JLiu15

[WIP] Lifted Truck with 3 steering modes

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Posted (edited)

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

Edited by JLiu15

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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.

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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.

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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?

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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.

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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.

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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. 

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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.

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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?

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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.

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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

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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

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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?

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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

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UPDATE 10/29/21

I've finished the chassis of the model. The front and rear axles are both in place, with live axle suspension. In addition, there's a V6 piston engine in the front driven by a C+ L motor that will run when the drive motors are running. I've also added panels to the sides to conceal the hub.

One issue I found is that when the suspension tilts left/right, the wheels drift forwards/backwards, i.e. the axles are pivoting a little. I think this is due to the angle at which the axles sit. I'll see if moving the shock absorbers' upper attachment point up a stud will help.

Let me know what you think!

Photos:

f64HwtO.jpg

iMeP6i6.jpg

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Wow! Like the way this is going. All I can say is to cover the towballs attached to the live axles. If you cover them on both sides appropriately, then they won't pop out, especially since this thing looks big and heavy.

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18 minutes ago, Scoar Sonander said:

Wow! Like the way this is going. All I can say is to cover the towballs attached to the live axles. If you cover them on both sides appropriately, then they won't pop out, especially since this thing looks big and heavy.

Thanks! Not sure what you mean by cover the towballs though - you mean like have another piece on the other side to prevent the link from falling off?

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2 hours ago, JLiu15 said:

Thanks! Not sure what you mean by cover the towballs though - you mean like have another piece on the other side to prevent the link from falling off?

Usually the link stays in place but the whole pin falls off... 

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UPDATE 10/30/21

Made some modifications to the chassis after yesterday's update. The shock absorbers' upper attachment point have been moved up by two studs, reducing the angle at which the axles sit. This helped reduce how much the wheels drift forwards/backwards when the suspension tilts. There's still a little bit of movement, but at this point it seems negligible as I've seen this on similar suspension setups (e.g. the 9398 Crawler's suspension). The links connecting the axles to the chassis are almost horizontal now, but the weight of the body should compress the shock absorbers a little, making the links even more horizontal. I was initially concerned that the front axle would collide with the C+ L motor for the piston engine when the suspension compresses, but it looks like the front and rear suspensions compress equal amounts. I've also moved the piston engine back by two studs, because now with the suspension lowered a little, I'm thinking of making this a typical off-roader instead of a cab-over truck.

Let me know what you think!

Photos:

3TyPp14.jpg

RorXQew.jpg

Edited by JLiu15

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5 hours ago, JLiu15 said:

Thanks! Not sure what you mean by cover the towballs though - you mean like have another piece on the other side to prevent the link from falling off?

Yes, exactly like that.

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7 minutes ago, Scoar Sonander said:

Yes, exactly like that.

I could definitely consider that - it looks pretty easy to attach a liftarm or something on the other side of the towballs. Not sure if it would collide with the wheels when steering though, as the wheels do get pretty close to the links when steered.

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UPDATE 11/9/2021

I've made a little progress on the bodywork - the hood and front grille in place. I've wanted to use the previous generation of Technic panels for a long time now since I had a bunch of red ones sitting around from mid-2000s Technic sets (e.g. 8436), so I used some here. The hood opens up to reveal the V6 piston engine, and I added some small details around it. As for the hub, I plan to cover it up completely as its display is quite bright, so it's likely the interior will have a full floor.

Let me know what you think!

Photos:

aJImMJn.jpg

NoAgmmz.jpg

Edited by JLiu15

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It looks awesome with the old technic panels, tbh. Looking  forward to seeing this finished, great job so far.

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Really nice! Maybe the new black wheel arches from the upcoming Batman car could be used here?

@1gor Seems like he used exactly your planned configuration with Defender Wheels and 42099 wheel hubs. So it seems to work :-)

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4 hours ago, Jundis said:

Really nice! Maybe the new black wheel arches from the upcoming Batman car could be used here?

@1gor Seems like he used exactly your planned configuration with Defender Wheels and 42099 wheel hubs. So it seems to work :-)

Yes this model looks very cool. Thanks for sharing experience and development process @JLiu15

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