A lot of trial trucks are Tatras.

They have one common link - the suspension.

What's so special about it?

Can anyone tell me advantages/disadvantages of this type and others?

I like tatras very much just because they use a special system but I really don´t know very well if they are goods or bads trucks... You can see tatras on you tube on trial trucks, I think that the suspension is better on high speed but maybe it is not as reliable as they should.

There are 25 articles on Lego Tatra models on BrickTruckTrial.com . In April 2010, Sariel made this Tatra T815 model. The independent suspension can be seen in these two YouTube videos:

Edited May 17, 201212 yr by DLuders

You can also google it.

As far as I know, the main advantages (in real vehicles) are its relative simplicity, the central big and strong tube so no strong and heavy chassis is needed, and a big advantage that it's modular. Because of the central tube and the non-existing chassis, trucks can easily be build with different wheel counts, wheel positions, steering etc.

In Lego, I don't know. Maybe it's just a cultural thing, Tatra's are legendary trucks. But I prefer other suspensions, because with Lego, this suspension is not simple at all. And I think a live axle system performs much better.

The main avantage of tatra suspension is that all the wheel are independant. In a rigid axle, when a wheel goes up, the other located on the axle goes down. Compared to traditionnal independant suspension, wheel doesn't stay perpendicular to the road but tatra suspension is stronger than usual one which can be found on car.

In lego technic, tatra suspension is actually bad to do truck trial. Indeed, all the weight is put on the transmission axle because lego tatra suspension don't use turn table. Now, with the release of the new mini-turn table it's maybe possible to create a suspension tatra with two turn tables ( the big and the small one), but it will ve bery complicated, surely not very strong and reducing ground clearence.

But tatra suspension is beautiful, it's a fact :p

I just like to differ from solid axles ever once in a while! Also the suspension angle is unique!

In a modern tatra, each wheel is suspended independantly on half shafts. The wheel is fixed to the angle of the shaft (except when steering obviously). This means that when the suspention is uncompressed the tops of the wheels lean outwards. When the suspention is compressed the wheels rotate to a more vertical position. This creates simplicity and therefore an inherant toughness and adds to the reliability. This part is easy to recreate in lego, but from here it gets more difficult. Each half shaft rotates about the same axis longitudinal to the vehicle, which in itself is not difficult to recreate, difficulty comes with the differential. It is not mounted directly between the wheels and it is not driven by an outer gear. Instead the outer case is fixed directly to a drive staft mounted from one end. Both the driven axles exit the differencial from the other side, one rotating inside the other. These then go to bevel gears which drive the half shafts going to the wheels. Incidentally the half shafts are offset to give the needed clearance between opposing bevel gears. As always, a picture speaks a thousand words, and a video is thousands of pictures!

Edited May 18, 201212 yr by allanp

Well, it's fairly simple independant suspension. However, this kind of suspension, which is technically called Swing Axle, has some disadvantages, which are detailed further in the Wikipedia article. In addition, Lego trucks with this kind of suspension flip over on their sides very easily, as Sariel found out the hard way.

Well, it's fairly simple independant suspension. However, this kind of suspension, which is technically called Swing Axle, has some disadvantages, which are detailed further in the Wikipedia article. In addition, Lego trucks with this kind of suspension flip over on their sides very easily, as Sariel found out the hard way.

Well seems to me that this type of suspension is very stable if you do not overdo the angle (like over 15 degrees)

Allamp, it's possible, I have already built such a mechanism, but it's powerless, unfortunately :

All the pictures

Well you've got the easy part

Like I said, the difficult part is the differential. You have one side of the differencial driving both the front wheels. What you need for it to be like a modern tatra is to have both driven shafts of the differential exiting from the same side, one rotating inside the other, these then go to drive each wheel separately. It's not impossible. You can try something like this:

The yellow cage is the outer cage of the differential. You would drive this from the back so that it rotates. More bracing is needed to prevent gears slipping but the idea should be sound.

Edited May 18, 201212 yr by allanp

Wow... I never seen that... amazing...

Well you've got the easy part

Like I said, the difficult part is the differential. You have one side of the differencial driving both the front wheels.

No. Each side of the differential drive a wheel. See more pictures to see that :p.

No. Each side of the differential drive a wheel. See more pictures to see that :p.

Whoops, I apologize I didn't see that! I would say your version is the most authentic I have seen, thanks for posting.

Edited May 20, 201212 yr by allanp

Sorry for resurrecting this old topic but i need some help. I have tried building a Tatra diff based of pictures of the real thing but failed. I did build something like what allanp posted but much bulkier and not working well. I thought that what allanp posted looked great and can't not see anything wrong other that is is incomplete for being driven but that isn't hard to add, nor can i see how what GuiliuG is supposed to work. Is the diff driven somehow other than by the axle it is on?

My truck will be driven but will not be a TT so it doesn't need to have as much power. It will however be big so maybe it does. Oh well i had given up on tatra diffs and was looking for pictures of the suspension when i found this topic. Funny how it is much easier to find Lego tatras than the real thing that i was looking for.

BTW what other pictures are there. I saw some posted on BS but those didn't help. Looking at this pictures again it seems that both the black and tan bevel gears are on the same axle. This would lock the differential. Or am i missing something? I hope i get an answer soon so i don't have to do too much rebuilding if i decide to use a more authentic design than the one i'm going for.

Does no one have any answers? Any link to more pictures that explain how this works would be welcome. Here is a video i found earlier that seemed like great help but building this in Lego proved to difficult. Wood would be easier due to the rounded shape needed and i'm not even good at woodworking. Unfortunately i have not means of making it in wood nor would i want to.

Any ideas on how to build a Lego version of the diff as seen here. Allanp:s solution seems great to me but i might be missing something.

Edited January 29, 201411 yr by EyesOnly

Sorry for resurrecting this old topic but i need some help. I have tried building a Tatra diff based of pictures of the real thing but failed. I did build something like what allanp posted but much bulkier and not working well. I thought that what allanp posted looked great and can't not see anything wrong other that is is incomplete for being driven but that isn't hard to add, nor can i see how what GuiliuG is supposed to work. Is the diff driven somehow other than by the axle it is on?

My truck will be driven but will not be a TT so it doesn't need to have as much power. It will however be big so maybe it does. Oh well i had given up on tatra diffs and was looking for pictures of the suspension when i found this topic. Funny how it is much easier to find Lego tatras than the real thing that i was looking for.

BTW what other pictures are there. I saw some posted on BS but those didn't help. Looking at this pictures again it seems that both the black and tan bevel gears are on the same axle. This would lock the differential. Or am i missing something? I hope i get an answer soon so i don't have to do too much rebuilding if i decide to use a more authentic design than the one i'm going for.

Take a look at allanp's other photos (there's a link at the bottom of post #10), especially this one:

It looks like he's running two driveshafts off the differential. One, visible from the bottom, comes from the axle on the wheel side of the differential, and it drives the tan bevel gears and one wheel. The other comes off the other side of the differential, going from the black 12t gear to the 20t gear above it, along that axle, and then (as far as I can tell) to another 20t/12t pairing on the far side of the wheels to drive the black bevel gears and thus the other wheel.

I think using these two parts may be good for a very solid driven tatra suspension: http://rebrickable.com/parts/92910 and http://rebrickable.com/parts/92911. I will soon try to make a good suspension with them. I only own two of them, so i can only do one axle.

Take a look at allanp's other photos (there's a link at the bottom of post #10), especially this one:

It looks like he's running two driveshafts off the differential. One, visible from the bottom, comes from the axle on the wheel side of the differential, and it drives the tan bevel gears and one wheel. The other comes off the other side of the differential, going from the black 12t gear to the 20t gear above it, along that axle, and then (as far as I can tell) to another 20t/12t pairing on the far side of the wheels to drive the black bevel gears and thus the other wheel.

That sounds like it could work but it also sounds overly complicated. Or maybe not. I like it more the more i think about it. The problem is of course that this might work for one axle, but how about 3? BTW the picture you linked to is from GuiliuG not Allanp. I'm guessing that running with the diff open causes the wheels to spin in different speeds if need be and locking it so it spins on the axle causes both wheels to turn as one. Nice. Still i'm worried about that comment regarding it being powerless. My vehicle will be 95 or so studs long so lots of force will be going through the differentials i make. I might try this out tomorrow. Talk about having i possible solution right before my eyes and not seeing it.

I think using these two parts may be good for a very solid driven tatra suspension: http://rebrickable.com/parts/92910 and http://rebrickable.com/parts/92911. I will soon try to make a good suspension with them. I only own two of them, so i can only do one axle.

That would probably not be Tatra like if you are planning to build how i think you are and it will be very wide. But try and post a pic so i can see what you mean. BTW that last link doesn't work.

That sounds like it could work but it also sounds overly complicated. Or maybe not. I like it more the more i think about it. The problem is of course that this might work for one axle, but how about 3? BTW the picture you linked to is from GuiliuG not Allanp.

Oops! Right you are.

I agree about this being a somewhat complex design for multiple axles, but it would work. Note the 16t clutch gear above the differential that engages with it. My guess is that another gear, connected to the motor, drives this clutch gear and thus the differential. The same setup could be repeated for an arbitrary number of axles, though it requires a lot of space (especially vertically).

EDIT: in terms of gearing, it also works to do this:

1. power the axle going into the 24t side of a 4L differential
   
2. connect the other axle to a 12t single bevel, which drives a 12t double bevel (and one wheel)
   
3. connect the 16t side of the diff to a 24t crown gear (which drives the other wheel)
   

However, I couldn't figure out a good way to connect the structure for the half-axles.

Edited January 30, 201411 yr by Hrafn

I don't doubt its function only the amount of power left by the third or so axle.

Nice - I tried something like this - not totally tatra but hey:

Also this guy did something similar http://www.brickshel...y.cgi?f=472779 on a hotrod though and it shares the diff for each side of the car which could be done for pairs of wheels (and maybe improve traction even)

I always wonder how the offset axles reach the wheels on the real life tatras?

Do they offset them to the centre of the hubs? or use portal hubs or are the wheels on one side of the truck different on each side?

Edited January 30, 201411 yr by Rockbrick

Here are more Tatra videos- Hope they help you understand the offset.

Well you've got the easy part

Like I said, the difficult part is the differential. You have one side of the differencial driving both the front wheels. What you need for it to be like a modern tatra is to have both driven shafts of the differential exiting from the same side, one rotating inside the other, these then go to drive each wheel separately. It's not impossible. You can try something like this:

The yellow cage is the outer cage of the differential. You would drive this from the back so that it rotates. More bracing is needed to prevent gears slipping but the idea should be sound.

I just made this, and unfortunetly as cool as it is, it will never work, just not enough bracing, and those old gears can't take any torque.

I'm also building a Tatra, and i never even considered making a diff.

Hrafn's looks great tho!

one other advantage of lego tatra axles.

If you use balloon tyres , they have more grip because they don't roll on the flat middle section of the tyre but on the grippy part on the outside of the tyre.

Grtz

Johnny