jtlan

This is what I originally wrote. I woke up this morning and realized this wasn't entirely accurate, as the P54s use popped-out wheelsets, and the T1 is a heavy locomotive with a lot of axles. I replaced the two stock wheelsets on the test car I had measured with technic axles and remeasured: Two axles with Big Ben Bricks small wheels took three 2x4 bricks to move. Two axles with the Power Functions train wheels (small) took four 2x4 bricks to move. A 2x3 brick is actually sufficient to move two stock wheelsets. So it's not quite "almost nothing". But a significant difference.

Ever wonder how much power you're actually getting out of your locomotives? Commander Wolf and I did! Of course there's Philo's motor characteristics page, but that only tells you the motor power ratings under the load he tested with, under his conditions. We wanted to see how much drawbar power we were actually getting, particularly with Power Functions locomotives. Here's our setup: A string is attached to a pin inserted where the magnet would normally go on the locomotive. The string is attached to a weight, which dangles off the balcony into the floor below (a 3-meter drop). Here's what we tested: AGEIR Power source: PF rechargeable battery Motor: 71427 gearmotor 2096 Power source: 2-cell 20C Lithium-Ion battery (custom) Motor: 2x PF M motor Baggage Car 999 Power source: Wall wart Motor: 2x 9V train motor HH1000 Power source: AA battery box with Eneloops Motor: 2x PF M motor U30 Power source: AA battery box with Eneloops Motor: 2x PF L motor We did two tests. Traction Test We ran each locomotive at top speed. If it moved the weight, we increased the weight until it no longer moved, then recorded the result. We then divided the max weight pulled by the weight of the locomotive to get an effective traction ratio (for 2096, we divided by the weight of the center powered section only). Unfortunately, since our weight was made up of two battery boxes, the minimum granularity in our measurement was the weight of a AA battery. Results: The locomotives with the PF train wheel, as well as the 9V motor unit, all had about the same traction ratio, from 0.25 to 0.27. No. 2096 had a much higher ratio of 0.337. I'll note that 2096 uses the large drive wheels with custom O-ring tires, rather than the official rubber band. Some locomotives had different traction ratios going forward and going backward. Power Test In this test, we fixed the weight at 98g. We then measured how long it took each locomotive to raise the weight a fixed distance. From this we could calculate the power output by each locomotive against that particular load: mass of weight (kg) * acceleration of gravity (m/s^2) * distance (m) / time (s) Results: Note the high values for 2096 and the baggage car -- this is due to their high top speed (large drivers on 2096, speedy 9V motor on the baggage car -- we ran the 9V motors at top speed). We ran the test on our top three winners with 2 more AA batteries of weight: Note that the power ratings for 2096 and U30 went up more than the power rating of the baggage car did. Interpretation: PF motors can continue to haul heavy loads at decent speeds, whereas 9V motors are gradually slowed by the addition of more weight. How much is 98 grams of load equivalent to though? The bonus round: Measuring Rolling Resistance We hooked up some unpowered rolling stock to the weight, and increased the weight until they began to move. Turns out the normal 9V wheelsets, lightly lubricated, have neglible resistance. The weight of a single 2x4 brick was sufficient to move a piece of 2-axle rolling stock. Of course, there are things with a lot more rolling resistance: - Commander Wolf's PRR T1: 52 grams worth of resistance - The entire rake of P54 cars (3 total): 32 grams worth of resistance Conclusions Effective traction is about the same regardless of your power source. If you want more pulling power, increase the weight of your locomotive ... or try to find some tires with more traction. U30 weighs 1020 grams and could lift ~ 250 grams. 9V train motors produce a huge amount of power ... if you want to go really fast. For pulling heavy loads at more sedate speeds, use the PF motors. We haven't tested the 9V train motors at a lower speed, but observational evidence suggests that their effective pulling power is drastically reduced at lower speeds. The rolling resistance of lubricated stock wheelsets is almost nothing compared to much lower than the rolling resistance of technic axles. Be prepared to fight lots of resistance if you make custom rolling stock that doesn't use the stock wheelsets. Until next time!

I don't actually have a PF train motor, so I asked @CommanderWolf to help me check this one. Turns out the axle hole on the motor has no friction whatsoever, so the design on the right will just fall apart. The ball-end pins on the left won't hold the center wheels tightly enough, since they're somewhat thicker than 1/2 stud. I'd go with the left-side design, but with the center wheels held on using the method on the right; you might be able to use 7-length axles instead of 8-length. I'll warn that this design might be a bit high on friction in curves.

You either have to power them using an external Power Functions motors (Railbricks #6 has instructions for a 3-axle truck), or do something sneaky like this. But you may have to lengthen the locomotive slightly.

It looks a bit too small; I get that you're trying to have it fit with your layout, but it looks odd on those bogies. I'd say try lengthening it by one bogie-length (10 studs) between the bogies. If you're not opposed to it, and there's no extremely narrow tunnels on your line, you might try widening it to 7-wide ... it'll look a bit better proportioned, and you should be able to fit more seats inside. Last thing: I'd enable the "Outlines on bricks" option in LDD, which will make the render look a bit more like the real thing since it shows the separation between parts. It'll also make it easier for people to advise since it's easier to see how the model is put together.

??? Shouldn't the model have 3-axle bogies? Although I suppose that might be hard with a 6-wide model this short (in length). The positioning of the grills on the long-hood end seems off too (they should be farther back).

+1 (cent?). I'll also note that there might be some additional friction pulling the long-bodied versions around curves due to the increased wheel spacing.

"G1" seems more correct, given what happened to the BB1...

Bases are used for convenience -- imagine the trouble it would be for an official set (aimed at children) if you had to assemble a somewhat fragile base out of a number of smaller parts. However, for a lot of MOCs builders will eschew the base in favor of a brick-built assembly. I'll note that in my experience rotational joints done using pins tend to behave a little better on rough track than the turntable versions. For cars like the ones you've built the difference is probably negligible though.

Nice model. I really like the use of the "grilled cheese" for the ladders on the boiler. I don't typically model all the valve gear, but I like modeling the driving rods at least. Lately I've been using this technique, which @CommanderWolf and @SavaTheAggie used on their models of the PRR T1. Basically, it consists of a reversed tile sliding in a slot; the tile is joined to some technic half beams with a pin. Note that the model will be 8 studs wide (plus a plate maybe) at the cylinders. If you send me the LDD file I can try to show you how it might fit on your model.

@Exa, if everyone thought that way no one would vote. In this case though, I think you've accurately described the reasons not to purchase it. @Duq, if you're really concerned, write Lego customer service an email or letter stating your point of view. It'll probably take only as long as getting the set would have (and be much cheaper!), and they might value the information.

This is a nice model. The boiler looked a bit large to me, compared to reference photos, but then I realized there were "large" and "small" boiler versions of this loco. It's sometimes annoying that the Big Ben Bricks XL drivers don't come in more colors, since green ones would suit this model nicely. I sympathize with the green issue, as I encountered it while building No 2096. I wound up going with the normal green due to the wider variety of parts available, but it looks like that's not a problem for you here. Classy. I look forward to seeing it in the brick!

I always wondered why it wasn't possible to push the tender in front of the locomotive. Granted, it would block the view somewhat, but you could make a lower version (sort of like a slug). I've heard it's not safe to push tenders, but locomotives such as the DRB Class 50 were capable of high-speed operation in reverse, so that's clearly not universally true...

This. 8-wide isn't really a defined scale. One way of working is to pick a scale (Tony's scale is convenient -- 15 in/stud or ~155mm/plate), find some engineering/technical drawings of what you want to build, then scale the drawing against some Lego graph paper, which will tell you how long/tall/wide the model should be. Alternatively, build a base and extend it in the middle until it "feels right". This approach is less rigorous but may be more convenient or enjoyable, depending on your personal style.

@barduck, I'll note that SP #4294 is an AC-12, which is slightly different from the AC-7 you're modeling. This is an AC-7: Note minor differences, such as the absence of an air horn on the front of the cab. I'll note that in both your and Cooper's renditions, the silver section on the cab appears to be slightly too tall, but I'd need an engineering drawing to verify. The tender also appears to be a bit too tall relative to the locomotive, although it could be a perspective problem in the rendering. Or you can cram coal in every available space, as was done on the GR670 (the version I modeled has a giant coal chute and bunkers behind the cab).

From what I've heard from other peoples' experiences, Sketchup is a pretty poor program for making printable .stl files; the shapes often wind up full of holes. Try using something like Meshlab to clean them up?

??? But you said: Are other wheels being powered?

??? Is there room for a tire? I'd be worried about lack of traction from metal-on-metal...

Better too tight than too loose, I guess? I'll note that Big Ben Bricks flanged wheels fit pretty tightly as well. The metal parts of the 9V motor's wheels are sprung, which means that weight on the motor is carried by the tires, which are rubber. The ridges on the flange of the printed wheels may also have a filing/scraping effect around curves.

Most metal printers use the Selective Laser Sintering technique. Small metal particles are slightly (but not fully) melted by a laser, causing them to stick together -- this is responsible for the grainy texture seen on the parts. Another layer of particles is added and the process repeated. The flange of the above wheels shows some ridges -- these are the individual layers of metal. In general, the parts will be a bit porous and somewhat weaker than equivalent parts machined out of solid pieces of the same metal -- but for this application that's probably irrelevant. I'd be more concerned about the ridges on the flanges clicking against the rails (and possibly wearing the metal coating on the rails). @legoman666, how is the grip on the cross axles? The manufacturing tolerances for Lego parts is quite high, and I'm curious how well the metal parts matched them.

This is going to be tough. Since the radius of the curve is 40 studs, a single-loop layout is, at its narrowest: 80 studs (diameter) + 8 studs (width of track) = 27.8 inches. You could run a second loop that's one straight track wider: 80 studs (diameter) + 8 studs (width of track) + 16 studs (one straight track) = 32.8 inches. But not any wider than that: 80 studs (diameter) + 8 studs (width of track) + 32 studs (two straight tracks) = 38 inches. You could run a single loop with a turnout (but only one on the outside!), or two overlapping loops?

So does the tram from 8404, and some real-life light rail systems too.

Perhaps the electrical wiper contacts have been bent? Try gently bending them away from the orange dial, so that they press more firmly against the circuit board.

Actually, cutting away from the mold would add plastic (since the mold is a negative of the part).

Are you concerned that you'll damage the Legos, or that it won't wrap well? In either case, I'd take a sacrificial part (maybe a 2x4?) and test the material there. You can use something else made of ABS (like a clone brand...) if you don't want to risk any Legos. However, I'm guessing that the decals were intended for use on a relatively flat surface. In that case, wrapping them around the door rail will probably result in major distortion. In that case you're probably better off cutting the decal into pieces and applying the pieces only to surfaces facing the same direction (so say, only the side of the door rail). Maybe you can include some pictures of the decal and where you intend it to go?