Zerobricks

Large steering pivot point compensation idea

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I think anyone who ever used the portal hubs came to this issue.

The hubs simply have the steering pivot point so far from the center of the wheel, that you need to either reduce the steering angle, or have a model with large fenders.

Today I came up with this simple mechanism to compensate for that by simply turning the whole front axle in the opposite direction.

640x360.jpg

The two tilted 6L links are usually used to keep the axle from moving forwards/backwards.

In my case they are attached to the steering rack at a high angle.

640x360.jpg

Moving the steering rack will cause the geometry of the axle to change - rotating it to (mostly) compensate for the large pivot point:

Pivot%20point%20compensator.gif

Of course this is just an idea for now, but it should be easy to implement on a real model.

The wider the axle, the better the compensation. Of course the axle has to be designed in such way, that suspension, drive and steering system will be able to work with this degree of movement.

Edited by Zerobricks

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Very creative indeed! I wonder how much more complicated trying to suspend and drive such an axle might get though as you mention

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It looks neat, but I doubt it's usable in its current form, for various reasons:

1. because the whole axle moves, and the mounting point is in the center, the whole thing will become much less rigid. The chassis basically has to go over it, rather than through it. That means you sacrifice chassis strength. That would be fine in a model with a live axle, where the chassis is above the axle anyway, but I think with a low model that would be quite a big sacrifice.

1 hour ago, Zerobricks said:

I think anyone who ever used the portal hubs came to this issue.

The hubs simply have the steering pivot point so far from the center of the wheel

2. The way you mounted the hubs, you increased that distance by another 3 studs. This would place a lot of unwanted force on the blue pins (when the steering angle is at its maximum), which introduces a lot of friction, especially on a heavy model. I think if you mount the hubs using ball joints with a 5-high axle, and use the axle drivers from set 8466 for drive, the actual distance between the pivot and the center of the wheel is actually very reasonable.

So, I think, with the current geometry, it's not usable.

3. There are already other ways to do a virtual pivot point inside the wheel, including a method with two 4-bar linkage I used for my TC7 Enforcer, which I borrowed from a fellow Eurobrickian whose name I have forgotten:

enforcer_3.jpg

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Just now, Erik Leppen said:

It looks neat, but I doubt it's usable in its current form, for various reasons:

1. because the whole axle moves, and the mounting point is in the center, the whole thing will become much less rigid. The chassis basically has to go over it, rather than through it. That means you sacrifice chassis strength. That would be fine in a model with a live axle, where the chassis is above the axle anyway, but I think with a low model that would be quite a big sacrifice.

2. The way you mounted the hubs, you increased that distance by another 3 studs. This would place a lot of unwanted force on the blue pins (when the steering angle is at its maximum), which introduces a lot of friction, especially on a heavy model. I think if you mount the hubs using ball joints with a 5-high axle, and use the axle drivers from set 8466 for drive, the actual distance between the pivot and the center of the wheel is actually very reasonable.

So, I think, with the current geometry, it's not usable.

3. There are already other ways to do a virtual pivot point inside the wheel, including a method with two 4-bar linkage I used for my TC7 Enforcer, which I borrowed from a fellow Eurobrickian whose name I have forgotten:

 

1. Yes, this is meant for live axles, off road models and this is JUST A CONCEPT, not a realised, mature full solution.

2. The hub was mounted in the exact spot like the PORTAL hub would be. The whole point of the topic is regarding PORTAL hub.

3. I am fully aware of this solution, but it does not work for driven wheels. It's much easier and reliable to tilt the whole axle to compensate.

My next off road model will have this solution implemented and than we can decide if it's practical or not.

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Just now, Zerobricks said:

2. The hub was mounted in the exact spot like the PORTAL hub would be. The whole point of the topic is regarding PORTAL hub.

Oops! I misread. Sorry! I thought you were talking about the hub you actually used. So you're talking about this part:

lego-medium-stone-gray-beam-frame-with-w

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I like how the Technic brings us great solutions for problems that didn´t have to exist and on top of that we have fun searching them, what a crazy hobby :laugh: .

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A common problem with portal hubs indeed and very interesting solution!

Will have to test it.

p.s. semi-offtop: is it just me or technic forum really misses a united trial/offroad ideas, tricks and pro solutions thread?

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Really interesting idea, I'm searching a way to use them in a pickup front axle, but the radius is quite big, and it leads to some issue with the force that you need to apply to the wheels to rotate...
During my searches I found this video by @nicjasno
https://www.youtube.com/watch?v=QT0YCePNB8o

It might help to reduce the force you need to turn, but I'm not sure if it will reduce the size of the fender...

 

23 hours ago, gate said:

p.s. semi-offtop: is it just me or technic forum really misses a united trial/offroad ideas, tricks and pro solutions thread?

I was thinking that too, I think I should be created.

Edited by Touc4nx

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36 minutes ago, Touc4nx said:

Really interesting idea, I'm searching a way to use them in a pickup front axle, but the radius is quite big, and it leads to some issue with the force that you need to apply to the wheels to rotate...
During my searches I found this video by @nicjasno
https://www.youtube.com/watch?v=QT0YCePNB8o

It might help to reduce the force you need to turn, but I'm not sure if it will reduce the size of the fender...

 

I was thinking that too, I think I should be created.

Actually using my idea it would take less force to steer the wheels, since they have to travel a much lower distance.

 

Also, Nicjasno's idea doesnt work well when you include teh forces created by drive/hitting obstacles.

Edited by Zerobricks

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Ok, thanks for the precisions, I will try to include suspension and drive to It when I will have the time.

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I managed to put dive into the idea
The axle that have the yellow gear is drive and the tan 28 tooth gear is for the steering
Edit : axle that link the chassis and the moving part with the differential is too weak, maybe it should be replaced by a turntable...
Portal%20Hub%20pivot%206.JPGPortal%20Hub%20pivot%204.JPGPortal%20Hub%20pivot%205.JPGPortal%20Hub%20pivot%203.JPG
I have made An .lfx for this to make it moree clear : LFX file

Edited by Touc4nx

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Well done. Yes, use the small turntable to stiffen the joint and reduce the fiction to the drive axle. Also increasing hub ratio might help.

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I had another idea how to implement the system:

640x338.jpg

640x338.jpg

640x338.jpg

Basically the servo motor drives the 24 tooth gears which move the axle holding links in order to rotate it.

I am using knob gears and 24 tooth gears as lever to compensate for 45 degree offset.

IMO this is a cleaner and sturdier solution.

What you guys think?

 

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It seems really nice, and quite compact.
But there is no drive in it, however the implementation of the suspension in this design might be easier.

Anyway it's a clever design, I will test it as soon as possible...

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I usually don't like to brag, but what I came up is IMO the ultimate solution:

800x372.jpg

The links used to hold the axle are attached above the center of the wheels. This way wheels are ALWAYS rotating in the center and the compensation is done automatically:

Improved1.gif

Moving the pivot point on the edge of the tyre reduces compensation and axle tilting, but it will increase steering angle:

800x372.jpg

Improved%202.gif

This means the system can be adjusted according to your needs.

I think this is an awesome new way to build rugged offroad machines :thumbup:

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Very nice solution to compress this problem with portal hubs. I will definitely give it a try in my incoming MOCs.

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Looks nice. I know it's all in theory now, but the axle is connected by 2 pins only - from the bottom and the top. These two force points can be reinforced vertically, but still it will be pretty weak for really heavy models. Which to be honest is every vehicle with tractor tires (>1.5 kg usually). What I assume is bound to happen on real obstacles - is the axle bending heavily. A few shock absorbers and panhard rod can make it more stable, but what I just described is a really weak spot imho.

Another thing is the drive. The axle drive connection point is moving basically in every possible direction, so it means it will require a sliding joint plus 2 u-joints most probably. This is a setup you can't really trust for 100% even with decent gearing down.

But then again, I should just find the time and test it and stop theorycraft:classic:

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I really like the smaller version, with the yello0w knob gears and 24t gears. Pretty ingenious system. :thumbup:

The large verson with the tractor tyres looks cool, but what I notice is that during steering, the axle becomes shorter. The wheels sort-of "slide inwards" when steering. I'm not sure how much of a problem that is. Maybe in reality it's almost unnoticable. Depends on the friction of the wheels I guess.

In any case, it's an original and new solution to an old problem, and may be perfect for places where space is limited. For example, for models with many wheels with little space in between, or when the wheels need independent steering, like in vehicles with different steering modes such as cranes. :classic:

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You can also use ball joints to create king pin inclination which moves the steering point onto the wheel:

 

800x552.jpg800x423.jpg

 

This is what many real trucks use, but the wheel still requires large bumpers.

Edited by Zerobricks

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