Didumos69

RC Off-roader with Dual Diagonal Drive I think I'm onto something that will get me through the winter. Summary Dual diagonal drive means: 1) having two separate drive trains with equal torque while 2) preserving the advantage of having an open distribution for cornering and 3) passing diagonal tests without using differential locks. Background I have been playing with this idea for a while already, especially after seeing @KevinMoo's dual drive models (Mitsubishi Pajero and Dual-Driveshaft Pickup). @KevinMoo rightfully addressed the vulnerability of LEGO parts in RC models and the fact that using independent drive trains for the left and right sides, loses the benefit of differentials while cornering. This got me thinking. Using independent drive trains for left and right in a 4WD model does indeed drop the benefit of differentials while cornering, but what if we would pair the wheels diagonally, so pair the left front (LF) wheel with the right rear (RR) wheel, and pair the right front (RF) wheel with the left rear (LR) wheel? The resulting 'dual diagonal drive' (I borrowed the term from the electric skateboard scene) would serve two major benefits: While cornering, the LF and RR wheels will average to a speed that is very close to the average speed of the RF and LR wheels. So not having an open distribution by means of a differential between the two drive trains is much less of a problem as with separate drive trains for the left and right side wheels. On a very uneven surface, where one or two wheels may lose contact with the ground, the wheels that do have contact are typically lined up diagonally, see image. With dual diagonal drive, the vehicle would still have traction, even without locking any differentials. Only on slippery surfaces, there are chances of spinning wheels. So this is what I'm thinking of. We start with the basic dual diagonal drive setup: Two separate drive trains, one for the LF and RR wheels and one for the RF and LR wheels. The drive trains cross using two 24t gears and an auxiliary 16t gear that sits right underneath the auxiliary axle for the other drive train. So no clutch gears are involved in this crossing. I inserted a 1L Technic liftarm inside each differential - idea from @Madoca 1977's Toyota Land Cruiser 80 - to prevent the bevel gears from popping out. Next we add a manual locking feature, which closes the differentials with a single lever. This locking feature will force each pair of wheels involved in one of the drive trains to have equal speed. Now we connect each XL-motor to one of the differentials, using a small 4-speed gearbox. That means; two separate 4-speed gearboxes. This may be a bit ambitious, we'll have to see in real-life whether this is feasible or not. I might fall back to two 2-speed gearboxes. I did pay attention to the amount of torque in the transmission though. I geared up the XL-motor outputs and geared down the transmission output. That makes the transmission spin faster with less torque. The gearboxes are operated synchronously using a 90-degree stepper, which is controlled by a Servo-motor. Each gear shift axle has its own 90-degree limiter. And finally the outputs of the XL-motors are transferred to a fake V8-engine via a normal differential. The sole purpose of this differential is to combine the XL-motor outputs for the fake engine. For the steering I'm thinking of using a servo motor. I don't really like the directness of steering with a servo-motor, but the steering link attachment points are moved one stud backwards, which confines the steering angle. This adds to better handling and protects the CV-joints in the wheel hubs. I don't know where this is going to end. I'm not even sure about the exact kind of car I will be targeting, but it sure needs to be some kind of all-rounder. Comments and suggestions are welcome.

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.

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.

Yes, sure, that would certainly something I can work with.

Is there someone who can share or pm me a stud.io file if the original model?

Thanks! It all comes down to suspension. The suspension arms should be able to move smoothly and as a rule of thumb the suspension should be compressed halfway its overall travel under the vehicle's own weight. That will allow the arms to expand as much as compress while driving.

I can confirm the 3l thin lift arms actually rotates around that pin. Because of the long suspension arms the rotation / suspension travel ratio is relatively small. So I preferred having a firm grip on the motors over a frictionless rotation. I think your idea may work, but I'm not sure if it increases chances of detached parts. You could try pulling the motor assembly out of its pivot points to compare your solution with the original one.

Rugged supercar - Hammerhead (1:9 scale) This project was not something I started very consciously. Also for me it evolved into something special. I was especially happy with the interference (in a positive way) of other builders. A big thank you to this community, for pushing me in the right direction on several occasions! The most special part - to me - of this build, is the chassis. It combines a simple 4-speed AWD transmission, a flawless sequential shifting mechanism and advanced suspension setups with Ackermann steering, anti-roll bars, torsion bars, 2 studs ground clearance and 2 studs suspension travel. All wrapped together in a very flat yet rigid and coherent structure with a mid-console width of only 5 studs. I did not want the bodywork to make any compromises to these features. I wanted the body to continue the line of durability set in by the chassis. Flex-axles do not fit that image, hence no wheel arcs. They would also sit 2 studs above the hood - not very elegant. The result is a car that does not only look fool-proof; it is fool-proof. After a rough treatment, you don't need to tighten connections or fine-tune gears to avoid friction. You can carry the car by the sides, by the trunk door (rear wing), by the nose and by the bumpers without displacing any parts. You can even grab the 2Kg build by the roof and turn it upside down to see the bottom side without a problem. So I did not intend to level with great bodywork builders. To me the biggest compliment is that some have referred to this model as the successor of 8865 and 8880. Drive train AWD with 3 differentials Sequential 4-speed gearbox One-finger shifter V8 fake engine Suspension Double wishbone suspension Anti-roll bars (front & rear) 2 studs suspension travel 2 studs ground clearance Steering Ackermann steering Gear-rack sliders Working steering wheel HoG steering Chassis Sturdy and durable Integrated bumpers Adjustable seats Narrow mid-console (5L) Bodywork Sturdy and durable Integrated roll-cage Lockable doors Openable trunk Liftable By the roof By the sides By the nose By the trunk door Instructions are available on Rebrickable. There is a full-featured version called 'Rugged supercar' and a chassis-only version called 'Flat AWD chassis'. The chassis-only version confines itself to part 1 of the instructions of the full-featured version. Special thanks to @Blakbird and @BusterHaus - with Blakbird being the driving force - for taking on the task of making these beautiful instructions! Making instructions for a build like this is a tremendous amount of work. Even more so, given the fact that I have been very demanding in sticking to my original design. - 32005a (Link 1 x 6 without Stoppers) - used for the anti-roll bars and steering tie rods - is preferred over 32005b (Link 1 x 6 with Stoppers), because each link has tow-balls inserted from both sides. 32005b can be used too, but in that case each link will have one tow-ball that needs quite some force to insert. - 32056 (Liftarm 3 x 3 L-Shape Thin) - used for the door locks - is preferred over 32249 (Liftarm 3 x 3 L-Shape with Quarter Ellipse Thin). 32249 can be used too, but makes it more likely to accidentally lock the door while it's open, which is not a big deal of course. - 76138 (Shock Absorber 6.5L with Soft Spring) - used for the door locks - should be soft springs. They are quite rare in red, but you could also use two LBG soft springs. - 85543 (Rubber Belt Small (Round Cross Section) - used for the 90 degree limiter and the return-to-center of the gear shifter - should be relatively new, say max 2 years. Not that they wear out quickly, but the older ones are slightly less tight. Images of the full-featured version can be found here. Images of the chassis-only version can be found here. See the entry on The LEGO Car Blog! P.S. Where real cars start with a sketch, evolve into a professional design and finally have their technical details filled-in, this project started with some technical details, evolved into a complete design and ended up in a sketch ;-). By @HorcikDesigns (http://horcikdesigns.deviantart.com/gallery/).

I made instructions for the engine with working valves and exhaust system. This is the engine I have in mind for this revisiting. See this video for the working of the valves.

I will be working on a studless version of 8844 Helicopter, my second set ever.

I took the time to make instructions for a gearbox concept I had laying around. 4 variations on the same concept, a gear layout I have not yet seen somewhere else. One of the main objectives: Clutch gears are only used for engaging with driving rings, not for transferring drive over axles running at different speed, which is a common source of friction. Ratios: 0.33 0.50 0.67 1.00 Centered heavy-duty manual 4-speed gearbox - Rear input (instructions on Rebrickable): Centered heavy-duty manual 4-speed gearbox - Front input (instructions on Rebrickable): Centered heavy-duty manual AWD 4-speed gearbox - Rear input (instructions on Rebrickable): Centered heavy-duty manual AWD 4-speed gearbox - Front input (instructions on Rebrickable):

It could, but it will give much more play, with chances of a slipping driving ring, see image (courtesy of @Attika).

Thanks for your comment! Your understandings are correct. The red driving ring and lbg extension are indeed older pieces, I wouldn't say from the studful era though. They have been produced until 2014. The changeover catch is indeed half a stud off, but it never fails.

Awesome. I like seeing this extreme RC plumbing a lot. Please take it to places no man can go and share some footage .

Is this better? They're static. I'll leave them in for now, but not as main headlights. I did change the main headlights to match the auxiliary lights better. You mean the 2x2 dishes as headlights? That would be too big imo. Here's a render for comparison. The whole front of my build is only 6 studs high.

For the front, perhaps something with a wink to the buggy will work...