[WIP] Tatra 6x6 midscale

[Teo LEGO Technic]

Hey guys!

I'm going to try something I haven't so far - a WIP thread for my new tatra 6x6 truck. I'd love to hear all the advice you guys have along the way!

The idea is to make a pretty small truck with servo steering and two L-motors, one powering each side to eliminate the need for differentials. Each half axle will be suspended by its own spring. I've already come up with a front axle that I'm happy with. It's solid, good ground clearance, good steering precision despite smaller steering radius, and it's just the right side. If it's not too tall, which I'll have to figure out, the plan is to stick the servo motor vertically right onto the 8-tooth gear, which will give it excellent precision. Another gearing, if I put the servo on its side, would multiply play in the steering system. 

What do you guys think?

IMG_6551 by Teo's Technic, on Flickr

 

tatra-t815-7m0r39-29-306-6x6-2014 by Teo's Technic, on Flickr

e4aae418a365981d46bcd6c97723a542 by Teo's Technic, on Flickr

1998_Tatra_T815_7_6x6_military_truck_trucks_q_1600x1200 by Teo's Technic, on Flickr

Here are what it will scale like. The 8x8 blueprint I will use for the front view scaling, which I couldn't find for a 6x6

[jorgeopesi]

I love all Tatras, you can see my tatras if you are looking for ideas, if you improve something make me know.

http://www.brickshelf.com/cgi-bin/gallery.cgi?f=513091

[1gor]

62.4 Tires are great choice to work with. As my good friend @jorgeopesi said once building small scales teach much more and you need less pieces... 

[Teo LEGO Technic]

6 hours ago, jorgeopesi said:

I love all Tatras, you can see my tatras if you are looking for ideas, if you improve something make me know.

http://www.brickshelf.com/cgi-bin/gallery.cgi?f=513091

I was looking through some of yours for inspiration this morning, awesome builds! I think I'll keep it simple myself haha

[HorcikDesigns]

I strongly recommend modifications of the shown axle that lead to decreasing the angle between the half-axles, to keep it as realistic, as possible with this dual-shaft spine-tube setup. Real TATRA trucks have only approximately 7° (maybe I am wrong, but it is not more than 15°) from horizontal position (relative to rest of the truck).

[Teo LEGO Technic]

2 hours ago, HorcikDesigns said:

I strongly recommend modifications of the shown axle that lead to decreasing the angle between the half-axles, to keep it as realistic, as possible with this dual-shaft spine-tube setup. Real TATRA trucks have only approximately 7° (maybe I am wrong, but it is not more than 15°) from horizontal position (relative to rest of the truck).

I'm hoping that when the truck is finished the suspension will be about half-pressed, which will make the wheels closer to vertical as you say. Here's what I've got so far, with the red parts showing where the cab will be. It turns out I have a good amount of space. I could even try adding in a gearbox, however the performance will probably be best without. Do you think it'll be heavy enough to compress the springs? They're LEGO's weakest grey ones, and twice the weaker due to mechanical advantage from being positioned halfway down the half-axle, roughly.

IMG_6552 by Teo's Technic, on Flickr

I'm quite happy with the robustness so far, and wheel travel. The steering is also very precise, despite having a fairly small turning radius. 

Edited March 20, 2018 by Teo LEGO Technic

[HorcikDesigns]

They'll probably compress under the load of moors and BB, but the possibility of being aligned also this way (as shown in the picture), will aso make riding performace especially when cornering and offroading. Maybe I am wrong, but I had similar problems with my first trial trucks.

[1gor]

Looks interesting so far, but I'm afraid that softer springs are not good for this setup, at least try using harder (yellow) at the front, at least I had that kind of problem on my MOCs...

[pagicence]

@Teo LEGO Technic: Take a look at my Tatra Phoenix Agro Truck (pictures and LDD on rebricable). It's 1:17 scale. The powertrain setup is the same as you want it to be. The suspension travel is not too big, because I put shock absorbers at an angle, and that's why it's sitting as a normal truck. It doesn't have that weird look with wheels hanging. Maybe it can give you some ideas. (My personal opinion is that it will look way more cooler if you put double wheels all around, it will give the truck that nasty, mean look, even though it's not correct).

Edited March 21, 2018 by pagicence

[MajklSpajkl]

@Teo LEGO Technic So far, so good. I really like the compact front axle. Could you provide some more photo material to study/copy? :-D

5 hours ago, pagicence said:

@Teo LEGO Technic: Take a look at my Tatra Phoenix Agro Truck (pictures and LDD on rebricable). It's 1:17 scale. The powertrain setup is the same as you want it to be.

@pagicence Your truck looks really nice. Have you built it already? I am affraid that your drive shafts have a very good chance of grinding/skipping gears - that corner connection with black 12 tooth gears is not braced at all.

Edited March 21, 2018 by MajklSpajkl

[Teo LEGO Technic]

On 2018-03-21 at 2:13 AM, HorcikDesigns said:

They'll probably compress under the load of moors and BB, but the possibility of being aligned also this way (as shown in the picture), will aso make riding performace especially when cornering and offroading. Maybe I am wrong, but I had similar problems with my first trial trucks.

So do you think I should set it up with harder springs so that at rest, once built, the axles are in the near-horizontal position and the only direction the wheels can travel over bumps is up? I was thinking if I do this, but that will mean the mudguards will be really high up. What do you think?

 

On 2018-03-21 at 7:09 AM, I_Igor said:

Looks interesting so far, but I'm afraid that softer springs are not good for this setup, at least try using harder (yellow) at the front, at least I had that kind of problem on my MOCs...

I'm planning to keep it pretty light, I'll see when it's fully weighted how it performs and go from there 

18 hours ago, MajklSpajkl said:

@Teo LEGO Technic So far, so good. I really like the compact front axle. Could you provide some more photo material to study/copy? :-D

IMG_6554 by Teo's Technic, on Flickr

IMG_6553 by Teo's Technic, on Flickr

Like I said the axle has great stability, the steering is precise and compact, and it can take sufficient torque. The suspension is long travelling and smooth. The only issue is it doesn't have a massive turning radius, but I'm willing to sacrifice that for the benefits. 

I'm deciding what gearing I should use for the L-motors. Do you guys think it is slowed down enough to have sufficient torque?

[pagicence]

I think you're good. You have 1:2 ratio, so the output speed and torque is pretty close to the XL motor. And your theoretical speed will be 1,6km/h (1mph).

[Teo LEGO Technic]

2 hours ago, pagicence said:

I think you're good. You have 1:2 ratio, so the output speed and torque is pretty close to the XL motor. And your theoretical speed will be 1,6km/h (1mph).

Yeah it's the same speed as my last Tatra, which was smaller scale. If I keep it simple like this it'll turn out roughly the same weight, and the previous one had more than enough torque. Plus the speed is nice. 

[HorcikDesigns]

Eh, find some pictures and videos of real trucks in extreme conditions (e.g. at prooving ground tracks, TATRA has very nice one), there it will be clearly visible, that the halfaxles can not move to angles similar to your MOC, even when fully unloaded (in air), and when it starts climbing, the last alxles on 6x6 goes up in order o allow middle wheels to stay still in contact with ground.

 

For example, here is image to slightly illustrate (not accuratelly) what I said.

https://goo.gl/images/Mqbj2C

[MajklSpajkl]

@Teo LEGO Technic Thx for the extra photos 

 

[BrickbyBrickTechnic]

Awesome so far. But without the offset in the wheels it isn't really tatra suspension? Or is it still?Also maybe the angle of your wheels is too big? I'm no expert, but I like where this is going!

[jorgeopesi]

I still love tatras but I think that it is for the use of that obsolete technology, I understand it is a great off-road configuration but being rational a truck doesn´t need to climb the walls, it needs above all reliability and for this a rigid axle is the best, for simplicity and hardness, I will continue doing tatras by the way  .

[Teo LEGO Technic]

7 hours ago, HorcikDesigns said:

Eh, find some pictures and videos of real trucks in extreme conditions (e.g. at prooving ground tracks, TATRA has very nice one), there it will be clearly visible, that the halfaxles can not move to angles similar to your MOC, even when fully unloaded (in air), and when it starts climbing, the last alxles on 6x6 goes up in order o allow middle wheels to stay still in contact with ground.

 

For example, here is image to slightly illustrate (not accuratelly) what I said.

https://goo.gl/images/Mqbj2C

So do you think the wheels should have less of an angle stationary or less overall range of motion? 

 

5 hours ago, MajklSpajkl said:

@Teo LEGO Technic Thx for the extra photos 

 

No problem!

2 hours ago, BrickbyBrickTechnic said:

Awesome so far. But without the offset in the wheels it isn't really tatra suspension? Or is it still?Also maybe the angle of your wheels is too big? I'm no expert, but I like where this is going!

Technically it's not real Tatra suspension, although it still has half-axles like a tatra. Thanks!

 

2 hours ago, jorgeopesi said:

I still love tatras but I think that it is for the use of that obsolete technology, I understand it is a great off-road configuration but being rational a truck doesn´t need to climb the walls, it needs above all reliability and for this a rigid axle is the best, for simplicity and hardness, I will continue doing tatras by the way  .

True, and they look cool eh!

So here's a temporary chassis to test torque and weight distribution. It can currently climb a slope until it falls back at around 60 degrees, so torque is good. The wheels are pretty evenly pressed, and when I put the rear battery box inside the chassis, the lower weight will increase stability.

IMG_6555 by Teo's Technic, on Flickr

 

[HorcikDesigns]

On 23. 3. 2018 at 1:29 AM, Teo LEGO Technic said:

So do you think the wheels should have less of an angle stationary or less overall range of motion?

The MOC is your. You decide.

I just really like TATRA chassis system, so inclination of the axles in static position that your chassis allow can not me leave not-commenting. ;) 
Here is video showing 3D model of T-Phoenix chassis (on the miniature are shown rear axles in extreme positions, the front one approximately in neutral)

 

[legotechnicus]

Huge fan of tatra trucks! Looking promising! Currently also working an a 6x6 tatra in the Same scale. I could share it If You like.

keep up the foto’s!

[Teo LEGO Technic]

2 hours ago, legotechnicus said:

Huge fan of tatra trucks! Looking promising! Currently also working an a 6x6 tatra in the Same scale. I could share it If You like.

keep up the foto’s!

Yes please I'd love to see!

3 hours ago, HorcikDesigns said:

The MOC is your. You decide.

I just really like TATRA chassis system, so inclination of the axles in static position that your chassis allow can not me leave not-commenting. ;) 
Here is video showing 3D model of T-Phoenix chassis (on the miniature are shown rear axles in extreme positions, the front one approximately in neutral

Ahhhh I get what you're saying the travel on the axles is too much, especially downwards. You're right about that, but I just did that n purpose to make the wheels have maximum contact with the ground. Im currently working on making the rear chassis with torsion bars, so that'll be done soon. It's turning out to be a challenge to fit in the battery box in between the rear axles as well as torsion bars as well as keeping the chassis resilient to bending over bumps, suggestions?

IMG_6557 by Teo's Technic, on Flickr

IMG_6558 by Teo's Technic, on Flickr

 

[Teo LEGO Technic]

DSC05674 by Teo's Technic, on Flickr

DSC05673 by Teo's Technic, on Flickr

Chassis done and the performance is amazing! 

[BrickbyBrickTechnic]

Wow, looks awesome! Do you have any video?

[HorcikDesigns]

Looks really good, I look forward to see it grow. :-)

[Teo LEGO Technic]

13 hours ago, BrickbyBrickTechnic said:

Wow, looks awesome! Do you have any video?

Thanks man! Not yet, I was going to make one after the bodywork is done.

7 hours ago, HorcikDesigns said:

Looks really good, I look forward to see it grow. :-)

Thanks man! I checked out your Flickr, awesome drawings man! 

 

Here's my question guys. On the actual tatra there are these rectangular containers on either side in between the first and second axles. I was thinking of leaving that out in the interest of keeping the weight low and making it more versatile, as those would reduce ground clearance. I'll build it that way, keeping the cab body light as I can, and then see if it looks ok.