[HELP] Pivot Steering Hinge and Frame for Large MOC

[cy-one]

Hey folks,

 

first post here, so let's make this proper.

I'm a 30 year old German, who recently got back into Technic. I loved Lego when I was young, and the 8880 Super Car is basically ingrained in my mind as one of my fondest childhood memories. Due to my (former \o/) financial situation, things like this and expensive hobbies in general were laid on ice for a decade.

My situation has improved, and I recently got back into Technic. Over the last 3 months, I build

• 42065 Tracked Racer
• 42055 Bucket Wheel Excavator
• 42063 BMW R 1200 GS Adventure
• 42052 Heavy Lift Helicopter

Being who I am, I love largescale projects. So I started dreaming of my own MOC. First something like a working tank with working rotating turret and liftable, obviously working, gun. While somewhat challenging, it's something that has been done to death.
Soooo I came to the conclusion I want to build a tractor.

Not any tractor, but one heavily inspired by the CaseIH Quadtrack-series. Not a replica, though. Tracks will be different and it will have implement hitches on front to back.
Current estimates will give it a footprint of something like 70x30cm length and width. Quite a large vehicle as you can agree. Dual-tracks (as in, using the track-pieces that are used in the Bucket Wheel Excavator, but using two of them side-by-side) kinda are the base for size-guessing.

Currently working on frame and central pivot hinge, which is also where my first problems appear.

I do lack the experience to figure out how to a) make a stiff frame that is touch enough to take the weight of such a large and heavy MOC without twisting and bending too much. As well as... I don't know if my central pivot is... worthwhile. I do like what I have so far, but I'm nowhere as experienced as you guys are.

So, to summarize, I'd like to ask for help and advice when it comes to the frame in general and the large central pivot point.

What I have so far: 

[M_longer]

Ok, it may sound a little harsh, but... try to build something smaller.
Gain experience with smaller model(s), see how parts works under weight and stress.

 

[mocbuild101]

11 hours ago, M_longer said:

try to build something smaller.

I would agree, the biggest MOC I have ever built (many years ago) turned out to be a complete failure...

Also, I would check out @Sariel's Technic book - it's got lots of information on building big structures, and heaps of great mechanisms too.

[Aventador2004]

On 12/20/2017 at 12:01 PM, M_longer said:

Ok, it may sound a little harsh, but... try to build something smaller.

I agree, it will help prevent mistakes.

[Carsten Svendsen]

Unless you join all of the turntables together, with a large enough vehicle, you will find that it will sag in the middle where the rotating part is.

You don't have to build anything massive just to test it, just build a frame that you think will work and then put some weight on either side, like 1 or 2 kg's to test out the rigidity and strenght of the join.

[TeamThrifty]

Using a tri-point arrangement prevents sagging and is used in large articulated agricultural machine.. basically you have an arm above the pivot thats attached to both sides on ball joints - this prevents the sag and also allows oscillation between the two halves. I've used it on a Case Steiger MOC recently, there's a thread for it. not sure how easy it is to see the pivot arrangement on the pics.

[Erik Leppen]

Why are there 4 LAs? What will each of them do?

i'm asking, because the way I know pivot steering is that the turntable is fixed to one half and the other half rotates. That woyd require 2 LAs, obe lefat and one right. I velieve thst's what 42030 does. But maybe I'm misunderstanding what you're planning to do. I don't know the source vehicle you're basing this off.