[WIP] Frontliner - off-road vehicle powered by brushless motor and RC setup

[Krxlion]

Hi everyone!

I want to create an off-road vehicle with these functionalities:

- Speed around 13-16km/h
- Positive caster angle
- Good steering radius
- Covering bottom of the car
- Vehicle must be as versatile as possible (on-road, off-road, climbing capability) - that is why it is called Frontliner
- No melting/damaged axles(or other parts) or at least minimal wear - this is with usage of brushless motor A2212 1000kv
- Weight around 1,2 kg
- Big wheels 100-110 mm (provide additional ground clearance)
- Two-speed gearbox (optional functionality, may be implemented in the future)
- Total gear reduction set to approximately 12:1 (including differentials reductions, etc. This still provides good speed of the model with usage of brushless motor)
- Pendular suspension (optional functionality, currently implemented and it's very useful)

What I will be using (non-lego):
- RC setup (DumboRC X6FG - provides gyro stabilization)
- Geek-servo motors (those works simply as servo-motor, but with 6 channels of the receiver I might use additional geek-servo motor as switch for gearbox)
- A2212 1000kv brushless motor (I was previously using different BL motor, but this one is 14-pole, which means it has shorten rotating angle per-pole and is more precise in working with the throttle than 2838 3200/4500kv BL motor)
- Metal universal joints (those are simply more robust than Lego ones)
- Lucas oil white lithium grease (used to lubricate gears and axle holes)
- 35A ESC
- 3s li-po battery

This is the first time I am seriously using Bricklink Studio to create a MOC. I had few attempts before, but this time I really pushed myself to at least design front and rear axle in it.

Front axle:
I used Geek-servo motor to steer the model (the front red weird stack of liftarms is actually it, dimensions 3x3x5). It also features planetary hubs, reinforced steering joints and planetary hubs.

 

Rear axle (heavily insipired on @gyenesvi 42129 C model):
We can see here the new differential (knock of part for now. I am soon gonna buy 42157 set to replace it with original Lego one). The yellow UV joint symbolizes metal version of it.

 

Middle section:
The yellow stack of gears symbolizes A2212 brushless motor. Between two 5x7 frames I hold battery and on top of that all RC components. This provides placement of all RC components in relatively small place.
A2212 motor can rotate around 11100 RPMs at max throttle, then it is gear down 20:28 (differential gear). The differential distributes the power between the front and rear axles, which in my opinion creates less axle load than with just regular 28-tooth double-bevel gears.

After joining above components into one setup I received the first prototype:
I bought third-party wheels just out of curiosity and I have found that they weight slightly less than Lego ones, with pretty much same radius - 103mm.
The body is just something I come up with in one day, I do not worry about that part for now as it is just prototype.

 

At first I wanted to use 23801 steering hubs, but after few test runs with above model they simply couldn't stand the pressure. Other than that, the small steering joints were popping out from wheel hubs during steering on bumpy road.
So that left me with only two solutions. Either I will use old portal hubs or new planetary ones. The first ones are more suited for big trucks, at least for me. So the choice was to go with the second option. (We need to wait for the Lego Audi set 42160, hope it will have good steering hubs, that support CV ball joints and are without planetary reduction)

With that setup I was afraid that main shaft will have too much speed (around 7900 rpm at max throttle) and axles will start to melt. I was surprised when I took apart the model after hard run, because parts were in perfect shape! Those positive results are I believe because of light weight and short driveshaft.

I am far from over with this model, that is why I submitted this topic. There is still room for improvement in those areas (at least :D):
- Steering radius is simply poor. I thought that If I will put servo on the front and steering rack as close to the center of front axle it will solve the problem, but appareantly no. If you guys have ideas how to solve that or know any good front axle solutions I will be more than happy.
- I need to cover bottom of the car. Shouldn't be problematic, but needs to be pointed out.
- Body will be totally new. With 42157 set going soon into my arms and 42136, 42149 already in my hands I will be going with one main color and I believe you know which one I am aiming at. :)
- Two-speed gearbox, but It will probably change overhaul look of middle section
- Extending rear section. This is tricky one, current solution do not put much stress on axles, but with longer rear driveshaft it would give more "Trophy truck" vibes into it (and I love that :D). Other than stress on axles, this modification will actually shorten steering radius even more, so I am really thinking about implementing it.

That's it. If you survived this wall of text I am more than happy.
Here is GALLERY for you.

Do not hesitate to write under this topic as I am open to suggestions and questions about this MOC.

Edited June 12, 2023 by Krxlion

[pow]

The structure is nice and tight. And looks great.  But if you move the steering linkage in front of the wheels like in the case of the car, don't you automatically get an anti-ackermann geometry? So the the curves outer wheel steers more than the inner wheel?

[gyenesvi]

Nice ambitious project, but could work out with all those non-lego components.

Indeed, your steering geometry is anti-ackermann now, which does reduce steering radius in my experience. If you want to place the steering rack in front of the axle, then you cannot move the ball pin one stud inwards if you want to maintain good geometry. The other thing is that your rack is not as close to the center of the axle as possible (longitudinally). Now it is 3 studs away, but it could be just 2 studs away. And then you can get rid of the anti-ackermann geometry too (the linkage will not hit the wheel as you move it outwards sideways), plus you will have better steering angle, because the link will be shorter (the same amount of rack movement will turn it more). But for that you need to make space for it, and you'll have to redesign the mounting points of the A-arms. Also, as an unfortunate consequence, as the steering link gets shorter, more power will be required for steering, but that won't be a problem I think, the servo will be plenty strong in this setup. The steering rack will get more complicated as well, it will have to be 9L, while still going around the differential..

[vergogneless]

Great project! Insane with those big wheels, it's going to go everywhere! Can't wait to see this monster in action, and I'll keep an eye out for the potential implementation of the 2-speed gearbox because I have a plan to build a model with one too. But for now, it's still a mystery to me how to do it lol.

[Krxlion]

On 6/12/2023 at 9:15 PM, pow said:

The structure is nice and tight. And looks great.  But if you move the steering linkage in front of the wheels like in the case of the car, don't you automatically get an anti-ackermann geometry? So the the curves outer wheel steers more than the inner wheel?

This is exactly what I got - Anti-ackermann geometry, which is good for drifting, but not for my purpose.

On 6/12/2023 at 10:59 PM, gyenesvi said:

Nice ambitious project, but could work out with all those non-lego components.

Indeed, your steering geometry is anti-ackermann now, which does reduce steering radius in my experience. If you want to place the steering rack in front of the axle, then you cannot move the ball pin one stud inwards if you want to maintain good geometry. The other thing is that your rack is not as close to the center of the axle as possible (longitudinally). Now it is 3 studs away, but it could be just 2 studs away. And then you can get rid of the anti-ackermann geometry too (the linkage will not hit the wheel as you move it outwards sideways), plus you will have better steering angle, because the link will be shorter (the same amount of rack movement will turn it more). But for that you need to make space for it, and you'll have to redesign the mounting points of the A-arms. Also, as an unfortunate consequence, as the steering link gets shorter, more power will be required for steering, but that won't be a problem I think, the servo will be plenty strong in this setup. The steering rack will get more complicated as well, it will have to be 9L, while still going around the differential..

Thank you Gyenesvi for commenting. Regarding your entry, it doesn't really bother me where I will put steering rack, because I simply want to learn the proper way of achieving good steering geometry. I read your comment few times, but it is hard for me to put it together in my mind and create useful front axle. Have you got any solutions on rebrickable or any other source, that I could follow to learn more about it?

[gyenesvi]

7 minutes ago, Krxlion said:

Thank you Gyenesvi for commenting. Regarding your entry, it doesn't really bother me where I will put steering rack, because I simply want to learn the proper way of achieving good steering geometry. I read your comment few times, but it is hard for me to put it together in my mind and create useful front axle. Have you got any solutions on rebrickable or any other source, that I could follow to learn more about it?

Many of my models on Rebrickable employ such steering geometry, but they are for floating axle suspension, not independent, which is slightly simpler to build, but the geometry part is the same. They have paid instructions though. Maybe it's best to look at this thread here on EB, which has detailed images of the axles and the steering geometry is quite visible.

I'll also try to reformulate my comments above for better explanation. Your current geometry has two problems now (anti-ackermann and low steering angle), due to where the steering links are attached to the planetary hub (red ball joint). To solve the anti ackermann, you'd want to move the ball joint one stud out towards the wheels. That alone would be problematic, as it would then collide with the wheel. To increase the steering angle, you'd want to move the ball joint back one stud. Luckily, if you move it back and out one stud at the same time, then it solves both problems and it will not collide with the wheel (you may also need to lower it one stud..). Then you will arrive to the geometry I have in the model I linked above. In order to do all these, you steering rack will also have to move back one stud and become one stud wider as well. Hope this helps!

[Krxlion]

5 minutes ago, gyenesvi said:

Many of my models on Rebrickable employ such steering geometry, but they are for floating axle suspension, not independent, which is slightly simpler to build, but the geometry part is the same. They have paid instructions though. Maybe it's best to look at this thread here on EB, which has detailed images of the axles and the steering geometry is quite visible.

I'll also try to reformulate my comments above for better explanation. Your current geometry has two problems now (anti-ackermann and low steering angle), due to where the steering links are attached to the planetary hub (red ball joint). To solve the anti ackermann, you'd want to move the ball joint one stud out towards the wheels. That alone would be problematic, as it would then collide with the wheel. To increase the steering angle, you'd want to move the ball joint back one stud. Luckily, if you move it back and out one stud at the same time, then it solves both problems and it will not collide with the wheel (you may also need to lower it one stud..). Then you will arrive to the geometry I have in the model I linked above. In order to do all these, you steering rack will also have to move back one stud and become one stud wider as well. Hope this helps!

I have bought your instruction once - "42129 C model". That model does have double-wishbone suspension, so if it also features good steering angle I can take solutions from that one. But if I will do that, soon my Frontliner will be more "yours" than mine MOC, haha. :D
Either way, I will take a look at your guidelines, I appreciate your input a lot! :)

[gyenesvi]

3 hours ago, Krxlion said:

I have bought your instruction once - "42129 C model". That model does have double-wishbone suspension, so if it also features good steering angle I can take solutions from that one. But if I will do that, soon my Frontliner will be more "yours" than mine MOC, haha. :D
Either way, I will take a look at your guidelines, I appreciate your input a lot! :)

Haha, no problem :) Well the difference between that and your current one is that in my case the steering rack is behind the axle, and because of that it has ackermann steering, not anti-ackermann. So flipping your front axle to have the rack behind the diff would improve it. I think the steering radius is okay on that one (not as good as the other buggy above, but good enough for such a buggy), so if that's a simple solution for you (I think you have enough space behind the diff) than maybe it's worth giving it a try first.