[Concept] In Search of the Ultimate Portal Hub Design

[gyenesvi]

For the eager ones, Studio part files are here: frame and insert.

 

Hello Technic Builders!

The existing technic portal hub was a nice piece at the time, but it was designed long ago before the existence of deeper rims (Defender) and it is unfortunately not really compatible with them in the sense that it cannot make use of the extra space (does not fit inside). Unfortunately, when used with regular rims, the current portal hub piece has a horrible steering geometry (huge scrub radius), as it sticks too much out of the wheel, and also takes away a lot of space from the center of the axle build (less room for springs, links, etc). In the past few years I learned a lot about realistic suspension geometry and the ways they are achieved (it turns out that kingpin axis inclination is essential for realistic portal hubs, as the upper pivot point must be outside of the wheel since it is lifted up). So lately I have been lamenting on what could be achieved with a better lego portal hub designs? How well could real-life portals be approximated in lego? This thread is about my findings and design for such a piece.

First off, let's list what I'd expect from an ideal portal hub:

Requirements

• it should be symmetric, so that only one piece is required for left/right side
• it should have a 3-pin rim mount (otherwise we can just brick-build something with a bare axle)
• it should accommodate 8:24, 12:20 and 16:16 gear ratios (even though the 16:16 does not fit into the Defender rim, there might be bigger deep rims out there, like the Ferrari one or future ones)
• it should accommodate both U-joints and heavy duty CV-joints. In case of U-joints, it should support a steering angle up to 45 degrees (the joint itself should not collide)
• it should be usable both in solid axles and in independent suspension (the joint should not collide even in case of up/down angled steering arms)
• the steering pivot should be as close to the wheel as possible (in case of vertical kingpin axis)
• it should support building an angled (non-vertical) kingpin axis, moving the steering pivot inside the wheel
• it should be easy to build a non-steered variant as well

That sounds like a lot to ask for. Good news is, that the above piece could satisfy all these criteria! :) Let's see how it works!

Basic design features

The hub consists of two pieces: a frame and a wheel hub insert with 3 pins (1 stud thick without pins). The hub itself can be inserted from the inside, and it has a ridge to hold it agains the frame to prevent it from being pulled out (the idea is taken from @efferman's design, but my frame designs allows the integration of the pins while still having space to insert the hub piece). The hub insert does not click into the frame like in case of regular lego hubs; this is useful as it can be taken apart for cleaning / greasing.

A key design in the frame is to let the whole bottom part be buildable to allow for many options. The piece incorporates the parts that are impossible to build due to the tight space, like the top mounting point and the frame around the gears.

In order to allow for independent suspension and give space for heavy duty CV joints as well, the top mounting point is fixed to be a towball. Such requirements would be impossible to achieve with a regular pin, as the pin would collide with the joint. But with the past introduction of planetary and Audi hubs, the integrated towball is an established practise for lego wheel hubs, so this piece uses the same technique. Hopefully more towball socket pieces will follow to allow for more mounting options..

Finally, the frame adds mounting points for connecting the lower steering arm and the steering links. This is done with minimal extra material and with care to leave space for the joints.

Of course, the exact shaping of the part can be polished, some edges could be rounded off, and some extra support bits can be added where it is needed. But the overall shape and mounting points are there, this is how I could easily model it in Studio Part Designer.

Gear and joint assembly

To assemble the gears, one more piece is required to close the gear housing from the back. A key feature of the frame is to allow for two options (5L thin beam and 5x3 thin T beam), resulting in two possible pivot positions in case of U-joints. In the outer position (aligned vertically with the upper steering pivot), the upper gear is supported from two sides, half a stud on each side. In the inner position (half a stud more into the wheel), the upper gear is held by a full stud of mounting on the outside (as in case of the existing lego portal hub).

In case of heavy duty CV joint, the same two positions are available, with even more support (always on both sides of the upper gear), and an extra support piece can be added right next to the joint head.

In all cases, there's space for more than 45 degrees of steering angle (if the joints allow), and more than 25 degrees of suspension angle.

The outer joint positions (aligned with the upper mounting pivot) can be used to build vertical kingpin axis geometry, while the inner joint positions where the joint pivot is half stud more into the wheel than the upper mounting pivot can be used to build a tilted kingpin axis geometry. In this case, the lower mounting point will have to be one stud more outwards (into the wheel) than the upper one, and the joint will be exactly in line with the kingpin axis halfway between the two mounting points, like this

 

Mounting the steering arms / examples

The only thing left is building the mounting point for the lower steering arm. There is a lot of space, and there are plenty of options, here are a few examples.

Here's a basic way to connect the top and bottom part of the frame with extra pieces, adding mounting point for a towball or pin at the bottom, both in an outer and in an inner position (U-joint could also be used as above).

 

Here's how it could be used in a solid axle (steered and non-steered version):

 

Here's an example for a (non-steered) independent rear suspension (in that case, the upper and lower mounting points can simply be aligned, no need for kingpin inclination):

 

And here's how the most complex one, and independent front suspension with kingpin inclination could be built. The same can be used for a solid axle with kingpin inclination, in that case the steering arms would not be angled but would be fixed to horizontal.

Note, the mounting position of a the steering link. In this height it is in line with the kingpin axis, so there is no ackermann geometry. If however, we move the steering two studs lower, like below, then we can achieve ackermann or anti-ackermann geometry because of the half stud distance to the kingpin axis at that lower position.

 

Here's how it would look with rim and large tractor tire on

And here's an image showing the kingpin axis from the front

 

One more note about suspension geometry. By making the lower suspension arm 1 stud longer in the above IFS example (aligned pivot points next to the differential), it is possible to implement changing camber angle (tilting of the wheel). In this case the top of the wheel would tilt inwards, when the steering arms are not in a horizontal position. This could work well for faster buggies when the resting position of the arms is close to horizontal, and when the wheel moves upwards, it would tilt inward at the top (relative to the chassis), keeping the wheel horizontal during fast cornering (when the body tilts outwards).

 

Compensating half stud offsets of joints

One additional difficulty about building the kingpin variants is that the joint will the be on a half stud offset relative to all other parts and that needs to be compensated somewhere. It's not trivial with the available lego parts, but there are some options:

• The 5.5 stud long axle can be used in case of solid axles where the with permits
• The old CV joint male part has a 1.5 stud deep hole in it. That can be used in case of an IFS or even in case of a solid axle, as a straight axle joiner. It is not a big problem that this old CV joint is weaker, because it is only used in the front axle, and only on the inside next to the differential, where there is less stress on it.
• In cases where there is independent left-right drive, there may be space for an extra half stud of axle in the center of the suspension axle
• In less stressful applications, a 2L axle with a half bush in the middle, leaving 3/4 studs on both ends could also be used to connect two joints. I've tried it, feels solid enough by hand :)

 

Updated variant with extra lower mounting point

Studio part file.

 

Let me know what you think of all this, if you see any problems or possible improvements!

For virtual testing, here are the Studio part files: frame and insert.

Anybody wants to try and make a printable version of it?

And of course, should Lego make such a piece? 

 

Cheers,

Viktor

Edited October 13, 2024 by gyenesvi

[Aurorasaurus]

18 minutes ago, gyenesvi said:

 

Let me know what you think of all this, if you see any problems or possible improvements! 

Can you attach 5m half beams with cross axles to the arms next to the towball to stop the ball joints disconnecting, while still retaining a high steering angle? The lego planetary hubs do not allow you to keep a high steering angle if you do this.

Aside from that this design looks fantastic, I especially like the ability to use 3 pins to hold the wheels in, but also 6 if you add 3 pins, I think thats a fantastic idea for supporting the old wheels but giving better strength to the new ones.

Edited October 13, 2024 by Aurorasaurus
I neglected to show my appreciation for the design in the original post

[gyenesvi]

1 minute ago, Aurorasaurus said:

Can you attach 5m half beams with cross axles to the arms next to the towball to stop the ball joints disconnecting, while still retaining a high steering angle? The lego planetary hubs do not allow you to keep a high steering angle if you do this.

No, in this regard, it has the same geometry as existing lego hubs. However, there's an interesting difference which might be important, because it may be that you could get away without connecting the two steering arms: as opposed to standard hubs, here both arms are connected to the hub from the bottom, the towball facing up. Hence, the lower one cannot disconnect downwards, only upwards, which is less likely I think. For example, if you attach springs to the bottom arm, the force of the spring cannot push it apart, because of the bottom support.

[Aurorasaurus]

3 minutes ago, gyenesvi said:

No, in this regard, it has the same geometry as existing lego hubs. However, there's an interesting difference which might be important, because it may be that you could get away without connecting the two steering arms: as opposed to standard hubs, here both arms are connected to the hub from the bottom, the towball facing up. Hence, the lower one cannot disconnect downwards, only upwards, which is less likely I think. For example, if you attach springs to the bottom arm, the force of the spring cannot push it apart, because of the bottom support.

Aha, thats very clever, I like it. I hope it works. Will you share the files? I'd love to try 3d print it and test it out for you.

[gyenesvi]

37 minutes ago, Aurorasaurus said:

Aha, thats very clever, I like it. I hope it works. Will you share the files? I'd love to try 3d print it and test it out for you.

I can share the Studio part files (added links to the main post), but I cannot make the 3d printable version, and that would require some adjustments I guess. Also, the insert would be better to print without the pins, only 6 pinholes, and add in lego pins.

[2GodBDGlory]

Cool design! That does look well-optimized, and allowing for kingpin inclination is very beneficial.

If you're wanting to make it printable, I think the only major issue would be printing the towball on the top, but I imagine that could be fixed relatively easily by changing it to an axlehole and then supergluing in an axle-towball part with the axle sanded down as much as it needs to be to clear the CV joint

[Krxlion]

I think I need a lecture regarding kingpin inclination, because to be honest I've never played much attention to that matter before. Mostly I was focused on achieving positive caster angle or ackermann steering, if a model would have anything from IRL cars/trucks. Your design seems already well planned and executed.  I actually didn't think that recent wheel hubs don't work with portal hubs, I was quite surprised with this, and just yesterday I was happy that I have them, because they provide additional ground clearance to the build. Regarding printing your design, I think it will be hard to do so, it is a complex model and many things can go wrong. Anyway, thanks for sharing, I am really looking forward to this topic.

[gyenesvi]

Upon consulting with @Attika we considered that the bottom part may need extra reinforcement as the mounting of the lower towball is quite indirect and relies on axle friction and hence not rock solid and may result in some flex and ultimately tilting of the wheel. So here is a possible solution to that, adding a pinhole to the bottom.

And here's how it could be built up. To be clean solution, the kingpin variant would benefit from having a towball pin with 2L pin end (would be a very useful part in many other situations as well). For now, a possible solution is adding a half pin and connecting them with a 3L bar (which just stays clear of the rim/tire). Why on earth doesn't even a 2L bar exist..?

 

6 hours ago, 2GodBDGlory said:

Cool design! That does look well-optimized, and allowing for kingpin inclination is very beneficial.

If you're wanting to make it printable, I think the only major issue would be printing the towball on the top, but I imagine that could be fixed relatively easily by changing it to an axlehole and then supergluing in an axle-towball part with the axle sanded down as much as it needs to be to clear the CV joint

Thanks, that's a good idea for adding in the towball in case of printing!

5 hours ago, Krxlion said:

Regarding printing your design, I think it will be hard to do so, it is a complex model and many things can go wrong. Anyway, thanks for sharing, I am really looking forward to this topic.

You might be right, and it's just getting more complex :)

Anyways, even if weak, a printed version may be useful just for testing out the geometry in a manual build and not stressing it too much.

[Aurorasaurus]

7 hours ago, 2GodBDGlory said:

If you're wanting to make it printable, I think the only major issue would be printing the towball on the top, but I imagine that could be fixed relatively easily by changing it to an axlehole and then supergluing in an axle-towball part with the axle sanded down as much as it needs to be to clear the CV joint

You can actually just print the ball a bit oversized and sand that down instead, but super glue and the Lego part might be stronger. Im going to try make these files printable today.

[gyenesvi]

5 minutes ago, Aurorasaurus said:

You can actually just print the ball a bit oversized and sand that down instead, but super glue and the Lego part might be stronger. Im going to try make these files printable today.

Cool, I've added a part file for the updated frame as well in the main post!

[msk6003]

Seems like this design will not work with normal 56908/15038 wheels. Looks to big for 56908 and both wheel has 0.5L protrude on both side which will blocked by axle hole on wheel mount part. 

[gyenesvi]

14 minutes ago, msk6003 said:

Seems like this design will not work with normal 56908/15038 wheels. Looks to big for 56908 and both wheel has 0.5L protrude on both side which will blocked by axle hole on wheel mount part. 

Well it's obviously too big for 43 mm rims (any design would be too big for that as you cannot fit a 5L liftarm inside, and hence no regular gear mesh would fit inside), it's designed for Defender rims. But it could work with regular 56mm rims, it would be possible to make room for the 0.5L protrusion in the center of the wheel hub, but it would be pretty pointless as you would loose the whole point of getting close to the wheel with the steering pivot.

[astyanax]

10 hours ago, gyenesvi said:

So here is a possible solution to that, adding a pinhole to the bottom.

Perhaps it would be possible to have the pinhole 1L higher? That would trivialize the kingpin variant, and also the other variant still seems possible and rigid. Not sure if this is naive and would complicate printing though. 

[gyenesvi]

6 minutes ago, astyanax said:

Perhaps it would be possible to have the pinhole 1L higher? That would trivialize the kingpin variant, and also the other variant still seems possible and rigid. Not sure if this is naive and would complicate printing though. 

The problem with raising the pinhole would be that it would be in the way for inserting the 3-pin hub (and maybe also for the 24T gear) from the back.

[Zerobricks]

How about fusing the 24 tooth gear and the hub bearing into a single part to reduce complexity.

[N1K0L4]

1 hour ago, Zerobricks said:

How about fusing the 24 tooth gear and the hub bearing into a single part to reduce complexity.

Than you would loose the ability to change gear ratios inside the hub, which is a good feature to have IMO.

[Aurorasaurus]

I have printed one of these, apart from errors regarding the sizes of some of the holes (the 24t gear doesnt fit and the cv joint rubs a bit) the concept appears to work, defender rims with 107mm tires fit just fine.

https://bricksafe.com/pages/Aurorasaurus/miscellaneous/ultimate-portal-hubs-

^ second photo thats in portrait and cant be resized small enough by bricksafe to display nicely without missing the point of the photo

Awesome work @gyenesvi!

Edited October 14, 2024 by Aurorasaurus
add photos

[gyenesvi]

49 minutes ago, Aurorasaurus said:

I have printed one of these, apart from errors regarding the sizes of some of the holes (the 24t gear doesnt fit and the cv joint rubs a bit) the concept appears to work, defender rims with 107mm tires fit just fine.

Well that was materialized fast at the other end of the world :) We've got to appreciate technology! I hope in 10-20 years from now we can just design a piece like that and print it in every home in high quality and strength!

Let us know if you make a more polished print and try it in a sketch build!

3 hours ago, Zerobricks said:

How about fusing the 24 tooth gear and the hub bearing into a single part to reduce complexity.

I'm not sure what you would benefit from that, but I agree that being able to swap in 12:20 gearing is also useful, many MOCs use that gearing with the existing portal hub.

[dantheman12]

I’m amazed how quickly this thread has progressed! Really cool idea, it’s always been very frustrating trying to design realistic suspension with the given parts, a lot of them seem to almost inhibit creativity, being designed in ways where plastic is put in unnecessary places, not taking into consideration possible consequences. 
 

Like @gyenesvi mentioned about keeping the option for different gearing, I think an important thing to include is compatibility and options for customisation, I often wonder if bringing out more parts is always a good thing, as maybe one day there will be a part for everything, not requiring solutions using only the simple parts available. But that said it’s all about balancing different design elements to get the ‘best’ design.

[everybrickasculpture]

Any chance you could upload a step file version of these parts?  I'd like to make a couple of modifications...

[gyenesvi]

4 hours ago, dantheman12 said:

being designed in ways where plastic is put in unnecessary places, not taking into consideration possible consequences. 

I feel that some times too! Glad you like the idea.

Quote

as maybe one day there will be a part for everything, not requiring solutions using only the simple parts available

I guess that day will never come :) The thing is we only need a new part for those things that are impossible to build from the simple ones, due to the inherent limitations of the building system (like discrete sizes and a family of shapes).

1 hour ago, everybrickasculpture said:

Any chance you could upload a step file version of these parts?  I'd like to make a couple of modifications...

I don't have them, @Aurorasaurus has, but I'd be curious what you'd like to modify? Any improvement ideas?

Edited October 14, 2024 by gyenesvi

[everybrickasculpture]

I would like to see if metal bearings could be squeezed into this for use with brushless motors.  I have been using some portal hubs based around the original lego portal hub design with bearings for a few models, but would like to experiment with these due to the scrub radius mainly.

[gyenesvi]

I had some interesting findings today regarding the towball axle piece. For one, the axle part is a little bit shorter than on the axle-pin (it shows both virtually and I confirmed it on real parts). Second, the collar on the towball axle lifts it a little bit if inserted into an axle hole. This can give extra clearance above the piece, which can be useful for our hub constructions. For example, if it was mounted above a U-joint like this.

Then the space up to the towball axle would look like this, allowing the U-joint to articulate up to 25 degrees before touching the axle.

So if the corner of the towball axle mount was chipped off like this

then the joint would have enough clearance to articulate upwards; 25 degrees would be pretty much enough for an IFS portal.

 

So based on all this, I have designed a simpler, updated version of the currently existing lego portal hub. This is much more simple than the main one in this thread; it would only support U-joints, and would not support kingpin axis, only vertical. However, there are two key differences wrt the existing lego portal.

• The top part is cut off, and the top reinforcement goes around the top gear (like in the main design, but an axle hole mount is used at the top instead of a fixed towball)
• The wheel hub insert itself is 1 stud shorter. It would use a similar click-in technique as the currently existing one. I think the shortening would not be a big deal, because of the through axle supporting the wheel as well in case of the portal (as opposed to a regular wheel hub).

Because of these, it would fit into the Defender rim and the pivot point would get as close to the wheel as possible (2 studs closer than with the current one).

The advantage of the axle-hole top mount is that in case of solid axles, there is no need to use a towball, which makes the axle build much more simple.

 

Here are the ways in which an IFS and a solid axle could be built. In case of the IFS, it would become possible to link the two steering arms, while retaining a max steering angle of 40 degrees!

 

It would look like this with tractor tire. Would already be a substantial improvement over the current one.

 

I think if TLG ever updates the portal hub mold, it could become something like this. Or something completely enclosed based on heavy duty CV joints.. :)

 

4 hours ago, everybrickasculpture said:

I would like to see if metal bearings could be squeezed into this for use with brushless motors.  I have been using some portal hubs based around the original lego portal hub design with bearings for a few models, but would like to experiment with these due to the scrub radius mainly.

I think that may be possible, I have also been thinking how the hub insert could be made better to have less friction and make it more stable. I think where currently the 3 pinholes are next to the 3 pins on the hub insert, there could be 3x 8mm diameter, 4mm thick bearings maybe..

 

Edited October 14, 2024 by gyenesvi

[Aurorasaurus]

9 hours ago, everybrickasculpture said:

Any chance you could upload a step file version of these parts?  I'd like to make a couple of modifications...

I have the STL files I printed available here. Please note that the tolerances are not perfect for my machine, and probably wont be for yours either. You will need to modify the file to make it print and fit the gears inside nicely. EG the 24t gear doesnt ft.

[N1K0L4]

9 hours ago, gyenesvi said:

So if the corner of the towball axle mount was chipped off like this

No need for cutting. All ends of all axles are rounded off, which is not represented in digital programs.