Bogie springs and pin point bearings.

Because with your weighted unsprung bogie the entire weight is unsprung. If your bogie hits (for example) a misaligned rail-end standing say 0.5mm high then the force of the forward motion is going to send the bogie upwards in a parabolic arc until the upward energy is dissipated. At speed that height is going to be large in relation to the size of the sideways guiding part of the flange. With a light weight but sprung bogie, the unsprung weight will press against the spring and thence against the vastly greater mass of the locomotive. You can get an idea of the difference by alternately riding a sprung and an unsprung bicycle over potholes or curbs. Keeping the wheels on the rails and the flanges between the railheads is the important factor.

Agreed.

We are not limited in axle loading the way the prototype is. I don't know of any model loco with trucks or bogies where it is not possible to load the loco way beyond the tractive effort required. (excepting tender drive models )-:

The point is to create a loco that does not act like a puppy in the park, aiming in every direction other than the direction of the intended path. The second purpose is to gain additional current collection points.

Your effectively 0-4-0 locos will only have 3 wheels on the rails at any given moment, 2 on one rail and one on the other. That gives you just one (reliable) current collection point that all current must pass through, so you either run your trains much faster than I do or you have wobbly baseboards. My locos on the other hand have 3+3 contact points (4-4-0) on the rails at all times or at least 2 on any one rail.

My 0-4-0t has one rigid and one rocking axle so there are always two wheels on each rail.

0-6-0t has two rigid and one sprung rocking axle - again two wheels minimum on each rail. 2-4-0+3 axle tender has the leading truck collecting on one wheel to the frame, two rigid driving axles (3 wheels touching), the rear tender axle collects on one wheel on the same side as the leading truck axle and the free bogie ( a brass block) under the tender collects on the opposite side, so I have up to 4 wheels collecting on each side and a minimum of two per rail collecting. Only the driven wheels need wipers. The only flaw with the loco is that there is _too much_ weight on the drivers for the power of the motor.

Why not put the c.of g. in the middle of the wheelbase and get consistant current collection and tractive effort?

You just lost consistant current collection on that bogie!

Yes.

I spent many happy hours with a yard of track on a board finding the angles at which wagons would begin rolling and at what angle they would keep rolling, and then calculating those friction values :-)

Stiction is the greater friction value, but it is additional to rolling resistance. It is the reason that a load might be too great for a loco to start but that load will continue to be moved by the loco if it is got rolling.

The above is true but it only is a problem for higher than scale speeds and larger than normal track defects. You have forgoten that I have lots of models with no spring on the bogie. It is unecessary for H0 models at scale speeds on average trackwork.

The difference in direction control is unobservable in H0 scale. The track geometry is the main creator of poor ride.

I use compensation, sprung drivers or tenders for extra pick up when required.

My 0-6-0 is compensated.

If your compensated 0-4-0 works OK then there is no need for more than 2 wheels each side for reliable operation.

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The tractive effort is consistent and so is the pick up. There is no noticeable difference in performance compared to models with the centre of gravity on the centre distance of the driver wheel base. With some models it is impossible to get the centre of gravity where you suggest without resorting to a sprung bogie, which decreases tractive effort. Other solutions are a big job. Removing a spring and adding a little mass over the light driving axle is easy to do and gets the desired results, a model that runs well and pulls well.

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My experience is you don't need to use the bogie for current collection on most models. Only on tank engines with ridiged wheel bases is it necessary. The combination of tender wheels and driving wheels is enough pick up for reliable running unless your wheel material is a dirt collecting material such as brass.

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Terry Flynn

For HO scale track standards go to

includes details of HO wagon weight and locomotive tractive effort estimates

My scale speeds are up to about 45km/hr. (mainline goods)

I'm running wheels with up to 1mm slop between flanges and rail faces (NMRA/NEM standards) An 0-4-0 or 0-6-0 (with bogies) can and will crab horribly with that amount of clearance. Adding side control to the bogies stops the end of a 4-4-0 0r 4-6-0 from wandering freely as much as 6mm down to a more reasonable 1-2mm

Well, that's reasonably true, but I don't have the space for 100% prototypical yard turnouts nor the will to build a vastly simpler layout.

So why ignore using the bogies?

Sure, but my coarser wheel/track standards force me to try to avoid or limit wheel drop at turnout frog crossings. :-(

There's "OK" and then there's perfection! The 0-4-0 needs frequent wheel cleaning while the 2-4-0 rarely needs it.

Try pulling a heavy train with a 4-6-0 in reverse. If the Cof G is near the leading driver the loco will pick up it's rear driver under load and will derail very easily at any track inperfection.

As I said earlier, I've yet to come across any 3 driving axle loco where I can't get more weight in than I need.

ahh well, we're doing something differently somewhere. :-)

My clearances are often similar, and I don't see any difference. This is because of 2 things. The taper on the wheel tread will centre the model and secondly as soon as you have a train behind your locomotive the tension from the train negates any visual advantage of the side sprung bogie.

As discussed to death earlier, it decreases tractive effort to much.

That's why I use light oil on my track. I still have a 4-6-0 which only has pick up on the driving wheels (no springs or compensation). I use this model as a 'clean track tester. If it makes it around then the track is clean enough.

This has not happened yet with my 4-6-0's when pushing maximum length trains.

Try one with a opening smoke box door and tube plates modelled.

Probably the oil on the track is one difference.

I'll let that one go in the interests of continued good relations! ;-)

Let's assume a 4-6-0: If your (4)-6-0 centers itself statically then the first and last driving axles will sit centrally over the rails and that long overhang will sit on the extension of the tangent with the front buffers/front beam way across from being centered over the rails. On my 4-6-0 there will be 4 points (bogie center, D.A1, 2 and 3) in tension centering the loco. The tangent line through my loco passes between the bogie center and DA1 at one end and DA 3-4 at the rear. Because of that the front buffer beam displacement is only about 1/3rd of yours. This is a quite noticable effect.

Now, one assumes you place your drawbar mounting _behind_ the rear axle, so any tension at an angle is going to pull the rear wheel inwards which is matched by the buffer beam swinging outwards. This swing is stopped when the front wheel flange hits the outer railhead. The 0.5mm movement of the front DA amounts to around 1mm at the buffer beam and the rear axle movement of 0.5mm amounts to another 1mm movement. On straight track that is a total of 4mm front beam wander centered only by your two driving axles. Assuming my 4-6-0 has it's drawbar in the same position then the ratio of buffer beam to leading guiding point : rear guiding point is about 1:3 instead of your 1:1 so the free movement of the buffer beam is about 1.3mm (2.6mm both sides) That is a noticeable difference.

I tend to make my drawbars as long as possible and beyond the first rigid axles where possible, which lessens the racking effect and allows closer coupling of loco and tender.

Sure, we're on different tracks on this point - I find the improvement in current collection improves tractive effort. I'll agree that my locos probably haul considerably less than yours, but they haul all (proportionately) that my layout allows so my focus is on operational appearance (current collection) and scale speed. (s l o w)

Well, we're back on parallel tracks again - I use fluid pad wiping wagons to soften gunge, clean cloth pad wiping wagons and then oil pad wiping wagons in sequence and clean cloth wiping wagons in service. I found long ago that getting the rails absolutely clean improved running for about 15 minutes before it started to drop off again. Wiping the oil on the rail heads kept the running near optimum. I assume the drop off in performance was caused by oxidation of the nickel silver surface, but whatever the precise cause the oil solved it.

No, but it will happen _pulling_ in reverse, assuming the coupler is loco rather than bogie mounted. It might also happen with the 4-6-0 pushing in reverse, depending on the design of the loco/tender drawbar. The particular loco I had was a Liliput 4-6-0, built in the same mechanical form as your locos. Pulling in reverse at it's maximum TE, the rear driven axle (leading) has almost no load on it and is quite unstable.

OK :-)

Full length tubes? ;-)

No. More likely my 2.75m maximum train length. :-(

Regards, Greg.P.