Leif

Portal hubs - a nail in their coffin

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UPDATE:

You can make it even more compact with the new 5L suspension arms:

indpsuspcompact.png

But remember suspension angle here is quite low because U joint and CV joint can rub on the arms. For higher angle you can seperate the arms a stud apart from the Cv joint.

Edited by Zblj

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You can make it even more compact with the new 5L suspension arms:

That design would be VERY weak in the fore-aft direction. Those narrow control arms are really only for small models.

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The heavier the vehicle, the closer to the wheel center you want your pivots to be. In this case i suggest a live axle with leaf springs.

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I've created a live axle with portal hubs, but I'm not quite happy with the result. As you can this axle is meant to have both drive and steering motors on the main chassis, not on the axle. This means there's a need to have two axles connected to the main body, the joint at the bottom and the smaller one right above. I expect this will lead to problems when compressing the springs, since the axle will pivot around the joint and the steering axle will consequently restrict this movement significantly.

Are there any better way to transfer both steering and drive from the body to the live axle?

iiYL7cQqBcuqS.jpg

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If you get the steering axle with the currently loose u-joint one stud closer to the ball-joint, the movement won't be too big.

Also, connecting the axle that goes into the u-joint with the CV joint to the chassis, it can compensate for most movement in all directions. For this, again take the Unimog as inspiration. It had it exactly like that.

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You're much better off if you use the f1 rear hubs instead of that. Your pivot point is much too far away from the wheel.

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Thanks for the tips, guys!

Wouldn't using the F1 hubs lead to having the pivot point out of line with the pivot points of the hub? With the portal hubs you can actually use an U-joint inside the hubs. With the F1 hubs you're restricted to using the CV joints, which seem weaker and have less turning radius.

I tried them previously, but some pointed out issues with the U-joint being a weak spot here:

ibtUjGVypvLyIj.png

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Using the CV joint correctly doesn't affect the geometry of the axle. But you are right, it somewhat limits the steering lock. But if you build it as shown in the picture it will not work very well because when having a steering angle of 45° the u-joint "bends" more than 45° and thus becoming ineffective and could possibly break. U-joints only work well with angles of 45° (or was it 55° like in angled beams=?) or less.

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Wouldn't using the F1 hubs lead to having the pivot point out of line with the pivot points of the hub? With the portal hubs you can actually use an U-joint inside the hubs.

Yes, but if you use the layout at the start of this thread to fix the tire-pivot offset problem you have the same issue - a 2 stud gap between the pivot axis and the universal joint. There's no way round that using the current Lego parts AFAIK. The choice is a 2-3 stud gap between the pivot and the tyre, or a 2 stud gap between the pivot and the centre of the universal.

The second problem is that a bent universal joint doesn't have constant velocity, so you're marrying up the (relatively) high-torque universal to a (relatively) low-torque CV joint, then loading them up. You could wreck a lot of universal joints this way.

The tyre gap just gives you bump steer, which is mostly a problem for off-road vehicles (and it makes the swing arc of the tyre bigger so mudguards have to be huge). The universal gap makes drive problematic, so motorised models will likely break diffs or CV joints.

One solution is to use Efferman's high torque universals with the sliding sleeve, but that's NOT LEGO!

Edited by Moz

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Portal hubs are good. They work great as a rigid axle member. Independent suspension with portal hubs appears to be to much for the axle set up around the portal hubs for intensive purposes.

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?

Zblj design is made correctly and is not affected by the steering problem you showing there in you situation. The presented U-joint issue is mitigated by aligning the center of the U joint with the pivot point on the portal hub. The wheel hub your working with the same does apply but it not the portal hub. The CV joint is the better option over the U-joint in the F1 hub case there. Notice how on the portal hub a portion of the U-joint is able to go inside the portal hub that is there so the steering pivot point can be right next to the portal hub other wise the same U-joint problem will happen on the portal hub as well. You probably have figure some of this stuff out by now.

I've created a live axle with portal hubs, but I'm not quite happy with the result. As you can this axle is meant to have both drive and steering motors on the main chassis, not on the axle. This means there's a need to have two axles connected to the main body, the joint at the bottom and the smaller one right above. I expect this will lead to problems when compressing the springs, since the axle will pivot around the joint and the steering axle will consequently restrict this movement significantly.

Are there any better way to transfer both steering and drive from the body to the live axle?

iiYL7cQqBcuqS.jpg

Yes there are better ways. You have basic idea you just now need to expand upon it. If you have good steering leverage on the portal hubs that will offset the bump steer problem with the portal hubs and the problem is solved to an extent. Another way to strengthen the axle design is to add triangulate suspension links in conjunction with the unimog ball joint. Then work towards having a proper suspension travel. Transferring both steering and drive from the body has its limits but its workable. You will probably need to have a some sort of telescopic axle connection that is able to expand and contract with the suspension travel.

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Portal hubs are good. They work great as a rigid axle member. Independent suspension with portal hubs appears to be to much for the axle set up around the portal hubs for intensive purposes.

Zblj design is made correctly and is not affected by the steering problem you showing there in you situation. The presented U-joint issue is mitigated by aligning the center of the U joint with the pivot point on the portal hub. The wheel hub your working with the same does apply but it not the portal hub. The CV joint is the better option over the U-joint in the F1 hub case there. Notice how on the portal hub a portion of the U-joint is able to go inside the portal hub that is there so the steering pivot point can be right next to the portal hub other wise the same U-joint problem will happen on the portal hub as well. You probably have figure some of this stuff out by now.

Yes there are better ways. You have basic idea you just now need to expand upon it. If you have good steering leverage on the portal hubs that will offset the bump steer problem with the portal hubs and the problem is solved to an extent. Another way to strengthen the axle design is to add triangulate suspension links in conjunction with the unimog ball joint. Then work towards having a proper suspension travel. Transferring both steering and drive from the body has its limits but its workable. You will probably need to have a some sort of telescopic axle connection that is able to expand and contract with the suspension travel.

Or use a linkage for steering, like a pitman arm.

The heavier the vehicle, the closer to the wheel center you want your pivots to be. In this case i suggest a live axle with leaf springs.

Why?

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What about this:

indepedentportal.png

Nice! It looks like you have a bush between the u-joint and the CV. You could replace the upper arm with a 5L one (connected to the chassis in the same place, but attaching to the hub further inboard), use a couple of half bushes to move the u-joint inboard half a stud, and get some kingpin inclination that would help with torque steer. The 5L arm would likely rub on the CV and u-joints, though, and the steering geometry would be made somewhat more complicated.

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Or use a linkage for steering, like a pitman arm.

If you use a pitman arm you will still need leverage to turn the portal hub. Pitman arm is definitely something the portal hubs are not designed to use well with. The rack and pinion setup is the probably the best path towards working with portal hubs.

Why?

I can answer this with the first two sentences in this chapter on steering and alignment... The steering system in a heavy-duty truck is expected to deliver precise directional control of the chassis at both gross and unloaded vehicle weight. It has to be able to minimize driver effort while retaining some road feel. In lego terms the portal hub would need to be designed to minimize the pitman arm steering so that the leverage is in working rage of the servo.

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If you use a pitman arm you will still need leverage to turn the portal hub. Pitman arm is definitely something the portal hubs are not designed to use well with. The rack and pinion setup is the probably the best path towards working with portal hubs.

I can answer this with the first two sentences in this chapter on steering and alignment... The steering system in a heavy-duty truck is expected to deliver precise directional control of the chassis at both gross and unloaded vehicle weight. It has to be able to minimize driver effort while retaining some road feel. In lego terms the portal hub would need to be designed to minimize the pitman arm steering so that the leverage is in working rage of the servo.

I meant why leaf springs.

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If the vehicle is meant to carry a cargo load or be heavy then leaf springs would be great to use for that. That's why you see a version of a leaf spring suspension system on all heavy-duty trucks. Shock absorbers are used to dampen spring oscillation and they also improve the ride quality in conjunction with leaf springs for front suspension systems.

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On 9/17/2014 at 6:41 AM, Zerobricks said:

What about this:

indepedentportal.png

indepedentportal2.png

indepedentportal3.png

would this work on set number 42110, it would certainly help with clearance. 

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54 minutes ago, 4x4mods said:

would this work on set number 42110, it would certainly help with clearance. 

42110's wheel wells are designed with the inset hubs in mind though, I'm pretty sure. So portal axles would push the wheels out and possibly cause them to rub against the wheel wells when turning.

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On 4/9/2020 at 7:06 PM, Bartybum said:

42110's wheel wells are designed with the inset hubs in mind though, I'm pretty sure. So portal axles would push the wheels out and possibly cause them to rub against the wheel wells when turning.

oh, that's too bad is there any other way to lift the defender (42110)? maybe moc portal hubs?

 

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11 hours ago, 4x4mods said:

is there any other way to lift the defender

For shure there are options, but, most probably, then "old" type rims needs to be used.

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3 hours ago, Jurss said:

For shure there are options, but, most probably, then "old" type rims needs to be used.

Between the hub and the rim one can insert 2 pulley wheels and 3 black pins to create some more distance. (This might introduce other problems... didn't think for more than 2 seconds about this... :ugh:)

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Just now, astyanax said:

This might introduce other problems

Of course. And then older type will be better.

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Just now, 4x4mods said:

so, does anyone know of a way to lift the defender (42110)?

 

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