[TC29] Liebherr R 926 compact excavator 1:21

[crazy technic]

here's my submission to this competition, I decided on a  compact excavator by liebherr., as it's the perfect candidate for this, it's: compact, has many functions and most importantly tracks :)

here's a first attempt at a undercarriage, it has track tentioning using shock absorbers, 2 motors for drive, 2 motors for other functions, currently I have a gearbox planned for the supperstructure.

I have exams coming up so I will only digitally design it at this moment, later I will do the physical design.

 

and here's the real one

 

[Auroralampinen]

Looks great so far:).

[crazy technic]

11 minutes ago, Auroralampinen said:

Looks great so far:).

thanks, I think it will get even better, Im not sure yet if I will use pneumatics or linear actuators

[1gor]

Do you plan to have all functions to be motorized? If so you need additional hub / battery box in upoer carridge...and better use actuators with motorizstion.

BTW looks good; a while ago I was thinking about blue wheeled version (I saw it on my way to work)....but I'll see. Perhaps I got some interesting idea from you...

[crazy technic]

4 hours ago, 1gor said:

Do you plan to have all functions to be motorized? If so you need additional hub / battery box in upoer carridge...and better use actuators with motorizstion.

BTW looks good; a while ago I was thinking about blue wheeled version (I saw it on my way to work)....but I'll see. Perhaps I got some interesting idea from you...

yes, all( or at least the most important ones) will be motorized, the contest only allows 4 motors, so I will have to use a gearbox for more functions, motorzed pneumatics are also posible, I just did it for a secret project that's 99% finished, but 5/6 pneumatic motorized functions will definitely be hard, even if I would use linear actuators it would still be difficult

 

[1gor]

1 hour ago, crazy technic said:

yes, all( or at least the most important ones) will be motorized, the contest only allows 4 motors, so I will have to use a gearbox for more functions, motorzed pneumatics are also posible, I just did it for a secret project that's 99% finished, but 5/6 pneumatic motorized functions will definitely be hard, even if I would use linear actuators it would still be difficult

 

Sorry I forgot about 4 motors...indeed gearbox would be complicated in such narrow space

[crazy technic]

I already have almost finished the gearbox the superstructure rotation is already connected. now I need to decide if I will use pneumatics or linear actuators

[1gor]

I would go with actuators because they enable smoother operation...

[crazy technic]

I am also more and more leaning that way, also because I could add a extra manual gearbox part, so that the motorized switching engages one of 2 functions that are then selected manually, because the 3 remaining  gearbox outputs aren't enough for 5 function

 

[crazy technic]

here's another update, the gearbox is done, it consists of 2 parts: a motorized selected part, and manual part, the motorized selector selects option 4 and then you have to chose between 2 other functions, 

this was the only option to get 5 functions + a gearbox in this small space. and you will rarely have to switch between the 2  manual functions as one of them is hardly used (and optional in the real excavator)

I also managed to build the dozer blade on the front, that will also be a manual function, because it wouldn't be possible to add more functions to the gearbox.

[crazy technic]

Im finaly back, exams are over so now I have time again, 2 days ago I bought the Volvo 6x6 articulated hauler( mostly for Parts), build it yesterday, and took it apart again today and used the pieces to finaly get a actual model. 

I completly mirrored the entire build because it alows me to put stuff in the cabin, the rear of the superstructure if completly filled with a gearbox, and all the motors + hub are in the undercarrage. If I only used Linear actuators in would need 3 driveshafts going through the first part of the boom( which is probably impossible at this scale). That's why I decided to use motorized pneumatics on the bucket cilinder( reply if you know a other way) 

 

 

After being stuck in this problem for multiple weeks, I have finaly made progress again, certain Parts needed some changes but overall I mostly used the( mirrored ) digital design. 

[dhc6twinotter]

This is looking good!  With the motors in the base and gearbox in the superstructure, how does the gearbox compensate for the rotation of the superstructure?  Seems to me the gearbox will be changing position whenever the superstructure is rotated.  Maybe I’m overthinking this. 😂

[crazy technic]

5 hours ago, dhc6twinotter said:

This is looking good!  With the motors in the base and gearbox in the superstructure, how does the gearbox compensate for the rotation of the superstructure?  Seems to me the gearbox will be changing position whenever the superstructure is rotated.  Maybe I’m overthinking this. 😂

It actualy happend, I locked the axle where they motor should be and shifted by rotating the superstructure, but I knew it was going to happen, I am planning to use the magic of programming to fix it: only if superstructure rotation is activated the shifting motor compensaties, but I still have to do it

[Aleh]

@crazy technic based on my own experience I'm reccomend to consider soft shock asorbers for tracks tension, because hard one make it too hard and obviously extra load for motor

[crazy technic]

2 hours ago, Aleh said:

@crazy technic based on my own experience I'm reccomend to consider soft shock asorbers for tracks tension, because hard one make it too hard and obviously extra load for motor

when I actualy build it I relized the distance is perfect so I decided to not use the track tention mechanism, I might still ad it again later.

 

[crazy technic]

made some good progress in the last 2 days, I fixed all the issues with gears clicking, and now all the functions work properly, I also added a manual tiltrotator and quick coupler for the bucket, and of cource the second part of the boom and stick.

On 6/26/2025 at 1:21 AM, dhc6twinotter said:

This is looking good!  With the motors in the base and gearbox in the superstructure, how does the gearbox compensate for the rotation of the superstructure?  Seems to me the gearbox will be changing position whenever the superstructure is rotated.  Maybe I’m overthinking this. 😂

not only the shifting is affected, but also the power to the gearrbox made the superstructure spin when there was too much torque, this was solved by driving the turntable by a worm gear, this however meant i had to use the old type of turntable, but at least now the other functions don't make it spin anymore :) 

I have also made a quick prototype for the pneumatic function, that currently seems to work pretty well, tommorrow I will try to do a bit more on that, unfortunately due to the size of this mechanism there will probably be no interior to the cabin. 

[CK28]

This looks really promising! I got a soft spot for excavators but most lego technic versions have a standard two piece boom. I can imagine it will be quite the challenge to fit everything in, i will follow your progress with great interest!

[Paul B Technic]

Nice work and great progress.

[crazy technic]

On 6/29/2025 at 8:44 PM, CK28 said:

This looks really promising! I got a soft spot for excavators but most lego technic versions have a standard two piece boom. I can imagine it will be quite the challenge to fit everything in, i will follow your progress with great interest!

it's indeed completely filled by the gearbox and electronics, so far everything works, but coding has been a bit of a issue especially the correction for the turning of the superstructure. 

it's pretty much finished, only a (manual ) dozer blade will be added to hide the motors a bit more, the rest works all motorized, instructions are expected end of August or September, since I had to change quite a lot due to not having the parts I will have to rework some parts of the digital model.

here are some pictures of the model

[Paul B Technic]

That is coming along really well.

[crazy technic]

8 hours ago, Paul B Technic said:

That is coming along really well.

thanks, but unfortunatly I am on vacation for most of the time left,  so I pretty much have 3-5 days left to finish it, so hopfully that will be enough to film the youtube video, and fix the last part of the code

[1gor]

It looks really beautyful. Years ago I planned to build one, but rear part of R9xx litronic compact excavators is much more rounded than curved panel 3 x 13, so I deciced not to make it due to parts shortage...and I wanted full RC with 8 functions...

Did you made scaling (into 1:21) based on sprocket size or width?

Enjoy your wacation.

[crazy technic]

5 hours ago, 1gor said:

It looks really beautyful. Years ago I planned to build one, but rear part of R9xx litronic compact excavators is much more rounded than curved panel 3 x 13, so I deciced not to make it due to parts shortage...and I wanted full RC with 8 functions...

Did you made scaling (into 1:21) based on sprocket size or width?

Enjoy your wacation.

I first decided on the scale because most of my other models are in the same scale so they fit together, after that I chose sprockets and everything.

coding works( I think) I just dicovered you can use varibles in the powered up app so that fixed most of the issues.

[CK28]

Absolutely great build you made in quit a short time! Is the machine turning smoothly tho? It looks like there is almost no space between the tracks and superstructure.

It kinda bugs me that the cabin is filled, but considering the scale and alle the functions you crammed in i will forgive you that 

[crazy technic]

it uses a worm gear now, and i had to switch to the older turntable for that to work, but the turning is very smooth, the only problem is I can't film it because I use the same phone to operate it, but i have an actual camera for the YouTube videos, before I used the worm gear it used to get stuck, that's why there is the wheel on the front below the boom, that does help when it has to get over the hub in the rear(but is only supported there)   also because the real machine has a dark grey stripe at the lower part of the superstructure, I accomplished that by adding tiles, so that makes the gap look smaller, but everything works perfectly fine, the driving is surprisingly fast but still strong enough for some off-roading.