Midsized excavator with 8 PoweredUp motors

[Appie]

I wanted to make a excavator as small as I could with PoweredUp and 8 functions, this is the result (so far). It's not based on any real life model.

It uses 2 Technic hubs with Pybricks. One hub in the undercarriage and one in the superstructure.

The hub in the base does the following:

• Drive with 2x L-motor (motors inside the tracks based on this design from crazy technic)
• M-motor for turning the superstructure
• M-motor for blade lift

The hub in the superstructure has the following motors:

• 1 L-motor to lift the base of the arm
• 1 L-motor for the two-piece boom lift
• 1 L-motor for the stick (hidden in the first part of the arm)
• 1 L-motor for the bucket (M-motor would have been sufficient, but the wire is shorter of a M-motor, which would make it to the hub barely, this L-motor is in the second part of the arm)

A few more pictures

 

 

 

 

 

Interior can house a Technic fig.

Easy access for a battery swap for the hub in the superstructure (on/off button is reachable from below, I might make a little mechanic at some point, but so far I like being able to just use my indexfinger to turn on the hubs).

A deeper look below the bodywork:

 

 

A few shots of the arm positions:

Folded

Maximum height

All LA's at maximum extension results in a bucket being level to the ground 

 

 

Maximum reach

Ideally it would reach the ground in this case, but 7 studs from the floor was the best compromise I think with how the boom stands when upright. In order to reach the ground I only need to turn in the "two-piece boom" LA about 0.5 studs in this case.

 

The blade sadly is unable to lift the model. It's a wormgear on a 8T gear. Maybe it would be able to if I replace the M-motor with a L-motor. I am currently considering it, since it would fit in the undercarriage, but where the extra wire length of the L-motor was a boon for the motor in the arm, it might be too much to cram in the undercarriage.

At one point I had a mini-LA in the undercarriage for the blade, but I wasn't satified with the kinematics of the blade and the general look of the attachment point of the LA. That mini-LA mounting point would have been about 2 studs above the desired (current) height of the blade.

Here's an image of an earlier version of the undercarriage with the mini-LA:

It was too far forward to be ideally functional, but I had very limited options to move it further back, wires (from one of the L-motors that handled drive) were in the way and/or I was sacrificing structural integrity, both not what I wanted.

 

Rear view of the underside:

In the final version the wires near the end of the the undercarriage are secured below some bars I inserted into some half pins. As you can see near the turntable I placed a bar accross the entire width of the hub so it wouldn't ever get caught on the turntable.

 

Besides the thing with the blade, there's another issue I still want to tackle. If the arm is at "maximum reach" and I turn the superstructure 180 degrees (facing backwards), the 12T bevelgear on the turntable will skip. This is pretty much the only scenario in which it does this since I moved the whole superstructure backwards 1 stud (it would do it any position of the arm before at times). I am considering a few options to fix this like the good old, but still in production (at least until 2021) Lego weight bricks or perhaps add another kind of support (like a wheel) bel;ow the superstructure that can run over a closed off front and rear of the undercarriage (in which case I will need a mechanism to turn on the hubs).

There's also another little issue with the turntable, which wobbles a little in certain spots of turning. It would even do this without a superstructure on top. Swirling the turntable a bit in hand and then putting it back would make it go away for a while, but it's not a permanent fix. Funny enough I found this problem with another turntable before I even started working on a superstructure and replaced it for this one which didn't have the problem, at first at least  Maybe a slightly better balance with the rear would help with this problem as well, but adding those weight bricks for example would mean adjusting the body work and I like how it looks now 

A video will have to wait a bit as I want to brainstorm a bit more about these issues. I do consider these issues pretty minor though. The wobble I don't really mind. A buddy suggested teflon spray to tackle that, but since I am not really losing any cargo while it wobbles, it's not a big deal to me. The skipping 12T bevelgear for a maximum reach arm turning to the rear of the model is a pretty niche situation I think (would an operator of an excavator normally even do this except for fun?), but I never like a skipping gear so I would avoid that scenario if I can't fix it. The blade not being able to lift also annoys me a little. It's still doing what I wanted it to do: act as a bulldozer in time of need, but still. The blade isn't even needed to prevent the model from falling over, but I still think it should be able to lift the model, but I can't think of a solution in the given space and desired blade kinematics besides slapping in a L-motor and hoping it does have enough power to move it. 

As always, thanks for reading and looking at my pictures 

[1gor]

Extraordinary build, just fascinating how you manage to squeeze all that electronic in such tight space.

[gyenesvi]

Wow that looks really neatly packed with electronics again, maxing out the two hubs, nice job :) Also it seems just the right size for lego motors. Does it have good playable speed? I like the simple but nice looks as well.

[Appie]

Thanks guys! 

19 minutes ago, gyenesvi said:

Does it have good playable speed?

Yeah it's good.

For the arm:

The main boom lift is on a 2x 12T:20T reduction (not sure if it is "needed", but figured it wouldn't hurt if I was able to), the second section is on a single 12T:20T reduction, the stick and bucket have no reduction in speed (both 1:1).

 

Tracks are 12T:36T reduction, so it has adequate speed and good torque to move the model. 

 

The turntable is a tad slow (you can't keep the superstructure in the same spot while turning the undercarriage in its place like the 8043 set) with a wormgear to 20T and a 12T bevelgear to a 60T turntable. In the given space it was the only possible gear combination with a decent gear reduction for the turntable I think. 

[thomas92]

Wow, very impressive build. And nice to see Pybricks mentioned. How are you planning to control the two hubs and do they communicate with each other?

Quote

There's also another little issue with the turntable, which wobbles a little in certain spots of turning. It would even do this without a superstructure on top. Swirling the turntable a bit in hand and then putting it back would make it go away for a while, but it's not a permanent fix. Funny enough I found this problem with another turntable before I even started working on a superstructure and replaced it for this one which didn't have the problem, at first at least  Maybe a slightly better balance with the rear would help with this problem as well, but adding those weight bricks for example would mean adjusting the body work and I like how it looks now 

This has been driving me crazy as well, I commented on it in the thread below as well. So far I only one (!) out of seven Z60 turntables that I own runs perfectly fine. Two mesh really badly with the 12T gear and the others are just not great either but okay-ish, sort of like what you describe. 

I am trying to figure out if this is a problem in older or newer sets. The thing is that 42042 is a set from 2015, and that uses a similar set up as yours. And I would assume it meshed fine back then. The Z60 beveled turntable gear was in sets between 2015 and 2021.

Edited 10 hours ago by thomas92

[Appie]

Thank you! 

1 hour ago, thomas92 said:

And nice to see Pybricks mentioned. How are you planning to control the two hubs and do they communicate with each other?

I use a similar setup as the Pybricks program for the 42146 Liebherr crawler crane.

The hub in the undercarriage of my excavator sends a signal to the hub in the superstructure to control those motors.

I did slightly adjust the waits in the program to 40ms for the undercarriage hub and 10ms for the superstructure hub, because it felt like a real delay in my input with both at 50ms, which was mostly annoying when you want to stop a motor (and not have the LA click because it is at the end already).

Maybe I can adjust those waits further or even the basic 50ms for the undercarriage and 0ms for the superstructure, but this works well as it is now.

And yeah, I came across that topic about that turntable issue last week or so and thought this was what you experienced, which is why I immediately tried another turntable which hopefully would work properly, but alas, it was short lived.

I have like 7-10 unused of these turntables, but only 2 unused are assembled as of now. I have had most/all for years and the few that are in other builds, aren't driven in this way with a 12T bevelgear (or driven at all even). 

[Jundis]

I don't like the looks of it.

This is where my critics end, the whole build is such a great package of functions! :D

You squeezed in all the essential in such a tight form, its fascinating , let alone the range of motion of the arm! Great work, Appie!

 

[Appie]

Thank you very much @Jundis! 

I understand that the looks are a little different from a conventional look for this kind of excavator (usually they have a higher and shorter rear and the superstructure as a whole is shorter compared to the tracks). Earlier in the build I did consider the hub and motors in a upward position on the superstructure, but this layout I ended up using (especially for the motors) turned out better and this also worked better as a counterweight for the arm. It not being based on a real life excavator, gave me some freedom to build it like this, but no problem of course if you don't like how it looks. 

Something specific you don't like about the looks or just in general? 

[Jundis]

It's hard to put it in word but I think the colours don't "flow" to my taste, can't really tell actually.... Maybe the DBG in the mix?

The shape itself is really nice, as street excavators need a short (or better non) overhang at all to not disturb any obstacles.

The 3x11 curved panel on the first boom is great, the second one also looks nice, only the third one seems a little thin imho.

Really care for your response about my humble opinion :)

[Appie]

I see @Jundis, thank you for the feedback. What DBG do you mean exactly, from the LA's, tracks or both? For the tracks I thought the undercarriage would be too much black with black tracks, but that choice was made before I even had a superstructure, so maybe I should revisit it again. 

As for the DBG of the LA's, I have black LA's which I didn't try actually, but those also have the DBG section and I think I like the LBG of the current LA's more on the model.

I agree the third section looks a bit thin, I wasn't sure how to make it thicker and the dark blue section of the arm kind of disappears into the white in the second section (which I like) that I did not want to reintroduce that colour in the third section, perhaps I should look into making it thicker around the LA with just white, maybe on the underside of the stick as well?