2GodBDGlory

Wow, I never realized how impressive the functions in that set were! I might have to build it some time. Good work replicating them at a smaller scale!

Nice work! That multi-stage boom looks quite ambitious at this scale! The model overall reminds me quite a bit of the entry I'm working on, since both sets are a similar size, with somewhat similar functions, being scaled down to the same scale.

I've now got the crane arm built, which means that the functional bits are now all installed (with the exception of pneumatic control stuff, and maybe a tilting cab)! Before that, though, I modified the outriggers to have a stop, like this: The plan for the arm had been to just include two pneumatic cylinders for the two joints in the arm, but then I realized that I can use the single-acting pneumatic strategy seen in the first Lego pneumatic sets in the '80s, using a distribution block: This will have the huge advantage of only requiring one hose to go to each pneumatic cylinder, which will allow me to use pressure for extension of the cylinders as usual, but then suction for retracting the cylinders. This suction isn't as powerful, because one is limited to atmospheric pressure, but everything is working fine with it, and this suddenly means that, given the fact that I can just fit four hoses through my small turntable, I can actually include four cylinders in the arm, just like the original Arocs! We've got the ones for the two arm joints, plus one for boom extension, and one for the clamshell bucket. Boom extension: The bucket was probably the hardest part so far in the entire MOC, needing to be extremely small, but also have pneumatic actuation! Additionally, I wanted to have the two halves geared together, but the two 8T gears teeth don't align correctly for that, so the one on the right in this picture is held in place by a lightsaber blade instead of an axle, and is then instead fixed in position by the profile of the end of the pneumatic cylinder, which forces it to offset by the half-tooth I need! I also had to include a rubber band to help the cylinder with retraction, because as mentioned before, single-acting pneumatics have weak retraction. Anyways, I think it looks nice and functions well now, and isn't too absurdly big!

Yeah, in the build I have shown here it would catch, but in the version I have now (unposted), I've shortened that drive axle and used an upside-down pin with stud for a stop, though I imagine it could also be done with a 1x1 round plate!

Thanks guys! Yeah, you've noticed the weak spot in the design! Really the only thing that keeps them from sliding apart when extended is that the racks are limited so that they always overlap each other by at least one stud. This still allows them a lot more wiggle than I'd like, but is enough of a limitation to keep them from falling out altogether, or disconnecting from the drive gears. I had thought about adding spring-loaded beams that would pop up to limit them when the other rack is out of the way, but the drive mechanism isn't really strong enough to deal with that extra resistance.

Good choice of set, and I agree, that steering is nice and clever! I may end up taking some inspiration from your bucket for the similar one I'll be needing on my mini Arocs, though I think our scale is different.

Thanks! String could work, but it tends to be fiddly and messy, so I'll avoid it if possible. It looks like limiting the drive axle should actually work fine!

Thanks! That's a good thought, and something to consider, but since the drive axle has to rotate well over a full rotation, the stop would likely need some gear reduction first. Edit: Well, that was completely wrong! Looks like I've rotation is all I need, so that is a much better option!

Here's my latest progress: First, I worked out where I wanted the outriggers to go, and came up with a simple solution to push a bush-pin down to extend the feet downwards: It required some weird half-stud offsets of the two bevel gear housings, but this setup is quite compact and works nicely, with easy control from the sides. The only real problem at this point is that there's nothing to keep the legs from going all the way out the sides, and I'm not sure how to limit them. I had tried putting a pin with stud in the other end of the racks, but that caused the racks to catch on the O-frames below them, and still lets them go out further than I'd like. Anyways, I also relocated the gears for the steering system to be underneath the O-frame, in order to fit a small turntable above the second axle. The final thing I've done is building the bed, and adding a small linear actuator to lift it, as well as a simple rotating latch to allow the rear tailgate to lock. The next step will probably be to start building the crane arm, which I'd like to have use two small pneumatic cylinders for the joints, and then after that I'll have to start the (likely) nightmare of routing pneumatic hoses in this tiny body!

Very nice work! The roofless look works well

I cannot accept such a statement as long as the 32T gear remains absent! Just kidding... Mostly! :)

Oh, I see! (Thought the low gear is actually 24:40, but I think that's irrelevant :) ) However, the thing is that all of my axle twisting is happening before gear reduction, so I'm not sure how adding more gear reduction would change anything. I suppose it would make it less likely for the model itself to get into a situation where it wants to stall, on the logic that by making it really easy for the model to crawl over anything, the path of least resistance would always be to do the crawling, rather than break parts. The question then, since I'm building this for a race, kind of comes down to how intense the terrain we're going to be going over will be! My feeling is that it might not be as intense as I built this for, and there might not really be any heavy-duty crawling, so I'd kind of like to keep my top speed up, but final drive and portal axle gear swaps are pretty easy mods to do, so I can change it as necessary when I know more about the course.

That's true; I've used that trick before, but I guess I would assume that it wouldn't hold up to extreme levels of torque, the 2L axle might not be long enough for the most convenient bracing of the portal gears. It is an option, though, and clever reinforcement could probably make it work! That is good advice, but I just don't see any way I can add upgearing earlier on, because my gearbox has extremely tight spacing and is dependent on gearing that works over a five stud space, which leaves the only options as 24:40 and 28:36, and I'm already maxed out with 40:24 gearing in high gear, and I really don't have room left to change the gearing! I may look into 56:8 gearing using large turntables, but that sounds a bit desperate and I doubt it'll work. Really at this point, I'd either have to remove the gearbox, which I'm rather attached to, or do some complete redesign of the chassis that makes more room for the gearbox, though I can't imagine how I'd do that! Really I'm only breaking parts in low gear, and there is a fair bit of warning before they break (motors running while the wheels aren't turning!), so I think as long as I avoid using low gear as much as possible, and drive carefully while in it, I should be fine.

Thanks for sharing! That's super convenient

Thanks for the advice! How would you recommend combining planetary and portal hubs? I've thought it would be a neat thing to do, but the lack of axle connections on the official hubs seems like it would have to make the hub far too wide for reasonable steering pivots. Unless you forego the official planetary hubs and use turntables or Power Miners wheels, but then you'd lose some strength. Would you say that 28T gears in that bracing are more secure than even knob wheels? I find that somewhat hard to believe, though bevel gears are definitely smoother and preferable in that regard. Strangely, though, I've finally reached a point in the project where everything is reinforced well enough that no gears are skipping, and axles and axle connectors have become the point of least resistance! Really, the correct way to fix this problem would be to move my reduction further down the line, probably swapping the 1:3 ratio I have in the portal hubs back to the 1:5 I started with, and then putting a good amount of reduction in the O-frame drive, keeping there from being high torque anywhere else in the model. The trouble here is that I really want to keep the gearbox I have in here, and it only just barely fits, so there isn't any option for me to decrease torque early on! I think I'm happy with where the model is now, because even though its ability to absorb torque is compromised, it's a compromise that allowed me to keep other features I wanted, such as its high power output and transmission, and large ground clearance.

Well, I've been grinding away at this for a bit now, and this is how it went: I found by replacing the 11L axle in the gearbox with a new one, it started working again, and is still working fine. They might become kind of disposable in this application, but they last for a while at least! Then, I spent a while creating more solid reinforcement for the 20:12 upgearing in the axles, but it still skipped, even when sandwiched directly between two half-beams! After that, I gave up on having that gearing, and eliminated it altogether, moving the ball joint back down to where it was before on the axle. After eliminating that weak point, though, gears began skipping in the O-frames in the axles, so I swapped those gears for knob wheels, restoring the higher speed I lost when I eliminated that 20:12 gearing. However, after making all these changes, I began getting issues like this on what seemed like routine, well-supported axle connections: I think that's a sign that I have reached the limits of the Lego system... Anyways, at this point, the only choices open to me are to reduce the gear reduction earlier in the drivetrain, which isn't really possible, run the motors at lower voltage, or just drive conservatively (especially in low gear). I think that last option should be fine; I'll just need to be careful!

Those are definitely exciting parts! Now the HD CV joint setup seems fully developed, and I doubt we'll see the old one much, if any, in future sets.

Also, @Jim, this question came up in my entry thread, and I thought it was worth asking here: Is it allowed to use "loose" shocks from Lego 6.5L shock absorbers? I'm using them in my current entry, though I could fairly easily switch them for rubber bands. I do think precedent would allow them, though, since I used a similar technique on my TC21 transforming Plymouth Superbird, as seen in these pictures: Thanks!

Yeah, that would be worth checking into. I actually had engineered it with rubber bands first, but then my brother suggested using springs, and it actually worked quite nicely, so that's what I went with. I could easily go back to rubber bands, though! These are the springs taken out of 6.5L shocks, though, and my impression is that it's fairly common for people to use these springs separated from their shocks, since it's not hard to take the shocks apart, so I guess I assumed it would fall within relatively puristic Technic bounds. I can check, though! [EDIT] I'm thinking that precedent should allow these shocks, since I used a similar technique without any objection in my TC21 Plymouth Superbird Yeah, kind of! It's definitely going to be tight, but I'm looking forward to the challenge.

I remember someone recommending this page to me for stud.io files: https://fogeyman.tistory.com/

[EDIT: Full presentation of the finished model on page 3] So, for this contest, the choice of set was quite easy for me! Naturally, I wanted to do something functional, but also something in colors I actually have. Given those two parameters, I decided to do the legendary(?) Mercedes Arocs set, which is special to me not only because of its all-around goodness, but also because it was my first ever Technic set, that I painstakingly researched and saved up for, and because I launched my MOCing career with its parts. Partly tongue-in-cheek, partly true section: **At first, I thought I'd use some 43mm tires to build my mini version, but that felt too... normal. If I built at a scale like that, I'd be able to put in all the functions I wanted without drama, and then I'd be expected to do boring things like make it look good, be solid, and be reliable. No! I reject such frippery! Instead, I will build with 30mm tires, making for a far smaller model, and then try to still put in as many functions as possible, which will be a fun challenge. Of course, that will give me an airtight excuse to build an ugly, fragile, unreliable model, because it'll have far too many functions for its size!** End of partly tongue-in cheek, partly true section Anyways, I'll still try to make the model reliable, but I think this small scale will be a fun challenge, which will force me to come up with interesting solutions to packing stuff in a small space. I haven't made a ton of progress yet, but I got a basic chassis done up now, including steering on the front four wheels (with different steering angles, just like the original set), and solid axle suspension on all four axles. In the front, this suspension is based on loose connections between the axle and body using flick-fire-missiles, with highly compressed springs from soft 6.5L shocks over top of them. In the rear, it is based on swingarms and rubber bands, making for a very low floor. I know I'll need it! Anyways, I'm looking forward to making more progress on this little guy! Also, just for fun, here's a couple pictures of the mini Arocs I made back in fall 2016 before I got the full-size one: Nostalgia tells me it was better than this, but it wasn't!

Very creative idea! I'm looking forward to seeing it play out

Thanks for organizing this! I've already got a set in mind, so hopefully I can get my Lada's issues sorted out soon and get started on it!

Yeah, I agree that it's an odd issue. Granted, I was testing on a slope of loose sand, which is a pretty worst-case scenario. The center of gravity is worryingly high, which could have some impact on it, but the suspension was easily keeping all the wheels on the ground. These tires aren't the stickiest out there, but they are nice and big, with helpful lugs on them. One thing I've done in the past on similar models is to stuff the tires with marbles, which adds lots of weight right where it's needed for maximum traction. I think that's not really purist enough to use for this race, though!

Well, I finally got around to taking an outdoor test drive, and immediately some major problems came to light. For one, the 11L axle in the gearbox is getting extremely twisted, and there isn't really anything I can do about it, other than scrap the gearbox. Additionally, the 20:12 upgearing in the rear axle began skipping like crazy, ruining the 12T gear. I'm not sure what I'll do at this point, but it seems pretty clear that I'll have to make some dramatic changes to the drivetrain... Removing the gearbox would really be too bad, but I'm starting to think it might be required in order to safely run the amount of power I'm wanting to have. It also has a worryingly high center of gravity, and worse traction than I'd hoped. That'd be harder to fix without essentially building a new car, but it would be good if I could come up with something to do about it. Anyways, I'll be thinking about what needs to be changed on this going forward!