Hi there. The one 3d artist who comes here with questions.
I have one question, again, with bogie wheels... with earlier 2-6-0 type engines, the pilot wheel was rigid on the frame. Did this wheel slide along its axle or no? If not, why is it that there is only one flangeless wheel and not two?
And if the
I am wondering because I'm making a more... unique engine that has combined feats of a ton of engines.
https://imgur.com/a/PSWWRAA (original 2-6-0)
https://imgur.com/a/h7uKrdv (unique 2-6-0 model)
The engines with one rigid 'pony' axle behind the cylinders were basically a solution made obsolete with the introduction of the Bissel truck (which you should study). It would be technically possible to use Cartazzi axleboxes to approximate the radial swing, but the force geometry and effects of lubrication and wear are not comparable to those for a trailing axle, and both the equalization of forces and proportional guiding are more difficult to arrange. Probably the correct thing to do in this case would be to use levers to implement a Krauss-Helmholtz 'bogie', but the effective wheelbase is short, the force on the levers high, and the effect of even a little slip in the pins (probably required to prevent binding on less than perfect track) severe.
A leading axle behind the cylinders suffers from polar-moment-of-inertia issues and does a piss-poor job of compensating for any non-overbalanced yaw (and, likely, roll, the two combining into 'hunting')
One of the 'jobs' that pilot axle(s) do is reduce flange and reaction forces on the lead driver axle. You could address this using the approach Stroudley took with his 0-4-4s, which certainly worked well when kept properly maintained; you could also address this with the 20/20 hindsight of now knowing how to use spherical rod-eye bushings and proper lateral-motion-control devices on that axle.
Nobody uses poleys (blind drivers) on a properly-designed six-coupled locomotive. If your curves are that sharp use something like radiating axles with a good lead truck and some method of steering the rear of the chassis (perhaps pushing the rear tender truck up to approximate a Jacobs-bogie position and using a spherical-section joint between engine and tender).
Personally the approach I'd look at for a better 2-6-0 would be to combine the chassis dynamics of the 'front 2/3rds' of something like Gresley's 2-6-2 (and treating the rear of the chassis as if it were an Atlantic modified along the lines of Chapelon's 4-8-0s) and then implementing three-axis guiding and equalization as N&W did on the A class. This should also, nonincidentally, set you up for the best boiler geometry for an engine of this size and configuration; you probably haven't gotten to weight distribution 'wet' yet, but when you do you'll start to see some of the advantages.
There is quite a lot of info here I havent seen before, including new types of axles and bogies! Buuut there are a handful of things I forgot to mention.
For starters, the unique 2-6-0 locomotive I'm modeling, that is an engine I'm trying to design. Aaand another thing to mention is... the leading pony wheel is ahead of the piston, which the pistons are inside connected. (The engine was heavily based off the Canadian 0-6-0 Scotia). I added a leading pint truck after seeing the "rigid 2-6-0" then realized they are just like a 0-8-0 in terms of rigidness. Which, due to the engine being inside connected, and how i'm trying to design the engine like an 1850-1860 engine, it might add some limitations to what I can do with axles...
Also, i couldnt find a mechanical description of the 0-4-4, how Stroudley designed them. ALSO, I never heard about spherical rod-eye bushings and lateral control devices. Are they all used on said 0-4-4s? Where could I find a good description for them?
The ''Bissel' truck only uses the radius bar to constrain swing geometry (in other words to keep the truck axle 'radial' to the line of the rigid wheelbase). There are formulae to pick the pivot and radius lengths. Since this bar has no buff or draft force it can be dropped far below the cylinders and motionwork; see some of the geometry in Klien-Lindner (not a typo) for more examples of implementing radial swing.
Equalization is more of a 'must' than English practice lets on, even on good permanent way. This is best imposed as the N&W A does it, with a single lever bearing directly above the center of the axle and, if you can manage it, swinging with the axle. (This lets the truck 'articulate' for cross level with proper weight bearing)
Centering is probably done best in your era with wedges and 'gravity assist' (the truck frame pushes slightly up on the locomotive frame and that weight is the restoring force). You can use small springs for on-center stability but be sure any small-period centering motion is well damped. Again look at some historical drawings of guiding arrangements for both these and Adams pin-guided trucks for mechanism and geometry.
A Cartazzi axle has both its pedestals and axlebox faces formed precisely as circumferences if desired radial swing of the axle, which is free to move laterally in the pedestal jaws, not 'technically' needing a radius bar. This arrangement was famously used for the trailing truck of a number of famous British engines; I believe Fryer indicated it could be made to work with a booster (which I wouldn't have predicted) but that the experiment did not lead to further adoption. It would be interesting to see if Franklin spring wedges could be adapted to work with the radial arrangement.
Most lateral in 'regular' drivers was accommodated with lateral play and slight additional clearance in rod bushings. The spherical rod eyes are to enable the use of roller rod bearings ( with tolerances that might be .002 or better) with lead-axle lateral motion (that is the essential axle for proportional lateral resistance).
The actual rod bearings were not pressed into the high-dynamic steel rods directly; there were very carefully shaped bronze bushings. These are where the spherically ground (to the circumference giving 'normal' rod angle side-to-side for the permitted lateral, about 2") and of course both the left and right rods went through the same angle as the driver pair did not pivot but only moved sideways. Ed posted a very good early article on these "100mph" Timken rods in one of the other threads very recently; download and keep it as it is one of the seminal resources for modern reciprocating locomotives.
Hmmmm alrighty. I actually do know of the bissel truck design (accidentally added that to my otherlocomotive model, the lincoln funeral locomotive with the short wheel base bogie.
And yeah, I decided to use a combination of the Cartazzi axle and the very early bissel design, with the angled plains helping center the bogie.
aaand with the rod bush bearings, i am a bit of a visual learner... I will have to look for the timken rods post you mentioned.
DevinCamaryI will have to look for the Timken rods post you mentioned.
Ed put the link in a recent post on the MR forum, and he will be happy to PM you a copy (he was the original source for my copy). I suspect he also has detailed drawings of the spherical 'system' (it includes specific discussion of the effective 'circumference' of the arc used) and the component parts.
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