Didumos69

Instructions are on Rebrickable under the name '4WD RC Race Buggy + BuWizz MOD. This includes instructions for the PoweredUp version and as a bonus instructions and a parts list for the BuWizz version.The instructions are on Rebrickable under the name '4WD RC Race Buggy + BuWizz MOD'. In addition to the instructions for the basic PoweredUp version, the instruction files of this MOC include - as a bonus - a parts list and instructions for the BuWizz version, which uses 2 x BuWizz 3.0 Pro + 4 x BuWizz Motor. -- The parts list for the BuWizz version differs from the inventory listed in this MOC. -- The list of LEGO-parts (.csv) and the list of other parts used (.pdf) for the BuWizz version can also be found here and here respectively. This model uses the following 3rd party parts: 2 x BuWizz 3.0 Pro+ 2 x BuWizz Motor (1 BuWizz and 2 motors in one pack, so you need 2 packs) 2 x Aluminium Metal Beam Bearing Block liftarm compatible with Lego Technic 2 x Traxxas Model#1985 PTFE-coated Washer, 5x8x0.5mm (they come in packs of 20, so you need 1 pack) 4 x RC4WD Tires Dick Cepek Mud Country 1.9 (they come in packs of 2, so you need 2 packs) 4 x 1.9 Foams RC Tire Foam Inserts Black 4pcs (4 pieces in one pack, so you need 1 pack) Hi, It's been a while, but a year ago I got my hands on the Audi RS Q e-tron set with the new yellow differential gears and the new wheel hubs for the strong (RC-capable) CV-joints. I also got 2 Buwizz 3 units and 4 Buwizz motors (their buggy motor remake) and with the hubs and diffs from the Audi I could finally continue a concept that I have working on every now and then over the past few winters. The idea was to create an off-roader with ruggedness and capabilities even better then my Greyhound 4WD RC Buggy and Make a build with an easily detachable body, just like with real RC cars Make the Buwizzes easily removable, so you can use them for other models Make it easy to reconnect the steering ball joints if impact caused them to detach Obtain a direct connection between the wheel hubs in the steering setup, without slack The wheelbase is 3 studs shorter and the track-width 2 studs narrower compared to the Greyhound. The roof top is also 2 studs lower. All in all I strived for a little bit more of a race look. One of the ideas that I started with (about 3 years back), was a setup with 9L steering links that are positioned with a small angle, such that they are actually a little too short (about 0.8%), which gives them a nicely tight fit. When you use them at both the front and rear side of the steering setup, this won't introduce any toe-in or toe-out. With this setup any rotation in one wheel hub translates to immediate rotation of the other wheel hub, without any slack. I also wanted to use 4 Buwizz motors to make the whole thing capable. At a certain stage I had a setup with the old wheel hubs and the new RC-capable CV joints, but I could only make that work for a RWD model, not for 4WD. With the new differentials and the new wheel hubs from the Audi RS Q e-tron I could revert to 4WD and I could finally complete this project. Still, getting the max out of 4 Buwizz motors turns out to be challenging. The main problem I ran into: the axle driving the rear differential melted and also caused the 5x7 frame around the differential to deform. I had to resort to 3rd party metal beams with ball bearings to avoid overheating of the axles driving the differentials (Aluminium Metal Beam Bearing Block liftarm compatible with Lego Technic). This works great! I also ran into the issue that the output axles of the differentials worked themselves out of the bevel gears inside the diff and started skipping, gradually carving a hole in the bevel gears. The problem was that the drive shafts had too much play in them. This I could resolve by adding a support halfway the drive shaft, which locks up the CV-joint exiting the differential (see image). In this image you also see the LBG #1 connectors that prevent the steering links from detaching. When they do detach, you only need to temporarily remove the connector to put them back. The next issue was that the big yellow gear attached to the differential house disconnected form the differential house under heavy load. That caused the differential to skip and to carve into the parts bracing it. To resolve this I've added a thin washer from Traxxas between the gear-side of the differential and the parts bracing it (Traxxas Model#1985 PTFE-coated Washer, 5x8x0.5mm). That avoids the differential house from disconnecting without causing any added friction. Finally, I've added RC crawler tires from RC4WD (RC4WD Tires Dick Cepek Mud Country 1.9). They are from much softer rubber than LEGO tires and for that reason they have much better grip and they absorb a lot beating. That also reduces the chances of having an entire wheel coming off, which never happened to me with these tires. Only when I crashed. These tires come with soft foam inserts. For my purpose, I replaced the included inserts with bigger ones (1.9 Foams RC Tire Foam Inserts Black 4pcs), to get a little more pressure in the tires. That makes them more suitable for racing.

I fear your model is either too heavy or there is some friction going on somewhere between the motors and the wheels. I used a 90 degree thin 12t gear vs thin 12t gear mesh in my recent 42129 b model without problems, also with a 1:1 drive ratio (the bracing had to be perfect to make that work). But that was with PU parts.

The way the 5L beams that brace the male part of the CV-joint could be mounted to the 5x7-frame better. Right now this relies on the pins with pinholes, which may be pulled out a little. These pins with pinholes are friction locked, not form locked. It would be better if you can somehow use vertically placed 3L pin with pinholes (the same piece you use to connect the 5L beams and hold the drive axle) and mount them to the 5x7-frame such that the structure relies on pulling pins sideways instead of lengthwise. The issue you're running into is not new. Many people have had problems with combining CV-joints with RC, even with plain PF parts. I don't know your build, but as a rule of thumb I would say: If your model is about speed, I would keep the old CV-joints, lower torque and increase RPM by gearing up the output of the motors. If your model is about trial or crawling, I would use the new CV-joints and the new portal hubs. And also in this case, you probably want to increase RPM by gearing up the output of the motors. That will reduce torque in your drivetrain and somewhat compensate for the gear reduction in the portal hubs. For increased RPM and lower torque in your drivetrain to be an option, it's important to have a drivetrain with low friction. Maybe those knob wheels are a source of friction, I don't know. You could try with different gears and check what happens.

I believe that was in a post by @PorkyMonster. These days you could also use something like: Btw, for the new CV-joints it might be useful to know that you can work with parts around the CV-joint on a diagonal grid:

You're quite right

Alright, let's fix that.

If you could build this Penrose triangle: you can build a strong triangular wall:

Thanks! I had a lot of fun building it!

Cool! That 4-wheel steering is great addition! Thanks for sharing!

Very nice B model! I like your style. You really put in the extra mile in getting the best out of an existing set, where others seem to rush things to a finish.

Congratulations Balazs! Your channel is the only YouTube channel I subscribed to. I'm still grateful for the video you made about my 42099 B model! Cheers!

Just did a slope test. I was not disappointed. Also shot some footage of it on CLAAS tires. When it gets steep, it underperforms the Zetros tires, but other than that it rides smoothly.

One down, one to go. With the power up app I should probably be able to program this.

I got seconds thoughts on the price for the instructions, which I set to 20 euro. I dropped the price from 20 euro to 15 euro. I also refunded the payments that were already made for this MOC, because I don't want to disadvantage anyone.

Instructions are ready: https://rebrickable.com/mocs/MOC-93255/Didumos/42129-b-model-hot-trot/

@Void_S, @pleegwat, @westphald, @2GodBDGlory, in the final video you can see what I mean with the diagonal test. At 2:23 you can see how the model moves back and forward over a hat shelf from a car. Every time when it returns (twice), you can see how one diagonal pair loses grip. It struggles a little, but it keeps on going, because the other diagonal pair still has traction.

Thanks for your analysis @Void_S! Another advantage I see over a regular scheme with locked center differential is that the regular scheme will fail when a diagonal pair loses grip like in a diagonal test. My setup will fail when both front wheels or both rear wheels lose grip. I read somewhere that people driving these military vehicles with H-Drive (I should call the diagonal setup X-drive) drove into the roadside every now and then (with one side) to release windup.

Quickly made some renders. Looks okay imo. Speaking of renders. I also have this mad-max style Zetros alternate design laying around. Uses the same chassis as the pickup. In fact, it was a pre-study for this whole project.

I know the Claas wheels fit, but I haven't driven them outdoors. Once I've put the model together again I'll give it a try and let you know.

Yes, thanks for explaining. It's also important to realize that the driving rings are actually floating. They're not mounted on a connector. There are 10L axles running all the way through the 16t clutch gears and driving rings into the differentials.

Instructions in progress...

Thank you all for the kind replies! Indeed, I didn't use the 4th motor. I wanted to keep the concept clean. Also, I used the 2 driving rings for driving the differentials, so anything like a differential lock or a gearbox was kind of ruled out from the start. I used the PU app and tweaked one of the preconfigured profiles to my needs: The mounting points of the springs can easily be moved 1 stud inward, so I suppose you could make it a street ride. Good question! In fact I started with a setup that had such a `bridge`. It had both motors running in the same direction and used a clutch gear to make the drive trains cross. However, it gave me 2 issues: The bevel gears making the 90 degree angles would not be symmetrical. In the rear the 90 degree gear mesh for one of the wheels would be at the wheel side and I couldn't fit in a proper way to brace that. Proper bracing is essential to prevent these gears from slipping. When one wheel loses traction, a hard `bridge` (without differential) will make all power (from both motors) flow to one drivetrain. When at the same time the vehicle hits an obstacle that blocks the vehicle, this led to slipping bevel gears. Too much power for those gear meshes. By dropping the bridge and having the 90 degree gear meshes at the center of the vehicle, I could rule out slipping gears entirely.

It is patented, but as I understand for different reasons (source). It states that when a vehicle accelerates while cornering, the wheels with the most grip and least grip are diagonal opposites. They also argue that it makes sense to transfer propulsion from the wheel with the least grip to the wheel with the most grip. If you wish to do so, supposedly by automatically braking the wheel with the least grip when it starts spinning, you need to pair that wheel with its diagonal opposite, using a differential. My doubt about this kind of system is that electronic systems that automatically brake a slipping wheel will only kick in when the wheel is already undoubtedly slipping. In sophisticated AWD system (Subaru, Volvo, etc.) you always first see a wheel slipping for at least a second, before the automatic braking kicks in. This doesn't seem to be something subtle enough to apply when accelerating while cornering. These kind of systems are improving rapidly though. Personally I think my setup with two separate drive trains arranged diagonally might be well suited for electric off-road vehicles with two motors.

Hot Trot - RC Trial Pickup w/ Diagonal AWD I would like to present to you my shot at a 42129 B model. About the name 'Hot Trot': On a very uneven surface, a vehicle typically moves its weight from one diagonal pair of wheels to the other as it proceeds from bump to bump. Hence the word 'Trot' in the name of this model. It refers to a horse proceeding at a moderate pace, lifting each diagonal pair of legs alternately. Instructions are on Rebrickable. Diagonal AWD With Diagonal AWD I mean: 1) having two separate drive trains with equal torque that 2) keep a vehicle going on a very uneven surface while 3) preserving the advantage of having a distribution optimal for cornering. We all know the downside of a classic 4WD setup with three open differentials; as soon as one wheel loses grip, all power will flow to that wheel, causing the vehicle to lose traction. One way to deal with that is to add differential locks like in the Zetros. Another approach that is commonly seen in LEGO Technic builds is to have separate drive trains for front and rear wheels like in the 42099 X-treme Offroader, in which case you need a slipping front wheel and a slipping rear wheel to completely lose traction. This approach however, has two downsides: There is no open distribution of torque between front and rear wheels, which is not optimal for cornering, because the front wheels are not free to average to a higher speed than the rear wheels. On a very uneven surface, for instance in diagonal tests, where wheels start losing contact with the surface, it's likely to have a front and (diagonally opposite) rear wheel loose traction. But what if we would separate the drivetrains diagonally: A drivetrain with a differential between the left front (LF) wheel and the right rear (RR) wheel, and a drivetrain with a differential between the right front (RF) wheel and the left rear (LR) wheel? The resulting 'Diagonal AWD' would serve two major benefits: While cornering, the LF and RR wheels will average to a speed that is almost equal to the average speed of the RF and LR wheels. So not having an open distribution between two diagonally arranged drivetrains is much less of a problem than with separate drivetrains for the front and rear axles. On a very uneven surface, where wheels start losing contact with the surface, the wheels that still have contact are typically lined up diagonally. With Diagonal AWD, the vehicle will still have traction, even without additional differential locking. The vehicle will only lose traction when two wheels at one end or at one side will lose grip. Drive trains I wanted to have the motors at the same level as the rest of the drivetrain to keep the center of gravity low. I came up with a fairly flat setup with longitudinally placed motors, a differential at the heart of each drive train and bevel gears to make the 90 degree angles towards the wheels. Each motor drives a 16t clutch gear locked to the differential using a 'floating' driving ring. After some trial and error the best option to properly brace the bevel gears that make the 90 degree angles to the wheels, turned out to be a symmetrical setup with the motors rotating in opposite directions. Because of these opposite directions, using a clutch gear to make the drivetrains cross in a completely flat layout, was not an option. The clutch gear would rotate in opposite direction compared to the axle it's attached to, which would give loads of friction, particularly in motorized models. But luckily, the Zetros has exactly the right gears to make the drivetrains cross independently. The biggest challenge was to prevent the gears that make the 90 degree angles from slipping. I've experimented a lot, but no matter how strong I braced the bevel gears, I could always make them slip with my bare hands, using 24t gears to put force on the axles. So the goal was to make sure the gears can at least handle the power provided by the motors without slipping, even when one drivetrain gets completely blocked. I eventually succeeded, but it has cost me long hours of tinkering and trial and error. I created completely locked up structures for the bevel gears, using the 4 available 5x7 frames and 8 of the 11 beams with alternating holes. These structures are also tailored to fit the main structure well and to provide form-locked mounting points for the suspension arms. The two assemblies are extremely hard to build, because you can only insert the gears and axles after the structure has been put together. Suspension I incorporated independent double wishbone suspension with the springs arranged in a pushrod style. The springs have been mounted such that they compress by approximately 33% under the vehicle's own weight. This gives a very nice road holding, because the springs can both expand and compress while taking bumps. I managed to optimize the spring setup for max suspension travel, which is about 3L, which fitted my objectives perfectly. The suspension travel shouldn't rule out the chances of having a wheel coming loose from the surface, because that's when the Diagonal AWD kicks in. It seemed obvious to use the new longer male half of the CV-joints for the rear axles, so the rear axles use 8L suspension arms. The suspension arms of the front axles are shorter, because I had to build the gear-rack assembly around the drivetrain axles and wanted the steering links to have the same length as the suspension arms to avoid bump steering. The steering setup has an Ackermann geometry. The steering links have been reinforced such that they never detach from the gear-rack assembly and the gear-rack assembly itself has been braced in a way that rules out unintended transversal movement. The 2 phone handsets came in handy for this purpose. Chassis and bodywork The main structure is as stiff as I could possibly make it. I even used the motors as structural elements to add to rigidity. I wanted to rule out flex as much as possible, because I wanted to demonstrate how responsive the suspension is and because a flexible chassis would reduce the chances of the Diagonal AWD kicking in. Apart from the extensions necessary to mount the springs, the main structure is just 5L tall. On top of this main structure I've build a strong structure for the cabin of the vehicle. The bodywork does not have any features like openable doors or whatever. People that know me, know that I'm mainly interested in drivetrains and suspension. The bodywork is robust however and I did pay attention to the interior this time. You can lift it by the roof and I also made it very easy to remove the battery box. Powered Up Profile Because I don't use the medium motor, and because I have the large PU motors running in opposite directions, I could not use the Control+ app to operate this model. However a default profile in the Powered UP app could be easily tweaked to what this model needs: Finally I want to mention that I started using Energizer Ultimate Lithium Mignon batteries for my MOCs. They are strong, long-lasting and most importantly; they are at least 20% lighter than alkaline batteries. Photos

Interesting read, nice to get an impression of the process. Very recognizable too. An alternate model always comes with compromises. And the end result is something to be proud of. Suspension setup is great as is the bodywork. I'm working on an alternate build of the Zetros myself and I can confirm it's very hard to put together a sophisticated suspension setup with the available parts.