[TC25] 42043 Mercedes-Benz Arocs 3245

[2GodBDGlory]

[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:

Spoiler

Nostalgia tells me it was better than this, but it wasn't!

Edited July 20, 2023 by 2GodBDGlory

[Jurss]

This is not micromising contest :)

Not shure about those springs. Better ask @Jim if that is allowed.

But most probably no

Quote

No cutting, sculpting or modifying parts.

 

[allanp]

1 hour ago, Jurss said:

This is not micromising contest :)

Not shure about those springs. Better ask @Jim if that is allowed.

But most probably no

 

I have seen springs like that on a very old official Technic set, the second auto chassis I think. Were they the same springs as on the 6.5 soft shocks?

[Jurss]

Did some small research. In set 8860 it looks like, on the box there really was pictures with some spring and axle combination, but set came with soft shock absorbers (8860 is set with which they were introduced). Maybe some very first sets really came with that solution, but can't find. Interesting.

[Jundis]

Looks more like something @SaperPL would do :D

Curious to see if you can fit all functions in there, but great set selection!

[2GodBDGlory]

11 hours ago, Jurss said:

This is not micromising contest :)

Not shure about those springs. Better ask @Jim if that is allowed.

But most probably no

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

8 hours ago, Jundis said:

Looks more like something @SaperPL would do :D

Curious to see if you can fit all functions in there, but great set selection!

Yeah, kind of! It's definitely going to be tight, but I'm looking forward to the challenge.

Edited June 27, 2023 by 2GodBDGlory

[TechnicMOCer]

Looks so good so far! I love doing models at such scale. Looking forward to see how you will make cab and all the functions.

[Jurss]

12 hours ago, 2GodBDGlory said:

it's fairly common for people to use these springs separated from their shocks

Heve been there, have done that :)

I understood, that Jim allowed this.

[GerritvdG]

A good choice, my first set after my dark age. Really a nice and difficult challenge to shrink the Arocs to this scale

[2GodBDGlory]

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!

[Frequenzberater]

Nice ambitious project and well executed so far! Maybe you can limit the movement of the legs by blocking the rotation of the driving axle at some point. 

[2GodBDGlory]

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!

Edited June 28, 2023 by 2GodBDGlory

[lmdesigner42]

Really nice progress! I briefly considered trying to shrink the Arocs, it's a very worthy set, but I never would have attempted going as small as you are. Great work on the steered and suspended front axles, I look forward to seeing the final product.

About the outriggers, could you tie a string to the inside end to limit them?

[2GodBDGlory]

21 minutes ago, lmdesigner42 said:

Really nice progress! I briefly considered trying to shrink the Arocs, it's a very worthy set, but I never would have attempted going as small as you are. Great work on the steered and suspended front axles, I look forward to seeing the final product.

About the outriggers, could you tie a string to the inside end to limit them?

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!

[Jurss]

That outriggers solution is genious!

[MangaNOID]

On 6/27/2023 at 10:47 AM, 2GodBDGlory said:

with different steering angles, just like the original set

I really like that steering solution 

[Paul B Technic]

This is coming along really well. I am not going to join in this challenge but I am really enjoying following the progress of all the builds.

[SaperPL]

I really like the outrigger approach - how are you keeping the gear racks apart though when they are extended? I mean the only thing holding them is the gear, but can they slide sideways on this gear?

[2GodBDGlory]

Thanks guys!

8 hours ago, SaperPL said:

I really like the outrigger approach - how are you keeping the gear racks apart though when they are extended? I mean the only thing holding them is the gear, but can they slide sideways on this gear?

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.

 

 

[lcvisser]

Can you put a single 1x1 round plate with the stud into the end of the gear rack, or does that catch on the drive axle of the other outrigger?

[2GodBDGlory]

11 minutes ago, lcvisser said:

Can you put a single 1x1 round plate with the stud into the end of the gear rack, or does that catch on the drive axle of the other outrigger?

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!

[2GodBDGlory]

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!

[gyenesvi]

That crane is looking really neat, ingenious idea with the suction based actuation, curious how it will work in the end, but at this small scale I can imagine it to be really okay! I wonder how much space you'll have left for the cab though..

[SaperPL]

I like the challenge of making those kinds of models, it's always interesting to see what people come up with in tight spaces, but it feels to me like this kind of approach ends up with everything holding onto mechanisms themselves with barely any frame. I did try doing those, but usually ended up with either something being too weak or not having enough space to fit something important. My small wheeled excavator would be the prime example of that :)

Aren't you afraid that handling of pneumatic controls will take too much space of the cabin?

Also what is that 1 stud long pneumatic/rigid pipe acting as a pivot point for the arm? Is that cut into length and allowed or is that an actual standard lego piece?

[2GodBDGlory]

3 hours ago, gyenesvi said:

That crane is looking really neat, ingenious idea with the suction based actuation, curious how it will work in the end, but at this small scale I can imagine it to be really okay! I wonder how much space you'll have left for the cab though..

Yeah, I'm hopeful that the suction will work!

I was surprised to see how far forward the cab goes ahead of the front wheel, so I'm hopeful that it'll work out fine. It'll probably be a nasty mess of valves, hoses, and a pump, though!

2 hours ago, SaperPL said:

it feels to me like this kind of approach ends up with everything holding onto mechanisms themselves with barely any frame.

I know that feeling well! Hopefully I can avoid it here, but maybe not

 

2 hours ago, SaperPL said:

Aren't you afraid that handling of pneumatic controls will take too much space of the cabin?

Well, I am afraid, but I'm willing to give them the whole cabin if necessary, so I think I've got a good chance.

2 hours ago, SaperPL said:

Also what is that 1 stud long pneumatic/rigid pipe acting as a pivot point for the arm? Is that cut into length and allowed or is that an actual standard lego piece?

It's a 4mm rigid tube cut to length. I think they're allowed, since cutting those tubes is a standard thing to do (I think required in certain old sets?), but I will admit that cutting them to 1L is somewhat bad form. I'm noticing that the boom can easily hinge at that connection, though, which it isn't supposed to, so I'll be investigating ways to change that.