Narrowest drive unit yet (steering, independent suspension, differential drive)

[Divitis]

Hey there, long time lurker with finally something to share.

After quite a bit of work, I managed to squeeze independent suspension, steering and differential drive in a 9-wide unit (or 11 between wheel hubs). And it works!

Tease picture attached, implemented in a 4wd design.

I will share better pics and a video soon.

Unfortunately I can't record a video with my phone while controlling the model with the Lego app, so I'll have to figure something out.

Also stud.io files if anyone is interested :)

 

Cheers

Edited November 30, 2023 by Divitis

[2GodBDGlory]

Nice! That is very skinny. It looks like you've got bevel gears attached to the CV joints  that then run out to differentials mounted behind the axle?

[Jurss]

11 hours ago, Divitis said:

I will share better pics

Put pictures on bricksafe.com, flickr.com or similar, then paste link here, it will embed

[Divitis]

You are a fine observer @2GodBDGlory, that is pretty much how it's laid down.

This is how the actual transmission goes.

You'll see there is only one differential. Since both pairs of wheels steer, the two on the left and the two on the right end up having the same turn radius at all times, and can be hard coupled. It's sort of an H-drive, I guess, although that seems to be only ever used on 6 or 8 wheelers.

I couldn't find any real life vehicle that employs this idea, so probably it's one of those that looks good in practice only?

Even then, it's a smooth ride. (Full video coming)

https://bricksafe.com/files/divitis/mini-4x4-full-steering-h-drive/wheeler.mp4.mov

[Bluehose]

I'd like to see how is the bracing behind the CV joint, attempts are often bulky / prone to clicking (if it's 4x4 I want to manage torque)

 

Glad to see your post.

[Divitis]

@Bluehose

Ensuring the bevel gears wouldn't slip was one of the big challenges, and this is the final design.

In the end I am satisfied with the result, especially given the small scale of the model.

There's no slip (clicking) during normal operations - managing inclines and rough terrain. It happens only when suddenly inverting direction, which makes the car rear up. But it recovers immediately.

 

Edited December 7, 2023 by Divitis
grammar

[2GodBDGlory]

Thanks for sharing that picture! Now I understand what's going on there--quite interesting!

[Bluehose]

Thank you ! It's nice, I didn't thought to half beams to have a spacing of an half bush on pins !

It's way more compact than with the Axle and Pin Connector Perpendicular Double Split ( https://www.bricklink.com/v2/catalog/catalogitem.page?P=41678&idColor=85#T=P&C=85 ), I thought it was madatory to avoid pin deconnection from the half beam but according your experience there is no need.

How big you think the wheels can be before it become an issue ?

Is the differential located up the wheels rather between the front and the back axles in order to have a shorter vehicule ?

 

I like your build.

[Divitis]

Thanks for the positive feedback :)

 

Pin disconnection has never happened during play. Yes, if I drove hard into an obstacle.  With only one L motor slightly geared down I think it's already a little overpowered for the size of the vehicle. I wouldn't give it any more.

I'm not sure if I got your question about the size of the wheels, but the limiting factor is how narrow the actual inner frame of the car is - 5 wide. A bigger wheel wouldn't be able to steer much before bumping into a support beam.

Vehicle length was a concern, yes. If you extend the driving axles too far out of the wheels then clearance becomes an issue when approaching inclines. Also, the two axles need to rotate opposite of one another. So having the differential above the wheels forces using an extra spur gear to transmit motion all the way down to the lower axle, which solves the problem. (At least this was the configuration before I though of meshing the differential spur 28 gear directly between the16 at diff. output and the 20, instead of going all the way down to the 16 at the bottom. This meant removing one gear instead of adding it, which always makes me happy)

[Divitis]

The video is finally out!