Steering/Pivot Points

[__________________________]

After watching Sariel's video about a steering system with excellent steering geometry, I'm wondering: what makes the pivot point on 8081 wheels so good, and would it be possible to modify other Lego wheels to improve their pivot points?

[Junpei]

It's not the wheels, it's the linkage involved. It causes the wheel to move a little bit sideways and turn quite sharply, you could use it with any wheel.

[Sariel]

Wheels on 8081 don't pivot so good, the pivot is where the vertical black piece sits, and that's easily 2 studs off the wheel's center. In fact, you could improve the pivot by getting rid of that yellow half bush used as spacer:

[__________________________]

Wheels on 8081 don't pivot so good, the pivot is where the vertical black piece sits, and that's easily 2 studs off the wheel's center. In fact, you could improve the pivot by getting rid of that yellow half bush used as spacer:

I meant the 8448 wheels lol

Any ideas (aside from removing the portal axles) on improving 9398's pivot?

Edited March 23, 2015 by Blakbird

[Sariel]

I meant the 8448 wheels lol

Hilarious. I'm done responding to your threads, it's a waste of time. If you want people to make effort of helping you, at least try to ask the correct question (and preferably start threads once, not twice).

[__________________________]

Hilarious. I'm done responding to your threads, it's a waste of time. If you want people to make effort of helping you, at least try to ask the correct question (and preferably start threads once, not twice).

What thread did I start twice lol Edited March 23, 2015 by TheLegoExpert

[Sariel]

What thread did I start twice

This one, but the mods are looking after you and removed the extra one. Just like they were looking after you when you called other EB member "your ni**a".

Edited March 23, 2015 by Sariel

[jeeves]

As far as I understood Sariel's video, a part of the problem is the fact that most of lego Tire/Rim assemblies are connected to whatever (cross-axle/three-peg) too close to the centre of the width of the tire, leading to that the actual pivot point is outside the tire's width centreline. Also, If I see it correctly, this problem is exacerbated whenever the tire profile is flat (such as with most super cars wheels) and less of a problem with balloon-type wheels - friction wise that is (although the problem of needing excessive space for the wheel to move within the chassis is not adressed by this).

I'll have to have another look at the wheels of the 8448 and 8428 respectively...

[__________________________]

As far as I understood Sariel's video, a part of the problem is the fact that most of lego Tire/Rim assemblies are connected to whatever (cross-axle/three-peg) too close to the centre of the width of the tire, leading to that the actual pivot point is outside the tire's width centreline. Also, If I see it correctly, this problem is exacerbated whenever the tire profile is flat (such as with most super cars wheels) and less of a problem with balloon-type wheels - friction wise that is (although the problem of needing excessive space for the wheel to move within the chassis is not adressed by this).

I'll have to have another look at the wheels of the 8448 and 8428 respectively...

Thanks! Always nice to get an answer which relates to my question.

[DrJB]

As far as I understood Sariel's video, a part of the problem is the fact that most of lego Tire/Rim assemblies are connected to whatever (cross-axle/three-peg) too close to the centre of the width of the tire, leading to that the actual pivot point is outside the tire's width centreline. Also, If I see it correctly, this problem is exacerbated whenever the tire profile is flat (such as with most super cars wheels) and less of a problem with balloon-type wheels - friction wise that is (although the problem of needing excessive space for the wheel to move within the chassis is not adressed by this).

I'll have to have another look at the wheels of the 8448 and 8428 respectively...

I'm not sure I agree that the problem is less with balloon tires (If I understood your comment correctly). The scrub radius, which is the distance between the center of the tire's footprint, and the point where the kingpin axis intersects the ground, is the same no matter which tire you use. Such scrub radius depends solely on the wheel's offset. The 'problem' with flat profile tires (as in 8285/8258) is that the contact area between the tire and ground is large, and that cause a large friction moment when steering. There are ways to make the scrub radius very small, and that entails using a multi-link suspension. Such geometry is typically reserved to high performance cars where handling (how fast the car responds to steering inputs) is a primary attribute.

[5imon]

If I'm looking at the 8448's wheels, it becomes very clear what makes them "better": their shape is very asymmetric, best seen when looking at the enlarged picture on Bricklink. With the attachment point of the wheel moved very far out of the centre plane of the wheel, the kingpin part can be placed completely inside the wheel and thus the pivot points are in the centre of the wheel.

My 1970s car uses the same principle, and it's not even a high performance one (but one with very advanced suspension for its time). You can see on ths car that the wheel centres also point very much outwards, so the kingpin can be placed inside.

The problem with modern Lego wheels is that they are largely symmetric, so there is no way to place the pivot points inside. The length of all the available hub/portal/kingpin parts further add to this.

[Brickthus]

...

The problem with modern Lego wheels is that they are largely symmetric, so there is no way to place the pivot points inside. The length of all the available hub/portal/kingpin parts further add to this.

Agreed. For most Technic sets the steering rake is not what it could be, so it makes less difference. It's mostly when we want to make proper models with a full steering rake that we notice the difference!

Some of the best Technic set steering rakes are on F1 cars, which is ironic, given that in real life they have less rake than most road vehicles!

8479 bar code truck was the best example of steering rake with the 62mm wheels. That was long ago though.

Mark

[__________________________]

Alright, thanks for the explanation, guys!