[MOC] SB Offroader

[N1K0L4]

Hello,

Almost a year ago I was figuring out what to build for this years Unlimited offroad category at the BuWizz gathering and I knew I had to have 4 motors to be competitive. But than as I was playing with different configurations I realized that I needed something simple and robust (because it was my first 4 motor model, so didn't want to experiment), yet not big and with a good balance between speed and torque. That led to this model.

I would usually talk how I came up with some creative solutions etc... but here I just don't have anything to talk about as it's the most usual electronics layout and drivetrain. There are a few things I can talk about however.

From the start I really wanted this model to be nice and low for better COM and looks, I think I did a decent job at that. I also made the bottom flat, as usual with my models, for better sliding over obstacles. Other thing I noticed when I built it is that I can't run normal tan colored bevel gears as they just melt into the frames from the crazy power of 4 BW motors, so I ended up using knob gears. Because of it's simplicity I could use many big parts (frames, panels) to make the chassis stronger. Why these tires you might ask? Usual 107s that people use for these types of vehicles were just too big compared to the height of the model so it just looked off. Also, the thing can actually crawl over rocks with some precision. 

Specifications:

• Dimensions (LxWxH): 39x27x17 studs
• Powered by 2x BuWizz 3.0 Pro and 4x BuWizz motors
• Independent double wishbone suspension on all wheels with adjustable stiffness using rubber bands
• Permanent AWD with no differentials
• 1:5.4 gear ratio (planetary hubs) from the fast output
• Ackerman steering geometry
• interior with 2 seats and a steering wheel

 

Now, if it's so simple, why am I even bothered to make a EB topic about it? Well it's because of what happened on the BuWizz gathering this year.

The thing actually won! It wasn't the fastest, it wasn't the torquiest, it wasn't the biggest, it wasn't even the smallest (kinda surprising for me :) ), I probably weren't the best driver either.

What it was is simple, robust and controllable, that's what got me the win, and that will give you the best chances in any competition.

 

And of course, a video showcasing the model:

*SB means "slightly bigger"; ik, ik terrible name :)

[bruh]

Wow! Looks really capable and compact. Great job!

[N1K0L4]

7 hours ago, bruh said:

Wow! Looks really capable and compact. Great job!

Thank you!

[gyenesvi]

I have to say that yours was my favorite model in that race exactly due to its simplicity and compactness, and because you made an effort to make it look good too. Well deserved win!

I actually got inspired for next year and decided to make something of a similar spirit for next year, although not this compact.

A few questions / comments:

• Mounting the steering linkage to the planetary hubs could be done simpler and with more clearance the same way as done in 42099, no? Did you try that?
• Are the 4 motors connected to the same axle? If you use 2 to drive the rear wheels and 2 for the front wheels without connecting them, there's less chance for melting I think. Did the knob gears get a lot of wear? Or is the reason why people don't like to use them for fast models because they are a bit noisy?
• Are those tires 95mm ones? Aren't those the ones that slip on the rim very easily? How did you solve that problem?
• Did you try pushing the Buwizz units a bit further to the back to have more space for the internals?

[N1K0L4]

9 minutes ago, gyenesvi said:

I have to say that yours was my favorite model in that race exactly due to its simplicity and compactness, and because you made an effort to make it look good too. Well deserved win!

Thank you very much!

10 minutes ago, gyenesvi said:

Mounting the steering linkage to the planetary hubs could be done simpler and with more clearance the same way as done in 42099, no? Did you try that?

Now that you say it.. it could've been built that way, yes, totally overlooked that . Although this way has some small advantages too. The link connection is in the better orientation (pointing vertically) so having bigger steering angles doesn't risk popping the links off. Other thing is that the two 2L halfbeams are extremely close to the rim so they kinda reduce slack in that direction.

18 minutes ago, gyenesvi said:

Are the 4 motors connected to the same axle? If you use 2 to drive the rear wheels and 2 for the front wheels without connecting them, there's less chance for melting I think. Did the knob gears get a lot of wear? Or is the reason why people don't like to use them for fast models because they are a bit noisy?

Yes they are all connected. That I'm not sure, but the rear motors would definitely experience more stress. Did the knob gears get wear? Actually let me check... there is definitely some wear, flat spots closer to the axle connection. Now the reason people don't use them is because they're not smooth. You can imagine a U-joint at high angles. For constant speed on one side the other side slightly changes the speed periodically. Similar thing with knob gears because point of contact in not always on equal distance to the center of the axle. (if you don't lubricate them they're like a propeller plane, very loud. Also you need to lubricate them like every 3rd drive).

29 minutes ago, gyenesvi said:

Are those tires 95mm ones? Aren't those the ones that slip on the rim very easily? How did you solve that problem?

Yes, the 94.8 mm tires. They do start slipping over time, but I just put a rubber band on one side of the rim where tire makes contact and the problem is fixed (sometimes 2 are needed). Had the same problem with 43.2x20 and 75.1 mm tires.

33 minutes ago, gyenesvi said:

Did you try pushing the Buwizz units a bit further to the back to have more space for the internals?

Didn't really need to, everything fit just fine, also what internals?

36 minutes ago, gyenesvi said:

I actually got inspired for next year and decided to make something of a similar spirit for next year, although not this compact.

Nice! One thing I have to upgrade for next year is the steering. The angle is kinda low and I was worried of links popping out (luckily it didn't happen), so double steering racks next year.

[gyenesvi]

1 hour ago, N1K0L4 said:

Other thing is that the two 2L halfbeams are extremely close to the rim so they kinda reduce slack in that direction.

Yeah, that's what I'd be worried about. They also add friction if they touch :)

1 hour ago, N1K0L4 said:

Now the reason people don't use them is because they're not smooth.

That's interesting to know, makes sense, thanks!

1 hour ago, N1K0L4 said:

Yes, the 94.8 mm tires. They do start slipping over time, but I just put a rubber band on one side of the rim where tire makes contact and the problem is fixed (sometimes 2 are needed).

That's a nice fix, I'll try that!

1 hour ago, N1K0L4 said:

Didn't really need to, everything fit just fine, also what internals?

I meant the seats, now they are kind of pushed onto the steering wheel :) You know, the general rules state "realistic spacing between seat and steering wheel" :D

[N1K0L4]

2 hours ago, gyenesvi said:

I meant the seats, now they are kind of pushed onto the steering wheel :) You know, the general rules state "realistic spacing between seat and steering wheel" :D

Ah, got it. IMO the spacing is right, just the steering wheel us a bit low so there isn't much space for legs :) There is one stud left to the BuWizzes behind though, it's a bit hard to notice.