Lipko

For a model at that scale, I don't think you need that complexity for getting a rigid build. One problem is that the more robust the model gets, the heavier it gets. I'm not sure which grows faster with the part count: weight or strength. To my limited experience, it seems that the robustness is inversely proportional with the "beautifullness" and building experience of a model. I'm struggling with these three parameters (strength, weight/performance, and style) all the time up to a point when I to give up on Lego, only to realize that even he best/most hyped/legend models have those flaws my models have. Like not fully constrained floating body parts (that you have to adjust carefully), or having a "soft" body, twisting chassis, wheels hitting he whel-arc and hat they can't be picked up without extra care, or that they have very crappy performance if they are strong.

That is pretty nonsense Anyhoo, I tried and it works pretty good. I was struggling with a locking mechanism for a day, and inspired by your idea, I came up with a totally different solution...

And how do you deal with the "interfaces" between the modules? I'm a machine constructor too but I find it hard to use those design methods with Lego, because the available parts and the weakness of the material is so constraining. In real life I can solve problems easily with custom parts (maybe it won't be optimal, but gets the job done) but with Lego, it's hard for me to come up with any solutions at all given the constrains. Even if I solve something, it will interfere with something else. And if I solve everything, and everything works okay, I still have an ugly messy build, not something I'd call art. In machine design, you usually come up with many solution sketch variations for a problem, but with Lego I find it extremely time consuming, because you can't just "sketch". You have to build variations which costs a lot of time and pieces. And no matter how I try to make plans, I always end up just hacking something. There's maybe a mental barrier or something. I'm thinking backwards. If I find a piece, I'm looking what to solve with it, not the other way around. The one thing does make building easier for me is to build in modules. It is much easier than I first thought, and it lets you to optimize modules without the need of disassembling the whole model. In fact, Lego design is so frustratingly hard for me that I'm really considering giving it up after my last model, which I'm building for a half year now. Rant over.

It depends on the project: if it's modeled of a real car, then I make the body first with a temporary chassis. I did that with the Hammer project, it failed for other reasons. Obviously the scale is the first to decide, based on the wheels and other factors, like fake engine size, whether the front axle is driven or not, etc. I usually start this process in LDD and try to find the best wheels. I usually make a prototype model first to see if the model looks as good as I imagined. It usually looks good, so usually my design process ends here...

My working area:

I want a small and strong solution. Of course, I want to work on that, it's just the thread called out for some idea tossing.

I would be interested in a small flex coupling to smooth out the very high acceleration of electric motors a bit. Starting/stopping/reversing a car with power function motors and the non dialling remote control shocks the drive train so much.

I envy the crap out of people who can build this tidy. This is the real talent and art of building, not the stuffing features in a model.

Are you a tourist type or a Globe Tracker type? If the latter, visit Scandinavia. I lived in Finland for a year. And it's just awesome. Both in the winter and in the summer. Lapland? Transsiberian Express? For a bottle of Vodka, you can do the train-guard woman.

Okay, I may have misread your post too. Anyway, I do believe that the two trailing arm + Panhard rod setup is common, you can see a drawing of it in your Piterx quote on this page. But As I said earlier, real cars don't bother with ball joins and hinges, pretty much every joint is a rubber bushing because it works almost like a ball joint but for only a very limited angle, so it is also a bit like a hinge joint. This angle may be comparable to the softness and backlash of Lego parts, so maybe you could use simple liftarms as trailing arms and other rods, but that's too much for my purist ego. EDIT bwah. I should stop posting in the morning. My reading is very selective and I missed all the info Dhc already wrote. Of course he's right and already said everything I wanted. The setup I push here like crazy is very similar looking to that radius arm setup, and it works quite well with Lego parts.

I was talking about a 2 trailing arms + Panhard rod setup, where the trailing arms have ball joints at both ends. And I have to correct myself: it's better to have a hinge at the chassis side of the Panhard rod. With a properly triangulated 4 link setup, there is no need for a Panhard rod at all, because there can't be sideways movement (think about triangulation to an extent that the lower and upper trapezoids become two triangles. Many Lego builders already used that technique with a single A-arm suspension part for the upper triangle). With a Panhard rod with two ball joints, Piterx' setup is okay. Again, my comment about he hinge+ball joint applies for a two trailer arm setup. I'm not at my PC for some time, so I can't make a video or an LDD animation to prove I'm right, so I'm backing out from the discussion.

@Dhc6: I don't think that's truth about the Panhard rod. If both ends are ball joints, and the trailing arms have ball joints too, the axle whole axle could roll. The Lego Unimog could use rods with two ball joints, because the other degrees of freedom were locked by the big ball joint.

Actually, I think it doesn't matter which end of the Panhard rod is the ball joint or the hinge. All that matters is that one and has to be a ball joint, and the other a hinge. So long story short: Go for the Panhard rod, especially because there's that new suspension part. With small suspension travel, you should be fine with a Panhard rod with two hinges (so a plain liftarm). My first MOC had Panhard rod suspension. It wasn't RC, but the suspension seemed to be stable and well defined without wobbliness.

Yes, you are right about the 4 axle setup. But note, that the driving (input) axle will change it's length if you articulate the suspension, even if the centre of the U joint lies on the plane defined by the 4 attachment points. The Panhard rod: I think (I'm not sure at all), that you need to have a hinge at the chassis, and a ball joint at the axle. And the 3 attaching points on the axle (for the 2 trailing rods and the Panhard rod) have to define a triangle, that is parallel to the suspension travel (perpendicular to the trailing arms). So the trailing arms should be below the axle, and the Panhard attachment point should be above the axle. So the Panhard rod is just like the upper triangle in the four link setup, but rotated horizontally by 90°. note, that these are truth for Legos, an in theory. In real life, I think every joint is the same with hard rubber bearings.

Oh, I guess the emphasis is on the WHERE. For a four link setup, you'll need to have the attachment points on planes (chassis and axle) that is approximately perpendicular to the planes defined by the links. Link The upper two arms could be substituted with a single arm with a hinge at the chassis end and a ball joint at the axle end. EDIT: I'm not sure about the Panhard rod.

Um, it's not very clear what you have can you post an image? Without that info I think I can only give some trivial answers. For a live axle suspension, you'll need some other links too. 4 links for example (with ball joints at every ends), making two trapezoids that are orineted in the opposite direction, and that are not in one plane. Or a Panhard rod (that's almost parallel with the axle) with a ball joint on the chassis end and a hinge at the chassis. Or you can use an arm with a ball joint at the axle and a hinge at the chassis. It's very similar to the 4 link setup, if you move the ends of the links very close to each other.

I have looked closely to many Lego cars (including pretty much all the iconic ones, thanks Jorgeopesi) and I've found that the fenders are pretty close to the wheels, even in models with suspension. Do your wheels hit the fender (I remember one of Sariel's cars did) when you push the car down and squeeze the suspension? Or do they only hit something when the wheels are turned (steering)? This is something that bothers me with my new touring car model, where the wheel arc is very close to the wheel even when It's not pushed. I even thought that I drop the suspension for this reason (touring cars have very stiff suspension anyway). So how much do you bother with his situation? Is it "lame" when the wheel touches the fender? Or do you stiffen the suspension to the point it became almost useless (because the chassis deforms more than the suspension itself)?

I didn't think about the new differential, since it's impossible to insert a fourth wheel anyway, because there is that box thing (I'm not sure why...)

@Allanp: you are probably right, but I was saying that it's theoretically perfectly possible. @TwentyLeggedHen: Just try the method DrJB and I said. You don't even need a differential.

Why would it be impossible to assemble? It wold require some manual skills but not impossible at all. As I said, you have to insert both output gears at the same time but from opposite sides (because inserting one gear would try to rotate bot spider gears in the same direction which is locked by the already inserted other gear), then slide the output axles into the output gears. I guess what Zblj was trying to say that it could make a limited slip differential?

Um..... I guess because it's much harder to assemble, because you have to insert both output gears at the same time but from the opposite sides (while the spider gears are already inserted)? Or more likely the molds would have cost a lot more....

Somehow I find it quite difficult to explain simply, but I try: Try to put the fourth gear (no third gear!) on the side of the differential housing without a pin. It just falls out even at negligible torques. This is no different when there is a third wheel (the fourth wheel doesn't "know" that there is a third wheel since it's not in contact with it), so the fourth wheel would still fall out under any load. The only reason it doesn't fall out is the fact that the third gear on the pin bares the all the load. Or: Build the four gear setup and put load on the whole differential (don't let either wheels turn). All the gears will be held in place (no slack) but the fourth wheel will still have some slack. A good sign that it doesn't bear any load, so does nothing at all.

Do you mean when both axles are steered? In that case my logic says the tip of the triangle should be in the centre in between the axles. Because that setup would mean that you could place a non-steered axle in the middle, and obviously the rule of thumb applies for that midle axle too.

Maybe just give stickers a try and see.

So that means MOCs from 1-2 years ago won't have a chance, or should we bump our old thread top have some chance? That would mean some bump storm. Plus: as I see it, many times the maker of the model that attracts the attention, and newcomers have to build even more awesome models to get that inertia many builders already have. Anyway, maybe I shouldn't care about this HoF, as I think I already know all the models that are to my linking, and most importantly I should stop wanting to get attention, I should spend those braincells on building or more important things.