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[quote]QUOTE: Originally posted by Overmod FM, the classical definition I learned for 'hunting' many years ago was a coupled resultant of nosing (which is yaw) and rolling. I have since seen many people apply the term more to the observed yaw component and its effects, but it is helpful to recognize in some cases that 'pumping' from loading and unloading of the suspension can drive some of the oscillation. The ForeRunner and its ilk do tend to be difficult to induce because their effective polar moment of inertia is enormous and their primary suspension is usually very closely constrained to keep the axles normal to the chassis; to the extent that the axle can yaw relative to the carbody, it's mostly 'shear' force taken by the springs, and that ain't usually much imho. Now, you have a consequence with the longer rigid wheelbase, which is greater prospective wear (for a given equal axle loading) of the tread profile, greater incidence of flange contact on sharp curves, more possible racking on transitions or laterally uneven track, etc. There is no equalization between axles, so we're back in the 1820s again in that respect. IN PRINCIPLE, I favor the 1950s idea of using separate wheels, able to turn at independent rates on the same axle, as was done on some of the lightweight passenger train designs, for single-container, four-wheel cars. I did some preliminary work on single-axle Talgo-style articulated container sets, but haven't pursued that approach lately. I recognize the implicit problems with bearings, lube, maintenance, suspension when the independent-wheel approach is used, but it does eliminate some of the problems that would otherwise require full proportional radial steering ... difficult with 36' wheelbase! -- to deal with. [/quote] When you refer to allowing wheels to turn independent of the opposite wheel on the same axle, is that by using a differential gear? I thought I read something about that in a TRAINS article awhile back, something to the effect that separate turning rates would cause more flange on rail contact, I'll have to dig back when I find time. I may need to talk to you offline on this, but what is your opinion of a "half rigid" wheelbase wherein one end of the car is a true single axle truck and the other is connected to an articulated two axle truck? The only example I can think of is the Trough Train, where the end trucks were single axle. I think it may even be possible now to have a true articulation over a single axle truck, by using radial steering arms connected to each corresponding car body. This allows the articulated truck to turn freely with the curvature, and could be used in conjunction with the half rigid idea on both ends of a two platform car for a more ideal load factor for typical TOFC and single stack domestic container moves. Whether or not that would create more problems than it solves remains to be seen.
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