Unimog MOC Trial truck

[Voldemort87]

Hello everyone,

I would like to showcase my first MOC - my interpretation of the Unimog.

It has 4WD with portal axles for good ground clearance and wheel articulation assisted by a flexible chassis like the real Unimog. The truck has 1XL motor for drive, 1L motor for RC gear shift for a 2 speed transmission and 1L motor for steering.

Cab can be tilted and there is a fake engine underneath the cab. 

Thanks to @Thirdwigg for guiding me into the Eurobrick forums and also giving pointers in the right directions.

I was also very much inspired by Unimogs of @Thirdwigg , @efferman, @Pat-Ard, @nico71, brickgimlas and the creations of @Madoca 1977, @rm8 and @Sariel. Thanks to everyone for providing the motivation for the MOC!

I will probably expand the model with added functionalities in the future once I get better in building and  will be happy to hear your thoughts!

 

Edited August 30, 2022 by Voldemort87

[1gor]

@Voldemort87 your Mog looks very clean. If you really want (kind of) trial truck then bigger reduction and 2 motors would be desirable. When you look at @Philo's page about motors you'll notice that new PU L motor is practically the same strong as XL motor, so you can use coupled 2 L motors (like on Mercedes Zetros)...

[Thirdwigg]

Great job, and I'm happy to provide a little inspiration. I'm glad you were able to finish this, and welcome to Eurobricks!

[suffocation]

That's a great first MOC! Did you design your own PU code for the gear shifter? If so, could you share it?

[gyenesvi]

Indeed it looks quite clean, I like the hood and the building technique for the front grille! The gearbox/motors placement is nice, though I agree that one PU XL motor will not be very competitive (it's significantly weaker than the PF XL). Maybe, putting 2 L motors side-by-side where the current two motors are is a possibility, which then would require moving the gearbox L motor to the front side of the gearbox, where the engine is now.. Also, I like the simplicity of the suspension using the ball joints, without creating a negative caster at the front (this is the only acceptable usage of it for me at the front). The only thing I don't quite like is that as far as I can see, the springs are limited in their tilting forwards/backwards (can only tilt freely sideways). So it cannot follow the inclination of the axle, it must bend a bit, which creates some friction and so it's not going to be articulating as smoothly as it could be.

[Zerobricks]

Looks good, though I would love to see more photos of the driveline and such.

[Jayden]

Wow this is good! (Or I'm a sucker for PU stuff. ) I was surprised at how narrow the driveline is.

1 hour ago, Zerobricks said:

I would love to see more photos of the driveline and such.

Echoed.

[Voldemort87]

Thank you everyone.

@1gor@gyenesvi Glad you liked it. I tried a lot to keep the body work neat and clean and also tried to stick to the correct Unimog proportions.

I am also considering to make one with the tractor tires but will increase the scale by a few studs.

 

@suffocation Yes I have a PUU code for the shifter. It is quite simple and I think there is already some nice guide available online for simple functions. you can also refer Sariel's gearboxes with instructions for ideas.

I am making a studio model of the MOC and once completed I will share probably along with instructions.

 

@Zerobricks@Jayden Yes, sure I will post more detailed pictures and maybe the studio model once I complete. I am providing more details below.

 

As 1gor and gyenesvi rightly pointed I also considered using 2 x L motors like the Zetros but I had to let go for the idea in order to have a ladder frame and tight packaging with the gearbox.

To overcome the constraint I have a 2 speed transmission with the total reduction of 34.8:1 - low speed and 4.188:1 - high speed  at the wheel.

To save the U-joints I have more reduction in the wheel axle.

Portal axles - 3:1

Diff - 2.33:1

Gearbox - Low - 3:1 and High - 1:2.77 

Motor to gearbox - 1.66:1

It can climb 44-45deg angles before the tires start slipping.

I will post some videos as well soon.

 

I do agree the suspension springs are not optimum links, yet it is well compensated by the flexible frame. Actually the wheel articulation is achieved mostly by the frame rather than the springs. This also helps in avoiding the tires rubbing against the body work too much. The Hard springs are almost rigid.

Edited August 31, 2022 by Voldemort87

[gyenesvi]

3 hours ago, Voldemort87 said:

Gearbox - Low - 3:1 and High - 1:2.77 

So that's a total of 8.3x difference between the two gears? That's massive! It looked like a simple 1.666x gearbox :) So there's more gearing inside there apparently..

3 hours ago, Voldemort87 said:

The Hard springs are almost rigid.

Did you try it with the soft LBG springs? Though I actually thought is could work with the hard ones as well as the springs are placed halfway on the axle. But maybe that bending does really hinder it from articulating properly.

3 hours ago, Voldemort87 said:

yet it is well compensated by the flexible frame.

By that do you mean the flex that simply comes from the beam structure, or is there some trickery in the way it is built to let it articulate? Does the Unimog frame have some special structure to facilitate this (I'd be interested if so)?

[Jundis]

Love the clean design on this one! And for your first MOC, this is even more impressive, great work!

As I am not so educated in Trial Trucks: Are the engine swapped to the center to give better weight distribution? The hood is quite empty now :D

 

[Voldemort87]

1 hour ago, gyenesvi said:

So that's a total of 8.3x difference between the two gears? That's massive! It looked like a simple 1.666x gearbox :) So there's more gearing inside there apparently..

Yes that's correct. When I first started I had based the drive train around Sariel's 4 speed RC gearbox. But I realized i didn't have space for the fake engine and also was increasing the wheelbase. So I created my own gearing which is a simple 2 speed gearbox.

Ratios are a bit extreme but I wanted a torquey drive for crawling and at the same time wanted a fast RC model to drive around level ground unlike the Zetros. In high gear it has very less torque such that it can be stopped even by a slight obstacle/gradient.

1 hour ago, gyenesvi said:

Did you try it with the soft LBG springs? Though I actually thought is could work with the hard ones as well as the springs are placed halfway on the axle. But maybe that bending does really hinder it from articulating properly.

Yes, started with a soft spring initially, but it was too soft for the weight of the model and also it had too much relative travel of tires with respect to the body work. So it was scrapping the body much more. I wanted to reduce the bodywork to tire relative movement but wanted high overall articulation of the model. So most of the articulation is entirely achieved by the chassis considering that the hard springs are stiff.

1 hour ago, gyenesvi said:

By that do you mean the flex that simply comes from the beam structure, or is there some trickery in the way it is built to let it articulate? Does the Unimog frame have some special structure to facilitate this (I'd be interested if so)?

The real Unimog has a flexible chassis that has high torsional flexibility. It comes from the beam structure and also the way the body work is mounted to it.

Unimog U 4023/U 5023: Chassis - Mercedes-Benz Trucks - Trucks you can trust (mercedes-benz-trucks.com)

Like the real Unimog I have mounted the cab by a 3-point mounting that also allows the chassis to flex independently of the cab. U can notice that in the picture above where the wheels are articulating. The Cargo bay I have mounted with just 2 pins since it is not very heavy except for the PF Hub weight that sits on top of it. So this also allows the articulation of the chassis. To sum it up, like the real unimog cab and loading bay can rotate relative to each other. Hope I am clear?

16 minutes ago, Jundis said:

Love the clean design on this one! And for your first MOC, this is even more impressive, great work!

As I am not so educated in Trial Trucks: Are the engine swapped to the center to give better weight distribution? The hood is quite empty now :D

 

Thank you :)

I am also new to the technic and the trial trucks and my references are only the online videos.

I believe the Unimog has engine below the cab and I have tried to replicate that. Please refer the image in the link below.

2014 Mercedes-Benz Unimog U5023 - Gallery | Top Speed

Yes, the hood is a bit empty now. I am trying to add a RC winch inside the hood but seems not enough space to mount a winch. I will try it once again. Ideas are welcome :D

[gyenesvi]

4 hours ago, Voldemort87 said:

Yes, started with a soft spring initially, but it was too soft for the weight of the model and also it had too much relative travel of tires with respect to the body work.

Sure, I see.

4 hours ago, Voldemort87 said:

The real Unimog has a flexible chassis that has high torsional flexibility. It comes from the beam structure and also the way the body work is mounted to it.

That's a very cool property I did not know about (thanks for the references), great that you replicated it! Would be interested to see how it works if you ever make a video of it :) I guess we should see the cab tilting relative to the bed if I get it right.

BTW, is there a reason why you didn't use 11x3 and 7x3 panels for the side of the bed? Seems like a perfect fit for an even cleaner look!

[Voldemort87]

2 hours ago, gyenesvi said:

That's a very cool property I did not know about (thanks for the references), great that you replicated it! Would be interested to see how it works if you ever make a video of it :) I guess we should see the cab tilting relative to the bed if I get it right.

Sure, will try to show that in the video. 

 

2 hours ago, gyenesvi said:

BTW, is there a reason why you didn't use 11x3 and 7x3 panels for the side of the bed? Seems like a perfect fit for an even cleaner look!

purely the part cost and availability reasons. It takes a lot of time for me to order the parts and receive - 1 to 2 months. That is why I tried to do as much as possible with what I have. I wanted to publish this MOC earlier, but I was waiting for 2 months for the yellow hood parts. Sadly I  lost 2 packages that I ordered.

[gyenesvi]

I see.

15 hours ago, Voldemort87 said:

Sadly I  lost 2 packages that I ordered.

Oh that's a pity :(

[1gor]

On 8/31/2022 at 5:01 PM, Voldemort87 said:

Sadly I  lost 2 packages that I ordered.

That sucks; if it is not enough that people doesn't have decent living standard, peasants must cheat also 

Edited September 5, 2022 by 1gor

[Voldemort87]

Started creating stud.io model. 

Here is the 2-speed gearbox used!

Gearbox output is be 4.98:1 (low) and 1:1.66 (high)

 

[Voldemort87]

....and the body work.

 

Edited September 2, 2022 by Voldemort87

[Voldemort87]

On 8/31/2022 at 12:18 PM, gyenesvi said:

So that's a total of 8.3x difference between the two gears? That's massive! It looked like a simple 1.666x gearbox :) So there's more gearing inside there apparently..

Hope this is clear from the images now.

On 8/31/2022 at 3:20 AM, Zerobricks said:

Looks good, though I would love to see more photos of the driveline and such.

Added! The digital model is almost complete.

 

I am new to the Bricklink studio as well. So any feedback/tips on that is also welcome!

Edited September 3, 2022 by Voldemort87

[gyenesvi]

4 hours ago, Voldemort87 said:

Hope this is clear from the images now.

Thanks, it is, I suspected something like that. I do like the drivetrain, I just wish the XL motor would be stronger so that such single motor builds could actually be useful for models of this size. I actually have a smaller car in the making with a single XL motor and planetary hubs, I wonder how well it will drive on some rocks.

On the other hand, I do see some points in the axles that may be problematic. For one, the steering geometry seems to be anti-ackermann, because the steering rack connects to the hub 1 stud outer than the pivot point of the portals. Also, the connection between the ball-joint's U-frame and the O-Frame of the axle seems to be weak, as far as I can tell the liftarms that connect them on the side can only go until the first pin-hole of the O-frame (on the rear axle at least), so that does not fix it against rotation, and though it is fixed by some other means, that probably isn't too rigid either. Connecting the ball joint and the frame is a typical difficulty when using those ball-joints I guess. On the back, don't the motors limit the articulation of the rear axle? It may only be an optical illusion, there may be more space under the motors which is not so visible from this angle, and I know in reality the axle is angled a little bit downwards, while on the render it is still horizontal, so that may be misleading for now. The springs are mounted a bit far from the center of the axle (longitudionally), which could also mean more friction if the axle itself is not very stable against forward rotation. Did you try placing them at the center of the axle? It seems possible though it does require raising the springs.

[Voldemort87]

4 hours ago, gyenesvi said:

Thanks, it is, I suspected something like that. I do like the drivetrain, I just wish the XL motor would be stronger so that such single motor builds could actually be useful for models of this size. I actually have a smaller car in the making with a single XL motor and planetary hubs, I wonder how well it will drive on some rocks.

I think XL motor with sufficient gear reduction seems to handle the load. I don't have experience in rock crawling, but in the indoor tests it seemed ok. Unfortunately I don't have videos yet.

 

4 hours ago, gyenesvi said:

On the other hand, I do see some points in the axles that may be problematic. For one, the steering geometry seems to be anti-ackermann, because the steering rack connects to the hub 1 stud outer than the pivot point of the portals. 

Keen observations! Yes, It is not ideal to have rack connecting outside the pivot. But considering the limitation of the portal axles with a minimum width, this is the best I could manage.  For the maximum steering angle of 20 degrees, wheels remain parallel. You can observe in the image below.

4 hours ago, gyenesvi said:

Also, the connection between the ball-joint's U-frame and the O-Frame of the axle seems to be weak, as far as I can tell the liftarms that connect them on the side can only go until the first pin-hole of the O-frame (on the rear axle at least), so that does not fix it against rotation, and though it is fixed by some other means, that probably isn't too rigid either. Connecting the ball joint and the frame is a typical difficulty when using those ball-joints I guess. On the back, don't the motors limit the articulation of the rear axle? It may only be an optical illusion, there may be more space under the motors which is not so visible from this angle, and I know in reality the axle is angled a little bit downwards, while on the render it is still horizontal, so that may be misleading for now. 

The U-frame and O-frame connection is also supported on the inside with the connector in the front axle and from the top with a beam in the rear axle. Yes, there is space below the motor. As I mentioned earlier the spring travel is not much. Instead the frame twists and compensates for the springs.

4 hours ago, gyenesvi said:

 The springs are mounted a bit far from the center of the axle (longitudionally), which could also mean more friction if the axle itself is not very stable against forward rotation. Did you try placing them at the center of the axle? It seems possible though it does require raising the springs.

I can try it out when I modify the chassis for tractor tires. In the current package it seems a bit tight without raising the chassis. 

I can already start fixing these points you mentioned in the next iteration :)  I also want to do an alternative body work for the mog, maybe an expedition unimog!

[rm8]

Great looking truck and presentation!

Waiting for video!

[arijitdas]

@Voldemort87 This is a great moc considering this is your 1st creation. I am from India too and I know how costly Lego is in here. And on top of it most people give the kind of awkward looks at AFOLs in our country as if its a great sin to own and build Lego as an Adult.

I am 38 years and recently purchased the 42131. Both my parents were gravely worried that I had lost my sanity for indulging in Lego at this age. 

[Voldemort87]

3 hours ago, arijitdas said:

@Voldemort87 This is a great moc considering this is your 1st creation. I am from India too and I know how costly Lego is in here. And on top of it most people give the kind of awkward looks at AFOLs in our country as if its a great sin to own and build Lego as an Adult.

I am 38 years and recently purchased the 42131. Both my parents were gravely worried that I had lost my sanity for indulging in Lego at this age. 

Thank you.

I can totally relate to what you are saying :D 

[1gor]

5 hours ago, arijitdas said:

@Voldemort87 This is a great moc considering this is your 1st creation. I am from India too and I know how costly Lego is in here. And on top of it most people give the kind of awkward looks at AFOLs in our country as if its a great sin to own and build Lego as an Adult.

I am 38 years and recently purchased the 42131. Both my parents were gravely worried that I had lost my sanity for indulging in Lego at this age. 

No worries about hobby; in my country (Croatia is member of European Union) most of people think I'm childish, so mostly my creations (or as they say my wiredness) keep for myself.

Kind regards 

[Voldemort87]

 

18 hours ago, rm8 said:

Great looking truck and presentation!

Waiting for video!

Thank you :)

25 minutes ago, 1gor said:

No worries about hobby; in my country (Croatia is member of European Union) most of people think I'm childish, so mostly my creations (or as they say my wiredness) keep for myself.

Kind regards 

haha!

Edited September 5, 2022 by Voldemort87