JLiu15

[WIP] Rock Crawler with 3 steering modes

Recommended Posts

With my Ripsaw Tank MOC essentially done by now (just waiting for some final pieces to arrive) and my PAB order for my New Flyer XD60 articulated bus model still yet to arrive (with more pieces coming for that), I've decided to start another MOC in the meantime. This will be my second model combining Control+ and Robot Inventor after my Heavy Duty Skid-steer Loader. It will have two identical axles, each with a steering motor (medium angular motor) to control steering, and thanks to their absolute positioning feature I don't think I'll have to calibrate it every time, like on e.g. the 42099 set. I was originally planning to use Control+ L motors for the steering, and have this be a Control+ MOC, but found the medium angular motor to fit better with the absolute positioning being another plus. I plan on creating a control profile in the Mindstorms app with different sliders for normal, crab, and 4-wheel steering modes.

The drivetrain consists of heavy-duty differentials and planetary hubs, so this eliminates the need for significant gearing down inside the chassis. For propulsion, I plan to use 2 Control+ XL motors, with a fake engine driven by a separate motor. This way, the fake engine can run at all times and there will be less friction in the drivetrain. I anticipate building the chassis to be pretty straightforward, as the entire chassis is essentially a mirror image with two identical axles. As for the bodywork, I'm leaning towards a red car-like body. If so, I will probably name this MOC "Red Beryl C", where "C" is for Crawler. It would be the third model in my Red Beryl series, after my Red Beryl GT of 2018 and Red Beryl X of 2019.

Let me know what you think, and any suggestions you may have.

Photos:

The front axle, with planetary hubs, long shock absorbers, and a medium angular motor for steering:

doHuZp5.jpg

The front axle, with the wheels attached. Note that this is the underside, with the heavy-duty differential visible:

irlW5kP.jpg

Share this post


Link to post
Share on other sites

Nice idea, I am planning to do a rock crawler MOC with the same key components you list here, although I was thinking of putting that steering motors sideways and using a lever mechanism. How is your steering implemented, is it with gearing or is it with a lever mechanism?

Are you planning to control it all with the RI app? Can that handle PU XL motors? I guess you'll be using the large 6-port hub then.

Instead of the U-joint going into the axle, I'd suggest using the CV joint that comes with 42099, that is less prone to break under heavy load.

Share this post


Link to post
Share on other sites
2 hours ago, gyenesvi said:

Nice idea, I am planning to do a rock crawler MOC with the same key components you list here, although I was thinking of putting that steering motors sideways and using a lever mechanism. How is your steering implemented, is it with gearing or is it with a lever mechanism?

The steering uses a rack and pinion mechanism, but the rack is placed on its side.

2 hours ago, gyenesvi said:

Are you planning to control it all with the RI app? Can that handle PU XL motors? I guess you'll be using the large 6-port hub then.

I will most likely be controlling it with the Robot Inventor app, as I did with my Heavy Duty Skid-steer Loader MOC. The 6-port hub is able to handle C+ motors, so I believe it should be able to handle C+ XL motors.

2 hours ago, gyenesvi said:

Instead of the U-joint going into the axle, I'd suggest using the CV joint that comes with 42099, that is less prone to break under heavy load.

Can they fit inside the ball joint? I'm using the ball joint from the 9398 set, and AFAIK only 3L u-joints could fit in there.

Share this post


Link to post
Share on other sites

Great start! What's the size you had in mind for the wheel base? That looks like a pretty short axle, or are you going to use a four-link suspension setup?

Share this post


Link to post
Share on other sites
2 hours ago, Teo LEGO Technic said:

Great start! What's the size you had in mind for the wheel base? That looks like a pretty short axle, or are you going to use a four-link suspension setup?

The model won’t be too big. As for the suspension, it’s just like the live axle suspension found on the 9398.

Share this post


Link to post
Share on other sites
19 hours ago, JLiu15 said:

Can they fit inside the ball joint? I'm using the ball joint from the 9398 set, and AFAIK only 3L u-joints could fit in there.

You're right, only the 3L U-joints fit into the ball joints. I wouldn't worry too much about the strength of any U-joints in the ball joints, though, because the ball joint creates considerable bracing around the U-joint.

Share this post


Link to post
Share on other sites
4 hours ago, JLiu15 said:

As for the suspension, it’s just like the live axle suspension found on the 9398.

Got it, looking forward to more progress, that axle looks really sturdy :wink:

3 hours ago, 2GodBDGlory said:

I wouldn't worry too much about the strength of any U-joints in the ball joints, though

I wonder if it wouldn't be a good idea to create some shared system of tracking what various transmission systems can handle in terms of torque before breaking or slipping (3L U-joints, old/new differentials in the 5x7 frame, etc). For example, with my current MOC, I would also be interested in knowing how much torque the 3L U-joints can take inside the ball joint. 

Share this post


Link to post
Share on other sites
4 hours ago, 2GodBDGlory said:

I wouldn't worry too much about the strength of any U-joints in the ball joints, though, because the ball joint creates considerable bracing around the U-joint.

Yup, that's like the main purpose of the ball joints - to protect u-joints in live axle suspension setups.

Share this post


Link to post
Share on other sites

Depending how purist you are there's always CaDA metal u joints. Every other piece on the model will break before those fail.

I like how you used that angular motor. I assume it has a position sensor like the XL and L motors?

Share this post


Link to post
Share on other sites
On 8/18/2021 at 3:43 AM, JLiu15 said:

The steering uses a rack and pinion mechanism, but the rack is placed on its side.

That makes sense, nice idea!

On 8/18/2021 at 3:43 AM, JLiu15 said:

Can they fit inside the ball joint? I'm using the ball joint from the 9398 set, and AFAIK only 3L u-joints could fit in there.

I thought you were going to do a 4-link suspension and not use the full ball joint, just one side. However, now I understand what you are up to, so in that case, the U-joint should be fine as others say. I think U-joints are only vulnerable if one of their ends are floating in the air, but the ball joint braces them.

Share this post


Link to post
Share on other sites

UPDATE 8/19/21

I've made more progress on the model. I've built the core of the chassis, which is pretty simple but also robust. 2 C+ XL motors are used for propulsion, and thanks to their abundance of pin holes they make for very good structural elements. All of the downgearing is done by the 28:12 reduction at the differentials and the ~5.4:1 reduction at the planetary hubs, which should be sufficient as my Bergmann Swivel Tip Dumper model last year had enough torque with just one XL motor and 28:20 reduction at the differentials. Add another XL motor, greater gear reduction at the differentials, and a lighter body, and I anticipate the performance will be pretty good.

The Robot Inventor hub will probably be placed directly above this central chassis section, and thanks to its abundance of pin holes it should also act as a good structural element, especially for bracing the front/rear of the chassis where it'll have to support the force exerted on the shock absorbers.

@amorti yes, I believe this medium angular motor has an absolute position sensor, as the output has a marking on it indicating where the zero position is. This also exists on the Spike Prime medium and large angular motors, as well as the C+ large angular motor from the 42114 set.

@gyenesvi I've always felt like 4-link suspensions aren't as robust, due to all the links involved. Better to have shock absorbers directly attached to the axle IMO, especially when you anticipate a lot of force exerted on the suspension. And yes, the ball joints were designed for the purpose of protecting u-joints, so the u-joints will be fine.

Photos:

KGzXU5Y.jpg

xwsZZ48.jpg

Share this post


Link to post
Share on other sites

UPDATE 10/17/21

Made some more progress. The central part of the chassis where the drive motors sit is a little different now, with the motors facing backwards instead of forwards. I replaced most of the pieces here with black ones, so there's less color vomit in the chassis. I've installed the hub above this part, which acts as a support element for the entire chassis. The teal color looks out of place, but I can easily cover it with black panels. As for the C+ L motor in front of the hub, I plan to include a piston engine which will be driven by it.

I still have to attach the shock absorbers to the chassis, which I will do once the chassis is more reinforced. Note the 3x5 liftarms - they will be attaching another layer of liftarms to give the chassis over the axles more stiffness. The rear axle still needs to be built, but it'll be identical to the front one. Right now I'm leaning more towards making this an off-road truck as opposed to a rock crawler, with a cab-over design and a covered rear so the hub isn't exposed.

Let me know what you think!

Photos:

tQSA5Qu.jpg

gkD2a4i.jpg

Edited by JLiu15

Share this post


Link to post
Share on other sites

Looks great so far!

Is there any way you could mod the axle to use the new reinforced CV joints instead of torque tubes & U-joints?

Share this post


Link to post
Share on other sites
2 hours ago, suffocation said:

Looks great so far!

Is there any way you could mod the axle to use the new reinforced CV joints instead of torque tubes & U-joints?

Thanks!

I'm sure it's possible, but they're pretty expensive right now as they're still in short supply. Once they become more widely available and their prices go down, I'll probably get some.

Edited by JLiu15

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Recently Browsing   0 members

    No registered users viewing this page.