Blind Drivers

[Wabash Willie]

I just received a new Mantua Pacific 4-6-2 and I have noticed it has blind drivers. The center set of drivers has no flanges. This allows the engine to use smaller radius curves. I had wanted to buy a Berkshire, but have not because I don't know whether it can do a 19" radius.
This is also done in 7 1/2" gauge with the bigger steamers. The Mogul I had would do 32ft radius with no problems. With any steamer there has to be enough side play in the axles and side rods. The side rods and valve rods probably not a problem with HO as they are not doing anything except going along for the ride.
Any body else have an engine with "blind Drivers" ?

Bill W.

 

[bnsf971]

I have an HO 2-10-4 with a blind center driver. I also had a Mantua 2-8-2 with two center driver sets blind. The 2-10-4 came with a flanged center driver, if I wanted to swap it. I did, and found the minimum radius went from 22" to 30", and 30" was tight.

 

[Selector]

The BLI Pennsy J1 2-10-4, their C&O T-1 2-10-4, and their Pennsy Duplex T1 4-4-4-4 all have blind drivers. It allows them to take curves in HO down to about 22", but only if they are well laid and truly 22". Some variance, some ripples, and you're on your own.

BTW, the BLI T1 Duplex only has four flanged drivers of eight, although they include the flanged replacements in the box, or did back in 2005. Even with half of its drivers blind, it can haul 5 Walthers Heavyweights up a 3.2% grade.

 

[kbkchooch]

My Mantua 2-8-2, and 4-6-2 have blind drivers, as well as my Bachmann 2-10-0 russian decapods have blind drivers, as well as Bowser 4-8-2 M1 mountains and Bowsers own decapod.
My 2-8-4 kanawah does not,, I guess its not a prevalent in brass.

 

[waltr]

I have a HO MDC 2-8-0 Old Timer with the blind center drivers. Some research showed that the prototype, ~1890, also have blind drivers. So this isn't only done on the models to run on tighter radius track.

Here is a PRR 2-8-0 photo showing blind center drivers.
http://en.wikipedia.org/wiki/PRR_H6

Another reference:
http://en.wikipedia.org/wiki/Driving_wheel
http://www.elmassian.com/trains/motive-power-mods-aamp-tips/aristo-motive-power/consolidation
http://www.flickr.com/photos/disneywizard/6030765747/

http://cs.trains.com/mrr/f/88/t/94904.aspx
http://www.trainorders.com/discussion/read.php?10,780355
http://www.trainorders.com/discussion/read.php?10,1165085

 

[trailrider]

Yes, there were prototype steam locomotives with blind drivers, though most were built in the 19th Century. IIRC, the Burlington had a 2-10-0 with the first set of drivers blind!

As far as HO scale models are concerned, Mantua's Mikado's and Pacifics are concerned, they have the center drivers blind, and will work okay on 18-inch radius curves, if the track is smoothly curved. (I generally have used Atlas sectional track.) With a little tweaking, especially around the inside of the cylinders, and some work on the trailing truck, you can also get them to run on 15-inch radius!

The Mantua Mikes and Pacifics can be the basis for bigger engines. I have kitbashed Mikados into 2-10-2's and 2-10-4's, as well as a 4-8-2, using Mike chasis and the forward frame of a Pacific. Several Pacific kits became a 4-8-4. All have the center drivers not only blind, but shimmed up by .010-.015" by placing a shim between the bottom of the brass bearings and the cover plate, with the end (flanged) drivers shimmed down with the same thickness of brass shim placed between the frame and the bearing bushing. Because the siderods on Mantua locos are hinged, like the prototype, they do not bind from the difference in the height of the drivers. This difference keeps the blind drivers from catching on the head of the rails as the engine comes out of a curve. These locos, too, will handle 18-inch radius curves, although some relief on the inside of the cylinders is required to permit the lead trucks to swing sufficiently. As my main lines have 20-in. curves (Shinohara sectional track), I have no trouble with these steamers derailing. (They have all been re-motored using the older 20mm dia. Canon coreless motors...no longer available...and Mellor gear boxes.) Someday, when I get flush, I may add DCC/sound decoders. For now, they run great on straight DC.

 

[DougC]

Wabash Willie:

Just to let you know for maybe in the future my Bachmann Berkshire (beautiful loco) goes around all my 19" radius curves just fine - and through all my Model Power 25-year-old turnouts too. And as I'm sure you know all the drivers are flanged.

DougC

 

[trailrider]

Wabash Willie:

Just to let you know for maybe in the future my Bachmann Berkshire (beautiful loco) goes around all my 19" radius curves just fine - and through all my Model Power 25-year-old turnouts too. And as I'm sure you know all the drivers are flanged.
DougC

If the center drivers have enough lateral play and the siderods will flex sideways, then it is certainly possible to negotiate tighter radius than would be the case if the frame permits only limited lateral motion. The prototype locos had some lateral play, though generally they didn't have to negotiate such tight curves as our models.

Basically, it's whatever works!

 

[Hergy]

Most HO Locos will take a sharper radius than its' prototype. Most large locos (prototype) could negotiate a 20 degree curve, which, if I remember correctly would scale out in HO to approx 44-46" radius. Somewhere in my junk I have the formula for converting curvature degrees to HO radius. Prototype always spec'd curvature in degrees. Oh yeah, I forgot to mention that I have a UP 4-12-2 that came with an extra blind driver. The real mcCoy did not utilize blind drivers.

Here you go. I just found the formula referenced above plus a lot of other good info on prototype curves. Get your slide rules out:

http://www.steamlocomotive.com/model/curve.shtml