# How do blind drivers work?



## Greg Elmassian (Jan 3, 2008)

Over on another forum, there is a heated debate on how blind drivers affect the pulling power of a model loco.

It brought some interesting points to light before several posts were deleted.

My friend, Ted Doskaris, posted some pictures showing how a 50 year old Lionel loco implemented a blind center driver, and illustrates the difference in tread width in this implementation.

Here's one of his pictures from the page on my web site:









Here is the URL for the entire page, showing the contact of the driver (or lack of) on the rails: Web Page on Lionel Adriatic with blind center driver[/b][/b] 
The intent of this topic (which may wander of course







) is to invite discussion on people's experiences with blind drivers on their locomotives.

Regards, Greg


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## Torby (Jan 2, 2008)

Nicely 

Often in models, not at all 'cause they're made smaller so they don't really touch the rail.


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## markoles (Jan 2, 2008)

I have/had three models with blind driver. Two are O gauge, one is G. The O gauge ones are a 1950s 2055 4-6-4 hudson. No problems, she's got magentraction. The other O gauge is a new MTH EP-5. Because it runs on tight curves, they made only 4 of the 6 wheels per power truck with flanges. It also has traction tires, so no problems. The third is a Bachman Big Hauler 4-6-0. Not much pulling power, but that'd be more attributable to the gearing not being all that great, rather than slipping due to loss of traction.

Frankly, until we see better, closer detail pictures, I think this is all pure speculation. What I can pull on my railroad will be a lot less than on most others, due to my grades. If a particular locomotive does not pull enough, I will add weight or decrease my train length. Not a really big deal. As I stated in the other thread, the blind wheels look wider than the flanged ones. It also looks like they are touching the rail head, but a real test should be simple enough. I think that in curves, yes, the flange will help increase the friction between the wheels and the rails. That can be a good and bad thing. If all wheels are flanged, that limits the minimum radius, a key factor in the marketing strategy of this particular locomotive. 

It doesn't really matter, since the flanged wheels are to be included, so I can change them out if I really want. Actually, I really hope that Aristo makes the main driver have the right size counterweight!!


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## Curmudgeon (Jan 11, 2008)

Interesting. 

Let's say you have 10 pounds of weight in the loco. 
Let's say it's a 4-6-0. 
IF you have center drivers blind and smaller diameter, the weight on 1 and 3 is 5 pounds if properly balanced. 

If you have all 6 drivers flanged and in sprung contact, the weight per axle is 3.333 pounds (if properly balanced). 

Which unit will have better tractive effort?


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## Havoc (Jan 2, 2008)

Both will have the same tractive effort...tractive effort is only related to the weight on the driven axles.


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## Snoq Pass (Jan 2, 2008)

Havoc,"Both will have the same tractive effort...tractive effort is only related to the weight on the driven axles." 

Soooo, since tractive effort is only related to weight on the driving axles, then doesn't that mean that the 4-6-0 with #2 axle blind and slightly off the rail thus have more tractive effort that a fully sprung, fully flanged 4-6-0? Since in TOC's post the 4-6-0 with #2 blind has 5lb traction with proper balance where as the 4-6-0 with full flange has 3.33lb traction with proper blance.


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## Curmudgeon (Jan 11, 2008)

Posted By Havoc on 10/07/2008 1:03 PM
Both will have the same tractive effort...tractive effort is only related to the weight on the driven axles. 

What did I just say?
The issue is there is LESS weight on each driver when all three make contact.

Granted, the entire weight is on the rails, and with rod locos, the power is transferred, but you have gained nothing.

You still have the weight, which has remained constant.

Now, two trucks, like oh, artics, logging, diseasemals, then you've got balance issues.

Even then, I recall my days in 2-rail "0", we balanced the engines on a balance beam, and since the available weight was centered, they out-pulled those locos that simply had weight thrown at them.

I do that with some large-scale locos, and get impressive results.

If all drivers will break loose at a specific load with 3.3 pounds per axle, what will it do with 5 pounds per axle?

Here's an interesting tidbit:

A Bachmann 4-4-0 will out-pull a Bachmann 2-6-0 Centennial, same motors, gears, driver diameter and weight.
Used to do it all the time until I retired both units.


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## toddalin (Jan 4, 2008)

My AristoCraft C-16s have both center axles blind. But, other than the flanges, the "tires" measure out the same diameter. They are a bit thicker in width at the tires. When the trains runs down the track, all tires _appear_ to touch the rails and they are electrically conductive.

Seems to me that no train goes perfectly straight down the rails even when going straight down the rails so there will always be times when the flanges touch. With no flange to touch, this bit of tractive effort is lost. And because the weight of the engine is not sitting on the sides of the flanges, touching, or not touching, does nothing to change the weight on the wheel loading.

BTW, the real C-16 also used the two center axles with blind flanges for the same reason, tighter diameters are possible.


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## Guest (Oct 7, 2008)

What a timly thread Greg, after seein Jim C.s K-4 an Martys layout last week i went and dug out the 2 i have left and lube them up to run tommarrow. i noticed that there was a center blind driver on these? never saw that before that might explain why the dont pull 10 heavyweights?also you can see by the video that the center drivers are pritty clean, no wear marks. the enigines only have a hours run time on them but never noticed the blind drivers before. talked to Cliff at AML couple months ago about pulling power he said these were designed for speed not power. i said i want to pull a decent train with them? so Cliff sent me free of charge some new motors that are geared way lower than whats in there now. he said it should pull great but i will loose a little top end speed with it but thats ok...also if you or Jim are watching, notice the center gear box moving around? does yours do that? bolth of mine do, not sure why?
Nick..


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## Snoq Pass (Jan 2, 2008)

Ach, blind drivers are not the problem with traction effort. Tractive effort is the force that a locomotive is capable of exerting, though its coupler, to pull a train. This is affected by the number of drivers and the weight of the locomotive. Tractive effort is NOT affected by blind drivers. Locomotives do not move by the friction of the flange to the rail. The flange should not even touch the rail. Yes, the flange does touch the rail, but it is due to the car sliding side to side. The tire of the locomotive is what moves the locomotive. The tire is the flat part of the wheel that makes direct contact to the rail. I should add that the tire is not completely flat (like what our G-Scale wheels are), infact the tire is tapered with the flange side being a wider diameter than the non-flange side. This taper is what keeps the locomotive, and rolling stock, on the rails. The flange is their for added safety.


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## pimanjc (Jan 2, 2008)

Nick,
The K-4 pulled nine of Marty's USAT UP streamliners without even breathing hard. I have the 19.5:1 geared motor installed. Like yours, it came with a 11:1 gear. Traction was not a problem at any time on Marty's layout. I have steeper grades and tighter curves on my layout than Marty. With the original gearing, the K-4 would slip the drivers pulling 14 freight cars. With the present gearing, it has no problems. The biggest difference is in startup. With the previous gear, sometimes the loco would pop the polyswitch on the throttle. With the new gear..... NO Problem. Whether I needed it or not, I added 1.5 lbs of additional weight to the boiler over the front driver.

The biggest problem I have encountered with the blind drivers is for the driver to drop on the inside of the rail if a curve/switch tighter than 8ft diameter is attempted. Exiting the curve, the driver then "pops" up and usually takes other drivers with it in derailing.










JimC.


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## Greg Elmassian (Jan 3, 2008)

Hey Nick you old troublemaker! Ha ha ha! 

Yes, blind driver, but all drivers are sprung and contact the rail well. I noticed the pulling power on mine was not what I had hoped. 

First, the stock gearing was way too high, 11.5 to one (the motor has an integral planetary gearbox) . Jim Carter got a 25:1 motor and he's happy. I got the 38:1 motor and now the loco will pull stumps. 

Also, you can add 3-5 pounds of lead into them easily, and it makes a **** of a lot of difference. 

See my site for what I have done to mine, there are several things you want to do. 

I believe that the major thing that worked against traction, besides the way too high gearing, was the stainless drivers are very smooth and slippery. Nothing to be done about that. 

See my pages: 
*[url]http://www.elmassian.com/trains-mainmenu-27/motive-power-mods-aamp-tips-mainmenu-35/aml--accucraft-mainmenu-242/k4-mainmenu-243* [/url]

There are 3 pages, see the menu on the left side... Be sure to visit at least the K4 misc info and tips...

I added 5 pounds of lead to mine, and with the lower gearing it works great. You really cannot add weight to the stock gearing, you will actually overheat the motor.

Regards, Greg


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## Guest (Oct 8, 2008)

Jim, Greg,
AAAA you guys left me hangin on this one, i didnt know about how much improvment there would be by changing out the motors? i have them so i will put it on the to do list, So tommarrow i guess my job will be to see if i can burn up the old motors and see how much they can pull?? he he he but i will also be bringin one of the new hudsons as well and i know that will pull stumps, should be a great run day. i have the new k-4 motors in my hand how do i tell whitch ones cliff sent me? all thou either should be a great improvement .... OK so now im goin to go some were and cry







cause you guys held out on me ... HE HE HE......
Nick..


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## Greg Elmassian (Jan 3, 2008)

Nick, the gear ratio should be on the label on the motor, take a look... if you can't find that, then send me the model number of the motor and we can look it up. 

Regards, Greg 

p.s. you should have read my site first!!!! All this info was there all the time... ha ha ha... just poking ya!


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## Torby (Jan 2, 2008)

Greg's favorite activity


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## Guest (Oct 8, 2008)

38.1 thanks Greg...








Nick..


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## pimanjc (Jan 2, 2008)

Nick,
When you decide to change the motor, after you take the old one out, go to the hardware store and replace the motor attachment screws with hex head bolts. *I guarantee that you won't regret it.* Of the three motors I had in the K4 while I was experimenting, two used ASA bolts/screws and one used metric screws. I would suggest a place like Ace Hardware or Lowes to find the correct replacement bolts.

JimC.


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## John J (Dec 29, 2007)

Posted By Curmudgeon on 10/07/2008 12:32 PM
Interesting. 

Let's say you have 10 pounds of weight in the loco. 
Let's say it's a 4-6-0. 
IF you have center drivers blind and smaller diameter, the weight on 1 and 3 is 5 pounds if properly balanced. 

If you have all 6 drivers flanged and in sprung contact, the weight per axle is 3.333 pounds (if properly balanced). 

Which unit will have better tractive effort?

I always hated "Story type" math problems. The always started out "Farmer Brown has six cows."


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## Torby (Jan 2, 2008)

Did you ever get to Physics? 

"Consider a spherical cow of uniform density..."


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## Mik (Jan 2, 2008)

The physics calculation that always baffled me was the problem where they PROVED that tire size and width makes absolutely NO difference in automotive handling... (except that in the real world it does... go figure)


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## Curmudgeon (Jan 11, 2008)

And, bumblebees (and 707's) can't fly.


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## Snoq Pass (Jan 2, 2008)

And flanges affect traction effort........


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## Greg Elmassian (Jan 3, 2008)

Posted By Curmudgeon on 10/07/2008 12:32 PM
Interesting. 

Let's say you have 10 pounds of weight in the loco. 
Let's say it's a 4-6-0. 
IF you have center drivers blind and smaller diameter, the weight on 1 and 3 is 5 pounds if properly balanced. 

If you have all 6 drivers flanged and in sprung contact, the weight per axle is 3.333 pounds (if properly balanced). 

Which unit will have better tractive effort? 
Given all other items equal, neither, the wheels with less weight will have less friction. Of course, it NEVER true that everthing else is equal, differences in the metal of the wheels (affects coefficient of static friction), weight balance, proper contact of all wheels to the rail... but in general the number of drivers has no effect on friction, i.e. tractive effort, given that our models typically have enough power to spin the wheels at any time. Regards, Greg


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## Snoq Pass (Jan 2, 2008)

"in general the number of drivers has no effect on friction" - Greg 

Yes it will. Traction effort is the amount of weight on the drivers. This means that if you have more drivers, there is less weight on the drivers. If there are less drivers, then there is more weight on the drivers. This is because the more drivers you have the more weight can be distributed, thus less weight per driver. 

The railroad I work for has an old (1889ish) steel through truss bridge. We have a huge mainline 2-8-0 that is cabable of going over the bridge, only because there are eight drivers, so that the weight of the locomotive can be distributed. In affect this lowers the weight of the locomotive.


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## Greg Elmassian (Jan 3, 2008)

Tractive effort, as long as there are effectively no limits on the power, is independent of the number of drivers... more drivers, less weight per driver. 

Think of it this way, suppose you have 4 wheels and 12 pounds... each driver gets 3 pounds each, times 4.... 2 drivers, each driver gets 6 pounds each... doesn't it just make intuitive sense that the drivers with 3 pounds each have only half the tractive effort? Whether it's intuitive or not, it's also a law of phyiscs and true. 

The tractive effort is not related to the distribution of the weight among other drivers, the load per driver, where more drivers spread out the same weight, the normal reason that locomotives had more drivers, to reduce the load per each wheel to avoid destroying rails, switches, and as in your example, bridges. 

The only thing wrong is when you say "yes it will"... friction is what I said, and you said tractive effort (basically the same, the max tractive effort is achieved just before driver slip) .... the number of drivers has nothing to do with it. 

Regards, Greg


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## Curmudgeon (Jan 11, 2008)

The problem is, real life. 
Maybe we could hold a seminar on it, you know, give it more validity. 

Cross level, coefficient of friction (now, how many real railroads do you know with stainless tyres and brass track?), cross-level, vertical curves, the whole shebang thrown in with 1:1 Mother Nature. 

Ever wonder why pregnant ant flanges won't work outdoors? 
Or, why you have to pull springs from journal boxes? 

How many real railroads try to pull 40-car trains at Warp Factor Two around 60' radius 1:1 curves on an 8% grade? 

You know what the best traction available is, right behind piXX poor cast pot metal drivers with the plating worn away on old aluminum track? 

Cast iron driver tyres on steel rail. 

Not just the prototype. 

"0" scale railroads used to do that. 
My ScaleCraft steamers all have cast iron tyres, still. 

I'm surprised you haven't dragged your buddy into this thread, Greg, to have him tell us all how the real trains ride on the fillet, and the tractive effort comes from flanges.....and that 14.5:1 gearing on a steamer is just right.


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## Snoq Pass (Jan 2, 2008)

What is phyiscs?







Phyiscs from my point of view is just a bunch of lab techs who have no knowledge of the outside world. I work for a railroad and I know which locomotives we have that will have good traction effort and which ones won't. And a common recurrence with the locomotives is the number of drivers it has.


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## Snoq Pass (Jan 2, 2008)

Okay, lets look at it this way. If you have a 100lb 4axle diesel like a GPunit, there will be 25lb per axle. Then if you have a 100lb 6axle diesel like a SD unit, there will be 16.66lb per axle. Now since traction effort, or friction or what ever the heck you call it, is the the amount of weight on the drivers, which unit will have more traction? The 4axle GP will. This is due to the fact that the weight of the locomotive has to go down due to gravity. This downward force goes through the axles, so the more axles you have, the less traction effort you will have. This is a very simple law of phyiscs. You should know that, since you seem to know sooooo much about phyiscs. Also this is very simple math, heck a three year could figure it out. 

How is them phyiscs for ya!!!!!!


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## DKRickman (Mar 25, 2008)

Oh boy... 

The amount of force needed to slide a brick across the floor depends on the weight of the brick and the coefficient of friction. Turn the brick on its edge, and the force changes by... wait for it... nothing! Even though the pounds per square inch went up, the number of square inches went down, cancelling each other out. 

The assertion that a GP has higher tractive effort than an SD for the same weight is absurd. Given EXACTLY the same weight (which doesn't happen in real life, but for the sake of argument...) they would have EXACTLY the same tractive effort. 

Think about it this way. A given locomotive has 8 drivers, and 8 lbs on the drivers, for 1 lb/driver. with a coefficent of friction of .25, that's .25 lbs of tractive effort per driver, or 2 lbs total. Now lift half the drivers off the rail, and let them hang in the air. There is still an 8 lb weight above them, do there's 8 lbs now on 4 drivers, or 2 lbs/driver. If the coefficient of friction hasn't changed, it's still .25, which means that each of the working drivers now has .5 lbs of tractive effort, or, amazingly enough, 2 lbs of tractive effort. You can re-ro the math any way you like, from 1 wheel to a million, and the numbers will ALWAYS come out the same. 

SO why have so many wheels? It doesn't "reduce the weight of the engine" - in fact it increases an engine's weight and driveline friction. What it does is reduce the weight PER AXLE. A 200 ton, 6 axle loco would crush 50lb rails. In order to allow it to traverse lighter, weaker track and bridges, the weight has to be spread out over more axles. 

So, in the model world, why bother with springs and equalization? A rigid chassis will pull just as well as a flexible one, given the same weight. What it won't do as well is stay on the track. For folks running track power, more wheels in contact with the rail means better continuity. For all of us, it means keeping the flanges beside the railhead, instead of above it. Also, and most importantly for tractive effort, when any one wheel hits a slick patch (a leaf, water, oil, etc.) it will slip. Using the above example, if you lose one wheel, you lose .25 lbs of tractive effort. with only 4 wheels in contact, you lose .5 lbs. 

To summarize: On clean, dry track, lifting a wheel makes absolutely no difference. The number of wheels makes no difference. The only things that matter are the total weight, and the coefficient of friction. Unless your model is so heavy that it can crush track or destroy its own bearings, axle loading also does not matter. The only cases where more wheels on the rail matter are in picking up electricity from the rails, and traversing dirty, slick track.


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## Snoq Pass (Jan 2, 2008)

Traction Effort is the adhesion between the driving wheels and the track depends on the *weight per wheel.* Bam!


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## DKRickman (Mar 25, 2008)

Posted By Snoq Pass on 10/10/2008 11:33 AM
Traction Effort is the adhesion between the driving wheels and the track depends on the *weight per wheel.* Bam! 



Ummm... and the number of wheels. You seem to forget that every wheel in contact with the rail is doing work, proportional to the weight on the axle. More wheels pulling means more pull. If you would try reading the post above, and follow the math, I'd be very curious to hear what fault you find with it. Of course, so would all the mechanical engineers and physicists in the world. It's pretty basic high school physics. The contact area is unimportant. Only the total weight and coefficient of friction determine the total drag or tractive effort. Thus, weight per axle doesn't matter. Since we cannot control the coeffient of friction (for a given loco/rail combination), the only factor of interest is the weight on the drivers. Not any one driver - all of them as a unit.


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## DKRickman (Mar 25, 2008)

Posted By Snoq Pass on 10/09/2008 9:37 PM
Phyiscs from my point of view is just a bunch of lab techs who have no knowledge of the outside world. 


I should have caught this earlier. Arguing with this viewpoint is like arguing with a brick wall - there's nothing intelligent that can be disgussed. But I'll try anyway, just for entertainment (I'm not sure whose).

Physics is DEFINED as the study of the "outside world." Without people sitting around studying how things really work in the outside world, we would all be sitting around a camp fire by a cave eating charred mammoth meat and grunting at each other. Do you think that someone in the "outside world" figured out that hydrocarbons polymerize and create a solid material from which things like wire insulation and model locomotive bodies can be made? Gaining a deeper understanding about the way the world works is what physics is about. It allows us to create new things and make a rational guess at what properties they will have, It also allows those of us with open minds and eyes to understand that what we observe is not always intuitive, but it is always rational.


By the way, be careful driving too far from home. Those guys in lab coats say you'll be fine and that the world is round, but don't you believe it! It drops off sharp at the county line!


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## DKRickman (Mar 25, 2008)

Posted By Mik on 10/09/2008 7:29 PM
The physics calculation that always baffled me was the problem where they PROVED that tire size and width makes absolutely NO difference in automotive handling... (except that in the real world it does... go figure)


And now, just for something fun... whoever proved that was wrong. If the tire were an inelastic material (like steel), they would be right, but elastic materials like rubber actually behave differently. They DO depend on contact area as well as pressure and coefficient of friction. That's why wider tires are put on high performance cars - to get more of the torque converted into traction.


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## Semper Vaporo (Jan 2, 2008)

What good would wider tires do on a locomotive on rails. The upper surface of the rail is ROUNDED so no matter how wide the tire, it would only touch the rail at a very small area! To make effective use of wider tires the rail would have to be wider and FLAT on the surface where the tire is in contact.


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## DKRickman (Mar 25, 2008)

Wider tires on the blind drivers were to help prevent the wheels from dropping off the rails on curves. They didn't do anything for traction. If you look at the page Greg linked to in the beginning of this thread, he's got some photos from underneath, showing how much the center wheel moves laterally, relative to the rails.


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## Snoq Pass (Jan 2, 2008)

What!!!! The world is round!!!!!









Also, Physics: "a science that deals with matter and energy and their interactions," websters
I do not see that is says the "outside" world, just that they study their interactions.....


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## up9018 (Jan 4, 2008)

Actually, Greg and Kenneth have it most right TRACTIVE EFFORT (not TRACTION EFFORT) was measured at the rear coupler, not at the rail. Since it is easier to get a train moving if it is already rolling, most locomotives were rated on STARTING TRACTIVE EFFORT, ie...the maximum amount of force the locomotive could produce from a dead stop. 

For normal 2-cylinder steam locomotives, the AAR produced a formula for calculating TRACTIVE EFFORT t = cPd2(squared)s / D 

t = TRACTIVE EFFORT; c = constant losses in pressure and friction (efficiency); P = boiler pressure; d = piston (bore) diameter; s = piston stroke; D = wheel diameter 

The AAR established the constant factor 'c' as 0.85 

Notice in the formula, the number of drives IS NOT a factor, the number of drivers merely distributes the locomotives weight, that's it. 

In real world locomotive design, BLIND drivers made equal contact with the rail as the flanged drivers did, and did and equal share of the work. The only reason for blind drivers were to help long wheelbase steam locomotives, such as 10 and 12 driver axle locos negotiate switches and yard trackage.


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## Curmudgeon (Jan 11, 2008)

Funny.
Let me copy the first line of the first post in this thread:
"Over on another forum, there is a heated debate on how blind drivers affect the pulling power of a model loco."

Not prototype locos, model locos.

Sorry, I addressed the issue of model railroads, my experiences and the results of testing (4-4-0 and 2-6-0), indicating in the real-world environment of 1:1 mother nature how our trains work.

BTW, the photo of the Lionel motor block shows incidental contact wear on center driver set.
Having been into Lionel for over 40 years, MOST of them you can see daylight between the driver and rail.


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## up9018 (Jan 4, 2008)

Funny, IF the MODEL locomotive is balance so all drivers make EQUAL CONTACT to the rail, it would affect the MODEL locomotive in the SAME WAY it would the PROTOTYPE locomotive. And the part about TRACTIVE EFFORT is only there to end the debate about how it was measured.


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## Snoq Pass (Jan 2, 2008)

WHY IS WITH THE CAPS????? MY EARS HURT FROM ALL OF THIS YELLING.


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## Havoc (Jan 2, 2008)

I should have caught this earlier. Arguing with this viewpoint is like arguing with a brick wall - there's nothing intelligent that can be disgussed.


You should have seen the writing on the wall indeed. It is so by design... 

On clean, dry track, lifting a wheel makes absolutely no difference.


That might be a good point to consider.


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