[TC29] Mini Excavator

[2GodBDGlory]

After deciding to enter this contest, I went through a few different model ideas before settling on some kind of excavator. Now, there's been a fair bit of discussion lately about how the latest Volvo excavator set has failed to advance on the legacy of 8043, so this seemed like a good opportunity to see how that classic set could be improved, while retaining its basic spirit. Coincidentally, the contest motor limit of 4 corresponds with the motor count of the original set, so a similar gearbox approach will be needed to create an RC model!

Now, in order for my model to actually advance on 8043, it can't just have one motor for shifting between two modes, for six motorized functions. No! It must have at least three different modes, for nine motorized functions! However, that means that I need more things to actually motorize, which brought me to the Mini Excavator topic. My model is certainly not going to be "mini," but it will be a model of a real-world "Mini Excavator" I've worked around these cool little machines on a few occasions, and have always thought they'd make a good Technic model, on account of their extra functions, which typically include an adjustable blade on the base, a claw for the bucket, and a rotatable arm. I don't have enough motorized functions to do the rotatable arm, so I'll gladly leave it out to avoid the absolute nightmare of trying to route all the driveshafts for the arm through both vertical and transverse pivots! So, the functions will hopefully be as follows:

Motorized:

1x Servo motor for switching between three modes.

3x other motors for running three functions per mode

Functions:

Mode 1: Drive track 1; Drive track 2; rotate superstructure

Mode 2: Lift arm; bend arm; operate bucket

Mode 3: Operate blade; operate claw; tool change/PTO

To expand on a couple of those. Operating the blade is a challenge, because I've already got two functions going through the turntable for drive. What I'm hoping to do to get around that is to use vertical motion of the inner drive axle (going through the turntable) to operate the blade. It's got a sliding 8T gear on the bottom, and will be able to slide through a gear on the top as well, which should allow some other method pushing down on the axle to push down the blade (A rubber band will have to work to lift it up). It sounds complicated, but should be interesting to try to make work.

I'd like to have a tool change function to match the Volvo excavator set, and I think having a PTO for some other attachments would be nice. To fit that within my function limit, I'm hoping that I can use one motor for both, that will run the PTO while slipping a clutch on the tool change function. We'll see if that works or not.

Anyways, most of that is far in the future, but this is what I've got so far!

It's always fun when a 40T gear turns out to be needed!

Note the small linear actuators being used for manual track tension adjustment. It seemed like a fun function to include, and I had room for it!

I realize that this is an ambitious model, and I'm in very early stages, but hopefully it comes together according to plan!

I just finished college for the year, and I have yet to find summer work, so for the next while, I do have a disturbing amount of time on my hands to build Lego!

[Jurss]

Since when this is mini?

[Aurorasaurus]

27 minutes ago, Jurss said:

Since when this is mini?

7 hours ago, 2GodBDGlory said:

My model is certainly not going to be "mini," but it will be a model of a real-world "Mini Excavator"

[2GodBDGlory]

Well, I have a bit more progress to show! The only catch is that this is where the progress was at as of maybe three weeks ago, and I haven't worked on it since, as my summer schedule is a bit busier than my college one, and other hobbies have been taking up my time lately. And I now want to build a Crawler MOC for our Toronto truck meetup later this summer. With all that going on, I have given up any intention of finishing this model in time for the end of the contest. However, I do still think it's an interesting model, and I do hope to finish it at some point, even if it's not until the winter!

Anyways, this is the progress that I have:

I finalized a lot of the base of the model, and added the scraper blade. As explained earlier, this blade is the third function below the turntable, and so is activated by pressing down on the LBG axle going through the center of the turntable, like this:

After that, I started working on the distribution gearbox, but didn't get very far at all:

Anyways, I probably won't be competing in this contest after all, but I just thought I might as well get my progress to date put up here!

[Teo LEGO Technic]

Loving it! Very ambitious project indeed, but even if it isn't done in time for TC29 it definitely seems worth pursuing. How are you planning to use the servo to operate the three "modes"? If it's the PF servo, will you set it to 90 degrees left for mode 1, center for mode 2, and 90 degrees right for mode 3? If so, how do you maintain it in modes 1 and 3 without allowing it to return to center?

On 5/23/2025 at 5:42 PM, 2GodBDGlory said:

Note the small linear actuators being used for manual track tension adjustment. It seemed like a fun function to include, and I had room for it!

Great idea with the actuator to adjust the tension, ingenious!

[2GodBDGlory]

10 hours ago, Teo LEGO Technic said:

Loving it! Very ambitious project indeed, but even if it isn't done in time for TC29 it definitely seems worth pursuing. How are you planning to use the servo to operate the three "modes"? If it's the PF servo, will you set it to 90 degrees left for mode 1, center for mode 2, and 90 degrees right for mode 3? If so, how do you maintain it in modes 1 and 3 without allowing it to return to center?

Great idea with the actuator to adjust the tension, ingenious!

Thanks! You're right, the plan is to use the -90, 0, and 90 positions for the three modes. That could be done by just holding a stick in position for long periods of time, but another possibility would be to use the PF train remote, since it can hold a position

[Paul B Technic]

Great to see the progress on this, even if you don’t make the competition cut off, it would still be worth finishing it when you can.

[Teo LEGO Technic]

On 6/21/2025 at 10:41 AM, 2GodBDGlory said:

Thanks! You're right, the plan is to use the -90, 0, and 90 positions for the three modes. That could be done by just holding a stick in position for long periods of time, but another possibility would be to use the PF train remote, since it can hold a position

Sounds good! Yeah, I like the train idea - it's more elegant than having to hold a stick in a position. Alternatively, maybe it can be done programatically, like how the BuWizz app interface lets you create sliders without return-to-center. 

[2GodBDGlory]

10 hours ago, Teo LEGO Technic said:

Sounds good! Yeah, I like the train idea - it's more elegant than having to hold a stick in a position. Alternatively, maybe it can be done programatically, like how the BuWizz app interface lets you create sliders without return-to-center. 

Yeah, programming could be a nice solution, but it would most likely require using a Buwizz, which I don't have (or using PU, which is possible but rather bulky). I think I've seen some programs that can control PF from a smart device, so there's probably a theoretical way, but not an easy one

[Teo LEGO Technic]

3 hours ago, 2GodBDGlory said:

Yeah, programming could be a nice solution, but it would most likely require using a Buwizz, which I don't have (or using PU, which is possible but rather bulky). I think I've seen some programs that can control PF from a smart device, so there's probably a theoretical way, but not an easy one

Yeah, that's a good point. Alternatively, since I think you will have a physical remote, maybe you can come up with a mechanical solution to lock the lever or dial into place? 

[2GodBDGlory]

1 minute ago, Teo LEGO Technic said:

Yeah, that's a good point. Alternatively, since I think you will have a physical remote, maybe you can come up with a mechanical solution to lock the lever or dial into place? 

Yeah, I definitely could lock the lever into place, but the train remote is already a pretty ideal solution, since the dial will stay where it is and the position will be held by default. The only downside is that one of the other motors has to be run off that controller.
I could use a locking mechanism on a normal remote's lever, but then it's burning batteries all the time

[Teo LEGO Technic]

1 minute ago, 2GodBDGlory said:

Yeah, I definitely could lock the lever into place, but the train remote is already a pretty ideal solution, since the dial will stay where it is and the position will be held by default. The only downside is that one of the other motors has to be run off that controller.
I could use a locking mechanism on a normal remote's lever, but then it's burning batteries all the time

Good point, in that case, the train remote is best, you're right.