Portal hubs - a nail in their coffin

[Leif]

I did a quick and dirty 4x4x4 in order to test some things and the test was good, but portal hubs was not.

We all know Ackerman steering, pivot points and such terminology when it comes to steering techniques.

I think - but I would love to be proven wrong - that the geometry is all wrong. no way a vehicle would have this kind of geometry that the portal hubs give you, right?

the LEGO Part 11949 - Technic, Steering Portal with 2 Pin Holes and 2 Ball Joint Arms from the 42000 is a good way to go.

But from what I heard it could be a bit wobbly on a heavier machine?

Anyway, here are some pics on my trial!

[Zerobricks]

You messed up the cardan length and position. Drive axle should be lower and same length as suspension arms...

[Leif]

You messed up the cardan length and position. Drive axle should be lower and same length as suspension arms...

Yeah I know, Quick and dirty is nothing to take lightly...

However, it turned and worked and is now teared apart, the build was just for confirmation of steering issues, and I am do not like the hubs steering qualities, am I wrong?

[Zerobricks]

The longer the steering handle, the less wobbly and stronger steering will be.

[Leif]

The longer the steering handle, the less wobbly and stronger steering will be.

yes that is correct but I think my original message and question maybe got lost on the way

- steering geometry with portal hubs; good or bad? compared to real trucks?

Edited September 15, 2014 by Leif

[Bricktrain]

if you reversed the connectors that the steering pivots on then the pivot will be centred over the line of the gears and the steering will be much improved. They are not the greatest for using for steered axles though, they are much better used like they are in 42030 in pivot steer models

[Leif]

if you reversed the connectors that the steering pivots on then the pivot will be centred over the line of the gears and the steering will be much improved. They are not the greatest for using for steered axles though, they are much better used like they are in 42030 in pivot steer models

A really good idea but can I still have the axel driven in that case, cardan positions?

[Balrog]

I don't think there is a good solution for the portal hubs to be driven and steered in a double wishbone suspension. Use a live axle instead as shown with the unimog.

If you want to do it like in the pictures, you need to get the position for tue driving axle parallel to the wishbones. That is the least necessary.

[Leif]

I don't think there is a good solution for the portal hubs to be driven and steered in a double wishbone suspension. Use a live axle instead as shown with the unimog.

If you want to do it like in the pictures, you need to get the position for tue driving axle parallel to the wishbones. That is the least necessary.

thank you for a very good answer. It may turn out as I suspected, portal hubs are not the proper component for driven, steered, suspended. too bad, I like how stable they are, no wobble or anything!

[Balrog]

I would have some ideas to optimize the suspension you have there a little, but it would be best to show it to you. I'll see if I can make a mockup when I am at home. But I am not sure if that will perform very good anyway.

One problem of the portal hubs is, that the pivot point of the steering is very far from the center of the wheel. Thus you will always have a lot of wheel travel when steering.

Another problem your current setup has, is, that the lower connector between wishbone and portal hub is too wide. When the suspension is uncompressed and you try to steer, it will push against the wishbone. This could force the pin connection to fail and go apart. A solution could be to place the wishbone "above" the connector.

And one more thing, but I am not too sure about this. If you have the connection to the steering link beyond the pivot point, this will give you inversed Ackerman steering geometry. If this is not correct, someone please correct. But placing the steering rack in front of the axle gives you inversed Ackerman steering anyway. Hm ... negative and negative becomes positive, so this might just work out correct. I am not sure here without trying.

[Leif]

I would have some ideas to optimize the suspension you have there a little, but it would be best to show it to you. I'll see if I can make a mockup when I am at home. But I am not sure if that will perform very good anyway.

One problem of the portal hubs is, that the pivot point of the steering is very far from the center of the wheel. Thus you will always have a lot of wheel travel when steering.

Another problem your current setup has, is, that the lower connector between wishbone and portal hub is too wide. When the suspension is uncompressed and you try to steer, it will push against the wishbone. This could force the pin connection to fail and go apart. A solution could be to place the wishbone "above" the connector.

And one more thing, but I am not too sure about this. If you have the connection to the steering link beyond the pivot point, this will give you inversed Ackerman steering geometry. If this is not correct, someone please correct. But placing the steering rack in front of the axle gives you inversed Ackerman steering anyway. Hm ... negative and negative becomes positive, so this might just work out correct. I am not sure here without trying.

If you have the time to build a mockup I would greatly appreciate this. My build was a quick & dirty mockup so suspension and some more things are really just thrown upon the build, there are some things to optimize if I shall go forward with the build.

the pivot point of the steering, too far away from the wheel is the biggest issue for me and I cannot really decide whether to go forward with a portal hub project or look into another solution altogether.

To get Ackerman as well would of course really push the solution forward!

[Balrog]

I guess the only real chance to get the pivot of the portal hub closer to the wheel is, when you don't drive this wheel. On the other hand, the portal hub is useless then.

[Balrog]

I did a quick mockup. Unfortunately, it will not work as I thought. Initially I wanted to reduce the space between the wishbones, but that will not work. Here you have the side view of what I made:

This picture shows the U-joints parallel aligned with the wishbones. This allows the driving axle to travel with the wishbones and turn at the pivot of the steering.

Here a second pic:

In the red circle you see, what I think is a problem. When turning, the black connector touches the wishbone and could possibly pry apart its own pivot point. This is not a big problem, when the suspension is more compressed by default or the angles of the wishbones not so steep.

Still, for the portal hubs I suggest using live axles as in the Unimog.

[Leif]

Thank you Balrog for the good design. yeah I am on the same track. there are unfortunately no way to build any more compact than this.

The red circle area is of course a problem if the angle of wishbone is to steep, so that has to be calibrated so to speak.

I also had a beam connecting upper and lower wishbone in order to keep them together at all time!

If I may hijack my own thread, what would be the best build for driven, steered, independent suspension and the Unimon tires - without any wobble?

the portal hubs can reduce wobble since they also have an axle through the wheel, not only the three pins.

they also make stronger drive train since you can have proper axle and U-joints, rather than the CV-joints which surely are quite fragile.

[zenzic]

they also make stronger drive train since you can have proper axle and U-joints, rather than the CV-joints which surely are quite fragile.

My guess is you'll still need some way to let the axle in between the wishbones lengthen or shorten, by allowing it to slide for instance, since the distance between the wheel hub joint and the joint at the other end changes when pivoting the wheel hub.

I started building the same thing a week ago and I must admit I underestimated the complexity of this structure. I think I found a relatively sturdy solution now. I'll post a picture in a few hours.

Edit:

LDD did not allow me to connect all pieces as I was able to in reality. The shock absorbers should be connected to the horizontal 3m axle in between the 11m beams. In reality this pushes the wishbones down. The two separate 3m axles fit between the CV joints and the fixed joints. If my memory serves me right the steering rack should be on the same plane as the grey spaceframe element, as it is drawn here, although it might need to move one stud towards the camera.

It might be desirable to add a 5m half width beam vertically to each pair of wishbones parallel to the 11m beams to avoid the pins popping out of the wheel hubs.

Edited September 17, 2014 by zenzic

[Lucio Switch]

I builded one MOC with portal hub and independent suspension, . i would post a picture from mocpages...but is down...su, for now i can only link the video on youtube.

This is the best solution I have found, it works, but is not very good for a crowler, and yes the geometry is all wrong!!;-)

Edited September 17, 2014 by Lucio Switch

[Balrog]

My guess is you'll still need some way to let the axle in between the wishbones lengthen or shorten, by allowing it to slide for instance, since the distance between the wheel hub joint and the joint at the other end changes when pivoting the wheel hub.

I don't think this makes much of a difference here, since the u-joints have some play as well. Even if you build a driven axle with CV joints and compress the suspension, you'll only see very little travel along the sliding axle.

Edit:

LDD did not allow me to connect all pieces as I was able to in reality. The shock absorbers should be connected to the horizontal 3m axle in between the 11m beams. In reality this pushes the wishbones down. The two separate 3m axles fit between the CV joints and the fixed joints. If my memory serves me right the steering rack should be on the same plane as the grey spaceframe element, as it is drawn here, although it might need to move one stud towards the camera.

It might be desirable to add a 5m half width beam vertically to each pair of wishbones parallel to the 11m beams to avoid the pins popping out of the wheel hubs.

The way you built it produces a wrong geometry for the axle. The u-joint is not in line with the pivot of the hub, thus travelling sideways. I don't think that this will perform very good and could possibly cause problems as well when driving.

And you are right about the steering rack. It should be higher to allow "parallel movement" to the wishbones.

I builded one MOC with portal hub and independent suspension, . i would post a picture from mocpages...but is down...su, for now i can only link the video on youtube.

This is the best solution I have found, it works, but is not very good for a crowler, and yes the geometry is all wrong!!;-)

I didn't think about the double wishbone part. I guess this would be the best method to use the portal hubs for independent suspension.

[zenzic]

Agreed, the geometry is off here. However the 3L axle between the two joints is still about 1L inside the CV joint when steering is at full lock, while the fixed joint is at angle less than 90 degrees which allows it to function properly. A nice side effect is that the angle of CV joint is very small.

The proper way to solve this would be switching the axle around and connect the CV joint directly to the wheel hub, which moves the pivoting point towards the wheel. The fixed joint is at a larger angle than the CV joint however, and using the CV joint at such an angle tends to pop it out. To prevent this from happening you would be forced to decrease your full lock angle significantly.

[AndyCW]

The strength of the u-joints is relative to the angle that they operate under. In the above case, where the u-joint directly drives the wheel, poses some issues. Depending on the power level and the wheel size, the u-joints are in real danger of breakage.

Nic Jasno made a live axle that uses portal hubs and incudes kingpin inclination. It does resolve some of the issues that have been mentioned. You can find the video by searching on Youtube for LPE Power Unimog. If reinforced and widened, they can withstand some power, but the inclusion of the cv joints is the weak point.

v/r

Andy

[Zerobricks]

What about this:

[zenzic]

The strength of the u-joints is relative to the angle that they operate under. In the above case, where the u-joint directly drives the wheel, poses some issues. Depending on the power level and the wheel size, the u-joints are in real danger of breakage.

Doesn't the same apply to Zblj's design above then? Or is the U-joint issue mitigated somehow by the gear reduction in the portal hubs?

[Zerobricks]

The higher the reduction in hubs, the less torque U joint has to carry...

[Leif]

What about this:

That is a very compact solution, may be the best so far. I cannot see if you are using double U-joints or u-joint + cv-joint?

good job, now if only the steering geometry...

[Balrog]

That is a very compact solution, may be the best so far. I cannot see if you are using double U-joints or u-joint + cv-joint?

good job, now if only the steering geometry...

U-joint + CV. You can see the sliding piece on the axle and part of the other half on the right side of the frame.

[Zerobricks]

I used CV+U jopint, but you can easily use 2 U joints, but remember to shorthen the swing distance of arms to match those of U joints. Steering geometry can be easily adjusted...