[WIP] 4x4 Unimog Trial Truck

[Teo LEGO Technic]

Hey guys!

I'm trying something new this fine Wednesday afternoon, my first WIP topic. I always present my models fully built, but this time I'd like to get feedback and advice as I build, to make a better final model, and to learn more from the Eurobricks experts as I go . So please feel free to expound productive criticism, and here we go!  

For this model, I want to build a 4x4 trial truck that's loosely based on the new Zetros in its diff lock system, but otherwise quite different. The scale is going to be such that it fits with the CLAAS tires, and the main features I want are a combination of a heavy-duty 2-speed gearbox (based on Sariel's: http://sariel.pl/2011/02/2-speed-heavy-duty-linear-gearbox/), combined with diff locks based on the Zetros system, on both front and back axles differentials, with no central diff. This will allow the truck to travel fast in high gear with open diffs and good u-turn capability, and slow and powerfully in the low gear with closed diffs for offroading. To sum up, these are the desired functions:

-Precise steering with servo motor 

-All wheel drive powered by 2 XL's

-Two speed heavy duty gearbox

-Differential locks on front and rear axles with M-motor

-Power by BuWizz

-No chance of gear slippage/damage anywhere along the drivetrain, steering, or locking systems    

For starters, what do you guys think is a good truck to model? Perhaps just a good old Mercedes Unimog? A Russian Ural trial truck?

 

Edited August 12, 2021 by Teo LEGO Technic

[1gor]

That could be interesting project, but I have one friendly advice; please post at least one photo of your project (in working progress)

As Unimog fan I'll go for Mog, but that is my personal opinion

Edited August 11, 2021 by 1gor

[MangaNOID]

1 hour ago, Teo LEGO Technic said:

Precise steering with servo motor 

Myself I would not use a servo motor for a trial truck. You want the steering to stay where it is when you are slowly navigating obstacles. 

M motor with worm gear reduction ??

or linear actuator ??

none of this self centering stuff from a servo I would  say

 

[Teo LEGO Technic]

5 minutes ago, MangaNOID said:

Myself I would not use a servo motor for a trial truck. You want the steering to stay where it is when you are slowly navigating obstacles. 

M motor with worm gear reduction ??

or linear actuator ??

none of this self centering stuff from a servo I would  say

 

Interesting idea. How bout an M-motor with a small linear actuator mounted on the axle? I've been trying to decide whether to place the steering motor on the axle or the chassis. The diff lock motor and drive motors have to be mounted on the chassis to transmit to both axles. 

[1gor]

16 minutes ago, Teo LEGO Technic said:

Interesting idea. How bout an M-motor with a small linear actuator mounted on the axle? I've been trying to decide whether to place the steering motor on the axle or the chassis. 

Put it on axle

(together with small linear actuator)

[nerdsforprez]

1 hour ago, MangaNOID said:

Myself I would not use a servo motor for a trial truck. You want the steering to stay where it is when you are slowly navigating obstacles. 

M motor with worm gear reduction ??

or linear actuator ??

none of this self centering stuff from a servo I would  say

 

Yup.  

 

1 hour ago, Teo LEGO Technic said:

Interesting idea. How bout an M-motor with a small linear actuator mounted on the axle? I've been trying to decide whether to place the steering motor on the axle or the chassis. The diff lock motor and drive motors have to be mounted on the chassis to transmit to both axles. 

It should be a small crawler then.  I think the power/strength and range of motion with a s linear actuator wouldn't be sufficient otherwise

Edited August 11, 2021 by nerdsforprez

[Teo LEGO Technic]

1 hour ago, 1gor said:

That could be interesting project, but I have one friendly advice; please post at least one photo of your project (in working progress)

As Unimog fan I'll go for Mog, but that is my personal opinion

Sounds good, I'll post a photo of the front axle as soon as I finish a prototype. I'm also a Unimog fan, so we'll go with that. 

59 minutes ago, 1gor said:

Put it on axle

(together with small linear actuator)

6 minutes ago, nerdsforprez said:

Yup.  

It should be a small crawler then.  I think the power/strength and range of motion with a s linear actuator wouldn't be sufficient otherwise

Seems like it's unanimous: actuator > servo. For a MOC roughly the scale of the Zetros you don't think the small actuator would do the trick? I'll try fitting the large one in and see how that goes. 

[nerdsforprez]

2 minutes ago, Teo LEGO Technic said:

Sounds good, I'll post a photo of the front axle as soon as I finish a prototype. I'm also a Unimog fan, so we'll go with that. 

Seems like it's unanimous: actuator > servo. For a MOC roughly the scale of the Zetros you don't think the small actuator would do the trick? I'll try fitting the large one in and see how that goes. 

I do not. But... a large would be perhaps too large. Check out this crawler (it just so happens I am completing my own review of this crawler, which is excellent!)  

where the builder uses a worm gear (along with 8x40T gear pairing).  I can confirm this is an excellent set-up (see the video I just posted on that thread).  

This builder (@PunkTacoNYC) also build his Rocket Crawler using the L actuator for steering.  It too is excellent but his Rocket Crawler is much bigger than the scale you are thinking of building at.  

 

[Teo LEGO Technic]

8 minutes ago, nerdsforprez said:

where the builder uses a worm gear (along with 8x40T gear pairing).  I can confirm this is an excellent set-up (see the video I just posted on that thread).  

Good idea, worm gear it is. The Chilli Crawler is indeed a great model, is the worm gear attached to an 8-tooth or 24-tooth gear I can't tell?

[nerdsforprez]

5 minutes ago, Teo LEGO Technic said:

Good idea, worm gear it is. The Chilli Crawler is indeed a great model, is the worm gear attached to an 8-tooth or 24-tooth gear I can't tell?

8.  He has instructions on rebrickable I believe. 

[keymaker]

6 hours ago, nerdsforprez said:

I think the power/strength and range of motion with a s linear actuator wouldn't be sufficient otherwise

I would not say that small LA is the best option, but.... It works pretty well in my Crawler, which is not the smallest one :)

[Scoar Sonander]

Unimog, but with a lengthened wheelbase! 

[Teo LEGO Technic]

9 hours ago, keymaker said:

I would not say that small LA is the best option, but.... It works pretty well in my Crawler, which is not the smallest one :)

Sweet crawler!! I guess the small actuator remains an option...

2 hours ago, Scoar Sonander said:

Unimog, but with a lengthened wheelbase! 

That could work, I'm looking at the U3000:

[nerdsforprez]

11 hours ago, keymaker said:

I would not say that small LA is the best option, but.... It works pretty well in my Crawler, which is not the smallest one :)

This indeed is a great build.  Loved to see the different shells that can go on it as well.  Seems like the small LA works pretty well.  But for more extreme crawlers, I would recommend a Large LA.  

But I suppose it does not really matter.  The OP is deciding to build a trial truck, which I conceptualize very much different from a true crawler.  One is made for just real rocky terrain, whereas the other specializes in boggy terrain, hilly, etc.  The upside is it is more versatile, the downside is I don't think trial trucks can keep up with real crawlers in terms of rocky terrain...but honestly I am not sure of the distinction.  

Edited August 12, 2021 by Milan
Do not quote videos or images from the same page.

[keymaker]

15 minutes ago, nerdsforprez said:

But for more extreme crawlers, I would recommend a Large LA. 

Yes, large LA would be unstoppable indeed. But it takes space, a lot of it. And I tried to keep rasional size, hide and secure main mechanisms. And so far during testing I didn't notice problems with lack of power with small LA in this configuration. Instructions are available without charges, so anyone interested can check out front axle construction in this MOC :)

Edited August 12, 2021 by keymaker

[Teo LEGO Technic]

4 hours ago, nerdsforprez said:

The OP

What's OP?

4 hours ago, nerdsforprez said:

very much different from a true crawler

I'm choosing a trial truck mainly because I want space for the gearbox and differential lock mechanisms.

3 hours ago, keymaker said:

I didn't notice problems with lack of power with small LA in this configuration

Yeah I'll either do a small actuator or a worm gear.

[2GodBDGlory]

1 hour ago, Teo LEGO Technic said:

What's OP?

Original Poster, I believe.

I like to do overkill on my crawler's steering, such as an L-motor and a large linear actuator. That way, if I need to wiggle the truck around with the steering while in an extreme position to get that last shred of traction, I know it won't let me down. Worm gears can work too, and are more versatile in the space they use, but can be fairly complicated by the time enough reduction is achieved.

[nerdsforprez]

5 hours ago, Teo LEGO Technic said:

What's OP?

I'm choosing a trial truck mainly because I want space for the gearbox and differential lock mechanisms.

 

Original poster. 

and  to your other comment....

[1gor]

UGH Unimog is very interesting and double cab - perfect for hiding battery box(es)

[Teo LEGO Technic]

15 hours ago, 2GodBDGlory said:

I like to do overkill on my crawler's steering,

Honestly same, if it's worth doing it's worth overdoing in the words of the immortal mythbusters

2 hours ago, 1gor said:

UGH Unimog

I looked this up and I can't find it, what is UGH?

Tonight I will continue working on the front axle, probably the most complicated part of the whole build. I have a couple different ideas for how to fit all three functions in (drive, steering, diff lock), and I'll post the prototypes to get your guys' feedback . 

[1gor]

UGH Unimog is this

(Model with torque tube suspension, pure offroader)

UGE Unimog is this 

(Unimog implement carrier)

 

 

[Teo LEGO Technic]

So here's what I've got so far. As it turns out I may have bit off more than I can chew, but with some patience and help from u guys, I think it's achievable. Like I said this is my most ambitious build yet. 

As of now, the width of the axle is just what i want it to be, using Zblj's custom portal axles to save a stud on either side compared with the Unimog set portal axles. Total reduction is approximately 11.6:1 which is going to provide a ton of torque, and all the gearing is solid and should be slippage-free . 

With this set-up (not yet strengthened by any means), the new diff sits inside the 5 x 7 case and therefore is as sturdy as it can be. The issue is, unlike, the older one, with the new diff there isn't enough room for this trick, so more gear are required to transmit power away and provide enough space, which takes up extra room:

And if I want to do it the way it is in the Zetros set to save space, I think I might run into the same issue of gear slippage, due to the lack of the 5 x 7 frame:

 So my question is, which gear locking mechanism do you guys think I should go with: the current one, with the clutch outside the differential, or the Zetros version where it sits right beside the differential?

Also, does anyone know of other builders who have made a steered, driven, and locking front axle? I could get some more inspiration for how to fit it all in, I'm pretty stumped at how to put it all together in a nice solid fashion   

 

[Lukes_Brick_Studio]

Your progress is looking good. I really like it that you are using the new differential. Maybe you can try to built two front axles one with the clutch outside of the differential and one where it sits right beside the differential, than you can look witch version works better and is more reliable.

I have built a 4WD truck last year with locking Differentials on all axles, maybe you can get some inspiration from it. https://bricksafe.com/pages/Lukes_Brick_Studio/mercedes-benz-zetros-4x4

 

[Teo LEGO Technic]

6 hours ago, Lukes_Brick_Studio said:

Maybe you can try to built two front axles one with the clutch outside of the differential and one where it sits right beside the differential, than you can look witch version works better and is more reliable.

Good idea, I can also probably stick an XL in each and see if it holds.

6 hours ago, Lukes_Brick_Studio said:

maybe you can get some inspiration from it.

Sweet truck! Very nice system for the front axle, I saw the same portal axles used by Functional Technic on his Unimog, they're very compact and sturdy https://www.functionaltechnic.com/2020-08-30/unimog-406-with-diff-lock-and-portal-axles

My only problem with them were the use of the CV joint that limit the steering angle (an issue with the LEGO Zetros for example that I want to improve upon).

It seems lots of people use pneumatics for diff locks, that might be something I should look into.  

[1gor]

I don't know if you have pair of defender wheels (and if portal axles hub from 8110 set fits in it); that could (perhaps) help you to gain stiffness