2GodBDGlory

Thanks for pointing me to that information! It's pretty intriguing that Lego is actually partnering with the Raspberry Pi people to make a lower-cost (higher skill-level, I assume) alternative to Mindstorms.

Very nice! I can imagine that programming that would be quite challenging. One question I have is how you're able to adapt the Lego servo wires to the Raspberry Pi? I was under the impression that that plug type was proprietary for Lego, and not something I'd expect to see for a Pi.

If you follow his link to Rebrickable, there's a video on that page

I just watched your video on Rebrickable, and I'm very impressed with the functionality! Collective and cyclic pitch on the main rotor, plus cyclic on the tail one is very impressive, especially for a B-model of a set without any turntables!

Looking good! I also found 13 studs wide to work well for my mobile crane.

Great! Out of curiosity, how many used to be on a page?

I'm not opposed to trying out a subforum for this contest, but as pointed out in this quote, it does seem like somewhat odd logic used to justify it. We start contests (at least partially) in order to increase activity on the forum, but then during the contest we feel like there's too much activity, resulting in less attention for other MOCs. Perhaps it's true that MOCs do get neglected in contest season, but on one hand having more traffic on the forum in general could definitely result in more people viewing non-contest related stuff. And alternately, if the purpose of the contest is to generate activity, hiding it away in a subforum will only tend to diminish how many people actually look at the contest entries, which are just as much MOCs as non-contest ones that get overlooked (though the constant updates do keep them artificially on the front page). The more I type, the more I become convinced that it would be counterproductive to put them somewhere else. More activity on the main forum is a good thing, right? Maybe I'm just a Eurobricks addict, but I'll always click on the second page if everything on the first page is new to me. (Though I check several times a day, so it never really gets that far for me anymore). It doesn't seem like a hard thing to do to see more new content, but I guess some people just aren't interested? As someone else mentioned, just allowing more posts per page would be really nice, but maybe that's not possible in this forum framework.

Update time! As you can see, I've just about finished the mechanical parts of the chassis, with the only thing I expect to add being a steering wheel in the cab hooked up to the wheels. (HOG wouldn't work well on the top thanks to the boom, and I think despair is the correct response to trying to route it to the back) Here I've got the boom lifted and rotated 180 degrees. Control knobs: Both the far left and far right ones run the outriggers for symmetry, the middle one runs boom lift and extension through the gearbox, the middle-left one runs the winch, and the middle-right one slews the superstructure. Also note the outrigger legs in the retracted position (They flop outside of my 13-stud width, because of a necessary half-stud offset in the geometry forcing them out, but they can easily be pushed into compliance, so I don't think they'll cause me volume issues.) Outriggers extended: I didn't have space for independent leg extension and lowering, and the simple 4-bar linkage type lowering and extending from the crane used in many official sets would have looked too minimal for such a long boom, so eventually I came up with this super compact setup that uses extra linkages to pull the legs down in the same motion. It's based on having friction with the black 10L axle on the left and the LBG 9L axle on the right extend, which forces the extension to pull down the legs. The time at which the legs lower is somewhat random because of variations in friction, but all four legs extend and lower easily in one motion, which is pretty cool. Obviously, these legs provide little to no support... Bottom view: It's really cramped. I've also got the wheels at a half-stud offset, aiming to have only a half-stud of ground clearance, allowing the half-studish protrusion of 12T gear on the top of my boom to fit within my 16 stud limit. Overall, it's getting strange proportionally. As I said, I scaled this to use 56mm balloon tires, but I realized that if I used those, they would be sticking up above the turntable, preventing it from rotating. In the end, these tires were the biggest I could fit. I think my issue with scale is that while the boom is the correct length for my planned dimensions, by the time I added the two-stage extension, it had become too large vertically, forcing everything below it to be squished down. I think this model is going to be more on the over-engineered side than I expected, so I don't see it being competitive in the contest, but it's still fun and I want to finish it. I guess in theory I might finish in time to throw together a second model to submit instead, but then I'd actually have to find something else eligible that I have interest in building!

You're right, that does look about as solid as you could get while having those 16T gears where they are, so it'll probably be fine, as long as the gearbox doesn't put up too much of a fight. The fact that it's AWD (without a central differential, if I followed the thread thoroughly enough) should help, too, since you're not really ever going to have it relying on just the front axle. And yeah, you would need to recreate that gearing on the rear axle to keep it even if you did decide to change it, but I don't think it would be too hard. (Though if you did put in a central differential, there would be no need to ensure that the gearing was the same; you'd just get torque vectoring to front or rear. I think the lower gearing on the front would give it a forward torque bias, though, which is probably not what a rally car would use)

Looking good! I'm a little worried about the gearing at the front differential, though. I mostly build RC models, and the bracing between the 20T gear and the differential would definitely not hold up to that. I assume this is a manual model, so forces will be lower and it might be ok, but one thing I would look into is replacing the 16:16 gearing you have coming from the differential with 12:20 gearing in order to reduce the forces on the differential further, kind of like using a planetary hub. I'm not quite sure whether gearing up or down there, but probably gearing up, so the 20T gear is on the U-joint axle, and the 12T is on the differential's axle. That way, the carrier will have lower torque, and be less likely to skip.

So I take it that this solution works except for the high friction in those axles sliding. I think something similar with sliding beams instead of axles could work, but it would get bulky. ... Pneumatic cylinders could maybe be used to stabilize it, simply for their relatively low friction extension? Even ignoring the ports on it, maybe some brace could be made? What else allows low friction extension? That's all I can think of. Maybe putting more beams on that O-frame to keep the axle straighter would help?

I think you might be looking at the wrong one in that thread. The first thing he takes apart is the large one, which does have the extra output, but towards the bottom of the first page, where he does the small one, you can see that it does only have one output, unfortunately.

This link @1gor put above looks like it could be used to buy them, but maybe you have to have some educational connection to do so? https://education.lego.com/en-us/products/lego-technic-small-angular-motor/45607

Well, electronics are ok, but I think he elsewhere said that no third party stuff was allowed. Either way, though, do go ahead with the model!

Looks like a fun little model! You mentioned that you wanted to use a CADA battery box, and while it's hard to tell, I think you've got CADA micromotors in there as well. Overall that should allow it to be very nice and compact, but I'd recommend that you get more confirmation from Jim that those are ok to use. I saw that you asked a couple times in the discussion thread, but never got an official answer as far as I can tell. I think it would be pretty cool if that stuff were allowed, but I would personally assume that they're not, especially since TLG supplies the prizes. Just thinking you might want to make sure about that before you put too much more effort in, though even if it would turn out to be ineligible, it'd still be a nice MOC.

Yeah, it definitely is hard. That dumper looks pretty nice too! I really like the way you integrated the portal axle housings with the bevel gear brackets, and the rotation of the bed is really neat too. Is that what you mean by the "vat"? I wouldn't call it that myself; I'd probably just call it a bed, or a dump bed, but maybe vat is a technical term I'm unaware of.

Congratulations on putting an automatic gearbox in there! It's such an interesting concept, and this design is actually pretty practical, but so seldom used! The rest of it looks thoughtfully engineered as well.

Yeah, I think the size of the boom is somewhat overkill, and will cause the model to be very cramped in other areas, but I think I can get it all to fit in the limit. It kind of doesn't feel like I'm building a mini vehicle, though, it feels more like a full-size model in a smaller space.

I've seen these on the side of the road, but never really figured out how they work, so I'll look forward to seeing your version!

So, for this update I've added the rest of the functional parts of the superstructure (A cab and paneling can come later), as well as the connection to the chassis, and the manual control gearing for the winch, rotation, boom lifting, and boom extension have been added. Here is the "hook." Because of a rather inefficient cable system, considerable weight was needed to keep it pulled all the way down. I started off with a simpler setup using just the magnets, which I figured would add weight without taking much space, and would give me a cool, unique way to operate it, by picking up metal things. That wasn't heavy enough, though, so I had to work in a weight brick, but I kept the magnets because while I may not need them for weight anymore, I still thought they were a fun idea. Here is the bottom view of the carrier part under the superstructure. The middle rear knob runs boom lift and extension through the gearbox, while the left and right ones control superstructure slewing and the winch. Here is the boom raised. The linear actuator positioning was a bit odd, but I didn't think I could route drive to have rear-mounted actuators like on most mobile crane models I've seen. This seems to work fine, though. Note the boom mounted on small turntables, and the winch in the middle. I would have liked to do a more typical winch, but space was super tight--the boom rests directly on top of the spool. The small spool seems to be working fine, though, because I'm using compact dental floss instead of regular string that would fill the spool too fast. This works nicely, especially since I don't have any normal string long enough anyways. I also got in the function I think most interesting, the two-output distribution gearbox with both outputs above the turntable, and the shifting control below it. Occasionally I'm getting skipping from one of my bevel-gear connections when trying to extend the boom, but overall everything is working pretty well, so I'll be able to venture into some other stuff on the chassis for my next update.

Is the universal joint going into the actuator working well at that extreme angle?

Yeah, I've got two weight bricks, and I'm hoping to put them in. I'm sure they'll help, but unsure if it'll be enough.

I don't think fitting it will be too hard, though I'll have to watch the height limit. It is more or less in scale, so the other stuff will hopefully work out, but I think the biggest problem is going to be stability.

I like the thinking there! I don't know if you have any old 14T gears, but I think those run more smoothly with the 20T single bevel gears.

That's the maximum; I believe Jim jokingly said in the general contest topic that the minimum was 1 cubic stud...