Live Axle Discussion

[MrNumbskull13]

Ever get bored of the usual live axle set up? Parallel steering arms and vertical kingpin axis? No advanced and interesting geometry & features? All this adds up to only a "decent performance". How can we improve our live axles?

I decided to start this discussion to generate some ideas on how we can all make better live axles. Personally I'm very bored of the basic live axle set up and I would like to add in some interesting geometry to improve performance...

[edit]: Things to discuss;

How many links does your set up use?

I'm stuck with [insert problem here]

Use of differentials

Universal joints vs. CV joints

And other stuff I haven't thought of/ whatever you would like to discuss...

Edited December 31, 2013 by MrNumbskull13

[Junpei]

Perfect topic and quite a good idea! I'll post my pics and question in a few hours maybe. Trying to mount suspension links for a live axle with 4 driveshafts

[MrNumbskull13]

Perfect topic and quite a good idea! I'll post my pics and question in a few hours maybe. Trying to mount suspension links for a live axle with 4 driveshafts

Great! There are plenty of people here that can help!

[Technyk32231]

You can use a motorcycle head tube (Part number 2904) to get kingpin inclination. I've been experimenting with it, and it seems to work well. I don't think you can then make the axle driven, though. This is the rough idea:

Edited December 31, 2013 by Technyk32231

[Junpei]

Nice idea, Technyk32231! I think I remember you made a topic about this a while back. Could be useful for a mostly display model, with only suspension and steering. Maybe something like Model team but with a little more functionality.

So here's my problem that I don't think has ever been brought up before- how do I attach the links for a live axle with 4 driveshafts?

Here's a pic of it so far (of course it probably won't be permanent):

Yeah, it's a bit of an odd setup. But I think it will work. It of course has slight positive caster angle (a bit hard to tell from the picture); the bottom driveshafts are offset by a half of a stud. Here's a picture that better shows this (don't mind the yellow liftarm ):

The articulation is actually better than I expected:

I figured that with the slight misalignment of the u-joints, I would probably need some form of telescopic driveshafts. I have used Andrea Grazi's design for telescopic driveshafts, and here is how it looks with them installed:

Since the axles inside the u-joints are 2L, it offers about 1 stud of safe extension:

So what do you guys think? I'd like to keep the length of this vehicle to a minimum- with the driveshafts being 8L it's almost too long.

Thanks in advance!

TLH

[Moz]

I think you'll get slightly under half a stud of extension, because any slope on the axles means the worm will slide to the bottom.

[Junpei]

That's what the rubber bands are for. They center the worm gear between the u-joints by making both axles always slide out of the worm gear at the same rate. Works even under relatively high load

TLH

[nicjasno]

There's reasons why nobody does it like that in real life applications. :)

Usually only 1 shaft per axle. The rest is done via hydraulics, or rods.

You can use a motorcycle head tube (Part number 2904) to get kingpin inclination. I've been experimenting with it, and it seems to work well. I don't think you can then make the axle driven, though. This is the rough idea:

Good idea, but what happens with the not quite half stud space at the bottom when load is applied?

[MrNumbskull13]

Nice idea, Technyk32231! I think I remember you made a topic about this a while back. Could be useful for a mostly display model, with only suspension and steering. Maybe something like Model team but with a little more functionality.

So here's my problem that I don't think has ever been brought up before- how do I attach the links for a live axle with 4 driveshafts?

Here's a pic of it so far (of course it probably won't be permanent):

Yeah, it's a bit of an odd setup. But I think it will work. It of course has slight positive caster angle (a bit hard to tell from the picture); the bottom driveshafts are offset by a half of a stud. Here's a picture that better shows this (don't mind the yellow liftarm ):

The articulation is actually better than I expected:

I figured that with the slight misalignment of the u-joints, I would probably need some form of telescopic driveshafts. I have used Andrea Grazi's design for telescopic driveshafts, and here is how it looks with them installed:

Since the axles inside the u-joints are 2L, it offers about 1 stud of safe extension:

So what do you guys think? I'd like to keep the length of this vehicle to a minimum- with the driveshafts being 8L it's almost too long.

Thanks in advance!

TLH

I think you should have a link for each u joint and attach the links at the pivot points of the joints, if that makes sense. :P

Edited January 1, 2014 by MrNumbskull13

[Technyk32231]

There's reasons why nobody does it like that in real life applications. :)

Usually only 1 shaft per axle. The rest is done via hydraulics, or rods.

Good idea, but what happens with the not quite half stud space at the bottom when load is applied?

In real life, you can fit a half bush there. It doesn't work in LDD. In real life, it slightly stresses the 3L pins, but so little you don't even really notice it.

[Junpei]

I think you should have a link for each u joint and attach the links at the pivot points of the joints, if that makes sense. :P

Yes, I see what you're saying. Might want to remove the quoted images, there's quite a few in my post. I'll try that, would a panhard rod work in such an application? While a very good idea, it doesn't have anything to prevent lateral movement.

Edited January 1, 2014 by TwentyLeggedHen

[Technyk32231]

Nice idea, Technyk32231! I think I remember you made a topic about this a while back. Could be useful for a mostly display model, with only suspension and steering. Maybe something like Model team but with a little more functionality.

So here's my problem that I don't think has ever been brought up before- how do I attach the links for a live axle with 4 driveshafts?

Here's a pic of it so far (of course it probably won't be permanent):

Yeah, it's a bit of an odd setup. But I think it will work. It of course has slight positive caster angle (a bit hard to tell from the picture); the bottom driveshafts are offset by a half of a stud. Here's a picture that better shows this (don't mind the yellow liftarm ):

The articulation is actually better than I expected:

I figured that with the slight misalignment of the u-joints, I would probably need some form of telescopic driveshafts. I have used Andrea Grazi's design for telescopic driveshafts, and here is how it looks with them installed:

Since the axles inside the u-joints are 2L, it offers about 1 stud of safe extension:

So what do you guys think? I'd like to keep the length of this vehicle to a minimum- with the driveshafts being 8L it's almost too long.

Thanks in advance!

TLH

Or this axle could be used in a rear wheel drive vehicle. I don't know how you would attach links to this... I've found that it's best to design the axle keeping in mind that you will need link attachment points later. Edited January 1, 2014 by Technyk32231

[nicjasno]

In real life, you can fit a half bush there. It doesn't work in LDD. In real life, it slightly stresses the 3L pins, but so little you don't even really notice it.

You don't understand... in real life, no vehicle will have 4 shafts connecting to one axle, because every engineer knows that it is not a good idea. :)

[MrNumbskull13]

You don't understand... in real life, no vehicle will have 4 shafts connecting to one axle, because every engineer knows that it is not a good idea. :)

I think he's making a vehicle that can zero steer so there isn't any other way?

[nicjasno]

Zero steer? There's always another way.

Edited January 1, 2014 by nicjasno

[Technyk32231]

You don't understand... in real life, no vehicle will have 4 shafts connecting to one axle, because every engineer knows that it is not a good idea. :)

Yes I do understand. I wasn't even talking about TwentyLeggedHen's axle when I said the half bush fits in real life. I was talking about my own axle, which has no driveshafts, or drive at all.

I think he's making a vehicle that can zero steer so there isn't any other way?

Motor on Axle, pneumatics, etc.

[nicjasno]

Technyk32231: Ah, yes. I see.

[kevman]

I build the live axle from Sheepo's MPS system and It is pretty good. I wish that I could incorporate lego Hubs into it becuase the wheels tend to be too wobbly on a single axle.

[Thirdwigg]

I have been working on some suspension designs for an upcoming supercar. Right now the front has a negative caster angle and a kingpin inclination (though still positive scrub radius), and has decreasing camber as it moves through the suspension travel. I'll try to post something tonight.

Also, I have been using more short arm/long arm suspension designs on driven axles, which has been working well.

[Lipko]

Do these advanced geometry stuff actually affect the performance of Lego vehicles?

I mean, Lego is wobbly, it's very hard to build tight constructions with minimal backlash. And in reality, as far as I know, these advanced angles mean pretty small deviations from the simple geometry. I wouldn't be surprised if the angles were smaller than the wobbliness of the Lego parts.

Plus these advanced geometry is not straightforward to build from Lego, which usually means quite a lot of extra pieces, which means extra weight for the model, which in my opinion, affects performance more.

So is there a point in making these, apart from realism? Please, correct me if I'm wrong.

Edited January 3, 2014 by Lipko

[nicjasno]

You'd be suprised how much more fun it is to use a HOG steering on a car with proper geometry, even with the slack in lego parts. It drives so much better than one without geometry.

It is totally worth it.

Edited January 3, 2014 by nicjasno

[Lipko]

You'd be suprised how much more fun it is to use a HOG steering on a car with proper geometry, even with the slack in lego parts. It drives so much better than one without geometry.

It is totally worth it.

Yes, but that's really truth for Ackermann geometry and caster maybe (of course, avoid negative caster), or no?

[nicjasno]

It's true for all angles. Kingpin and caster being the most important ones.

If you have a kingpin, the steering gets a tendency to return to center and if you have a positive caster, the vehicle is much more stable in a straight line. Both combined make for a very fun drive.

Name the wheels of your choice and i'll make you a simple suspension, so you can test it out yourself.

[MrNumbskull13]

I've been really struggling to make a driven live axle with kingpin using 81.4 tires...

Edited January 3, 2014 by MrNumbskull13

[nicjasno]

Have you seen my unimog front suspension?