Articulated truck question

[Mechbuilds]

My plan is to make a 6 wheeled  4 wheel drive truck that has four rear wheels for drive and two front wheels only for steering. 
It'll be servo steered and the front axle has no suspension at all. Instead, the front of the moc is attached to the rear of the moc by a large turntable. 
So the battery box + servo + receiver is mounted in the front half and an XL motor is mounted to the rear half. 

Basically the front of the moc is just a one big unit that can steer and the rear of the moc is one unit that can push the truck forward. 


Questions:

1. If i use a servo to steer instead of two linear actuators (articulated steering) will the moc try to push forward instead of turn due to no driven front wheels? 
2. If i use sideways pendular axles for the rear and a turntable in the middle, will the rear of the moc just flop to the side if no springs are added?
3. Should i use forward/backward pendular suspension for the rear wheels instead? 
4. Would having only two rear wheels increase the performance of the moc due to only two rear wheels pushing the moc forward and decrease pushing when steering? 
5. If i use only two rear wheels instead of 4, if i add springs to the rear, will offroad capabilities increase? (remember, the front half has no suspension at all.)


I do not have room for the front axle to have driven wheels. (unless i completely redesign the front axle and have a driveshaft go trough the turntable.)

Moc is going to be 11 studs between tyres (total width 15 studs), 60 studs long and 20 ish studs high. 


Front of the moc will be a "one size fits all" truck front end and the rear will be a modular frame for different applications. 

[jorgeopesi]

If I told you everything you ask you will lose all the fun of build with Lego When you have done a lot of MOCs you still won´t know all the answers for your questions, almost all of us get our answers by building and making mistakes.

[Leonardo da Bricki]

My friend, trial and error is all that will lead to you to the answer. Depending on what you build, and how it is designed, it will either work beautifully, or be a total failure. You are the only person who will find out, by building your own design.

[MxWinters]

I agree with @jorgeopesi and @Leonardo da Bricki, building MOC's is very much a trial and error process. If at first you don't succeed, try again and again and again until you get a result that you are happy with. This is one reason why I love building things with LEGO, it allows you to try different things without costing anything or generating any waste. If something doesn't work, you rip it apart and try something new. My artic lorry has gone through like 8 different design revisions before I was happy with the rear end of it and it cost me nothing other than time.

[M_longer]

So basically you are going to make this?

[Mechbuilds]

18 minutes ago, M_longer said:

So basically you are going to make this?

Basically yeah. But instead of the front end being articulated, it would have turning tires instead. 
But i'm thinking "should it have turning tires instead of articulated steering" because the chassis is currently easy to redesign before i actually make the bodywork. 

Instead of having the bucket at the rear, it'll have a bed for carrying battlemechs. 

[Bartybum]

How about the front both articulates and steers? That could be fun

[Mechbuilds]

8 minutes ago, Bartybum said:

How about the front both articulates and steers? That could be fun

Fitting both steering and articulation inside a tiny 15x20 stud box is very compilcated.  

I opted for steering + front wheel drive instead.. Basically the front end has everything. Driven wheels + steering + XL motor + servo + receiver and battery box. 
Everything in one big package. 

The rear is attached to a large turn table. 
This way, i can build different things that attach to it and have the ultimate modular truck.. 


But i gotta agree, articulated steering + regular steering + shocks + turn table center mounting would make a truck impossibly flexible. It could be considered a crawler by then. 

[Magical Duck]

3 minutes ago, Mechbuilds said:

Fitting both steering and articulation inside a tiny 15x20 stud box is very compilcated.  

You could try looking at the 42080 for inspiration...

[Mechbuilds]

6 minutes ago, Magical Duck said:

You could try looking at the 42080 for inspiration...

I'm making it RC. Already fitting a servo + XL motor is already over 16 studs long and 5 studs wide and 5 studs tall if you make it as compact as possible. Currently i have a good module done that's as compact as i can make it. 

front side of the axle has the XL motor in the center and the rear side of the axle has the servo for steering. 
I'm using those black wheel hubs with axle holes on the sides. 
I could basically make the moc two studs narrower by flipping the tires. 

[ben20]

Articulated steering combined with turned wheels was done in this model

 

 

[BusterHaus]

You can look at tractors with dualsteer for inspiration. They are articulated with front or rear wheel steering. The turn radius on them is very small. 

You can also get a Ferrari branded tractor: http://www.ferrariagri.it/en/product/tractors-53fae2b9a2387c362f7b23c7/vega-v80-v95-dualsteer-56a9e4d8fd60884c68ad9449

 

 

[Bartybum]

11 hours ago, Mechbuilds said:

But i gotta agree, articulated steering + regular steering + shocks

Oh yeah nah screw my idea in that case hahah, trying to RC that all in a stable structure is gonna be a nightmare for your tiny base

[Mechbuilds]

I have a tiny issue though.. When i have full steer lock and drive, the CV joint tends to vibrate and jump. Also it slows the XL motor down a bit.. But when i go forward, it goes faster and doesn't jump. 
Can i just ignore this? I can't find a way to reduce the steering angle without completely disassembling the front end..

[doug72]

Some photos of the problem would be useful so others can view and maybe see a solution.

Edited June 17, 2019 by Doug72

[Mechbuilds]

21 hours ago, Doug72 said:

Some photos of the problem would be useful so others can view and maybe see a solution.

The problem is that i have a honor phone currently (gonna replace it soon) and windows refuses to co-operate with it so i can't get any pictures out of my phone to my PC. 
I'm not that tech savvy so i've given up trying to make it work. 

But i can try to make a LDD copy of the thing and post that. 

The issue is having this part:

connected to this part:




And when the servo turns the hub to it's maximum steer lock, the hub and cv joint starts to jump and vibrate when i turn the wheels. 
But it's normal and works if i put no steering input and the moc is going forwards. 

[doug72]

Your steering angle is probably too large.

Max steering angle is approx 30 Degs with that part

 A universal coupling can still work up to 45 Degs.

Either reduce the steering angle or use a uni coupling.

Servo steering angle is 45 Degs when using a normal PF controller I.e left 45 Degs - centre - 45 Degs right only but with a train controller you can turn in 7 steps each way, with auto centre when stop button pushed, so you can do slow turns or large turns up to the limit of the flexible coupling.

Edited June 18, 2019 by Doug72

[Mechbuilds]

So i probably shouldn't try 45 degs on that part. 

That means i get to redesign the steering system again.. 

[Leonardo da Bricki]

You can do 45deg with a U-joint, but the CV-joint is maxed at about 30deg.

I'd recommend designing custom hubs to fit a U-joint in the middle in order to get the results you're looking for.

[Mechbuilds]

29 minutes ago, Leonardo da Bricki said:

You can do 45deg with a U-joint, but the CV-joint is maxed at about 30deg.

I'd recommend designing custom hubs to fit a U-joint in the middle in order to get the results you're looking for.

I feel the same way.. But it needs to be very durable. I need an axle which has the servo and XL motor attached, it needs to be as compact as possible (13 studs wide if tyres are flipped and 11 studs if tyres are going outward) 
It needs to fit under the mercedes arocs cab.

I'd love to use those hubs because they have a very solid connection for the tires and they don't bend under weight unlike just hanging on axles does. 


I love the tight turning radius that i can get.. But it's beginning to be very difficult if i want front wheel drive. 
This would be so much easier if i just went rear wheel drive.. My battery box and receiver are mounted behind the arocs cabin. 
I wonder if i'd have enough wire length to put the XL motor trough the large turn table and mount it immediately after it. 

But then i wouldn't have the possibility to just have a moving front end that attaches to different types of rear modules. 

Edited June 19, 2019 by Mechbuilds

[powerwindows83]

you could make the motor easily removable from the rear section and the wire from its connector, then just pop the motor into the next rear section and thread the wire back through possibly?

also try messing around with half beam triangles and the U bracket (4558692 this thing...) with pins connecting them. with fairly little effort you can make a steering system with a u joint, and steering system thats only a little bit floppy (i care a lot about steering flop and i consider this design passing). the ground clearance under the design im referring to is pretty much the most you can possibly achieve, with just over one stud below the center being the lowest point. im at work thus not near LDD so i cant draw it for you, but the only issue i can imagine you might run into will be the overall height. but hey! engineering! :D