[WIP] RC Heavy Buggy

[Daniel-99]

Hello everyone!

Lately, I made several posts of my finished models, some of which was build many year ago, so i cant make more photos of them and add your suggestions to the build. Today i would like to share with you my recent project. Im building (developing) an RC Buggy in big scale. Im not trying to make a version of a real one, but the general principles i follow are the same with real buggies.

General principles:

 - independent suspension with a big travel

 - Rear wheel drive

 - big positive caster on from wheels 

 - 2x Buggy motors for power (1 per each wheel)

 - lack of the body - only the structural elements... 

 - double steering arms (for stability and stiffness)

I have begun this project a month ago, but then got interrupted with some 4x4 cars (i will make posts on them later).

 

 

The first prototype

 

This car is actually closer to trophy trucks than to buggies, but nether mind...

Features:

 - Rear drive with live axle. Long travel, soft suspension.

 - Dual driveshaft: Buggy motors are connected to the rear wheel independently.

 -  McPherson front suspension, positive caster, extra steering arm for stiffness (like in 42099)

 - anti-row bar at the front

The main goal of the first prototype was to test the McPherson setup and the gear-ratio (find a good balance between speed and torque). I made a several tests, and was very pleased with them (see videos below) but many observations has been made for the future development. Main benefit of the McPherson setup is it`s compactness, since there is only one wishbone. But it also became the problem for the car, since additional wishbone gives more ridged structure. Also all axes in transmission has a lot of plastic dust in them - Buggy motors have made their job too well! 

Summing up, Im very pleased with the first prototype, but the general scheme should be changed! So the development continues...

Im waiting for your comments and suggestions... It is not that easy to build a thing from lego that can drive "properly". THIS SECTION WILL BE CONTINUED! ;-)

[FriedlS]

Looks great!! 👍

[Daniel-99]

Thank you! The main goal for this project is the good performance, not the overlook ;-) But i will make my best on bodywork after the chassis will work like a charm!

Also I forgot to mention, that it is very fun that on first several photos buggy is standing close to my Red coupe. The red coupe was build first and I made many outdoor driving with it, but after a while i got tired from the amount of attention you need to keep on the road in order to find a flat path, cause over-wise you will end your driving experience with a crash! The new buggy should forget me going not only a flat road ;-)

Edited November 21, 2021 by Daniel-99

[Johnny1360]

Looks like a lot of fun too! I do think to make it look more buggy like though the whole front end should be stretched out a bit and also use different tires on the front. A smaller, narrower tire is usually on the front to make it steer better.

[FriedlS]

I can imagine! I like the most my trophy truck driving outside, it doesn‘t matter where you drive 😀👍

[Daniel-99]

43 minutes ago, Johnny1360 said:

Looks like a lot of fun too! I do think to make it look more buggy like though the whole front end should be stretched out a bit and also use different tires on the front. A smaller, narrower tire is usually on the front to make it steer better.

Your idea with making a smaller tires on the front is very interesting one! By the way, these are not final tires ;-) I think i will use some RC tires for a better grip. But an idea of placing smaller tires on the front is very cool! Although i will try to keep the front disks as they are now - since these are the only lego asymmetric discs.

17 minutes ago, FriedlS said:

I can imagine! I like the most my trophy truck driving outside, it doesn‘t matter where you drive 😀👍

except water, I suppose 

[Daniel-99]

The front suspension [prototype 2]

Here is a new front suspension I managed to came up with... I took quite a lot of ideas form this two trophy trucks - this are the best examples i could ever find

https://rebrickable.com/mocs/MOC-52788/GooberReboot/trophy-truck/#parts

https://rebrickable.com/mocs/MOC-90031/GooberReboot/trophy-truck/?__cf_chl_tk=j_VvIOUIGLDv1nYTTrNe4icIUDHHKSCXV5JX8_htJfk-1637526577-0-gaNycGzNCeU#details

There are steering arms missing... (see grey pins on the hub), but an extra-arms are there, but they are not connected to the steering motors, playing the supporting role as in 42099.

There was the question of geometry: how to make a proper caster angle of the front axe without "braking" the horizontal structure of a cage (middle part)... the suspension arms has 9L length and the steering arms as well... The steering rack is parallel to the suspension arms in order to keep the angle of the wheels in all possible positions of suspension, which has wide interval of values (long travel suspension). I placed the steering motor horizontally as a structural element of a cage, so the steering gear meets the steering rack by an angle! - and it is not that good! There will be a potential problem with such placement - weak place of a front suspension. Also, bigger gear (than usual 12-tooth one) make the car uncontrollable and the steering motor looses it`s torque, that is important! So... i need to build another version... 

 

 

[amorti]

On 11/21/2021 at 9:45 PM, Daniel-99 said:

 the steering gear meets the steering rack by an angle! - and it is not that good! 

Could it be solved with a planetary hub as a torque multiplier?

Just spitballing.

Edited November 24, 2021 by amorti

[Daniel-99]

On 11/24/2021 at 3:15 PM, amorti said:

Could it be solved with a planetary hub as a torque multiplier?

Just spitballing.

That is too clever idea for me to think of it by myself!

[Daniel-99]

Here is a small update.

The main goal for me was to make the connection of a steering rack with a gear straight! At first, i tried to use joints and keep the steering motor horizontal.. After several unsuccessful attempts i understood that a single universal joint cant turn this big angle i have, and two universal joints brings too much unwanted structures - heavy, not very stable, messy...

So i decided to place the steering motor at the same angle as a steering rack.

Suspension will be mounted to the 7x11 frame

 

[Jim]

Hi,

You are embedding large images. Can you limit the size of the image to max 1024 wide? You are now letting the browser resize the big image. You can use a url like this

https://bricksafe.com/files/danil.nig/heavy-rc-buggy-chassis/IMG_0581.jpeg/1024x768.jpg

So simply add

/1024x768.jpg

Although I do think that you can let Bricksafe create this link for you.

Thanks.

[Daniel-99]

Here is my second version of a car. And as you can see, it became a trophy truck - sorry! 

Features:

• Soft suspension with big travel. It is well balanced, so the car compresses it by 1/3 under its weight. It allows to keep good contact with ground when the wheels fall into holes.
• Double wishbone front suspension with 9L arms - yes, I made it, since McPherson suspension was too weak for jumps and stability.
• Double steering arms and a PF Servo for steering
• Asymmetric discs and RC tired works a lot better than the tractor tires, lowering the resistance for steering
• Big caster and flat surface of tires provides a stability on straight lines.
• Anti row-bar for stability in tight corners
• RWD with 18L arms and progressive shocks hardness (learned form https://www.youtube.com/watch?v=KNmC-PlUCp4)
• no gears in transmission
• 2 Buggy motors for propulsion
• 2x Buwizz 3.0 for power
• Low center of gravity (all electric components are placed as low as possible)
• 1.3 kg of total mass
• About 10 km/h

Here is my first drive test:

I never thought that driving on icy road is so fun!

  Is it worth it? - yes it is! And finally i got myself a car that goes with a decent speed and does not afraid of bad road (cant tell this about my Red Coupe)!

 

Edited December 25, 2021 by Daniel-99

[amorti]

Funny you mention progressive suspension. I was messing with that on a motorcycle a day or two ago.

Real life:

In LEGO:

Worked really nice: first half of the shock travel got 2.5L travel at the wheel, second half got 1.5L at the wheel.

However, it does add 3 pivots where there is no option but axle in pinhole, so it won't work out for RC purposes. Too much added instability.

Real shame Lego didn't do this on the BMW though, they had plenty of space.

 

 

[Daniel-99]

8 hours ago, amorti said:

Funny you mention progressive suspension. I was messing with that on a motorcycle a day or two ago.

Real life:

In LEGO:

Worked really nice: first half of the shock travel got 2.5L travel at the wheel, second half got 1.5L at the wheel.

However, it does add 3 pivots where there is no option but axle in pinhole, so it won't work out for RC purposes. Too much added instability.

Real shame Lego didn't do this on the BMW though, they had plenty of space.

 

 

Well, your ideas are more complicated than mine. I basically used two sets of shock in such a way that second pair of shocks activates only at 1/2 of suspension travel. This solution does not require axles in pinholes but an extra pair of shock.