NASA's 6x6 rover mobility system

[jam8280]

Robust working 1:12 RC model of the 6x6 rocker-bogie mobility system used in Mars rovers Perseverance and Curiosity...

Tons of play value. Works well over most neighborhood surfaces and terrains, but sometimes gets stuck in loose sand.

What you put on top is up to you.

NB: The NASA rovers are 6x6x4 platforms, with 6 wheels, all 6 driven, and the 4 corner wheels steered. At 1:12 scale, steering individual wheels with LEGO motors is out of the question. So this model is necessarily a 6x6x0 platform — but one with reasonably effective skid steering.

Several years ago, made a pretty faithful working 1:12 model of Curiosity with more emphasis on visual realism than on mobility system performance. The current model vastly outperforms the old one...

 

Purist alert: SBrick RC receiver, non-LEGO elastics used to suppress wheel spread.

Edited December 10, 2020 by jam8280
Improved text

[JGW3000]

Nice, looks like it almost has a personality! This is what Technic is all about!

 

[jam8280]

39 minutes ago, JGW3000 said:

Nice, looks like it almost has a personality! This is what Technic is all about!

 

Thanks! BTW, the video contains an error. The best overall wheel+tire combo is not the one shown at 4:40 but the combo seen at 9:45 instead. Makes a surprisingly big difference on some surfaces.

[braker23]

Lovely job, mate. I tried to implement this suspension years ago, but I failed. Your rover performs very well, thanks for sharing!

[BrickBuildingFox]

Wow that's a great idea for a MOC. Thanks for sharing. I already put it on my ToBuild-list.

Are you planning to make instructions?

1 hour ago, braker23 said:

I tried to implement this suspension years ago, but I failed.

I would like to see some pictures, especially about the suspension, since it seems to be very difficult to implement.

 

[JintaiZ]

Excellent idea for a MOC. The shaping looks almost exactly like the real one!

[amorti]

Very cool how well it gets up and over obstacles 

[jam8280]

Thanks for all the kind words!

Sorry, no instructions. Photos are very tedious for me to prep for upload here, but I'll see what I can do. Meanwhile, take a close look at the stills and turntable segment in the video after 9:04 for construction clues. The key part is the recently released 3x3 Technic connector, here used for front and rear motor mounts.

[howitzer]

This is so cool, that suspension works amazingly well on various surfaces, I'm especially impressed about the rock-crawling abilities.

I just might have to get some more motors and build myself a similar one at some point...

[2GodBDGlory]

Nice work!

I like the use of the 11x19 "baseplates"; I think this may be my first time seeing them in a Lego model!

[jam8280]

Sorry, having a hard time uploading even one 320x240 photo due to a ridiculous 0.02 MB file size limit. So anyone interested in building this rover chassis should go to NASA's web site and study suspension arm geometry in the many rover photos there, as I did. Use Technic liftarms (not axles as I did previously) for the suspension arms and stay as close as you can to the angles and proportions you see in the NASA images.

Critically, note that the rockers (the suspension arms carrying the front wheels only) connect through a differential gearbox inside the hull and also through the pivoting black "differential bar" crossing horizontally above the hull, as in the real thing. These essential connections maintain hull attitude. The hull does NOT balance on the rocker axles going into the hull.

 

Edited December 10, 2020 by jam8280

[howitzer]

56 minutes ago, jam8280 said:

Sorry, having a hard time uploading even one 320x240 photo due to a ridiculous 0.02 MB file size limit. So anyone interested in building this rover chassis should go to NASA's web site and study suspension arm geometry in the many rover photos there, as I did. Use Technic liftarms (not axles as I did previously) for the suspension arms and stay as close as you can to the angles and proportions you see in the NASA images.

Critically, note that the rockers (the suspension arms carrying the front wheels only) connect through a differential gearbox inside the hull and also through the pivoting black "differential bar" crossing horizontally above the hull, as in the real thing. These essential connections maintain hull attitude. The hull does NOT balance on the rocker axles going into the hull.

 

You must upload the photos to an external site like Imgur or Flickr, Eurobricks doesn't host your photos. After uploading them to another site, you can embed them in your post just by copying and pasting the direct link in the post.

[jam8280]

Thanks, @howitzer! Some images here show a PF receiver, but the final version in the video uses an SBrick.

Upper deck removed. The differential connecting rocker axles inside the hull (see my last post) is built up from parts and anchored to hull bottom...

Suspension arms on port side without motors. Note black differential bar above upper yellow hull cover and empty wheel motor mounts.

The hull levels out once the receiver and battery are installed.

Front geared wheel hubs. The 3:5 reduction shown is the best general-purpose gearing.

You'll need some undercarriage elastics to keep the port and starboard wheelsets from spreading apart.

The centaur-like biomechanical reptilians inhabiting Mars also use this mobility system to get around...

 

Edited December 10, 2020 by jam8280

[Horologist]

Amazing build, I love complex suspensions like this one. How much backlash is in the differential mechanism inside the body?

[BrickBuildingFox]

@jam8280:thanks a lot for the pictures and additional explanation of the suspension! I think with this knowledge it is possible to build a similar suspension system...

[jam8280]

51 minutes ago, BrickBuildingFox said:

@jam8280:thanks a lot for the pictures and additional explanation of the suspension! I think with this knowledge it is possible to build a similar suspension system...

You're welcome. Good luck! Make sure the front and rear motors can't hit the hull when negotiating rough terrain.

1 hour ago, Horologist said:

Amazing build, I love complex suspensions like this one. How much backlash is in the differential mechanism inside the body? 

Thanks! Short answer: Not enough to affect performance if you phase the gears properly.

The differential inside the hull ensures that if one rocker is at angle A from the horizontal, and the other is at angle B, the hull is always at angle (A+B)/2. Among other things, this helps the rover stay right-side up in rough terrain.

The differential bar above the hull helps to keep all 6 wheels firmly on the ground. And that reduces the chance of getting stuck -- especially in soft soil, any rover's greatest nemesis.

 

Edited December 11, 2020 by jam8280