Ngoc Nguyen

Technic is not doomed. In fact Technic as a building system is very much alive and evolves every year. As it get more new parts, new possibilities open up. It's just Technic as a brand feels stagnant, but that is when the Technic spirit should be found elsewhere. (Like my JCB 3CX Compact Backhoe perhaps )

As explained above, this MOC is considered done, but the quest for perfection makes me feel restless when the superstructure tilt exists. Thanks to the consultation of Milan, who has extensive experience with cranes, I had to redesign the turntable. The main reason is that the supercarriage only rests on a turntable which has a lot of slack. The superstructure design is also not optimized in two ways: the connection point with the boom is not placed far enough to the back, and the counterweight can be made bigger. As you can see be low, the connection point, which is where the yellow axle is, is rather close to the center. This creates another problem, which is that it takes a lot of force to lift the boom. Therefore, for the superstructure, I made the counterweight thicker, and moved the connection point 4 studs back. That's the furthest that it can be moved. Since the new position decreases the maximum angle of the boom, I replace the medium LA with the large LA. I also fortifed the area at the front of the superstructure, under the large LA (the black 3L connector). That is where the superstructure will lean on. A slight downside is that the boom can't rest in a position parallel with the body anymore, but that hardly matters. The fact that the boom is at a slight angle can be explained to allow the operator to see the mirror on the other side, even. For the undercarriage, I used the gear rack quarter from the set 42160 to form a ring that the superstructure can rest on. This means I had to replace the big turntable with the small turntable, and rework the gearing that drives it. The result is that the model looks better now, and doesn't show as much tilt as before. It also requires less force to raise it. I had to redo all the renders and the function sheets, and that's a huge chore, but I have to do it since the design has changed considerably. At least I can find comfort in the fact that this model has reached the best form that it can be, and I can finally feel at ease.

I love those renders too! Even though they are a pain to make, the final results are totally worth it. Thanks mate

How the two mode steering and the steering shift works:

The reel is fixed. There's no space in that area to make a functioning rotating reel. Hence the jackhammer's hose is connected to the DBG hose connector behind it. The mini LAs are connected through a 12L axle that extends only to the left side (the other side of the model) and can be driven only from there. The hose is connected to the black connector through a black 2L axle with notched.

Thanks a lot! Please try it out, it's very fun to build and play. The whole model fits perfectly into a 17 stud width. Thanks a lot!

I realized it didnt actually take much time so I actually went back and redid all the renders. Thank you! Thanks a lot! Thanks for the support! What do you mean similar breathing

Shoot you're right... Thanks for pointing that out. I've just updated the instruction. As for the renders they took too much time to do so I'll just leave them there.

I know right, the jackhammer is very fun to play with The steering is actually very smooth. It's just that my hand is big while the opening is small, and I can only use one hand as the other hand is holding the phone. It is possible to route it to under the rotating seat to transfer motion to the HOG on the roof, but doing so will requires making the seat rotation manual, which is not very desirable as it's hard to reach inside, or removing the seat rotation altogether, which doesn't make sense for a backhoe. So I decided that routing it to the steering wheel is the best solution.

Thanks a lot for the support!

WOW I got frontpaged I've never thought I could get frontpaged yeahhhhh (Actually I got frontpaged once already but that was for the 42113 Review, not for any MOC)

INTRODUCTION The collective interest in a Technic backhoe has been around since as far as when I first joined this forum, which was 10 years ago. Such intense interest is understandable: a backhoe is one of the most complex, if not the most complex vehicle for a Technic model, since it has a lot of functions while its main body is rather compact. Hence, as I see it, a backhoe is like an apex of Technic or at least Technic construction machines. Yet there are not many official Technic backhoe. Before this year the most recent iterations were 8069, a medium sized backhoe set released in 2011, and 42004, a mini version released in 2013. That means there was a whole interval of 11 years with no new backhoe. Then this year a backhoe appeared in the lineup, but it turned out to be a mini version, an arguably worse iteration even, given that it has less pieces and functions than the 42003. Even though the full 2025 lineup is not revealed, since there's already a mini backhoe, it's unlikely that there will be another medium sized or flagship sized of the same subject. Therefore I decided to publish my own backhoe this year. DEVELOPMENT The design process for this model actually started in late 2021. Back then I wanted to build a road construction playset that contains a backhoe, a trailer, and a truck from the Heavy duty Tow Truck 42128. I don't have the file for that model with me anymore, but here's a custom digging bucket I built from 42128 parts. At that point I already finalized the digging arms. Its design stay unchanged in the final model. But then for some reasons I lost interest along the way so I stopped working on it. Then last summer there was a Technic Contest that involves building models around the 49.5 tyre. That was when I took that backhoe out of the freezer and combined it with features from my 42157 alternate model. Then I encountered two problems. The first problem is that I've always wanted to build the JCB 3CX Compact. It has to be the 3CX Compact and not 3CX or 4CX because the 3CX Compact has 4 small wheels, which allows more space in the body. In real life there are versions of JCB 3CX Compact that use truck tires like the 49.5, but I think it just looks stupid. I want it to have proper tractor tires. The second problem is that I was stuck at the rear wheel arch. In the real vehicle the arch is yellow with a thin black line. I struggled to recreate that in the small scale. So even though I made quite some progress, I lost interest in the summer and left the model in the freezer again. By that time I got most of the main body done. You can also see an attempt at the wheel arch. Then in November I happened to open this file again, and I felt that I can finish it. I spent a couple of weeks in November on it to finish the preliminary design, then wait for the parts. When I did the test build, most functions turn out fine, except the front loader arms. There will always be something that looks nice on Studio but doesn't actually work and require a redesign. This is how the prelim looks like. I already revealed it in my Technic corner. You can compare it with the first image to see how the front loader arms have changed. In the end I managed to make everything work flawlessly! DESIGN HIGHLIGHTS Since it's a small scale backhoe, most functions are directly driven through knobs, so there's nothing fancy in that regard. However there are other nice things I want to share. Chassis: The whole chassis is nested in side a pair of 3x19 yellow frame. This piece is very usefull as you can form a chassis right away without having to extending it with beams. It is only 5L wide, so I have only 3L in the middle to squeeze 3 functions: drive train, steering, and rotating seat. This is how everything is arranged. Inline 4-engine: I managed to make everything black while giving the piston heads yellow half bushes, so it looks very cool and luxurious. Two-piece hood. In the real 3CX, the lid together with side walls can be lifted up separately from the front grill. In my model I made them openable separately too. I managed to put a fan behind the grill as well. Cabin interior: I managed to replicate some details. In the real cabin there are 3 pedals, two gray ones on the left and one black one on the right. The seat is only rotatable counter clockwise, because there's a control panel on the right side. There are 3 joysticks, and the two in the back are adjustable once you turn the seat around. Sliding digging arm: This is the function I like the most and want to incorporate into the model at all costs. For a compact backhoe, it's very important that it can slide the digging arm to one side to fold it up stay compact while travelling on the road. The sliding is designed like this. You use a long axle to spin the axle connectors on both sides to move the arm. Jackhammer and hose reel: On the right side of the model I put a reel, a pneumatic connector, and a jackhammer. If you have a spare pneumatic tube you can connect the jackhammer to the vehicle. This setup is based on this real life variation of the JCB 3CX Compact. FUNCTIONS I had a lot of fun designing and playing with this model. Most importantly, this model satisfies my burning long-held desire to have a functional Technic backhoe. So if you're like me, you can gather the parts yourself and build this model too! According to Rebrickable, the total costs for the parts are around 150 EUR. I'd say it's a fair price for a 1100 piece Technic set with full of functions and playablity. I tried to minimize the use of rare parts so that it's easy to gather the parts for this. The only uncommon parts that are used are the 3x19 frame in yellow, which can be substituted with the more common 3x19 frame in black if you don't mind the color, and the Bionicle tooth in yellow, which will be available later in 2025 in the Chevrolet set. INSTRUCTION: https://reb.li/m/207516

Now that I've implemented the new gearing for the rotation, the model is in its most perfect form and I can finally move on to the next one yay. But before that I would like to share some design highlights, which are the solutions that I used in this set and felt very good about. Front Mudguard: The only solution that works is two #4 connectors, but they will be off center. Therefore I offset them with cranks and the cranks are held on the other side by thin 3x3 liftarms. Bullbar + number plate: This white piece keeps the bar in place and serves as the fake number plate. Sun Visor: A full liftarm is too bulky, while a half liftarm can't be secured through one point only. Fortunately I remember the existence of this plate, very useful. Steering: Since the truck is 9L long only, the distance between two steering connectors is only 5L. Therefore usually at this scale the steering is not done with a steering rack, and at first I didnt think it was possible either. Fortunately I discovered this way of connecting it. It sticks out a little bit but since it's black it's hidden quite well. Compact rear body: In the original model the rear body is 10 studs tall. When shrunk by a factor of 3/5 the rear body of the mini model should be 6 studs tall. But the best part is that I don't even use 6 studs for all the gearing and mechanisms. Only the side walls are 6 studs tall. The middle sections are confined in a 5 stud height. And there's nothing that sticks out below the floor either. Crane design: In the real life truck that 42128 is based on, the lights are mounted on the crane and should rotate with crane. In the official 42128, the lights are mounted behind the cabin instead. I managed to put the light on the crane and got the slanted design of the body too. That's all I want to share. Overall I'm very happy with and proud of this set.

As requested by some, here's a version without the crane and front counterweight: https://reb.li/m/205443 .

Thanks a lot! It's nice to have someone who shares the same experience Actually, I'm a fool... You were right. Earlier I said this. And I realized I have not actually tested the possibility of putting the 8z gear there instead. So I opened the Studio file and messed around. I moved the pair of 8z-8z gear to the bottom, and the 20z gear to the top, and voilla, it actually worked!

Haha thanks you're not alone in seeing it wrong Are you Tuco (Breaking Bad reference) Thanks a lot! Thank you for the praise! I do think this is my best mini model so far as well, at least in terms of look. It's very fortunate that the original contain dimensions that are easy to shrink by a factor of 3/5. Unfortunately on both sides there are supporting structures of the cabin. Very tight space in there. There are only two gears that can stay directly above the worm gear and don't interfere with the blue 20z gear: a 12z gear or a 8z gear. Space constraint is a huge headache for me when I design this part.

I just learned that my total sales on Rebrickable surpassed 1000 EUR today!

Thanks a lot for the support!

Crane rotation needs quite more force than normal, indeed, as it tils heavily towards the end. Normally when I put force into the knob and rotate it slowly there is no problem.

For this mini replica I managed to achieve a new level: The proportion is so accurate that at first look quite a number of people thought it's the original 42128!

Model in action:

Another addition to the collection!

DEVELOPMENT It's time to level up the mini replica game, and for the next entry in my collection I wanted to work on the 42128. For a Technic head 42128 is easily one of the best models in recent Technic, as it has a lot of functions. It is also an interesting model to build a mini replica from, since its original scale is 15 studs wide, which means the mini version will be the 9 studs wide scale. There hasnt been many official 9 studs wide truck in Lego Technic. The most recent one is the 42167 Mack LR, and the second most recent one is the truck in the set 42023 released way back in 2014. I have done only one mini replica in this scale, which is the mini 42078 B model, but it was not a model designed from scratch but a mod of the 42167. Therefore I want to truly challenge myself with this model. The original 42128 turned out to be very conducive to the shrinking of a factor of 3/5. Most of the main parts in the original 42128 have lengths that is multiples of 5. For example, the width of the rear body, from behind the cabin to the end, in the original 42128 is 35 studs. The height of this body is 10 studs. The hood is 11 studs long, while the cabin and the sleeper is 14 studs long, which add up to 25 studs from the front to the sleeper. The cabin from floor to ceiling is 10 studs. All of these numbers make it easier to calculate the corresponding dimensions in the mini model. When it comes to functions, the first thing I decided is that there will be no openable hood. At this scale there's no space for a drive train, let alone a differential, and if there's no drive train, then there's no point to do a fake engine. Not to mention, the structure under the hood around the front axle is only 2 stud tall, so an openable hood with cause that area to not be structurally supported. On the other hand, making the hood fixed to the chassis will allow more possibility with styling the hood and routing the steer axle. And that's the direction I chose for the front. The next problem is the outriggers. In the original models, the side and rear outriggers are linked. However, in this small scale, there might not be space for a linking drivetrain. Therefore I decided to make the rear outriggers and side outriggers two separate functions. This creates the next problem, which is the crane rotation. In the original model, there are only four knobs on two sides, and they control 4 functions: linked outriggers, tow arm, third axle, and crane rotation. Now one knob is used for the second outrigger function, one of those four original functions must be controlled from elsewhere, or is not controlled at all. I noticed that the area under the cabin and the sleeper is not fully utilized, so I routed the crane rotation to the sleeper, which is where the HOG steering used to be in the original model, and I put the HOG steering further front. The rest of the functions are pretty straightforward. Both the tow arm and the third axle lift use a simple worm gear that meshes with a 20z gear. The side outriggers is also driven through a wormgear, Everything is simple and fun until I did the test build. The crane rotation turns out to just not work. Originally, I used a pair of 12/20 gears that is connected to a trio of perpendicular 12-20-28 to drive the turntable. It turns out the crane is very heavy, so that gearing is not enough to steer it. Another problem is that the 20z gear is parallel with turntable, so it is not secured on top and often breaks out, causing the 12z to skip. I spent a whole two day redesigning that part along with surrounding structure. This is how the final gearing of the crane rotation. You can see that the controlling knob goes through a bunch of gears to gear down the ratio to reach the turntable. The hardest part is to squeeze a worm gear into the drivetrain, but in the end I managed to do it. This is how all the functions are driven in the chassis. Overall I'm very happy and very proud of my model, and I hope you can feel the same too if you decide to build it. Instruction: https://rebrickable.com/mocs/MOC-206979/nguyengiangoc/mini-42128-heavy-duty-tow-truck Function sheets:

DBG actually looks good.

Why big JCB when small JCB would suffice?