Ngoc Nguyen Posted July 10 Posted July 10 Another month, another new creation! Folks here seem to like backhoes. So I did one backhoe (JCB Compact 3CX). Folks seem to want more backhoes. I looked at my first backhoe and think: It needs 1000 pieces to buid, can I make a smaller one with the same number of functions? Then Lego releases a small scale backhoe (42197). So I decided to do a small scale backhoe too, to see how much I can cramp into it. DEVELOPMENT The first thing I started with is the rim and tyre. It is tempting to use the tractor tyre, but that tyre is actually too wide compared to the real tyre. On larger model that isnt a problem, but since this model is meant to be small scale, I went with the narrower version, which comes in yellow thanks to the Bugatti Bolide. Lego has done a small scale backhoe before, which is the 42004, so I used that as a base to work on. In fact the bucket tilt and the digger arm movement are taken directly from there. Now Technic is all about the cool functions, so what functions should I put in? First, it should have proper outriggers. So I put two worm gears and 8z gears. Then I think back about the JCB Compact 3CX I did earlier to look for functions I can replicate. At this smaller scale there is no point putting a differential or a drivetrain or a fake engine. Then I realized that I made the digger arm slideable in the 3CX Compact, and I made the claim that that function can only be done at that scale. But what if I was wrong? What if I can make the digger slideable at this scale as well? In the JCB Compact 3CX, the digger arm is slideable because its width is 17 studs, which means it can accomodate a 13 stud gear rack. But this model is only 11 studs wide, and the only smaller gear rack is 7 stud long, with an effective travel range of only 3 studs. So what did I do? I used this! Two adjactent worm gear driving a fixed 8z gear will allow a movement of 4 studs. It doesnt sound like much but that's actually the maximum traveling with, as the two sides are blocked by the 3L connectors required for the outriggers. To slide the digger arm, you turn the knobs on the two sides. That creates a new challenge. The distance between two knobs is 13 studs, and there's no space for an axle connector anywhere between, as you can see above. So what 's the solution? I used two 5.5 axles on each side and a 2L notched axle between two worm gears. The rear arm, as I mentioned above, is just taken directly from 42004. The only new thing is the custom bucket, because the smallest technic bucket (part 24120) is still too big for this scale. This custom bucket is only 3x5, while the 24120 is 4x7. The slewing must be done manually as there's no space for any gear. And so that should be it right? Or is it? If you follow me long enough you will know Im not contented with just that. After all, there is no engine and drive train, which means the whole portion under the cabin is unused. Surely there's something else I can put in there. And that thing is the thing that causes me the most trouble to get right. May I present, the two steering modes: Two wheel steering and Four wheel steering. In the original design of this model, I actually tried to put 4 wheel steering and crab steering. And there is actually space for that. And not just space for that, there is space for two different ways to arrange it. The setup above is used in my mini 42082, in which a sliding axle will change the number of gears meshed with the steering axle of the rear axle. In the current position the driving will go through 3 gears. When shifted 1 stud right, the driving will go through only 2 gears, thus reversing the direction. The setup below is the sliding selector mechanism taken directly from the set 42054. But during actual test build, none of them worked, because of the backlash between the gears. I was very dismayed at first because I didnt want to leave this area unused, but I couldnt make the steering modes work. Then I realized I could have just actually gone for a more ordinary version: switching between two wheels steering and four wheel steering. Two wheel steering means I just need to find a way to lock the drive train of the rear axle instead of having to reverse its direction. And that turns out to be much simpler, and it's also a new problem to work on too, because I have never developed a steering lock before. The solution is as follows. In the current position, the connector 42003 slides into the highlighted 2L notched axle, which connects to the steering axle of the rear axle, and thus preventing it from moving. The worm gear on top can push the whole setup one stud to the left, which will cause the left knob gear to mesh with the transmission input from the steering column, and cause the right know gear to mesh with the knob gear that steers the rear axle. I cant really describe how relieving it was to see the whole thing work flawlessly in the test build. See the steering modes and other functions in action here: Overall I've had great fun developing this model and I'm very happy with how it turns out in the end. Instruction: https://reb.li/m/227596 Quote
Ngoc Nguyen Posted July 10 Author Posted July 10 33 minutes ago, vascolp said: Very very cool! Thank you!! Quote
DanOfBricks Posted July 11 Posted July 11 Good design technics style. Just 2 nitpicks. The backhoe's arm(boom and dipper portions) needs to be bigger as it looks disproportionate. If you look at the JCB 4CX, you will see the boom peaks above the rooftop. Also, nice touch on the vertical lifters/stabilizers, but you need to place technic 1x3 pieces with rounded ends at the bottom(with peg pieces), so the back tires are lifted above a flat surface. Quote
Ngoc Nguyen Posted July 12 Author Posted July 12 17 hours ago, DanOfBricks said: The backhoe's arm(boom and dipper portions) needs to be bigger as it looks disproportionate. If you look at the JCB 4CX, you will see the boom peaks above the rooftop Indeed it should, and it was like that in the original design. However in the test build, I had to reduce the size a little to make the tilting work consistently. Since the tilting is controlled through a worm gear and a 8z gear, it can't really lift the arm if the arm is too hevy. 17 hours ago, DanOfBricks said: you need to place technic 1x3 pieces with rounded ends at the bottom(with peg pieces), so the back tires are lifted above a flat surface I don't really get the setup you're referring here, can you illustrate? As for lifting the back tires, the current stabilizers work fine. In the photo below the rear wheel was off the ground and I was spinning it. Quote
Ngoc Nguyen Posted July 13 Author Posted July 13 2 hours ago, 2GodBDGlory said: Impressively functional and compact! Thanks for the support! Quote
LEGO Train 12 Volts Posted July 13 Posted July 13 The 2 or 4 wheel steering function is wonderful! Great MOC! Quote
Ngoc Nguyen Posted July 14 Author Posted July 14 12 hours ago, LEGO Train 12 Volts said: The 2 or 4 wheel steering function is wonderful! Thank you! I love it too!! Quote
DanOfBricks Posted July 18 Posted July 18 (edited) On 7/12/2025 at 7:06 AM, Ngoc Nguyen said: Indeed it should, and it was like that in the original design. However in the test build, I had to reduce the size a little to make the tilting work consistently. Since the tilting is controlled through a worm gear and a 8z gear, it can't really lift the arm if the arm is too hevy. I don't really get the setup you're referring here, can you illustrate? As for lifting the back tires, the current stabilizers work fine. In the photo below the rear wheel was off the ground and I was spinning it. Basically what I'm saying is you need to give the rear lifts platform attachments. A bit of shadow that doesn't make it so clear the rear wheels are off the surface. Edited July 18 by DanOfBricks Quote
Ngoc Nguyen Posted July 19 Author Posted July 19 5 hours ago, DanOfBricks said: Basically what I'm saying is you need to give the rear lifts platform attachments. I still have no idea what this might be referring to... Quote
Paul B Technic Posted July 19 Posted July 19 Very nice build, you have managed to add a huge amount of details. Quote
Ngoc Nguyen Posted July 19 Author Posted July 19 5 hours ago, Paul B Technic said: Very nice build, you have managed to add a huge amount of details. Thank you Paul! Quote
gyenesvi Posted July 23 Posted July 23 Looks great and it's amazingly function packed! But I'm also missing some 'ends' at the bottom of the outriggers. Maybe some 1x1 technic bricks upside down on both sides of the 5L beam, connected by a 1x3 tile? Quote
Ngoc Nguyen Posted July 23 Author Posted July 23 1 minute ago, gyenesvi said: Looks great and it's amazingly function packed! But I'm also missing some 'ends' at the bottom of the outriggers. Maybe some 1x1 technic bricks upside down on both sides of the 5L beam, connected by a 1x3 tile? Thanks for the support! As for the end of the outriggers, it's hard to put anything there due to several limits. There's no place for your suggestion because there is a space of only 2 studs behind the rear wheel for the outriggers, and the outrigger has to be offset 0.5 stud inside, which leaves only 0,5 stud on both sides. The only feasible option is this part, but without an axle hole to hold it in place, the outrigger occasionally presses it and flips it up 90 degree when it hits the ground, which is effectively the same as not having it in the first place. Quote
gyenesvi Posted July 23 Posted July 23 1 hour ago, Ngoc Nguyen said: There's no place for your suggestion because there is a space of only 2 studs behind the rear wheel for the outriggers, and the outrigger has to be offset 0.5 stud inside, which leaves only 0,5 stud on both sides. Oh, I see now, I thought there would be more space. Quote
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