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This model (and it's prototypes) are a result of the following topics:

 

Basically the idea behind this project is to make an offroader capable of driving on all kinds of terrain with a simillar perofrmance as the Wildcat 6x6 but having a lower weight

So, why would I want to reduce the weight? While the wildcat 6x6 works great most of the time, it's high weight of 2,5-3 kg has some drawbacks:

  • The model requires a lot of expensive electronics (12 BuWizz motors, 6 BuWizz 3.0 bricks)
  • High part count (1869 pieces)
  • Tendecy of front wheels falling off at hard landings
  • High wear and tear of the individual components, which lead to premature failure - planetary hubs, CV joints
  • And lastly high wear and tear of the handler due to it's heavy weight :laugh:

Of course decreasing the weight also means decreasing the power to weight ratio, since there will always be components which are needed regardless of the number od drive motors like wheels, hubs, steering system, suspension and frame.

The first protoype, which I simply call Light 4x4 used only 2 BuWizz motors coupled to a 2 speed gearbox:

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While the model worked good in low gear, the high gear proved much trickier. The single gearbox put a lof of strain on the drive axle in high gear, causing it to melt, even with lubrication.

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Another issue was the high load of the motors in high gear, resulting in them overheating, while the motor could not even remotely apporach the 15 km/h top speed of the Wildcat 6x6.

But not all was bad, I really liked the free-moving front suspension which acts like a suspended pendular axle, while having a much lower unspring weight. While I could make the rear suspension act like a pendular axle instead off front, i decided agaisnt it, since most of the weight is shifted back when crawling and I wanted to keep the rear stable.

With that knowledge, I went back to the drawing board and decided to up the power for the next version...

Medium 4x4 prototype:

This version used 4 BuWizz motors coupled in a manner simillar to my 1:10 Acura NSX which negates the sideways load on the output axle of the gearbox.

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As you can see, this version was quite bigger and it used the reinforced differentials. The increased power drastically improved the performance, the top speed and overall power being simillar to the Wildcat 6x6.

BUT the model had a few problems, main being the exposed gearbox which would get clogged and jam while driving outside. This version was aslo wider compared to the first prototype.

Medium version prototype 2:

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This is another concept where the entire front axle is designed to pivot, but I ultimately decided to go agaisnt it due to the higher center of gravity and higher unspring mass.

The final, universal 4x4 model:

I have built and tested the model, but have yet to make any media, that's why I'm using LDD photos for now.

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I had to way to make the model more ingress resistant and narrower. This is where I came up with the idea of using the new, reinforced differentials as 28 tooth clutch gears for the high gear of the gearbox:

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This way the gearbox's output axle was moved a stud lower, allowing me to cover the bottom of the model with panels which prevent the dirt from getting into the gearbox without sacrificing ground clearance:

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The model inherited the front axle from the prototypes which acts like a free pendular axle. This keeps the weight even on both side of the suspension sosimple open differentials sufficed without a need for lockers.

The gear ratios are a bit of a compromise comapred to the Wildcat 6x6, with low gear being 0,89x the ratio and high gear being 0,83x the ratio. Even with these differences, the model still reaches a very simillar speed in high gear, probably due to lower friction losses and lower rolling resistance.

All in all I think this is a worthy successur to the Wildcat 6x6, even though it may not be as flashy, massive or functional (no skid steering).

Final part count is 774 pieces which is 41% od the Wildcat 6x6 and the weight has been reduced to around 1,4 kg - around half of the Wildcat 6x6.

I will be creating a proper in-depth video about the finished models and the protoypes, so I suggest you to watch this space for more upcoming details.

Edited by Zerobricks

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Nice work, that looks like a very fun model!
I do worry about that gearbox though, especially the new differentials being used. I'd imagine they'd wobble a lot because they don't allow for the axle to pass all the way through them, but hopefully it works fine!

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10 minutes ago, 2GodBDGlory said:

Nice work, that looks like a very fun model!
I do worry about that gearbox though, especially the new differentials being used. I'd imagine they'd wobble a lot because they don't allow for the axle to pass all the way through them, but hopefully it works fine!

Indeed they wobbled a lot, so I used a lot of half beams to stabilize the transmission rings on the bottom. I will talk about that too in the video.

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47 minutes ago, Zerobricks said:

Indeed they wobbled a lot, so I used a lot of half beams to stabilize the transmission rings on the bottom. I will talk about that too in the video.

Ok, sounds good! I missed the fact that you'd already built and tested it, so I'll assume it's good!

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I like this compact design a lot. The way the motors are installed is quite nice, giving way to a simple gearbox and overall drivetrain. Let's see over time how the diff in the gearbox handles all that power. I think 4 motors and 2 Buwizzes are kind of a sweet spot, that's the most I would ever put in one model, both because of not owning more :) and because of considering quite probable wear of parts, but at the same time that seems to give high enough speed and a lot of power to really become fun to drive.

As for avoiding grass to enter the gearbox, what I did and plan to do is instead of covering the bottom with another stud thickness of panels, I just put some duct tape at the bottom (given that the gears don't stick out from the bottom-most layer, which is not that difficult to achieve). This way, I can also use the duct tape (maybe also a layer of cart-board under it) as a skid plate that I don't need to worry about being scratched.

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It is really interesting to read, how and which challenges are solved.

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As promised, I took some time during the weekend to prepare more media.

First is a photo of the model on my new vinyl floor, I really like the bright colors:

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And a couple of outdoor photos, showing the suspension in action:

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The front suspension is inspired by 8475 and acts like a pendular axle and always splitting the weight evenly on both sides of the wheels (important with open differentials):

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Tech specs:

  • 773 pieces
  • 34 x 23 x 17 cm
  • 1100 g
  • 4 BuWizz drive motors
  • 1 PU L servo motor for steering
  • 1 PU M motor for the gearbox
  • Top speed 13,4 km/h

Lastly here's a very detailed video where I explain the issues faced during the design phase and showcase the performance of the finished model:

 

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