u/AshieAshe

This all started with me simply wanting a bouncy lil car fidget toy that I could push down on and mess with. So I took 4 elastics to an old set I had and achieved that in a few minutes. 2 months later, my boredom sprouted into productivity. I mixed in some money and a week+ of work and ended up making this.

Note: You can create something of equal or better quality for much less. I used 2 BuWizz 3.0 Pros + 4 BuWizz Motors, which runs you $500 before any discounts. It’s RWD so you could easily use half of that and even reduce the size (and weight) a bit and end up with a similar/better performing car for significantly less, especially if you already have the parts to make the car. I went overboard with the motor quantity so I can take it apart, thanks to the strong but modular design, and make multiple more vehicles.

I used RacingBrick’s gear swap tune and partially installed a light kit. The other mods I did myself.

This was done via BuWizz in-app functionality. You can achieve the same with LEGO’s hubs with PyBricks if you know some basic Python, which wouldn’t take you long to learn

The first 17 seconds where the passenger is loaded was obviously controlled manually, but all of the driving and maze navigation was autonomous. The assignment provided 2 distance sensors, 1 touch sensor, and 1 color sensor, hence why all of our vehicles had to collide with the wall in front to trigger a 90 degree turn.
The project was to design an autonomous vehicle for disabled passengers. The design I went with, namely the passenger loading mechanism and vehicle aesthetic, were draconic and absurd for fun :3

Left side pictures are before and the right side ones are after, of course. I was born with CRSDA (congenital condition similar to Crouzon) among other things, but was able to get this massive corrective treatment which is very cool :3

It was performed at Phoenix Children's Hospital

Overall took me like 7 days, give or take, to design and build the whole thing. I iterated through 3 main powertrain configurations (mid-engine dual driveshaft, mid-engine single driveshaft, direct drive) to get this final high-power result. Perfection of the rear multi-link suspension was the most finicky but satisfying component to finish.

There’s a water bottle on top of the car to give it a bit of weight since I didn’t make any actual mount to hold the car. It took me like 10 mins as you can tell by how crappy it is, but was fun and I’ll probably make a much better one later on.

I started work on the rear and front but, as you can tell, the proportions and aesthetics are pretty awful. I’ll need some more parts to make the front match the width of the wheelbase and also start the mid/cabin area. The rear “trunk” can actually perfectly fit the 107mm wheels on the spare mount area, I just have no spares of that size to show it yet. The 1x4 light bars will be on the roof once said roof exists. And all the wiring will obviously be concealed securely, with those blue lights in the trunk area being stuck to the body as they’re adhesive. In addition to more parts, I obviously need a lot more skill to make any of this start to look half decent. Overall fun first project.

Funny thing I’ve noticed is that I keep dropping it, even higher than I did earlier tonight (which caused a part to break) and yet the same parts are not breaking. Kinda makes a few people look dumb for somehow concluding it’s user error. If you ask me, this repeated testing with more extreme heights lends credence to that broken part being the fault of a quality issue rather than my design. Unnecessary distinction but this makes me happy because, contrary to the other community members’ claims, I don’t feel it is “unethical” for me to request a replacement of that part. The left-side beam is the same one I put in since the very first build so it has been eating a higher quantity and severity of drops as the right-side beam that broke, and yet no breakage. Also, naturally, my thumb releases first, causing the left to drop earlier and eat more of the impact. Still no breakage. Sounds like a quality issue :3 lego community full of cornballs

I broke a bunch of elastics. Cool, I use thicker ones now.

I ruined an old, spare axle through a handful of minutes testing it unlubricated with BuWizz motors. Cool, I used some old spare for a reason. I never skip applying synthetic grease now, even for short testing.

My tires are “dirty” and one has a tiny hole from a lil thorn. Cool, shoes are made for walking, tires are made for driving.

The truck chassis is “dirty,” too. Good.

A beam snapped after days of extreme limit testing my first ever technic MOC, which happens to be high-powered (relative to LEGO) off-road trophy truck. Cool, I know now to stop repeatedly dropping it from above 2 feet to gauge and reinforce chassis failure. I better understand the limitations of the product. Creativity enjoyed, failure experienced, rebound made. There’s no problem.

I succeeded in learning very basic level engineering design through a week of hands-on experience with this great product LEGO makes. I’ll never understand why it seems many feel the obligation to shun and discourage such activities, when no one does the same to them for how they choose to engage with the product.

I haven’t even used the missing pieces service to replace that black beam which people were upset about me for stating my intention to. But I’d wager if I email customer service directly and explain to them exactly what happened, they would happily place the order for the singular part out of the set that cost about $180 and tell me to have a great day. I thought this was a cool place to share my experience in making what I thought was a fairly impressive and highly robust car (again, my first MOC!) ESPECIALLY by sharing my failures and how I learned from it, but the reaction to 1 broken part just reminds me why Reddit has a reputation for being out of touch and just weirdly negative. Like I said, I have a strong feeling customer service will happily just give me the 1 part even after I tell them how it broke lol. Be a little happier.

Additionally, there were 2 of those black beams (one for each side of the rear axle) and only one snapped, despite both serving the same role and facing identical stress and force. The other one shows absolutely no signs of breakage, no white discoloration which would be apparent at the pinhole, no deformations whatsoever. The severity, nature, and frequency of the drop tests are such that no one side of the car would have absorbed notably more or less impact. Therefore, the argument can be made that the snapped beam was a defective part. I may be ignorant, but I don’t believe one could form a sound argument against this, not that any argument is even necessary.

I put a good bit of time and effort into repeatedly testing my MOC truck chassis’ suspension by dropping it from 2 feet, assessing the failures, and double and triple reinforcing everything so no pins detach during extreme durability testing. Now, it’s so securely locked together that all the stress from the impacts just breaks through the beams of the suspension arms. I’m happy with this because this is my first time ever making a technic MOC, let alone a pretty complex and effective suspension system, so to see this degree of success is satisfying. Hopefully I can replace those parts through Missing Pieces because I got them from 42160 haha. Metal Technic Parts does not offer this particular piece so unfortunately I’ll just have to acknowledge the limitations of plastic and stop tossing the car around at such ridiculous heights :3

Idk how fast it goes but obviously not as fast as most of what you guys have here. It’s RWD with 4 2.2k RPM motors configured in direct drive (and the wheels are 107mm diameter) so it does a bit of drifting and is pretty fun.

This shows my early design process in making a drivetrain and rear axle for my truck chassis. It had 2 “engines” (4 BuWizz motors in pairs of 2) with 2 articulated driveshafts sending power to gears in the rear, converging into the differential before reaching the wheels. It was my favorite due to the mechanical complexity when compared to the current direct-drive configuration. However, the 2 driveshafts were unstable and kept failing. The car was able to drive but not able to withstand impacts or rapidly accelerate and reverse, the driveshafts would fail as seen in the last clip.

V2 resolved this by moving the 3 large grey gears to the main chassis rather than rear axle, which completely eliminated the “twist” seen when running at full throttle and also reduced from 2 driveshafts to just 1. Unfortunately I did not record any videos of it though. This version was significantly more stable and passed all tests, however the geometry of the articulated driveshaft was suboptimal and impossible to remedy or work with beyond low speeds. Too much power was being lost in trying to rotate that shaft under the stress caused by the angles so it never reached max speed and just sucked, but I still liked it.

The latest and greatest version is simply a complete redesign where all 4 motors are now mounted onto the rear axle and linked directly with the rear wheels, 2 per. The result is the best achievable performance (torque, responsiveness, efficiency, everything). And it eliminated the 9 gears which the previous 2 designs used, so no more lube needed and no more axles destroyed. Less than 5 mins of unlubricated, intermittent testing with V1 and V2 cooked an axle completely.

Very happy with the outcome of designing this. You would be surprised as to how finicky it is to nail a multi-link isolated axle. It took about 2 days of testing and tweaking the linkage geometry to achieve this design where the links do not fail under any (practical) drive and drop conditions.

My only upset comes from the limitations of LEGO and BuWizz but those obviously come with the territory. For my next projects I’ll probably move up to “real” R/C and gas-powered engines so I can work with some real engineering.

Front axle has double wishbone suspension with positive caster angle and 9.5L shocks which can easily be swapped with different strengths or replaced with 6.5L shocks. Rear is an isolated live axle with triangulated four-link suspension. The 4 drops are progressively higher to test suspension effectiveness and chassis rigidity. Due to the mounts of the front shocks being accessible as well as the rear suspension using elastics, the stiffness is easily adjustable to make it softer or harder and the assemblies will not experience any failures during driving or drops regardless of height. These drops show it with 3 orthodontic elastics on the left and right rear suspension arms for a total of 6.

The last clip was recorded before I greatly improved the multi-link setup. With the redesign, the rear is significantly more stable, durable, compact, and incredibly aesthetically pleasing. You can see a close- up pic of the new rear multi-links in the pics on my previous post.

It is very high performance, has instant torque, and can drift and spin at will by reversing throttle and maneuvering. When I take it out with my friends I’ll have one of them record it driving around.

Nerd yap edit: Torque and speed can be adjusted by swapping the 1:1 wheel hubs for 5.5:1 planetary gear hubs, and/or moving the rear wheel axles back by 3 studs and linking them to the outer axle ports of the BuWizz motors which are internally geared 1.35:1. Both can be done independently or in conjunction in roughly 20 mins as the rear wheel hubs are secured by 2 frames each, with support axles hammered into axle holes and beams bracing everything together with the 4 motors (I used off-brand, compatible axles because they happen to fit extremely tight with LEGO which makes the assembly indestructible). And the latter would also increase rear axle ground clearance by 2.5-3 studs, making it more of an off-roader for very rocky roads.
Additionally, 2 gears can easily be added to each rear wheel assembly at a ratio of 2:1 or 1:2 to further tune torque and speed, but the added complexity and the introduction of drivetrain loss outweigh the benefit of the gear ratios. Though I may test it in the future for fun.

I spent 5 days designing and building this chassis, with the goal of making a high-speed, high-torque, off-road, trophy truck-inspired R/C truck. It’s my first time making a technic MOC and I’m extremely proud of it. I guess this is what happens when an engineering student plays with LEGO :3

Pictures 1-10 are of the current, best iteration, with 42099’s chassis for scale in a few. It has remote toggled headlights and RGB “taillights” (built into BuWizz brick) which I’ve set to red. It’s RWD with 2 motors per rear wheel, configured in direct-drive for maximum torque and top speed with 0 drivetrain losses.

Pic 11-16 shows my iterative progression, starting from a smaller front axle design and then making a larger v3 with double steering racks, resulting in an indestructible front axle with extremely steady steering assembly (practically no wobble). You can also see I initially mounted the motors to the center of the chassis and used 2 double-jointed driveshafts and 3 gears to transfer power to a differential. This design was poor because the isolated rear axle would twist against the rotation of the gears because physics. Pic 16 shows how I addressed this issue by mounting the gears before the driveshafts which solved the twist/rotation issue and only needed 1 driveshaft. This design was fair but failed under load due to the instability of the articulated driveshaft. It worked at low speed, but at max speed the shaft caused significant efficiency loss due to vibrations, lash, and backlash. I was disappointed because no-load testing showed the drivetrain functioning similar to a real car’s design and I was proud of it. Finally I made v3 in which I simply designed a new rear axle built around all 4 motors and mechanically linked 2 motors directly to each rear wheel’s axle. Testing this drivetrain under load at max speed has gone flawlessly, with the vehicle able to quickly reach max speed, drift, and perform maneuvers like instant 180 degree turns by reversing throttle and steering.

The front axle suspension features a positive caster angle, and the rear isolated axle features a fairly complex and extremely impressive multi-link suspension setup using durable orthodontic elastics for massive travel distance and easily adjustable stiffness (add or remove bands). The overall suspension system and chassis structural integrity can handle drops up to approximately 2-2.5 feet. Beyond that and the front axle detaches from the chassis, but can be snapped back together in seconds. The front axle itself can’t break even when I throw it straight at the ground from above my head, it’s just the area where it’s mounted to the chassis that detaches from extreme impacts. I aim to completely remove that issue, but because of how I completely improvised the entire build process, there is not much room for me to work with in the front without causing obstructions to the wheels during turning. Just yesterday the chassis would fall apart like an android phone from very insignificant drops or the rear’s link arms would snap off. So I’m very happy that I was able to achieve a solid 2-2.5 feet max drop height with the current connections and bracing. I solved the link issue by using ball cup parts (the kind used to connect wheel hubs to control arms) to make stronger link arms and spent 2 days tweaking the geometry and testing, failing repeatedly until finally succeeding. I’ll post drop tests and drive videos later on if I can.