Mercedes Unimog U4000 [MOC]

[Daniel-99]

Hello everyone! I am glad to introduce you my Mercedes Unimog U4000. I made it last autumn for trial competitions and it became my first successful RC Lego model with Brushless RC motor. 

Technical aspects:
- Brushless RC motor 1000kv with a custom 3D-printed planetary gear.
- Custom 3D-prined planetary 2-speed gearbox with remote control (by Geek Servo) gear ratio 1:1 or 1:5
- RC remote control
- 3S Li-Po for power
- Geek Servo for steering
- Transmission with metal bearings
- Planetary wheel hubs
- 4-link live axe suspension at the front
- 3-link live axe suspension at the rear with free articulation
- 85 mm RC tires
- Light-weight bodywork, total mass is about 1.2 kg

I tested this car on various terrain both indoor and outdoor. It reaches about 8 km/h on normal speed and about 1,6 km on low gear. Since the transmission has several reduction gears (made with planetary gears) Brushless motor feels good in this trial car. It gives the truck more power than it will ever need, so the truck can take a significant weight on board (if one change shocks to the hard one).

Oscillating real live-axe and grippy tires provide a constant contact with road, so the truck climbs rocks easily both with closed and open differentials. Due to the reference, the gravity center of the truck is moved to the front, so it struggles a bit with going down the hill, but appears to be a great climber. It can beat Lego Zetros both on low and high gear!

 

 

Edited February 9 by Daniel-99

[2GodBDGlory]

That's quite an interesting model, with such a high concentration of custom parts! I'd be interested in some more information on the planetary gearbox you've got in there!

[Daniel-99]

7 hours ago, 2GodBDGlory said:

That's quite an interesting model, with such a high concentration of custom parts! I'd be interested in some more information on the planetary gearbox you've got in there!

Thank you! There is a video about this gearbox made by its creator, but it is in russian. If you will need an extra details, I will try to answer your questions with more photos and technical aspects.

 

[2GodBDGlory]

Quite cool!

I love all those unique Russian Lego RC solutions!

[gyenesvi]

Nice model, I like the free swinging rear axle. Though seeing the whole suspension work feels a bit like watching a fast buggy rather than a trial Unimog, which is usually taking things slow.

You guys hack the hell out of the lego system, I also love all those extra RC components that you guys print. The gearbox is really interesting. If I understand correctly, in one position it locks the planetary housing to the drive axle (1:1 ratio), and in the other position it locks the housing to be stationary (1:5 ratio). I wonder if only one of the two locking mechanisms would be sufficient for switching gears though. Or even whether this could function as a continuously variable automatic transmission. What happens if you just leave out the whole locking mechanism? :) I could imagine that if there is little friction, the drive axle would take the planetary housing with itself, but if there is more friction then the housing could spin slower and result in higher torque. Maybe it does not work out like that in practise, but it would be nice to see what happens!

At the end of the video there's a lower suspension arm for the planetary hubs that I'd like to have as well.. :)

[2GodBDGlory]

1 hour ago, gyenesvi said:

Nice model, I like the free swinging rear axle. Though seeing the whole suspension work feels a bit like watching a fast buggy rather than a trial Unimog, which is usually taking things slow.

You guys hack the hell out of the lego system, I also love all those extra RC components that you guys print. The gearbox is really interesting. If I understand correctly, in one position it locks the planetary housing to the drive axle (1:1 ratio), and in the other position it locks the housing to be stationary (1:5 ratio). I wonder if only one of the two locking mechanisms would be sufficient for switching gears though. Or even whether this could function as a continuously variable automatic transmission. What happens if you just leave out the whole locking mechanism? :) I could imagine that if there is little friction, the drive axle would take the planetary housing with itself, but if there is more friction then the housing could spin slower and result in higher torque. Maybe it does not work out like that in practise, but it would be nice to see what happens!

At the end of the video there's a lower suspension arm for the planetary hubs that I'd like to have as well.. :)

If it helps you follow the working principle, I think that planetary gearbox has largely the same working principle as this one I made a while back, only mine was automatic, rather than using a servo for control. Mine didn't have the second lock, which I think is part of what made it automatic, but it was a similar idea:

(I made a V2 version lower in the thread)

 

Edited February 9 by 2GodBDGlory

[gyenesvi]

4 hours ago, 2GodBDGlory said:

If it helps you follow the working principle, I think that planetary gearbox has largely the same working principle as this one I made a while back, only mine was automatic, rather than using a servo for control. Mine didn't have the second lock, which I think is part of what made it automatic, but it was a similar idea:

Thanks for that reference, it is indeed almost the same idea, and nice trick to use the planetary hub for that. So in your version you need to add the rubber part to force the drive axle to take the planetary housing with itself in fast gear (but in slow gear it is causing excess friction which is not so good, as it is both inefficient and wears out). I am guessing that without that rubber piece it would always go in slow gear, at least for your heavy model, right? Or even with a lighter model, it would go somewhere in between fast and slow until it hits some obstacle, where it would slow down.

Now if that's true, then we'd only need the mechanism to enforce fast gear, which is just the job of the clutch on this 3d printed version. So the whole gearbox might work with a simplified setup with just a classic clutch mechanism, which would not need the second 3d printed custom selector with the rotated axle hole, but an existing selector (even the wave selector) could be used. Only the custom planetary housing would be needed, and even that could be simplified as it would not need the winglets on the side, so it would be a bit narrower. Do you think that could work?

Oh no, I forgot that if the housing is not fixed stationary then it can counter rotate and the model is not moving, so that does not correspond to slow gear. Then indeed both mechanisms are required.

Edited February 9 by gyenesvi

[2GodBDGlory]

1 hour ago, gyenesvi said:

Thanks for that reference, it is indeed almost the same idea, and nice trick to use the planetary hub for that. So in your version you need to add the rubber part to force the drive axle to take the planetary housing with itself in fast gear (but in slow gear it is causing excess friction which is not so good, as it is both inefficient and wears out). I am guessing that without that rubber piece it would always go in slow gear, at least for your heavy model, right?

Yeah, that's correct. I think without the rubber part it would virtually always go to the low gear, regardless of the weight of the model, which is unfortunate, because the wear is a big problem.

1 hour ago, gyenesvi said:

Oh no, I forgot that if the housing is not fixed stationary then it can counter rotate and the model is not moving, so that does not correspond to slow gear. Then indeed both mechanisms are required.

I think you're correct that both would be required

[Daniel-99]

 

 

14 hours ago, gyenesvi said:

Nice model, I like the free swinging rear axle. Though seeing the whole suspension work feels a bit like watching a fast buggy rather than a trial Unimog, which is usually taking things slow.

Yes, I am slightly mad at fast lego cars. My Unimog is build in 1:18 (approximately), so the top speed in real life is 8 km/h x 18 = 144 km/h and it is not realistic, but it is fun to play outdoors! The low gear was build especially for trial purposes, in order to obtain a good control over the truck.

14 hours ago, gyenesvi said:

You guys hack the hell out of the lego system, I also love all those extra RC components that you guys print. The gearbox is really interesting. If I understand correctly, in one position it locks the planetary housing to the drive axle (1:1 ratio), and in the other position it locks the housing to be stationary (1:5 ratio). I wonder if only one of the two locking mechanisms would be sufficient for switching gears though. Or even whether this could function as a continuously variable automatic transmission. What happens if you just leave out the whole locking mechanism? :) I could imagine that if there is little friction, the drive axle would take the planetary housing with itself, but if there is more friction then the housing could spin slower and result in higher torque. Maybe it does not work out like that in practise, but it would be nice to see what happens!

At the end of the video there's a lower suspension arm for the planetary hubs that I'd like to have as well.. :)

As I understand "automatic" gearbox in real live does not mean "mechanically automatic", there are plenty of sensors of speed, torque and so on.. and a smart controlling system that swiches the gears (of NORMAL gearbox). Modern automatic gearboxes use the same principle with planetary gear several times to archive wide range and small steps. 

 

[Daniel-99]

Hello Eurobricks! 

I am back with improved version of Unimog U4000, currently it is a WIP! List of changes:

• redesigned live-axles
• new suspension
• raised body by 1 stud
• new RC tires 95 mm (instead of 85 mm)
• Front fender lowered by 1 stud
• thickened cab roof
• flat-bed and rear lights added

Spoiler

Old version is too low comparing to the reference:

Well, now I want to widen the whole body by 2 studs to fit the reference even closer. Also I made a driving test and found a technical issue with the new chassis. To fix it I have to make the front driveshaft longer by 1-2 studs.

[Daniel-99]

Here is final V2 of my Unimog U4000. From the previous update I have changed:

• A-pillar design
• Front fenders 
• Raised the cabin and the flat bed over the chassis by 1 stud
• Raised mounting points of the springs by 1 stud

This changes solved all problems with the front axle, and now truck is ready for serious off-road actions!

 

V2 has a chassis similar the chassis from my previous MOC Pathfinder, but with several changes:

1. planetary wheel hubs
2. locked rear differential
3. different gear combination in the transmission
4. Softer spring setup
5. relocated battery box and RC controller

 

As a result, Unimog perform better in trial than my Pathfinder! I will make a video soon!

 

[Daniel-99]

Finally I made a video for you guys! 

 

[Krxlion]

I have watched your video recently and I love this MOC. Clean cable management, robust design, clever suspension and driveshaft, good steering angle. On top of that I envy this two-speed gearbox, I would like to try this solution myself, but I feel like I would need a lot of 3d-printed parts, haha :D Keep up the great work and I am looking forward for your MOCs releases. :)

[Daniel-99]

8 hours ago, Krxlion said:

I have watched your video recently and I love this MOC. Clean cable management, robust design, clever suspension and driveshaft, good steering angle. On top of that I envy this two-speed gearbox, I would like to try this solution myself, but I feel like I would need a lot of 3d-printed parts, haha :D Keep up the great work and I am looking forward for your MOCs releases. :)

Thank you! Currently I am working on another trophy truck, but it will take me quite some time to finish it up. Probably I will start a WIP topic soon.

[Krxlion]

Good to hear that! I was thinking myself to update TROPHIC topic as I heavily modified my MOC. I was experimenting with three different BL motors but each have its own upsides and downsides. Main goal was to actually build up torque in a smallest possible area (something like you use with 3d-printed components on A2212 BL motor). We will see how it goes, tomorrow I will probably run some tests.

[vergogneless]

Great job! It's all very inspiring to me :D 

[Daniel-99]

On 5/29/2023 at 9:42 AM, vergogneless said:

Great job! It's all very inspiring to me :D 

Thank you! I am following your progress as well!

Edited May 30 by Daniel-99

[Krxlion]

I have an unusual question for you @Daniel-99 about gear ratio in your MOC and in general solutions. If I can see correctly you have:

- 5:1 gear ratio in 3d-printed planetary tranmission
- 1.4:1 gear ratio in 28-tooth gear to 20-tooth gear (those gears are to move force to main driveshaft)
- again 1:1.4 gear ratio due to differential usage
- 5.4:1 in planetary hubs
- AND If you put your gearbox into first gear it will add another 5:1

Those all transmissions puts model in situation where you can approximatelly have 96.428:1 gear ratio(first gear) or 17.857:1 gear ratio(second gear), which is pretty huge gear ratio for first gear. Are you not having issues with that? For example If you drive on first gear at full speed on normal road and then suddenly realese the throttle, the force in the driveshaft cannot go anyway, because of such big gear ratio, or am I wrong? Can you move the car freely on first gear with your hand on a ground like kids toy, without any power?

If you cannot understand what I am saying it's okay, I could have overcomplicated it, haha :D

I am struggling myself with similar topic and I cannot just gear down the motor speed infinitely, because If I do that too much, the car will each time I release throttle bend the axles and bricks in general.

[Daniel-99]

14 hours ago, Krxlion said:

I have an unusual question for you @Daniel-99 about gear ratio in your MOC and in general solutions. If I can see correctly you have:

It was all correct except the reduction in the gearbox, it has 1:4 gear ration on the low gear.

14 hours ago, Krxlion said:

Those all transmissions puts model in situation where you can approximatelly have 96.428:1 gear ratio(first gear) or 17.857:1 gear ratio(second gear), which is pretty huge gear ratio for first gear. Are you not having issues with that? For example If you drive on first gear at full speed on normal road and then suddenly realese the throttle, the force in the driveshaft cannot go anyway, because of such big gear ratio, or am I wrong? Can you move the car freely on first gear with your hand on a ground like kids toy, without any power?

If you cannot understand what I am saying it's okay, I could have overcomplicated it, haha :D

I understand the mechanical principles you are talking about, but they do not occur in my MOCs since I use a "weak" BR motor. I made a test by releasing the throttle both on Low and High gears. Nothing gets broken. Though there is no reason to do such things while driving since the car is not that fast, and one can always stop the car smoothly. By the way, I am using carbon fiber axles to connect the gearbox to the motor and inside the central 28:20 gear housing. Probably they are not necessarily, but I do not want to bother about it ;-) 

[Krxlion]

14 minutes ago, Daniel-99 said:

It was all correct except the reduction in the gearbox, it has 1:4 gear ration on the low gear.

I understand the mechanical principles you are talking about, but they do not occur in my MOCs since I use a "weak" BR motor. I made a test by releasing the throttle both on Low and High gears. Nothing gets broken. Though there is no reason to do such things while driving since the car is not that fast, and one can always stop the car smoothly. By the way, I am using carbon fiber axles to connect the gearbox to the motor and inside the central 28:20 gear housing. Probably they are not necessarily, but I do not want to bother about it ;-) 

I see, good to hear that you do not experience any unwanted behavior :). What is also great, is that A2212 motors have 14-pole in them, which means the "jumps" of rotor are not so big (only about 25 degree). When for example I was using 2838 motor it has only 4-pole (90 degree jumps). With that motor it is very hard to drive gently, haha. :D