jtlan

Four-wheeled Toby model is canon.

Conditions at shows are different. A motor run continuously will heat up, changing its internal resistance and thus current consumed. In addition, the current consumed by motors depends on their load -- a stalled 9V train motor will draw almost 1A, for example. My suggestion was that an unexpected increase in current draw could indicate overheating or some other problem, at which point it's probably safest to shut the motors down.

No; for the situation you described, you would be connecting the batteries in parallel. Two batteries in parallel would provide the same voltage as one battery, but would last twice as long for a given load because each is being drained half as much. Connecting them in series (as described in zephyr1934's post) would provide twice the voltage of one battery, which is probably not what you're looking for. Connecting two batteries in parallel forces the positive terminals of the batteries to be at the same voltage, measured relative to the negative terminal (this is Kirchhoff's Voltage Law applied). If the batteries are not at exactly the same voltage, current will flow through the loop, resulting in one battery trying to charge the other one. However, the Lego PF battery contains some complex circuitry, so it's not exactly clear what would happen with those. This seems like the most straightforward scenario for your use case, although if it's possible to design the locomotive so the battery box can be easily removed you can avoid having to build an entire other locomotive. See some of Commander Wolf's PF models for inspiration.

The non-connectivity seems to be a sign that you probably shouldn't do this. Also, the 9V cables won't work for this because they connect the C1/C2 wires and not the +9V/GND wires.

In theory. More likely, one of the receivers will miss a command, causing the two to run at different speeds, draining your batteries and generally being bad for the motors. @Paperballpark, If you have room, I would try to use the AA battery box; Using this battery box with good rechargeable AA batteries should provide about twice the capacity of the Lithium PF battery.

This sounds like the thermistor in the motors cutting out. I've heard that they degrade with age, which could cause the variation you saw. I've also heard that removing the thermistor is unlikely to cause problems; I'm not sure how much I believe that. If you're using a custom motor controller you can try to limit the current to the tracks, which should help preserve the motors.

For the length of this span, I'm not sure it makes a huge difference, but you could use 6L half-beams or the bent liftarm to get triangles. The main point of weakness I was concerned about is that the shear force for the entire bridge passes through only 4 16L beams, so it's important to be able to divert some of those forces into the side of the table.

Right. It's part of why I suggested that the bridge would be stronger if placed against tables with a tall side, because then the forces would be redirected into the table which would resist the bending moment in the bridge: I still need to test with longer spans, but I think the design could be improved from a strength perspective. The goal was to highlight the technique of making the floor of the bridge level with the track, which makes the bridge easier to integrate into layouts.

Happy November, Train Tech. I feel like I've occasionally seen bridges posted here, but for most bridges some sort of elevation change or slope is needed to integrate it into the layout. I wanted to share a simple design I came up with that addresses this issue. The basic idea is that the parts of the bridge that hold on to the edge of the gap don't extend underneath the track, so the "floor" of the bridge is at the same level as the rest of the layout: I tried to keep the bridge easy to build, using mostly basic bricks, plates, and Technic beams. The trickiest parts to find are probably the studless beams. While writing this post I realized I had made a mistake, and the bridge shown in the first photo actually spans a gap of 34 studs, instead of some multiple of 16; I've since fixed it in the CAD files. The idea is that the bridge should be as long as common baseplate lengths to integrate into layouts easily. For example, here's a 48-stud long version: Since there are repeating 16-stud sections in the bridge, it's easy to extend it. I haven't tested to figure out what the longest stable length is, but the bridge should be stronger in scenarios where the table extends down and gives the underhanging part of the bridge something to push against (like in the second image above). What do you think? I've attached the CAD files if you want to play around with them. Brickshelf (pending moderation). girderBridge_32.lxf girderBridge_48.lxf

You mean this one ? @THERIZE, I like the use of handles as side windows. I usually have mine hauling gondolas. The nice thing about gondolas is you can just fill them with different stuff to change the type of railway you're working on, and they also make sense being shunted while empty.

It won't. I've never seen a problem with two Ms on one receiver, an a number of official Lego sets use that setup.

Right, I get that, but someguy said "I did this for one of my engines so I could spin the control clockwise for forward instead of backwards." Maybe he (?) meant "for one of my motors"?

????? Why did you need to do this? There's a switch on the remote that reverses the direction.

Well, I guess it sort of does. There's a lot of friction though.

2 M motors driving the small wheels at 1:1 reduction should be enough to pull twenty cars (this was the setup used in Commander Wolf's RF-16). In general, Ms are way easier to hide in a model and will give you sufficient pulling power. In basically all cases weight, rather than torque, is what limits the pulling power of a locomotive. On No. 2096, I have M motors mounted vertically powering bogies with no turntables (no room), and I've never had any problems. The correct arrangement really depends on the shape of the space inside your locomotive. You might also consider more complex setups with gearing. I would strongly vouch for building a "sketch" of the geartrain and making sure it works (this reveals things that LDD doesn't -- for example, the locomotive in your first post with three-axle trucks won't actually go around curves!). The hole in some of the older turntables isn't big enough to pass a cross axle. The combination of this piece and this one should produce a thinner turntable.

I'd argue that's actually too long already. The spacing on the two-axle cars from the 90s is probably better. In general I've found that 10 studs, measured between the centers of the axles, is a safe limit (the cow car and other modern Lego two-axle cars are one longer than this).

There's nothing "proprietary" about the charger -- the plug on the box is actually a reasonably common type, and the charge circuitry is pretty forgiving so it'll accept a wide range of input voltages (there was a Railbricks article about this). There's no reason to shell out $25 for the "official" charging brick (I found the one I use in a box of discarded electronics).

Even if the XL drivers fit, you probably don't want to mount them on the PF train motor. The PF train motor turns very quickly, and the XL drivers don't have much traction (no tires), so basically the wheels will just slip immediately and the locomotive won't go anywhere. If you're building a locomotive with XL drivers, the best way to power it is probably to power the small wheels in the tender with a Power Functions M, L, or XL motor. This makes it easier to concentrate weight on the driven wheels. See this thread for some of the trouble you'd be in for.

Greetings Dutchiedoughnut, Nicely done. Hiding the IR receiver is always hard, so you might have to sacrifice the cab interior to get it to fit. Alternatively, a different gear train (with the M motor mounted vertically) might give you enough room inside the body. I agree with Beck that given the weight of this model the gear ratio is likely overkill, but if your goal is to conduct slow shunting maneuvers then that sort of reduction is probably appropriate (you can see for roughly how fast that would be -- the small locomotives are powered by micro motors).One thing I'd watch out for is that the mounting points for the couplers look really far from the wheels, which could cause problems in curves. I'd try mocking up a chassis with the same spacing to make sure it works in real life. Side comment: I'd turn on the "Show Outlines on Bricks" option in LDD, which I find gives a better recommendation of what the model will actually look like in real life, because it shows the seams between bricks.

In general, the PF train motor is not as good for pulling heavy loads slowly -- the amount of torque it puts out is low, so it's not as good for low-speed heavy-lifting. Also, in a lot of cases traction is the limiting factor, not available power -- see this thread (which I keep linking to...). At any rate, if you're not trying to go really fast, a pair of PF motors should be more than enough; for example, Commander Wolf had a locomotive with two PF motors that could . In general, I've found a 1:1 gear ratio on PF motors works well.

Worse, I think the math is wrong. The official small wheels have a "nominal" diameter of 17.6mm; measuring with my calipers yields values closer to 17.9mm. Doubling that gives 35.2mm or 35.8, both significantly larger than the lego drivers, even accounting for the added thickness of the rubber band. Those values are also smaller than the Big Ben Bricks XL drivers, which have a nominal diameter of 36.8mm. The nominal sizes lead to the inconvenient ratio of 19:11. Since those are both prime numbers for which there don't exist Lego gears, a design with this exact ratio is does not exist, so this approach isn't going to work ... or is it? What happens if you use a close but not exact ratio? If there isn't enough friction, one set of wheels will slip and be pulled along by the other set. That means they basically contribute nothing to traction or pulling power, so there's no point to the design. If there is enough friction, the two sets of wheels will be forced to turn at the same speed. This works, but since at least one of the motors is being forced to turn at a non-ideal speed, you will be wasting some electrical power. In fact, there is a mechanism that allows driving multiple sets of outputs at different speeds -- the differential, which is used in cars to drive the left and right wheels at different speeds of the same output when the car is making a turn. It's also seen in four-wheel-drive vehicles connecting the front and rear axles. Here's an example: When power is supplied to the grey differential cage, this mechanism will power the blue and red axles without slipping, even though they are turning at different speeds, regardless of what the ratio between their speeds is. However, the axles are at the wrong height for the chassis to be level -- solving this is left as an exercise for the reader. You'll also have to figure out how to pass the power between locomotive and tender. At this point, I have to ask what your objective is, since the right course of action will depend on if you want to pull light loads fast or heavy loads slowly. About half a year ago, Commander Wolf and I ran some tests to figure out how much power our locomotives put out. One of the conclusions we reached is that pulling power is usually limited by traction, and not power supplied by the motor. Traction can be improved by using better tires, increasing the weight of the locomotive, or concentrating the weight on the powered wheels. The third option can be achieved by adding more powered wheels, or by distributing the weight differently -- one way to do that might be to only power the wheels in the tender, and then move all the PF gear there as well (to get the weight from the battery). You can then fill extra gaps in the tender with weight to get even more traction. Hiding all the PF gear in the locomotive is an option as well, but tends to be much more difficult.

Strongly disagree. While it doesn't make much of a difference when mounting the motor longitudinally, the increased height and length are inconvenient if you're trying to pack the motor in a confined space, and also reduce the number of alternative mounting options. For example, in my No. 2096 and CommanderWolf's RF-16 and HH1000, the M-motor is mounted vertically where the L-motor wouldn't fit. Additionally, you can't always use the extra power available from the L-motor, In which case you're just wasting your battery power. Unless you're pulling heavy cars at high speed, the M-motor should suffice. Also, with the PF-9V adapter cable you can use the older 9V motors with the PF system, and they may be easier to integrate by virtue of having studs. They also tend to have form factors closer to a cube than a cylinder, which may or may not be helpful depending on the nature of your "limited space". Don't forget about the E-Motor, which while nominally not part of the Power Functions line is still compatible with it.

Charger is actually way less than that -- you don't have to use the official Lego charger. Any charger producing between 9V and 18V will work (as seen in this thread), although 10V is "optimal". I use a charger from a discarded modem.

What's the scale you're intending to build at? That has a strong effect on the answer: If you're working at a smaller scale, and not opposed to using the PF train motor, see the discussion in this thread. For a larger locomotive, take a look at Railbricks Issue 6, page 62, which has instructions for a 3-axle bogie with the first and third axles powered.