4x4 Rock Crawler [MOC]

[drdesignz]

I designed and built this 4x4 rock crawler as a conceptual design study for the upcoming Technic challenge. It is remote controlled, with two L-motors and a servo. Both motors power all four wheels at once. The axles are solid, instead of the typical differentials. This makes sense to do, because crawling over rough terrain can cause the truck to balance on three wheels, which will result in the one floating wheel turning by itself. That will simply cause the truck to get stuck there. The problem with transferring power to all four wheels at once is stress on the motors and gears. This wouldn't be as much of an issue if speed was variable, but with the current setup the power to the motors is either on or off. I think clutch gears may be the only real solution to this issue, unless variable speed can be introduced.

The suspension design is experimental. Unfortunately, it does not work well. Actually, it's a total failure, despite why you may think initially from the pictures. The springs are not strong enough to support the truck with all six batteries. In fact, it's just barely strong enough to hold the truck up off the ground without the batteries and if it is sitting still. The whole idea behind the design is that the springs only compress about four or five studs worth in length and I needed a system to exceed that significantly. The configuration I came up with allows travel far beyond those limits. In that regard the design is successful, at least.

Also, the steering radius is too wide. There is a good reason Lego's crawler has four wheel steering. I built the front and rear suspension the same with the intention to add a second servo to the rear later. I thought about it and realized if I do that the wheels will turn in opposite directions. I'd have to add a remote and receiver to make that work. Plus another extension, which was required for the one I have. All of those extra power functions becomes quite a bit more expensive, so now I see why Lego designed their crawler with the servo in the center.

I figured I'd take pictures and post them, even though this is for an upcoming competition. I don't mind because I'm going to tear it down and rebuild a new design from scratch. There's no point in somebody copying the suspension design because it is seriously flawed. Besides the springs not being strong enough, the Technic beams get stressed beyond what is acceptable. You may not have noticed that in the pictures if I hadn't have pointed it out, but they actually twist and bend excessively. The ball joints also come apart easily. There isn't much else original about the chassis design, so there's nothing to keep secret there. And I'm not 100% satisfied with the body design, so I decided to redesign that too. It can't be removed easily either, like Lego's crawler design, so there is no real access to the battery box. Again, this is a conceptual design for studying purposes. The pictures may look nice, but functionally it is terrible. Nevertheless, it was a fun build and I learned a ton.

[rumpletump]

Hey looks pretty cool,

You have the beginnings some good Ideas

Don't share too many secrets shhhhh

[bricky300]

I build somrthing similar, with the same springs, but much smaller...Its for the challenge too

[rm8]

I see it has some problem with steering because of castor, is it?

[efferman]

1.) keep the chassis so simple as possible

2.)a lego crawler dont needs much suspension travel. you should concentrate yourself on the torsion ability.

3.) your wheelbase and trackwidth is much to large. the dimensions of 9398 is a good when the center of gravity is low enough.

[Alasdair Ryan]

Its way too long.......

[drdesignz]

I see it has some problem with steering because of castor, is it?

Caster isn't as much of an issue as the length of the wheel base. It is too long. A bigger gear would have helped.