2T or 3T Shay?

[TBat55]

Is there a big difference in minimum radius or grade between a 2-truck Shay and a 3-truck Shay? Which handles tight curves better, and which handles steep grades better?

I have a steep 4% grade with 18" curves. I'm guessing the 3-truck would be better at pulling upgrade, but may not handle tight curves as well as a 2-truck.

[Anonymous]

I don't know the answer, but do know that when using a "T" in reference to a Shay or other steamer it refers to its weight in Tons. Thus your question could lead some to think of a "2 Ton or 3 Ton Shay".

Bob Boudreau

[tigerstripe]

This isn't your question but 18" is huge for a Shay. 4% is acceptable.
The Spectrum 3 truck Shay is a great runner with beautiful detailing. Very good slow speed operation.
I have heard many horror stories about the Roundhouse 2 truck kit version, but I think the RTR is OK.

[nedthomas]

Test the engine you wi***o operate. Run it both directions over the radius you wi***o use. Due to the U-joint and coupling between the tender and engine of three truck shays it is hard to make a general statement about them. The shaft on the U-joint must be long enough to make a sharp left turn but this may prevent sharp right hand turns. I have found it best to make one end of the drawbar between the units solid so the tender tracks like a trailer and is not free to move both ways.
Also on heavy grades and loads the front truck will tend to lift up due to the torque on the drive shaft.

[ARTHILL]

I have a brass 3 truck shay that will do 18 inches and 7%, but it does not like 15 in curves. I took the drive line off the third truck and it does the curves but lost traction. I think that some modifications would help but I have not gotten to them yet.
The big issue for me is looks and I am in the market for a small 2 truck shay for my switch back branch, for the looks. My Climax looks great up there.

[jeffers_mz]

The Bachman 3 truck will handle 15 inch curves without a problem. It is all wheel drive and mine will pull 7 ounces of free rolling cars (2 MDC RTR OT boxcars) up a 5% grade on a 18" curve, but will not pull 7.5 ounces of free rolling cars (three MDC Overton shorties) up that same grade.

I have an MDC RTR 2 truck Shay in the mail, it was shipped yesterday, I'll let you know how it does when it arrives, probably Friday.

[TBat55]

Thanks all for the comments. Never thought of the left- vs right-hand turn problem (nedthomas).

[jeffers_mz]

The MDC 2 truck Shay that arrived last night will pull 0 cars up a 5% grade, because it doesn't move at all, on a grade or on the flat.

The motor turns, the drive shafts from motor to trucks turn, the wheels and the driven external truck gears, drive shafts, and piston rods do not move. The mechanism is designed as follows, motor to gearing to drive shafts to truck worms, truck worm gears to axles, wheel gears to exernal shaft gears, which then are supposed to drive the cylinder rods.

The truck worm gears (all four of them) spin freely on the axle without turning the axles. Either this unit fails to maintain a friction fit on the axles/worm gears, or else the driven external driveline produces too much friction/binding to allow the wheels and axles to turn.

The external shafts rotate smoothly in isolation.

Back to the drawing board (and back to the supplier).

[Anonymous]

not having any knowladge of steamers of any sorts, but just drawing on my version of common sense, id imagine that a 3 truck shay would have greter pulling power, and the 2 truck shay would be better on the corners. (sort of like the difference between EMD GPs and SDs)
GEARHEAD426
[8]

[fwright]

From an engineering point of view, the prototype 3 truck Shay is designed to be heavier, carry larger fuel and water loads, and has more wheels to provide extra traction. The tender (3rd truck) did not have a big enough wheel base (compared to the engine) to influence minimum radius. Except for the extra friction in the drive, and the extra cost to buy one - a 3 truck Shay was a winner for situations where the extra load capacity an/or range was needed.

In models, the 3rd truck often causes extra problems (Bachmann appears to be an exception but I don't own one to say with certainty). If the tender is not weighted sufficiently it tends to "torque roll" when starting or accelerating. Even then, the interaction while rounding curves or entering grades between the tender draw bar and the drive shaft can cause all kinds of wierd binds. The two have to be carefully engineered to work together. This tender drive shaft/draw bar interaction also applies to any three truck geared locomotive where both are present.

The Roundhouse Shay (the Keystone Shay has same "feature") has an issue of interaction between the line shafts (the ones on loco right side that are geared to the wheel faces) and the drive shafts (Roundhouse used a center drive shaft like many diesels for the wheel drive). Both sets of shafts are geared to all wheel axles unless changes are made during assembly. In most cases, the different tolerances of the gear trains eventually cause one set of gears to bind up. The fix is to open the "closed loop" of the 2 sets of shafts geared to the same axle, usually by removing gear teeth or by preventing gears from meshing. The MDC Shays, when "tuned", runs very nicely and pull well. The Keystone Shay also runs very nicely and is an incredible puller, but the Keystone is not as simple as the Roundhouse to build, not is it available as an RTR. Keystone comes in non-motorized kit form, and requires an NWSL motorizing kit.

Size-wise, the Bachmann is a large Shay (80+T), the Roundhouse a medium (50, 70T for 2 and 3 truck), and the Keystone represents a much smaller prototype (20T). Imported brass models have been made of many different Shays - some run well, some don't.

My thoughts, your choices
Fred W

[dinwitty]

QUOTE: Originally posted by tigerstripe

This isn't your question but 18" is huge for a Shay. 4% is acceptable.
The Spectrum 3 truck Shay is a great runner with beautiful detailing. Very good slow speed operation.
I have heard many horror stories about the Roundhouse 2 truck kit version, but I think the RTR is OK.

I built a 3 truck HOn3, actually I didnt have all the parts or I broke a part, so I made it into a 2 truck. I couldnt get it to stop running... :D

loved it but sold it. But gonna buy another soon.

[dinwitty]

QUOTE: Originally posted by TBat55

Is there a big difference in minimum radius or grade between a 2-truck Shay and a 3-truck Shay? Which handles tight curves better, and which handles steep grades better?

I have a steep 4% grade with 18" curves. I'm guessing the 3-truck would be better at pulling upgrade, but may not handle tight curves as well as a 2-truck.

I believe a shay was designed to handle the grades and sharp curves..period.
If you have a 3 truck and dissapointed if a 2 truck hits sharper curves, play with the mechanism so you can hit the sharper curves.
I would believe 15" radius it should handle although on our club we limited to 18 inch.

[jeffers_mz]

Fwright,

Good info on the MDC drive problems. This one is still going back, RTR means RTR, and I have no way of knowing if gear damage has occurred without violating the warranty. Next iteration will either be RTR or have the gear loop isolated. Nearest I can tell, at least one side rod needs to have both wheel gears removed to eliminate the loop. However, each truck has its own gear loop in addition to the larger one caused by the drive train/running gear train. Is removing two wheel gears from one truck enough, or do you need to remove one of two wheel gears on the second truck too, for long term smooth operation?

The Bachmann 3 truck has an unusual drawbar as you indicated. The front attachment of the drawbar can pivot, but the tender attachment cannot. This forces the tender's centerline to always point at the drawbar pivot point on the cab. The tender can swing, but cannot shift laterally back and forth, side to side. Additionally, there are radiused bumpers on both the cab and tender that interact at extreme tender swings to resist any swing wide enough to bind the running gear. Extreme swings also cause the middle truck to pivot, via the side rods.

The running gear is also the drive train on this unit, and the driveshaft to the tender truck is similar to the two truck mechanism, a two part shaft, a square tube extending back from the center truck u-joint, and a square rod nestled inside it going back to the rear truck u-joint. With the tender set to pivot only, this keeps tender swing from binding the two rod interface. While on the track, tender swing is not enough to seperate or jam the two rods, but when off track, the rods can seperate, but getting them back together is easy if you spot the problem. It will run with the rods seperated, but that prevents an entire truck from adding drive traction to the communal pot, and really cuts down on pulling power.

[fwright]

jeffers_mz

Jeff Johnstone, author of "The Roundhouse Shay Handbook" recommends disengaging all but one set of wheel teeth on one truck - that's all that is needed to turn the line shafts and the Shay engine (crank shaft and cylinders).

My personal opinion - I'm still building my Roundhouse 3 truck Shay kit - is that if you carefully time the center points of the gear backlash at least on any given truck you should be able to operate the truck with no problems. Of course, timing the centerpoint of the gear backlash means rotating the gears on the axles ever-so-slightly until everything lines up. In information on building the Keystone Shay, the recommendation is to modify one of the sliding square tube joints on the line shafts so that it can rotate inside the other tube as necessary to avoid gear binding. This would seem to me to be less noticeable than shaving wheel gear teeth. As usual, there are several ways to skin the cat.

Thanks for the info on the Bachmann Shay. It is very useful and interesting to compare different approaches to the same basic problems.

Good luck on getting your Roundhouse Shay repaired. I suspect parts are drying up, and it will not likely be re-run by Horizon Hobbies. From what I have seen, the return rate and customer service/questions must have (and would in the future) wipe out any profits from even strong sales. A shame, because I believe the Roundhouse Shay, even with its many problems, filled a needed niche in the hobby.

yours in gearing down

[jeffers_mz]

I bought it new, and a return UPS label is on its way to me. The company says they have another one in stock which will ship as soon as they receive the DOA one I have now.

From your posts, I know what the problem is now, and could fix it, but having paid for RTR, it's worth at least one more try to get RTR, we'll see.

Again, thanks for the info, who knows how long I might have putzed around trying to figure out what was wrong.