[MOC] Red Dune Buggy with Buwizz

[gyenesvi]

Hi Eurobricks!

Let me present one of my models built for the 2025 Buwizz camp, this one is for Ultimate off-road category. This is a descendant of last year's Blue Bird Ultra4 Buggy, aimed at making it more competitive. Well, I did not score a good place with this one either, but I thought I make a writeup about it before dismantling. The model turned out to have a couple of tricky flaws that are worth sharing, so this will be more of a problem analysis than a success story.

The problems I identified with last year's model was the front axle being overly complex and a bit weak and the steering being very unprecise. Having caster on the front axle required routing the steering shaft through CV joints, which introduced a lot of lag to the system, becoming somewhat slowly responding and giving me a hard time driving through obstacles. Hence, I decided to change that on the successor. On the other hand, the rear suspension and the drivetrain held up pretty well, so I decided to keep that. Furthermore, I decided to keep the body as simple and light as possible, and I think I managed that quite well :)

For the front suspension, I decided to simplify and ditch the positive caster, I don't feel that it would add much to the controllability anyways. This allowed me to drive the steering rack directly. Also, to maximize steering response, I decided to use a double steering rack with tensioned links with the racks placed one stud further from the axle center. Furthermore, I used shorter springs placed on the top to avoid complications resulting from the long spring going through the top A-arm and weakening the construction. Here is the new front axle.

As neat the construction may look, unfortunately it is not as bullet proof as I though it would be. It has the following problems:

• Since the A-arms are necessarily built from thin liftarms (6 and 7L), those can slide apart much more easily that thick liftarms could, even though I tried to pin them together as much as I could. The reason why it needs to be built from these thin ones is because the 6L thick liftarm does not exist, and also the top and bottom arms need to be connected to be stable, taking up space. So anyone trying to convince me that the 6L liftarm not being produced is not a real problem because the thin version exists will never succeed..
• The other problem is caused by the planetary hub's (2L) steering link mounts, and this one is nasty. It's more often in the way than it is useful, I really don't like its design, should have been like the Audi hub. For one, that is what's not allowing the connecting thin liftarm between the top and bottom A-arms to be shifter outwards 1 stud, and ultimately allowing 7L liftarms to be used in the A-arm. But it has an even more nasty problem that I did not foresee. When the suspension articulates a lot (and this one does, especially on high bumps and jumps), that part that sticks out can hit the steering link and pop it out. And that happened during the race after a big jump.

So the conclusion is that it's hard to build a really strong suspension even if it's the good old double wishbone one.

The rest of the chassis was similar to that of the blue buggy. This time I put the 4 motors to the back as much as possible, with the trailing arms going around it. First I though I would put the Buwizz units to the sides and put one seat in the middle, but I decided that I wanted a light weight look with open sides, and there was plenty of space in the back for the Buwizzes; this allowed to full seats. I managed to make some nice triangulated support around the seats into the floor paneling that made the structure solid with minimal parts.

However, putting all the electronics to the back may have contributed to other problems, as there was more weight resting on the rear suspension / drivetrain. For one, the 12T gears did start skipping more often than in last year's buggy. More problematically, the extra weight on the back made the rear suspension become a bit too soft, sitting a bit low, resulting in less ground clearance and more rocks being hit. But the real big problem, that turned out after the race, during filming a video, was that the weight is probably too much for the trailing arms, and while bashing the model hard, turning around at high speeds and occasionally hitting rocks as well, I managed to break both of the rear trailing arms (11L flip-flop beams, not at the same time) right under the point where the spring is connected. So I think this suspension should only be used if there's less weight resting on it, or it needs to be beefed up, with different mounting points for the springs.

Anyways, here's a video that I've recorded. Unfortunately, I had to record with a camera without image stabilization, so it came out somewhat shaky, but maybe it resonates with the general mood of the bumpy roads it is driving on :) It does drive pretty well though, with the suspension working a lot, and it is fun to play with, but at some points I really felt this speed is too much for the plastic. For example sharp cornering at high speed on this kind of surface can put a lot of stress on the parts..

 

 

The rest of the design, the bodywork is as simple as I could get it, I am actually happy with my first use of flex axles along with some tubular structures, they complement each other nicely. I like the overall character of the buggy, despite it's flaws, and its performance is certainly great when it holds up :)

Here are more photos and renders of it.

More pictures are available on Bricksafe. The Studio model is available for free on Rebrickable, due to all the shortcomings I did not make instructions.

Let me know what you think!

Best,

Viktor

Edited yesterday at 09:37 PM by gyenesvi

[N1K0L4]

Overall, really nice model!

 

12 hours ago, gyenesvi said:

and also the top and bottom arms need to be connected to be stable,

In this case not really IMO. As you have the shocks acting on the upper wishbone, that one is pushing against the hub and pushing the ball joint together. Because of that the lower wishbone only has to keep the hub in place and doesn't push/pull it up/down that could otherwise disconnect the ball joint. With all of that in mind you could have used the 7L liftarms. BTW, I agree with you about the thick 6L liftarm, they should definitely start producing that one.

12 hours ago, gyenesvi said:

I managed to break both of the rear trailing arms (11L flip-flop beams, not at the same time) right under the point where the spring is connected.

Wait, like.. physically broken or just disassembled?

 

Also what gearing did you use?

[gyenesvi]

3 hours ago, N1K0L4 said:

Overall, really nice model!

Thanks!

3 hours ago, N1K0L4 said:

In this case not really IMO. As you have the shocks acting on the upper wishbone, that one is pushing against the hub and pushing the ball joint together. Because of that the lower wishbone only has to keep the hub in place and doesn't push/pull it up/down that could otherwise disconnect the ball joint. With all of that in mind you could have used the 7L liftarms. BTW, I agree with you about the thick 6L liftarm, they should definitely start producing that one.

I agree that it's not soo necessary. However, I was afraid that when doing jumps and driving fast on rocks, it could just fall apart by the vibration if it's not form locked. I remember someone built a model without those cross connections, was it yours?

3 hours ago, N1K0L4 said:

Wait, like.. physically broken or just disassembled?

Physically broke.. though I have to admit I was using cada parts there, just in case it breaks :D And those may be weaker moulds.

3 hours ago, N1K0L4 said:

Also what gearing did you use?

The gearing was 20:12 up-gearing from fast output of motors, then 12:12 at the differential, and then to the planetary hubs.

[N1K0L4]

4 hours ago, gyenesvi said:

I remember someone built a model without those cross connections, was it yours?

Well, yes in 2024. on my Mini Offroader. That one had the shocks on the bottom one + the rubber bands pulling the 2 together and making the suspension harder. Although that one was much slower (5 km/h) and half the power.

4 hours ago, gyenesvi said:

Physically broke.. though I have to admit I was using cada parts there, just in case it breaks :D And those may be weaker moulds.

Wow, interesting. I guess next time definitely make those stronger  as you said :)