[WIP] Building a krAZ 255 6x6 Truck

[[WIP] Building a krAZ 255 6x6 Truck]

For the rear axles, I really liked the idea of replicating the dual drive lines which I think would be really cool, and if anything, would distribute the motor load across more cv joints for better reliability.

So I started with a mock-up, to see if there would actually be room. Straight away I decided that I would need to use some shortened suspension links (4 studs) to achieve the desired spacing. I also liked the idea of using the soft axles as leaf springs but they seemed too complicated to mount and would require an additional torque arm to stabilize the axles on both axis.

I decided the drive system was viable. The hard part would be making the axles stiff enough. After a few iterations, I decided that the topmost links that would form the 'leaf' would also need to be shortened by a stud, which shouldn't be too laborious with a blade and file.

Again, the axle is subject to a real-world build test, however, I am quite satisfied with the general design. The first axle is slightly less stable than the rear due to only being connected to the top beam by 3 studs rather than 4, which is to allow room for the second drive line to pass through. I did some basic tests and I think the front and rear bracing between each 'hub' using the 7L thin liftarms should be sufficient. The mounting of the central pillar to the frame rails will probably have to be improved a little to increase rigidity. The only concern, apart from the usual overly soft suspension, is the tires rubbing on the frame during full travel. I'm hoping only one stud of travel should mean the axle doesn't pivot too much.

I quickly mocked a simple geartrain to get the drive shafts rotating in the correct direction, and here is a rough assembly:

Next will probably be figuring out how to mount the motors in a reasonable way. I'd like them to be central in the chassis, perhaps the steering motor under the hood and the drive motor behind it, all concealed by the cab, and the battery box positioned behind the cab next to the spare wheel.

Thanks again for reading and any thoughts are appreciated. Also, if anyone is interested in throwing together one of the axles in real life that would be amazing :D

[[WIP] Building a krAZ 255 6x6 Truck]

12 hours ago, gyenesvi said:

This is a nice tight start, I like the general idea and how the driveshaft comes in, but wonder how the axle front/rear/top/bottom sections are connected, because I don't see much possibilities for that in a stable way. For example what is the main load bearing 7L cross beam connected to? How is the rubber piece connected to it in a way that it will transfer the force from the wheels? If you push the wheels up, and the rubber is pushed down by the body, how will the two not separate?

Yes, you are right about this. Two friction pins are what keep the two parts from separating. Once I have some physical parts and the chassis is rolling I will have to test its rigidity, I'm really not sure how to get around this. I tried some stronger designs but they all result in a 1 stud higher profile. We will see how the rest of the build goes and see if its a major problem.

7 hours ago, keymaker said:

I'm glad my MOC can be inspiration for other builders I'm curious what you will create with even smaller scale, but you didn't mention what this scale would be. My KrAZ 255 is 1:23 which leads to 15 studs wide body. This gives me 11 studs of place with standard rims for axles (or as in my KrAZ 2.0 13 stud axles with special rims).

 

I don't have the dimensions of the real wheel so I'm not sure about the scale, however, given the size of the tires used in the blueprint I found, it would seem a total width of 14 studs for the axle and 15 for the widest part of the body (the cargo bed). Upon closer inspection, it looks like we are using different blueprints :D

[[WIP] Building a krAZ 255 6x6 Truck]

Hi there. So I was inspired by @keymaker and their awesome krAZ 255b build to create my own krAZ 255 truck at a similar scale (56x26 Wrangler tires), first a bit of back story. I've been tinkering with compact driven, steered, and suspended axles for quite a while, with the initial intention of making an RC chassis for the 42122 Wrangler or 10290 Creator 50s Pickup Truck. Anyway, the result was a pair of 11 Stud wide axles, but it took me so long that by the time I created a chassis, I had moved countries and hardly have any Lego with me. Therefore this new project will be for the most part CAD only (apart from some component testing) until I can get some more parts. 

Goals:

• I wanted the scale to be as accurate as possible using the 56x26 tires, which means an axle narrower than my current design is required, preferably 9 studs.
• All 3 axles should be fully driven and suspended.
• The body and cargo bed should be brick built if it's not too heavy, and the body/bed should sit as low as possible on the frame rails so as to not look like it has a suspension lift kit.
• The axles and chassis should be constructed favoring simplicity and low part count.
• The drivetrain should somewhat resemble the real truck, i.e. offset drive, dual rear drive lines, where the 3rd axle's drive line passes over the 2nd axle.

 

I'll also point out that I don't mind modifying parts slightly if I think it is worth it, especially at such a small scale. Anyway, as keymaker did, I'd like to start with the front axle because it has the most constraints.

After some experimenting, it became apparent of a few restrictions due to the scale.

• Springs are too big, rubber connectors should be used as springs and can give a maximum of one stud travel, however, these are very soft.
• The steering angle will be limited due to the steering rack contacting other parts. If the steering rack was filed down a little it could increase the angle but may end up causing the wheel to contact the frame anyway...
• A 20-tooth bevel gear is too big and too much effort to integrate, so no gearing down in the axle. Hopefully, with the light rubber springs, this doesn't lead to too much axle torque roll under load or CV joints breaking.
• Wheel flex could be an issue but again hopefully the overall weight is not too high and the amount of flex won't be too tragic.

I'm not too worried about these, however, as I think it's just what happens when you shrink things, compromises have to be made. I also tried shortening the axle of the female CV end for the drive shaft to 1 stud, just because it looked better, might be a bit wobbly, who knows.

Positives:

• Chassis rails are only one stud above the top of the tire, which I think is close enough to the blueprint
• There is nothing protruding above the rails that could interfere with the cab or motor mounts
• The axle is firmly held in place and lateral movement should be minimal.

That is all for today. I have already almost finalized a rear pair of axles, however, I didn't want to make this post too long. Thanks for reading :D Thanks again to keymaker for the inspiration.

 

[Axle Collection Thread]

I've been experimenting with compact, driven, and steered axles to suit the 56x26 Wrangler tires for a while now, and here is one of the final designs I came up with, as well as a 'matching' rear axle. Both are 4 link and use only heavy-duty cv joints. I built it into a chassis with an M motor for steering and L for drive and it has plenty of performance, suspension travel and a really decent steering angle.

 

[[WIP] Tayga 6455B (aka KrAZ 255 2.0) off-road truck - Snowrunner series Ep.2]

Loving the design story! I've been experimenting with driven & steered axles at this scale for a little while. The main issue for me was avoiding wheel flex, especially with a heavier model, the small deflection causes the wheels to walk off the short cv joint axles. I was just wondering how your final design copes in that situation, as it appears quite flexible given the steering pivot arm is only half a stud thick and hinges on a frictionless pin.