A couple of weeks ago my wife and I were out for a walk. A portion of the footpath we were on parallels a railroad track, and at one point we saw some kind of track maintenance machine. It wasn’t in use at that point, so I couldn’t see how it worked. It appeared to have a hoist at one end of it, and pneumatic tires for traveling over ground. It had two railroad-wheel axles (one axle at either end of the machine) that could be lowered hydraulically so that it could ride the rails.
So here’s the weird thing. On the outboard face of each railroad wheel, there was a longitudinally-grooved steel cylinder maybe 10 inches in diameter, 20 inches long. The grooves were deep, maybe 1 inch, but they weren’t sharp; these didn’t appear to be power transmission splines or cutting edges. There didn’t appear to be a bolt circle on the outboard end, so I’m guessing it doesn’t attach to anything.
It this a pic? (A few pictures down) I don’t have a clue, but maybe it helps in transitioning from a road to the tracks. At road crossings there can be pavement right up to the level of the tracks.
Oh, I know. The rail wheels have no drive mechanism, so in order to drive them with the road tires fully suspended off the ground those cylinders rotate into contact with the 4x4 tires and when you put the vehicle in reverse you go forward.
If that’s the case, both of those pictures allow the vehicles actual (rubber) driving wheels to propel the track (steel) wheels. When they put the steel wheels down, the truck lifts up off the ground and the splined part comes in contact with the tires.
I wonder if they have to put the truck in reverse to make it go forward?
I believe the alternative was for narrower wheel-based vehicles to drive the machine forward with the road tires on the tops of the rails with the rail wheels providing guidance.
But these are just retrofitted on regular road vehicles. My daily drive takes me down the length of some tracks for a few miles and I see all kinds of regular cars on tracks. You’d also have the problem of losing traction if the track was at all slippery (rain/grease). But looking online, it seems that some are set up that way.
Isn’t that how the contraption moves on the rails? When the railroad wheels are lowered, the grooved drums rub against the tires, rotating the railroad wheels, moving the vehicle forward?
You guys are all brilliant. From looking at the pics people have linked to, yes, it looks like that splined cylinder gets pressed up against the vehicle’s tires. That way you don’t need to have an independent drive mechanism integrated into the railroad axle(s). Makes it easy/cheap to retrofit an otherwise standard roadgoing (or off-highway) vehicle.
The truck in MonkeyMensch’s link would have a railroad axle on its back end identical to the railroad axle on its front end, so it wouldn’t need to be in 4WD mode.
But yes, it sure looks like it would need to be in reverse to go forward. Alternatively, you could just put it in “D” and plan on moving backwards at high speed. Steering isn’t a concern, since you’re guided by the rails, so it’s just a matter of watching out for obstacles on the track. The mirrors are probably adequate for that.
I would think the truck has them on front and rear wheels, so they engage the drive wheels at the back. Why the front engages? 1) Save utility on parts, make them the same, rather than separate front and rear sets. 2) The front ones engage the front wheels to allow use of the brakes on the front wheels to help when slowing down. 3) Engaging the front helps tie the steering so it doesn’t float.
Did anybody happen to click on the “Next” link at the bottom of that page of pics? There’s an anecdote on the next page about heavy equipment operators and tin-foil hats.
We have a couple of railroads through our town, have seen such trucks on the tracks (but with plain rail wheels) not moving very fast, so I guess the reverse gear would drive them O.K. If they wanted to make real time it would be no problem to switch to the highway.
