[TC30] Mini Backhoe and Dump Truck

[2GodBDGlory]

Well, I just got back to my apartment (and Lego) for my next semester, and conveniently, I've got a much lighter class schedule than last semester--plus my 3D printer projects are winding down! Altogether, I might actually have some time for Lego this time around!

For topic, I decided to go with a backhoe, since they're infamously function-heavy, and I was curious what I could do with that at a small scale. For a companion model, the obvious choice seems to be a dump truck that it can load up, but I haven't actually started that, and I suppose it could change if I think of something better

This is what I've gotten put together in my first night of work. I'm not sure the wheels match each other too well sidewall-wise, but otherwise I'm quite happy with the combo; mainly since I think I've only used the front tires one other time, and the rear ones never!

We've got basic steering on the front:

And a basic, compact worm-gear traverse for the rear arm:

There's also a worm gear and 20T gear for the first stage of the boom:

Finally, we've got another worm gear meshing with one of those weird 12T gears with an axle sticking out of it, to allow for boom rotation:

That's the last part I built, and I'm not 100% happy with the worm gear mesh there, because it's technically 1/4 stud too tight. If I could move the worm gear downwards 1/2 stud to have it mesh with the beveled part of the gear it would work better, or if I could drive it with a 1L worm gear at a half-stud offset longitudinally. Unfortunately neither of those options appears too easy at the moment, and it does work as is, so we'll see what happens.

We're currently sitting at 110g, which seems like a good amount for this stage of progress

I've quite enjoyed the work so far, and am glad to be back into the Lego!

Edited January 11 by 2GodBDGlory

[Jurss]

Finally see good use for that weird gear wit axle. Also have them, but never have found use.

[2GodBDGlory]

I've made some good progress over the last couple days! The rear arm has been finished, with worm gears for the joint and bucket, and the front arm has been added. A worm gear lifts the 4-bar linkage, and another worm gear runs the bucket. I also added some simple outriggers to the rear, and got gearing for the steering set up. Really I've just got to do a little bit of bodywork and interior, and this model should be done!

[2GodBDGlory]

I guess we're done! Got the cab and some details added, and I think I'm happy with the result! Weighing in at a comfortable 254g

Now to build the second model!

[Jurss]

Could be MOC with most worm gears, where each has different function.

[gyenesvi]

That's a pretty cool one, nice feature density and simple, recognizable shaping! If only it was yellow :)

[Thirdwigg]

Great job, and quite a density of function in this little backhoe. Keep it up.

[2GodBDGlory]

8 hours ago, Jurss said:

Could be MOC with most worm gears, where each has different function.

At least for the size, maybe! I think there's 7 different worms/functions in it

3 hours ago, gyenesvi said:

That's a pretty cool one, nice feature density and simple, recognizable shaping! If only it was yellow :)

Thanks! Yeah, yellow would be more fitting, but I still have virtually no yellow. Rebrickable tells me that (aside from axles,  bushes, shocks, pneumatics, and pistons) I have only 157 yellow Technic parts, from only 15 types of elements...

13 minutes ago, Thirdwigg said:

Great job, and quite a density of function in this little backhoe. Keep it up.

Thanks, I appreciate it!

[1980SomethingSpaceGuy]

This looks nice!
But I agree with @gyenesvi; a brighter color would do it more justice...

[Timewhatistime]

On 1/11/2026 at 4:50 AM, 2GodBDGlory said:

 

Finally, we've got another worm gear meshing with one of those weird 12T gears with an axle sticking out of it, to allow for boom rotation:

 

I really like the fact that you not only use the weird 12T gears with the even weirder axle sticking out of it, but additionally use its weird pinhole to brace the black 12T gear which controls just another funtion.

I never managed to find a good usage for this weird part.

[Jundis]

I really like the brick built rear bucket!

But the front one looks strange... is the 7x10 bucket too big? 

[2GodBDGlory]

11 minutes ago, Jundis said:

I really like the brick built rear bucket!

But the front one looks strange... is the 7x10 bucket too big? 

Yeah, it did feel like an imperfect solution.

I don't have the 7x10 bucket, but I do have the older 8x10 one (https://www.bricklink.com/v2/catalog/catalogitem.page?P=2951&idColor=11#T=S&C=11&O={"color":11,"iconly":0}), and I recall thinking it looked too big. I think the width from one front tire to the other is about 10 studs, which would make the larger bucket as wide as the model. I didn't think that looked right, but I could look at whether a change would be better!

Looking at blueprints of backhoes does suggest that buckets should be as wide as the model, so maybe it would be a good idea!

[2GodBDGlory]

Thoughts on the bigger bucket, @Jundis?

[1980SomethingSpaceGuy]

Looks better to me!

[Jundis]

Yeah definetely better!

But maybe you have to shorten the main boom a little bit? 

As I understand, you have a steady lift with the parallel arms and the tilt of the bucket via the worm gear, right?

If you have some grams of the weight limit left, alternatively you can also extend the front axle a little bit more.

[2GodBDGlory]

I managed to move the bucket two studs back, so I think the proportions are working properly again!

Thanks for the feedback

[2GodBDGlory]

All right, the dump truck is well under way now!

I feel like it's probably at a somewhat smaller scale than the backhoe, but I think the difference is no greater than it was between the truck and the loader in 42023:

So we've got steering on the front axle, and a micro V6 driven by the two rear axles (no differentials at this scale, but it doesn't seem to be a problem)

Then we've got a tiny 4-bar linkage to raise and lower the second axle:

And that small linear actuator to raise and lower the bed:

I had considered such wild ideas as trying to get some kind of suspension or gearbox installed, but I don't think those are particularly realistic. Functionally it's largely done, but I was thinking it would be really cool to add some kind of mechanical cover for the bed to prevent the load from flying out on the highway

Like the bars on the side of this truck's bed

However, I'm really not sure what I could use for the material for the cover. A real truck appears to be some form of fabric that can roll up, but that's not really an option for a purist, contest-spec build. Maybe I could figure something out with chain or track links? Or a flexible construction of liftarms? I'm not sure if I'll be able to come up with anything workable, but it would be cool if possible!

[Thirdwigg]

I'm happy to see the dump truck has a draft now. I'm looking forward to see the bodywork you use to cover all those functions. Great job so far.