Eagle V2 an RC Trophy Truck [MOC]

[Daniel-99]

Hello, EuroBrickers!

I am pleased to present to you the second version of my RC Lego Trophy Truck EAGLE. To be more specific, this is the third deep modification of the second chassis. Not surprising, as I've been working on this project for over three months now. For a better understanding of this topic it is worth reading about the first version. A better quality photos could be found on my BrickSafe. And a video: 

 

 

First looks:

 

 

 

Features

• Independed suspension at the front with positive caster angle.
• 4-link solid axle suspension at the rear with anti-roll bar
• RC shocks (80 mm at the front and 110 mm at the rear)
• Brushless motor A2212 1200 kv for propulsion, Geek Servo for steering, 1500 mAh 3S Li-Po for power
• Strong and efficient transmission with metal U-joints and metal bearings.
• 95 mm RC wheels
• Light-weight bodywork

Main goals

"It's never a good idea to stop if you have something to improve."

With these thoughts I was preparing a post about my Eagle a month ago. Here's a list of things I wanted to improve:

• Weight distribution: the heavy electronic components located in the cab loaded the front suspension more than the rear suspension. 
• Rear axle geometry: due to triangulation on the rear axle, the driveshaft and lower suspension arms were located very high off the bottom of the truck, which limited the maximum compression angle of the rear suspension, and the entire chassis was not set to the horizon.
• Rear suspension setup: a true trophy truck requires a suspension with progressive stiffness. 
• Front axle: steering was very sensitive, rather unusual front triangle shape and tilted lower suspension arms.
• Overall bulkiness of the chassis. 

Spoiler

Some photos of Eagle V1 which visualise some problems.

 

Electronics
The Eagle V2 utilizes the same electronic components as the Eagle V1. The story of my choice of such components is given in the post about Eagle V1. Therefore, I will be brief here. 
Motor: A2212 1200 kv
Battery: 3S Li-Po 65C (30C is more than enough) 1500 mAh
Controller: 2-3S 35A
Transmitter: FlySky FS-GT5

Pros: 

1. Brushless motors last longer than brushed motors. 
2. High speed and torque in a compact size (about 3 BM in an XL motor)
3. Radio control (best for fast RC cars)
4. Cheap components (compared to Lego electronic components) available at local RC stores.
5. External Li-Po battery allows for different layouts and unlimited power flow.

Cons:

1. Requires advanced techniques to build strong transmissions (requires lubrication) Otherwise can easily damage plastic parts.
2. Not an easy decision for purists. Difficult to share instructions with others.
3. Have to take care of tangling wires (same goes for large Lego-is designs).
4. Non-universal solution, suitable mainly for RC Lego machines without a list of additional features.

 

Frame & layout
The Eagle V2 has a new "tube frame" (or chassis). This is why I decided not to call it a modification of my Eagle. Let's take a look at it from front to back. All important terms in this section are marked with bold text. In addition, this terms are highlighted on pictures.

The front triangle uses the same "almost right" triangle with 14,15 and 6 stud lengths as the Eagle V1. The lower tube of the front triangle is made of two flip-flop beams that have been stacked together. This solution provides a sufficient level of stiffness and resistance to torsion. In addition, I was able to bring the suspension arm mounting points as close to the center as possible. 

The lower tube of the front triangle is adjacent to the flat bottom made of panels. The upper tubes of the front triangle intersect with the front wall. Further they pass into the side tubes of the cockpit. These tubes are made with flip-flop beams, which allowed me to secure them in place with a 15L front cross-brace  (the Eagle V1 cockpit was 2 studs thinner). 
It's worth noting that the GeekServo motor squeezed perfectly between the lower front triangle tube and the cross-brace of the front wall. Thus, it practically reinforces the front triangle.

The cockpit ends at the rear wall, which is reinforced by a rear triangle and structure around the transfer case housing. The side tubes pass into the rear H-tubes (horizontal). At the same time, the rectangular rear triangle is mirrored to form another rectangular triangle at the very back of the truck. The cross-brace on the rear wall is made using L-beams and 3D printed motor housing. 

Now let me describe the layout of the electronic components. Using a custom transfer case housing, I was able to move the brushless motor out of the cab. It is now located directly behind the rear wall. 
More importantly, I was able to move the Li-Po battery out of the cab. It is now located above the motor. It is true that this solution increases the center of gravity, but on the other hand it provides excellent weight distribution, which is very important for a trophy truck. The controller is located in the cab next to the driver's seat. Both battery and controller have no pin-holes, but I was able to fix them in place quite greatly.
To load the rear axle even further, I added the spare wheel.

 

Bodywork
My main goals with bodywork of Eagle V2 were the following:

1. keep it light
2. keep the original shapes of Eagle V1
3. improve the proportions

As a result I made the whole truck one stud longer and two studs wider than the first version. Now cockpit is wide enough to fit the driver`s seat. Also I changed the bonnet and the front grill. Finally I changed the very back of the truck to make it closer to real prototypes. I have to add, that not only the bodywork make the car look good. More importantly to keep the proportions in the chassis. The authentic look of the Eagle V2 is achieved with the proper settings of the suspension.

 

Transmission
I'd like to make a 3D model of my truck and show you a nice rendering of the drivetrain, like some great technical builders do. However, the Eagle V2 has a lot of custom parts and a bunch of "illegal" techniques like "almost rectangular" triangles. So I will just mark out the transmission components:

1. Brushless motor with custom housing with planetary gear inside (1:4 gear ratio)
2. Central transfer case with 28:20 gear ratio
3. Rear differential with 12:28 gear ratio

The transmission is built on carbon fiber axles and metal U-joints. It is separated from the frame by metal bearings. Metal bearings are used in the center transfer case, in the 5x7 frame that holds the differential, and in all the wheel hubs. I also lubed the planetary gear inside the engine case.

 

Suspension geometry
As I've said before, trophy trucks are all about suspension. So the main reason I did a V2 of my Eagle is to try and improve the suspension (both front and rear).

Spoiler

Eagle V1 suspension.

Front suspension:
Truth be told, not all custom parts turn out to be universal. On the contrary, the idea of efficiency in certain places and the idea of universality are not compatible at all. The Eagle V1 front wheel hubs are a prime example of this principle. They were originally designed for IFS street cars with smaller wheels. Therefore the basic ideas are present in their geometry:

• An inverted ball joint for the lower suspension arm (which is great in general). Combined with the tilted front suspension, they looked nothing like real trucks. 
• The steering arms were 0.5 studs long, which resulted in very sensitive steering.

I also didn't really like the 8 stud length suspension arms, which required custom of steering links to work properly. So I designed a new front suspension system that includes:

• 9 stud length suspension arms.
• New hubs (originally designed for live-axles) with 1 stud length steering arms. Thus hub does not use the ball joints!

The new design is a deep modification of the Falcon trophy truck front suspension, which has proven to be reliable. In the V1, I used 8-studs suspension arms to fit within a certain chassis width and maintain a strong lower tube of the front triangle. However, by using stacked flip-flop beams, I was able to keep it 1 stud wide without losing stiffness.

Rear suspension:
It won't surprise you that the Eagle V2 has a new rear suspension. Here's a list of the changes:

• A new rear axle has been designed (again with a different set of custom hubs). It's more compact than the one the V1 had. 
• The upper triangle of the suspension arms has been inverted (to match the real-world examples).
• New lower arms have been build. Now the live-axle was given the necessary degree of freedom. 
• The attachment points for the suspension arms were lowered by two studs. This modification was possible due to the changes in the drivetrain described above.
• The anti-roll bar has been redesigned to match real prototypes. It resists to the twisting effect of the rear axle that appear in the acceleration. 

Shocks
"Once a perfect suspension geometry is achieved, one may look for a proper set of shocks springs"

The best springs Lego ever made are the hard 9.5 L springs, because they have a good amount of travel and responsiveness. For example, the 9.5 L soft shocks are not as good because the spring force has a hard time overcoming internal friction.  On contrary, the 7L hard shocks have little travel and not enough stiffness to work properly with the hard springs. So I used 9.5L hard springs in the Eagle V1 and early versions of the second chassis. I tried to build a progressive rear suspension using Lego springs, but was not successful. The resulting design was either too unreliable or too bulky. I guess I lacked luck and skill, but I couldn't build a suspension that was both soft and shock resistant. It was either too stiff to absorb big bumps or too soft. 

So I decided to use RC shock absorbers to properly address this issue. RC shock absorbers have different springs that allow you to adjust SAG and progression without having to move the shock absorber mounting point along the suspension arm. I once tried to adapt RC shock absorbers to Lego, but couldn't find a suitable way to attach them to the Lego pins. Fortunately, a working solution was offered by Ryokeen in his Generic Brushless Trophy Truck. I again had to modify the chassis to fit 1:10 scale RC shock absorbers. 

Front suspension has 80 mm shocks with 2.5 studs travel. I mounted it behind the suspension arms as it is done it real Trophy Trucks and many RC scale models. There was a way to place it through the upper A-arm, but such solution required 4L liftarms. In addition it had not freedom in the choice of mounting points. 

Rear suspension uses 110 mm shocks with approximately 3 studs of travel. Additionally they have a dual spring setup, which give the desirable progressive hardness to the rear suspension. Again, I tried to mount rear shocks in the same way it is done in real Trophy Trucks. 

 

Developers diary.

3-7 Sep An Eagle V1 was finished. The driving tests started. Front wheel hubs are the same as in Hornet 4x4 Buggy.

Spoiler

11-15 Sep The new front triangle has been built. Now truck has a tilted lower tube and positive caster. The differential has been changed from yellow to red one.

Spoiler

17 Oct I stated developing a new chassis with a different set of ideas behind. (mostly with the triangulation in the rear axle removed and central transfer case added).

Spoiler

24 Oct First prototype of the new chassis has been built. In addition to the redesigned rear axle, I made a new front axle with a shock coming through the upper A-pillar.

Spoiler

27 Oct I started building a bodywork for a new chassis.

Spoiler

1 Nov The first modification of the second version of Eagle has been finished. I started the driving tests. The rear suspension has a new idea if mixing anti-roll bar with additional shocks to achieve progressive suspension hardness.... that was a total madness... 

Spoiler

8 Nov The whole chassis has been widened by 2 studs for better proportions.

Spoiler

14 Nov A new rear suspension ideas has been applied. The back of the Truck has been changed. Now the rear suspension has two sets of hard 9.5L springs on each side. Progressive stiffness... Bulky realisation. 

Spoiler

25-28 Nov RC shocks has been added. For that reason both front and triangles has been redesigned. 

Spoiler

 

Edited December 25, 2023 by Daniel-99

[Ryokeen]

Already wondered when an update would come and wow that are some really impressive improvements. The chassis and suspension geometry look so clean now and i think it could take quite a beating. Great job there.
Even a little driver seat, i mean..who needs a copilot :D

Use what works and improve the rest, nicly done. Components are also well protected, nothing should happen on a roll over.

Another hint, as i couldn't see how you supported the screws. M3 screws also fit well through frictionless pins. That can fix them better in place without screwing to tight on the liftarms.

And btw, you present your progress so well, that it's fun to read.

To bad we won't be able to have a race :D would be interesting, as your truck is lighter and might have the better suspension, where i have more powaaa

 

[gyenesvi]

This looks really great, the chassis and suspension geometry is really clean and elegant! You really did dig deep into the subject! It's great to read. I like how you simplified it all and it became so lightweight, really can see the tubular structure, which is usually not the case with lego builds.

Those wheel hubs are interesting, especially the ones designed for floating axles. Can you show some close-up images of those when not mounted? Do they work with U-joints when driven? Where do you get these? Also the rear ones are interesting.

Is that big block in the middle the 3d printed mount of the motor? Do you have more pictures? Is the planetary reduction part of it or is that not 3d printed? Do you have a file for it? 

[Daniel-99]

15 hours ago, Ryokeen said:

Already wondered when an update would come and wow that are some really impressive improvements. The chassis and suspension geometry look so clean now and i think it could take quite a beating. Great job there.
Even a little driver seat, i mean..who needs a copilot :D

Thanks for appreciation! Indeed, who need a copilot. Instead of him I placed a controller, so all the wires are covered in the cockpit.

15 hours ago, Ryokeen said:

Use what works and improve the rest, nicly done. Components are also well protected, nothing should happen on a roll over.

Yes, great solutions rarely come in dreams, most of the time they appear as a result of intensive work. Honestly, this is the reason I still use Lego rather than RC car chassis, because I can realize my ideas with the bricks and see if they work or not.

15 hours ago, Ryokeen said:

Another hint, as i couldn't see how you supported the screws. M3 screws also fit well through frictionless pins. That can fix them better in place without screwing to tight on the liftarms.
And btw, you present your progress so well, that it's fun to read.

Thanks for your suggestion, I use 2L friction pins for my needs. I am glad that you found the developers diary interesting. It took me additional hour to add it to the post. 

15 hours ago, Ryokeen said:

To bad we won't be able to have a race :D would be interesting, as your truck is lighter and might have the better suspension, where i have more powaaa

Agreed! That is very frustrating, that I can not meet with people sharing same Ideas and passion for RC Lego cars!... I have been trying to raise a little Lego RC community in my city, but there are very few people who build their RC MOCS with Lego, and only several people were able to participate meetings... Indeed yours Trophy Truck is way more powerful than mine.

[Daniel-99]

On 11/30/2023 at 12:00 PM, gyenesvi said:

This looks really great, the chassis and suspension geometry is really clean and elegant! You really did dig deep into the subject! It's great to read. I like how you simplified it all and it became so lightweight, really can see the tubular structure, which is usually not the case with lego builds.

I am grateful for your comment on chassis, suspension and most importantly, on the tubular frame. It has even more value for me, because I was given by a man with a great experience and skill in building RC chassis and, in particular, tubular frames! 

Quote

Those wheel hubs are interesting, especially the ones designed for floating axles. Can you show some close-up images of those when not mounted? Do they work with U-joints when driven? Where do you get these? Also the rear ones are interesting.

Is that big block in the middle the 3d printed mount of the motor? Do you have more pictures? Is the planetary reduction part of it or is that not 3d printed? Do you have a file for it? 

Let me briefly describe main custom parts I use. I have no files available, since all this parts was purchased from other designers. 

 

Central transfer case

Black box, which is visible from the bottom is the Central transfer case. There is nothing that special in it. It has dimension 6x5x3 studs. It is designed for two main gear ratios 24:24 and 28:20, since it has 3 studs in between input and output axles. Actually, this transfer case was designed specifically by my request to work in combination with a BR motor. Indeed both input and output axles has metal bearings from both sides on inner walls. Such a transfer case could be replicated with Lego parts and connectors with metal bearings, but in such a way it wont have that much mounting points and structural rigidity at once. It can be seen on the following picture (can not take one out right now, since they are placed in a very center of the chassis).

BR motor housing

I am the one of the first testers of this motors. So I have every right to say that the designer has done a great job of improving his product. I asked him if he has plans to sell them abroad. He answered that he yet is not 100% satisfied with the quality of his product, so he need more time for tests and improvements. After that his products will, hopefully, be available in Europe.  A very respectful answer, I would say! Current version is made with molded plastic, except the satellites and sun gear (they are made out of nylon). The hub consists of the main parts:

• back wall, which has the mounting point for the motor itself
• gear carrier
• Front wall, which covers the planetary gear.

The main issue for now is that under heavy load, gear carrier could break. Even being lubricated, it can overheat in extreme situations (example of such situation can bee seen in the very end of the video). In normal conditions it did not happened. I regularly check the planetary gear which significantly extends its live. (on the second picture there is an old version with 3S-printed satellites and gear carrier).

Front wheel hubs

This wheel hubs was also designed for my special request for Live-axle suspension. They do not have gluied-in pins and both mounting points being inverted. This allowed me to build very compact front live-axle for my pathfinder. Apart from that they use the same principle as the other hubs I use:

• strong metal bearing
• modified metal bearing to translate the moment to wheel
• 12 mm hex platform to connect RC wheels

On my opinion, these are the most universal wheel hubs I have. I used them both at live-axle and in independed suspension. Speaking of IFS, I am happy that I was able to get away form the ball connectors by dividing axles of steering and suspension. Now one can replicate this design with original Lego hubs by inverting connectrors 92907.

Spoiler

 

Edited December 7, 2023 by Daniel-99

[Ryokeen]

@Daniel-99 was wondering, which brand are your shocks now ?

[Milan]

Besides very interesting and clean build, I must commend the incredible detailed and thorough write-up.

[Daniel-99]

14 hours ago, Ryokeen said:

@Daniel-99 was wondering, which brand are your shocks now ?

These are made by INJORA. They have a dual spring setup. In addition, there is a second set of softer springs in a box. Hard spring setup without additional pre-compression is slightly harder that hard 9.5 L Lego shocks. So I would not use them in your Trophy truck without switching to a harder set of springs.

13 hours ago, Milan said:

Besides very interesting and clean build, I must commend the incredible detailed and thorough write-up.

Thanks a lot! I didn't expect to get a comment from a moderator ;-) .

[Ryokeen]

@Daniel-99 thx mate, almost bought them aswell, but damn 4 weeks of delivery time :D Did they came prefilled with oil ? As a lot of injora shocks i found were not oil filled

[gyenesvi]

On 11/30/2023 at 6:08 PM, Daniel-99 said:

On my opinion, these are the most universal wheel hubs I have. I used them both at live-axle and in independed suspension.

Thanks for the detailed answer about the custom parts. They look really interesting, wish I could buy some, especially those wheel hubs. What is the material of those hubs? Are they 3D printed or are they molded, or are they metal?

Also very interesting that the other parts are made with silicone molding, that's something I have been looking into as well, seems promising technology, though would be a bit finicky to do at home.. Those white ones are the silicone molding shapes on the picture, right? As for the planet gears, do you mean the gears themselves are made of silicone, or did you refer to the molding shape?

On 11/30/2023 at 6:08 PM, Daniel-99 said:

Speaking of IFS, I am happy that I was able to get away form the ball connectors by dividing axles of steering and suspension. Now one can replicate this design with original Lego hubs by inverting connectrors 92907.

Dividing the axles of rotation of the steering and suspension can be indeed useful, but only works in non-driven front axle, as the drive joint can only work when the two rotation axles are at the same position, and I more often build driven front axles for the slower crawlers.

[Daniel-99]

On 12/4/2023 at 11:33 AM, gyenesvi said:

Thanks for the detailed answer about the custom parts. They look really interesting, wish I could buy some, especially those wheel hubs. What is the material of those hubs? Are they 3D printed or are they molded, or are they metal?

This hubs and transfer chase was made out of photopolymer plastic. I now that such plastic is the weakest, but It was not me who decided to use it. Currently they are unavailable even in Russia, so I use them with care! 

On 12/4/2023 at 11:33 AM, gyenesvi said:

Also very interesting that the other parts are made with silicone molding, that's something I have been looking into as well, seems promising technology, though would be a bit finicky to do at home.. Those white ones are the silicone molding shapes on the picture, right? 

As for the planet gears, do you mean the gears themselves are made of silicone, or did you refer to the molding shape?

Yes, the silicone molding gives a very sturdy parts. White forms from the picture are made with silicone, but the gears are made out of nylon (edited), this was a misprint. 

On 12/4/2023 at 11:33 AM, gyenesvi said:

Dividing the axles of rotation of the steering and suspension can be indeed useful, but only works in non-driven front axle, as the drive joint can only work when the two rotation axles are at the same position, and I more often build driven front axles for the slower crawlers.

I agree with you. My idea works only for non-driven front axle, but it works greatly there! 

I love Lego so madly! With Lego technic parts I do not need any special equipment to load my shocks with oil, because I can build one in 1 minute!

[Daniel-99]

Hey, guys!  I was clearing disk space on my PC and found some footage with driving tests of Eagle V2 (not a final version yet).

 

[Daniel-99]

Hey there, I found some time to release a video review about EAGLE V2. You can find the link at the beginning of the main post.