the motors relatively high up, and using larger drive wheels, improved the track-following  characteristics profoundly.

Meanwhile, observe this picture of a pair of DD1 chassis:

The most efficient motors built for the desired hourly/instantaneous rating at that time were both very large and very heavy, and would not fit in the ‘gauge’ between drivers as some later motor designs would. To connect the motor to the tall drivers with gears would have involved expensive bearings, tooth metallurgy, lubrication, etc.   — when a simple counterweighted and quartered jackshaft and rods did the business as well as on any contemporary D-class 4-4-0.  Articulating two of these back to back gave a good ‘eight-coupled’ express locomotive.

An important issue with rods, though, is that while steam pressure is elastic, the inertia of a big rotating armature sure isn’t.  So suspension action or buff/draft can produce much damage (see the Kando drive for one version of dealing with this).

Those wretched ‘20s L5s retained the deflicted features but threw out most of the characteristics that made the DD1 so good.  

 

 

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Posted by erikem on Friday, September 29, 2017 11:48 PM

The big motor used in the DD1 had a large number of poles, with the benefit of the magnetic circuit in the motor doing a great job of supporting field control. Without field control, the DD1 would have had only two running speeds, i.e. half-speed and full speed.

One other advantage of the side rod drive was a much lower unsprung weight than would have been achieved with nose mounted traction motors, though not necessarily lower than a quill drive.

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Posted by rcdrye on Saturday, September 30, 2017 6:25 AM

Initially at least, the DD1s were maintained at shops that were also used to maintain steam locomotives.  The jackshaft drive was easy for such shop forces to maintain.  The DD1s' cabs were designed to lift off as in the photo, so swapping out the motor (which could be tended to elsewhere) was as complicated as running repairs got.  New Haven even got one jackshaft drive experimental before going all in on single and dual geared quill drives.  Contemporary New York Central engines (T- later S-motors) used gearless quill drives, with the the armatures surrounding the axles and the field coils mounted to the engine frame.

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Posted by Overmod on Saturday, September 30, 2017 9:58 AM

rcdrye
Contemporary New York Central engines (T- later S-motors) used gearless quill drives, with the the armatures surrounding the axles and the field coils mounted to the engine frame.

S came well before T; in fact upon that hangs an interesting tale.  As Wilgus designed the locomotives, they were 1-Do-1 with Batchelder (most definitely NOT ‘quill’) drive.  I have always thought there was some remaining ‘controversy’ over the use of high-speed Bissels on NYC from the LS&MS Prairies getting shut down arbitrarily; anyway there was a god-awful wreck on the second day of the electrified service, attributable at least in part to great overspeed, and the official NYC response was to pull the engines and shoehorn Adams pin-guided pony trucks into them to make them S-class ... without consulting Wilgus, who actually retired early in rage over the decision at the very moment of his greatest triumph ... it may speak volumes, though, that the resignation was quietly accepted.

rc, you might want to discuss the somewhat unusual truck arrangement on the T-motors, which accounts for the seemingly unusual truck spacing...

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Posted by CandOforprogress2 on Saturday, September 30, 2017 11:13 AM

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Posted by 54light15 on Saturday, September 30, 2017 12:20 PM

Side-rod electrics were common in Europe, especially Switzerland. I recall seeing the famous "crocodile" types in the 1970s when I was there. I have about 6 side rod electrics on my N scale layout set in the 1960s. Much as I love steam engines, watching the electric's pantographs sliding along the catenary on the layout is pretty cool I must admit. 

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Posted by erikem on Saturday, September 30, 2017 1:15 PM

rcdrye

Contemporary New York Central engines (T- later S-motors) used gearless quill drives, with the the armatures surrounding the axles and the field coils mounted to the engine frame.

 

The term used for the traction motors in the NYC T & S locomotives was "Bipolar" where the armature was rigidly attached to the axle and as you stated the field coils were mounted on the engine frame on the T's and truck frame on the S's. Also part of the engine/truck frame was magnetic circuit for the field coils.

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Posted by Overmod on Saturday, September 30, 2017 4:08 PM

erikem
... as you stated the field coils were mounted on the engine frame on the T's and truck frame on the S's.

We need some care here.  The Wilgus locomotives were built as class T (1-Do-1) and became S class when given the 2-axle pony trucks.  Most people know only the subsequent T-motors (Bo-Bo+Bo-Bo) which are the design with powered trucks.

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Posted by CandOforprogress2 on Monday, October 02, 2017 10:42 AM

How would this work in a Model DD2 Engine in O or HO scale? I suppose you could tie the electric moter to the Driving Wheel.

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