Blakbird

I love the title! There are a couple of possible solutions for intermittent motion. One would be a Geneva mechanism. Akiyuki also invented such a mechanism for the wheel of his bucket factory.

@Myers Lego Technic and @BusterHaus, please stop the feud and get back to talking about the excellent model that is the subject of this thread.

This type of crane is called a knuckleboom crane for fairly obvious reasons. It curves back on itself like a finger. Although these cranes are very space efficient, you have identified their structural weakness. Because one of the arms is in a different plane than the other, this offset causes a twisting of the main boom and a lot of bending on the rotation axle. This is the inherent weakness of a single shear joint. You've found a rare double shear variant that still folds up. I like it! You've created a real dilemma for me here. I already own your dump truck, and it would be totally unreasonable to own both (even for me). So now I need to decide whether or not to teat apart my dump truck and build this. If it was basically just the same truck with a crane instead of a bed, I think I would stick with the dump truck. But you've changed and improved so many things that it really is a totally different truck. I have some thinking to do. Your crane came out really well. I like how smoothly it is integrated into the model, and I like that you can see the position of all the pneumatic switches behind the cab. The suspended cab is inspired, and are the suspended seats. I wish I could shrink myself down and drive around in this truck.

Yes, you can do that in the profile editor for SBrick. Of course, you will have a lot less power if you slow a motor down versus gearing it down.

It doesn't matter which one you use; they both work. The flat top is shown in the instructions because these are the current mold and therefore easier to buy.

It's OK but it could be bigger.

Now we can get back to talking about your awesome LEGO creation! You know, your tr..... frame.

For me, everything is an engineering problem! No, a truss is a truss based on the geometry and constraints. It will always be a truss no matter how it is loaded. I can apply a load in any direction at any joint and the whole thing is still two-force members. A structure which happens to be composed of two-force members under a single load condition but would cease to be so if the load changed would not be called a truss. I don't know what you would call it! A structure which starts out as a truss but then rusts into a solid brick also has no name. Maybe in Dutch....

Any charger with 10V should work. If the plug is wrong, you can always put on a new one from Radio Shack.

True, but you should go ahead and try the rocket anyway.

In this particular ideal example, there is no stable solution. Two massless, rigid links oriented horizontally cannot support a vertical load, as you correctly surmised. It's is impossible because there is no restraint in that direction. Of course, there is no such thing as massless or rigid which is why it works in real life. OK, I finally understand what you are trying to say. If the structure were pinned and then allowed to strain into a stable static position, then you are correct that converting the pins to fixed would not change anything. However, as soon as there was any variation in the load, including removal of the load, then the structure would respond in a different way. So you are right, but in practice this situation cannot really exist. Even the action of building the structure in the first place results in a variation of loading, and for something like a bridge, anything crossing it or even the wind would change the load. For your LEGO structure, picking it up and moving it would change the load and it would respond to that differently once the pins had been fixed. I get your point though. If you could really change a joint from pinned to fixed once the structure was already at equilibrium and nothing else changed, then the stresses would not change either. Stress is indeed force per unit area, but the way it is distributed is different in different modes. In tension, stress is uniform and a function of cross sectional area which is typically of the second power to geometry. In bending, stress is non-uniform and a function of first moment of inertia which is fourth power to geometry. This is why the bending stress can be locally much higher even for the same load. Consider a 0.1x0.1m beam with a length of 1m and a load of 1N at the tip. If this were hanging vertically, the stress would be pure tension. The area is 0.01m^2 and the stress is 100Pa uniformly distributed across the section. Now consider the same beam horizontally fixed at one end with the weight hanging from the other end. The beam is now in bending and shear. The moment of inertia is 8.33e^-6 m^4 and the moment is 1N-m. The peak bending stress is 6000Pa at the extreme fiber, but varies to zero at the center and -6000Pa at the other side. As you can see, in this example the stress is 60x higher when the beam is in bending. This factor is not constant though, because it depends on the length of the beam and the shape of the section. But it does illustrate why limiting a structure to only tension and compression is so efficient. I think we just describing two different problems. If I draw a truss bridge and then put a load in the middle and solve for the forces and stresses in all the members, I'll get a totally different answer if the pins are fixed versus pinned. However, that's not the problem you are talking about. You are talking about changing the joints in the middle of the problem. The pinned structure strains, reaches equilibrium and THEN you change to fixed. In this case, no forces or stresses change. I've never seen an engineering problem presented that way though. The default solution methodology is to start from an unloaded state and then transition to a loaded state.

Wow, that new wing really looks a lot more realistic. Good job.

Sure you can. If you are going to use your own motors and controllers and just want to use LEGO for the structure and mechanisms, then you can buy pretty much any Technic set from the last 40 years and use it for parts.

I don't think there has been any official announcement, so we don't have an answer. Historically, all 1H sets are available by March 1 (today), but it is not consistent. In some years they come out in NA and Europe on the same day.

Nope, the forces (actually stresses) are completely different once the pins are locked, even with the same load. I can't really think of a good way to describe it in text, but it becomes really obvious when you draw a free body diagram of the forces and moments. Consider this as a simple example. It is not a truss, but it shows the principle. Imagine a straight horizontal beam made from two members, pinned at the ends and in the middle. Now hang a weight from the middle joint. The beams can't support any moment, so they start to rotate. At that point, they start acting like a rope with a weight in the middle and go into tension. Now apply the same weight but this time lock the middle pin. Now the beams CAN support a moment and they do NOT go into tension. Instead they go into bending. Depending on the shape of the cross section, the bending stress may be vastly greater than the tension stress. The same thing applies to a truss. The bottom surface of a truss is made from many individual links, generally in tension. If you weld or lock them together, then they are instead one continuous beam and not individual links. Every place those vertical or diagonal truss members tie in to that horizontal beam, they will be introducing an out-of-plane load which gets reacted as bending. When every joint is pinned, bending cannot occur so that load gets transferred out to adjacent members in tension or compression instead. That's the best I can do without diagrams. Check out any Static or Mechanics of Materials textbook and you'll find plenty of equations and examples that demonstrate the principle. One of the big analytical benefits of a truss is that it is statically determinate. What that means is that if I write out the equations of equilibrium, there will always be a greater number of equations than unknowns, and therefore I can solve for the exact forces in every member no matter how many members it has. On the other hand, if the members are fixed then the structure is statically indeterminate. This means that I can't solve it with Statics because there are not enough equations. I need to use Deformable Body Mechanics to take into account the stiffness and deflection of each member to solve. It is vastly more complicated to do by hand, and also represents a less efficient structure. I had to solve an 8 member system like that by hand in college and it took half a notebook. It is theoretically possible to design a very simple structure in which the boundary conditions don't matter. For example, imagine a vertical link of 5 members with a weight hanging from them (a chain). In this case, it doesn't matter if the links are pinned or fixed, you'd still get exactly the same forces and all the stresses would be tension. But as soon as you have a load that is applied in a direction that is not parallel to every link, then the answer does change with the boundary conditions. I always marvel at how far we can go down into the weeds in analyzing even the simplest structure. The very first thing you learn about in Statics is analyzing beams, and the simplest combination of beams is the truss. However, in the real world it is impossible to ever have a real truss. A real truss has load applied only at the ends, but in the presence of gravity every member needs to support its own weight which is a distributed load and NOT applied at the end, so there is always bending present to some degree. In most engineering disciplines you can ignore this and say "close enough for all practical purposes" because you have a nice big safety factor on top of the biggest load you think you'll ever see. But in other disciplines like aerospace the safety factor is small and you can't ignore much of anything or you end up sending a billion dollar mission to Mars which crashes because the legs didn't deploy. If I've gone too far into the theory here, feel free to tell me to go away. I find it interesting, but others may find it annoying.

Curse you for making this so awesome. Now it is going to have to be on my shelf.

Technically, no. There are lots of joints in that boom that are not at the end of beams. However, the diagonal members will always add a lot of stiffness and are helpful even if the structure cannot be categorized as a truss. Whether or not a load is applied is not relevant to determining whether something is a truss. The geometry and constraints will determine how forces are distributed, and as long as every member is a two-force member then it is a truss. Your example with welded pins would not be a truss. As soon as you have welded pins then the beams are not two force members because there is a moment constraint and therefore bending can be supported. Releasing the moment constraint at the ends of beams by pinning them is a very important technique for reducing the stress in structures. So welding the pins in place DOES change the forces acting on the members. In fact, it has a very major effect on the overall stresses. As above, whether or not there is a load it is not relevant to whether or not the structure is a truss. Unless the bridge is in zero gravity, it will always have to support at least its own weight anyway. For your thought experiment, if a bridge was designed as a true truss with pinned joints and those pins and joints rusted and jammed, then that would indeed change the forces in the members and vastly decrease the strength of the bridge. Of course, as I mentioned above, bridges don't actually use pinned joints anyway so there is no such degradation in the real world. There are real trusses in other applications though like cranes, spacecraft, and aircraft. The joints have to be inspected regularly. Interesting engineering discussion folks! I didn't expect this one on a LEGO forum, but it makes sense when designing such an ambitious model.

I was finally able to find the steering cup module. This is not an Akiyuki module so wouldn't appear in this topic. The fast ball sorter is an Akiyuki model, but as I've said from the beginning those EV3 modules are outside the scope of this project. I'll work on adding the instructions for the zig zag stair when I get a chance.

I haven't done any instructions for the zig zag stair yet. I don't know of any steering cup module. Is this an Akiyuki module? The fast ball sorter is an EV3 module and not part of this topic.

I love that Futurama quote! I use it myself from time to time. You may very well be right that the flexibility of the pins is more important than what you get from the diagonal members. Glad to hear it made some small improvement. If the deflection under the weight of the horizontal beam alone is noticeable, then it is likely that the diagonals will help even more when you are suspending a load. Interestingly, as long as we are talking about "technically correct", almost no real world trusses are actually trusses. Even a steel truss bridge does not actually have pinned joints. The joints are usually welded plates or have many rivets. In either case, they introduce bending into the members and therefore they are no true trusses. A real truss is remarkably hard to build because you need very strong pins which connect a stack of many members. And LEGO sets which have apparent trusses, such as the boom in 8288, are not true trusses either. Many of the pin joints in that boom are in the middle of members, and true trusses only have pins at the end.

What is out of date? Everything looks correct to me.

"Truss" and "triangle" are a matched set. Building from triangles is the thing that makes a structure a truss. You can't call something a truss which is not made from triangles, which Wikipedia concedes in the example you referenced. More technically, a truss is made from all two-force members. This means that a free-body diagram of any element of a truss has only two forces, and they are along the direction of the member. The result is that all truss stresses are only tension or compression. This results in light, efficient structure which cannot deform unless something buckles. The way you built your structure is also stable, but it relies on bending stresses in the corners of those 5x7 frames to become so. Bending produces vastly more concentrated stress risers than tension or compression, and therefore much more material is needed to build a structure of equivalent stiffness. By using triangles instead of frames, the structure is not only stiffer but can also be much lighter which, cycling back to the beginning, means less deflection. Don't get me wrong here, I think you've achieved something remarkable structurally with the rigidity of the frame at this size. I'm merely pointing out that "truss" has a very specific engineering meaning and this isn't a truss. Even adding some diagonal members won't make it a truss because the presence of those frames means that you have bending stresses in your structure. I do think that some well placed diagonals will help though. You might even choose to pick a length that is slightly too short which will force the horizontal member to be slightly bowed up without gravity, and therefore closer to level when supporting weight.

As far as I am aware, this part does not exist in white. I used DBG for my build. I have no idea where Akiyuki got a white one unless he painted it.

I originally built mine using the rechargeable battery, but once I realized it could not be easily removed I changed to the recommended 6AAA battery box which is the same size. Given the very low power consumption of the LEDs, the batteries should last almost forever so you don't need to worry much about replacing them.

It's huge, but it's not a truss. A truss is made of all triangles, and this looks like all rectangles. If you added some diagonal members, especially in the horizontal part, it would be much stiffer and would sag less.