FALCON RC Trophy Truck [MOC]

[Daniel-99]

Hello everyone! I would like to introduce you my new top-tech mid-scale Trophy Truck "Falcon". This car is a TRUE RC car in Lego clothing.

 

Technical characteristics

 

1.  Full independent suspension with positive caster on all wheels
2.  Minimalistic and strong transmission with metal CV-joints
3.  4 - wheel drive
4.  4 Buwizz motors for propulsion (1 motor per wheel)
5.  Custom RC controllers adapted for Lego
6.  3S Li-Po 35C 2600 mAh for power
7.  GeekServo for steering
8.  soft RC wheels 75 mm
9.  Custom wheel hubs with metal bearings
10.  Light bodywork, 1270 gram of total mass

Instructions?

Some of you might be interested in instructions. Well, there will be non, I am sorry! Here I will explain why instructions for this car are impossible.

Falcon has 4 Buwizz motors for power, which can be easily changed to Buggy motors or Mould King version. Power source and controllers could be replaced with two Buwizz 3.0 units (in theory). But there is no way to replicate both suspension and transmission with lego parts only. 

Non-Lego solutions:

•  Custom 3D-printed parts, such as wheel hubs, steering arms, suspension arms with 4,5 stud length
•  Modified Lego parts
•  Hand-made parts from plastic bottle ;-)
•  Broken Pythagorean theorem in suspension
• metal parts, which make the whole car rigid

 

Chassis

Falcon has same chassis as a Wilde beast, but with shorter  wheel base and suspension arms. So I will not dive into details here.

Bodywork
I was inspired by a Trophy Truck by Keymaker`s armored Trophy Truck.
Though I reduced some details and widen the body by two studs to fit the chassis.

Made for outdoor driving
This car is not a shelf model. It was made for regular, extensive and extreme driving. Recall, that the elder brother Wilde Beast had a problem with motors: they were not strong enough to translate all the power from Li-Po battery to 90 mm RC wheels. That is why Falcon was made in a smaller scale to fit 75 mm wheels. Now motors does not struggle at all! Enjoy drifting on sandy road? - easilly!

Lego Outdoor cars usually struggle from dust and dirt filling the transmission. This car has a minimalistic transmission without Differential, so there is noting to break. The weakest parts of lego cars (wheel hubs with CV joints) have been replaced with custom hubs with metal bearings - no more plastic dust in transmission! And nothing to brake!

Massive 3S Li-Po provide an hour-long continuous driving. 
RC controller with physical buttons is very comfortable to use.

After two weeks of tests I added fenders for the front wheels to keep the inside of the car from being filled with stones. 4WD drifting is a fun thing to play with, but I got tired from cleaning the car from small stones after each driving session! 

[gyenesvi]

Not sure why, but I completely missed this build. Maybe I was on holidays at the time..

Anyways, it looks really interesting, I like the simple and streamlined bodywork, and I have been wondering lately about this setup for drive and the front suspension. It is using slow output of motors, right? Wonder how much of this could be replicated using Audi hubs..

Can you tell/show more about the front suspension geometry? I can't completely make out how the caster tilting is achieved. When you say broken pythagorean geometry, do you mean the triangles are a bit forced? I see that the core of the chassis and the motors themselves are not tilted, only the suspension arms around it, which is something I have been thinking of doing but haven't gotten around yet. Also, how does that effect the steering linkage? I guess the steering shaft and linkage isn't tilted either, so how do you get a good geometry that does not result in toe in/out? Is it approximate? Does the toe change during articulation? Or is it something that you just omit because it has some slack anyway, and it corrects itself during running?

[Daniel-99]

On 5/29/2024 at 12:43 PM, gyenesvi said:

Not sure why, but I completely missed this build. Maybe I was on holidays at the time..

Anyways, it looks really interesting, I like the simple and streamlined bodywork, and I have been wondering lately about this setup for drive and the front suspension. It is using slow output of motors, right? Wonder how much of this could be replicated using Audi hubs..

Hey! Thanks for your questions! Yes, it uses the slow output, because of the front suspension structure, also I wanted to save motors from extremal loads. I guess, you can use some ideas to build a similar front suspension with Aude hubs, but it will require a list of changes (mostly because the wheel hubs I use have inverted lower suspension arm).

On 5/29/2024 at 12:43 PM, gyenesvi said:

Can you tell/show more about the front suspension geometry? I can't completely make out how the caster tilting is achieved. When you say broken pythagorean geometry, do you mean the triangles are a bit forced?

Yes, I tilted both lower and upper suspension arms. The "right triangle" has a longer cathetus has the same length as the hypotenuse, but it works okayis with admissible level of tension.

On 5/29/2024 at 12:43 PM, gyenesvi said:

I see that the core of the chassis and the motors themselves are not tilted, only the suspension arms around it, which is something I have been thinking of doing but haven't gotten around yet. Also, how does that effect the steering linkage? I guess the steering shaft and linkage isn't tilted either, so how do you get a good geometry that does not result in toe in/out? Is it approximate? Does the toe change during articulation? Or is it something that you just omit because it has some slack anyway, and it corrects itself during running?

To be honest with you, this was my first experience with new hubs, and I totally failed their geometry. They were designed for the IFS with steering rod behind suspension arms, but I needed the steering arm in front of  suspension arms. As a result, I get an inverted Ackerman steering geometry, that is rather unfortunate. 

Indeed, the toe changes during articulation, and I tried to keep the wheels parallel under the load of the truck. Since the speeds were not extremal, the truck was controllable. Again, positive caster angle helped me with the steering. In addition, full independent suspension influenced positively the controllability of the truck. By the way, I used dual GeekServo setup to make the steering strong, but it was an overkill. 
 

The biggest problem for me was not the steering (with its weird geometry) but the difference in speed and power of Buwizz motors, since they worked independently on each wheel. RC setup with 3S Li-Po battery provided more power, then the motors could handle, and one of the rear motors was the first who started overheating under the load. I guess, switch to 2S Li-Po would solve this problem, but this would make the truck slower... 

 

[NoEXIST]

Nice looking, nicely working, overall great! To continue with our discussion about speed and 4 buggy motors configuration. Motors inside CaDa buggy's seems to be more efficient, as they have more rpm and it doesn't seem they're missing torque. So far I didn't overheat them a single time. But I did that with buwizz motor:)

Feeling of 4buggy with small 56mm wheels can be described as "I always have enough power to slip all 4 wheels on a bit dusty surface" I also tried same setup with 68mm wheels and it still was enough powerful, but you're missing this extra bit of power. Faster output of the motor does similar thing, but makes car go even faster:)

 

So talking about the speed your trophy truck goes I would guess there's something near 20km/h