[WIP] Pacific-Tatra T16-7

[AdamFMX]

Hello, few days ago I got idea how to do almost real Tatra chassis. Out there are a really lot of Tatra chassis designs, hovewer majority follows two concepts: either central shaft (halfaxles swinging around one axis-for this is real Tatra famous) design without differentials (no place for them-in reality Tatra uses shaft-in-shaft design-so technicaly it is not Tatra while very similiar) or two shafts, each with own motor (no diff needed but since halfaxles are swinging around two axes, it is not Tatra). I did't want to use either design, I had to came up with my own. My concept uses halfaxles swinging around one axis-central shaft, while each axle module (again like in reality-Tatra is basicaly Lego-they can assemble every chassis which you can imagine with ease) will have own diffential (sadly no difflock as there won't be place for it). Shaft from first, closer to diff axle was not problem-it is direct. Problem was how to get shaft from second halfaxle to diff. Solution was quite trivial-reroute it above halfaxle swing points and diff, descend to original heigh and from back to diff. Just plus 4 gear wheels. Problem solved. I decided to use Audi RS Q e-tron Dakar car tires as I liked tread and Arocs (because my first set with these 62.4x20 tires, which I used quite lot) tires were kinda small but classic 81 balloons were too wide. Here are some photos of front axle (rear will come later as it will be easier, front can stop project). But I must come up with some reinforcements, as I am excepting to final model be heavy and this can work with lightweight things.

This all was during this Friday, Saturday and particulary Sunday. Now, second toughest part-steering. This will be interesting but I have some ideas. But I will appreciate some tips and ideas. And why is topic named Pacific-Tatra T16-7? Funny story. I got idea to make offroad logger Pacific P16 after playing Snowrunner for while. But I thought that it would deserve better chassis. Yes, real one is very good, but which truck is current road legal offroad king? Without doubts, Tatra 815-7. And idea was on world, to combine these two beasts into one ultimate truck. With ultimate design tool. Lego Technic. That's it for today, I will post here after some progress is made.

Kind regards and happy building, Adam

[2GodBDGlory]

Interesting suspension and drivetrain setup with the differential!

[AdamFMX]

Thanks. Today I made some progress, still working only at front as it is hardest part. I did the most important thing-steering, then suspension (it will have very small suspension travel according to LDD but LDD hinge tool is questionable) and for last 30 minutes I was working on motor placement and bodywork attach points. Rear axles will be easier but I am curious how will turn out main power shaft to rear as there won't be much vertical place. But since I overcame front axle (I think), I should be able to finish it. ANd if not, I have pair of helping hands, which have some experience too.

Steering (so moving) components are highlighted but ignore few connection parts, as I used zone select.

Powetrian layout will be similiar to 42129's (MB Zetros) one but difference will be no diff lock as there is really no space for it. For now. And I am slowly begining to think, that LDD hates me for that halfaxles as it sometimes looks like whole model is weirdly rotated. More coming at Friday (the soonest option, maybe later) as tomorrow I have veeery long school day (still high school student, so I am taking up as much free time as possible without influencing school results).

See ya next time, Adam

[1gor]

As someone who is much much older than high school student, I would like to see it in real bricks; so far I'm following with an interest

Edited September 11, 2024 by 1gor

[Zerobricks]

While it looks good digitally, you will have big issues:

• Differential planetary gears skipping
• Bevel gears skipping
• CV joints failing
• Large friction because the drive axle laso have to support the weight and all the loads generated by driveline
• Big suspension flex, due to low gearing which will cause one side of the arms to go up and other to go down - tilting the body a lot when driving

 

I recommend using planetary gear hubs as start...

P.S. press Ctrl+K to take a screenshot in LDD

Edited September 11, 2024 by Zerobricks

[AdamFMX]

Zerobricks: Are we talking about 1:1 gear ratio or same gear ratio as Zetros? Because planned gear ratio will be 1:1, no gearing at all. That friction thinga is different story though. But I will see how it will work.

1gor: I want to carefully plan it as I will be ordering bricks (minimaly tires) and delivery time is 15-28 work days so even if I would have it done now, still I must wait for order to arrive. And order is still not final. But Iwill try to advance with it as fast as possible. But thanks for interest.

P.S. Thanks for that screenshot shortcut

Edited September 11, 2024 by AdamFMX

[Zerobricks]

25 minutes ago, AdamFMX said:

Zerobricks: Are we talking about 1:1 gear ratio or same gear ratio as Zetros? Because planned gear ratio will be 1:1, no gearing at all. That friction thinga is different story though. But I will see how it will work.

I'm talking about 5.4 gearing from Zetros/42099 hubs. Real Tatras also use planetary hubs. 1:1 gear ratio will cause your driveline to fail at any larger load in multiple spots.

[AdamFMX]

Hmmm. Gearing on Zetros is quite ridiculous, so if I will use gearing, it wont be much. And doesnt have Zetros other reductions than hubs? It was some time ago when I was building it. And that real Tatras-depends on customer-they have three types of reduction-any, light and heavy. I really need to build it and test it.

[bruh]

Hey, I like this idea! By the way, is LDD still available to use/download? I use stud.io, but I would like to look into other possible softwares. 
Can’t wait to see the finished product!

[AdamFMX]

6 hours ago, bruh said:

Hey, I like this idea! By the way, is LDD still available to use/download? I use stud.io, but I would like to look into other possible softwares. 
Can’t wait to see the finished product!

Yes it is, but from third party sites. But I found reliable source internet archive or something like that. Search for version 4.3.11. And here on forum is topic with part updates, although it is not easy to do

[HorcikDesigns]

Well, it looks like an interesting way to build Tatra chassis with differentials, but I must agree with Zerobrick's list of issues. And mainly with the enormous friction caused by the driveshaft acting like pivot axle for the halfaxles. The friction will be increased by not only the gravity, but also by rolling resistance - the whole half axle will probably act like lever pulled against the movement of the truck. And do not expect the pin and axle in the DBG adaptor part (61904) to hold all weight of the truck with 81mm wheels. ;) 

And the gearing is really good for manual model, but in case you would like to make it RC, the preformance will be probably very poor. 

Also the steering arm with 4L liftarms will be very weak spot. These parts like to crack in axle hole. 

But I might be wrong and you will build an excellent MOC with ingenious mechanics. The idea of mounting that rugged cab from Pacific truck on the Tatra chassis sounds kind of cool.Wierd (from point of view of a Tatra fan), but cool. :) 

[bruh]

16 hours ago, AdamFMX said:

Yes it is, but from third party sites. But I found reliable source internet archive or something like that. Search for version 4.3.11. And here on forum is topic with part updates, although it is not easy to do

Thanks for the info!

[AdamFMX]

Guys, for rear double tires which option is better:

A:) tight version-no shaft extension between rims, rims are as close together as tires allow (81.5x29 tires)

B:) wider version-with classic shaft extension between rims, rims as close as extension would allow

I prefer more A, but since B is wider, I will build rear axles in mind with B and if in case that A will be better, there won't be problem

[AdamFMX]

Progress report: gearing issues cleared (I think), steering reinforcement and main point of program-rear axles! It is really modular system if you can forgive gap between rear axles and bit complicated front axle.

Kind regards, Adam

[HorcikDesigns]

Good progress. But keep in mind structural stiffness and rigidity. So far it would be a nice and faithful to original static model, but for RC am I affraid that it would be torn apart by its motors or its own weight in first 2 meters. Unfortunatelly I still do not belive that your axles are stiff and strobg enough for truck this size. 

Have you built some physical prototypes yet? 

[Zerobricks]

As I said before, i really recommend you build a physical version first before wasting time on digital failure... And yes, as Horick said this "chassis" will simply slide apart, pulling the axles out of bevel gears and you will loose all the drive. I recommend 19x3 frames for starters.

[2GodBDGlory]

Yeah, you'll definitely want to add some longitudinal beams to the rear part of the chassis to keep the axles from sliding apart. It is looking pretty cool, though! The double tires look great, though I'm unsure how practical that would be in the real world with the angle the axles are on. You don't need justification like that for Lego, though!  

[AdamFMX]

Yeah, I know about rear. For now it is just copypasted and doubled front axle stripped of steering mechanism and reworked halfaxles to fit double tires. It is loong way from finished product. But today I have time, so I am starting to work on real world prototype

Edited September 17, 2024 by AdamFMX

[AdamFMX]

So here is first tech demonstrator. It is kinda different than in LDD because I don't want to disassemble models currently on display (they have what I need) and plus parts which will be ordered. For now no tires and no steering-latter is for purpose-tech demo won't have steering. In following days I will connect wheelhubs and add one old PF XL motor to test gears. Suspension travel looks good enough, it is sturdy enough and it doesn't force shock absorbers to bend. Only problem or issue currently present is higher rolling resistance than anticipated but still it is not too bad-I have seen worse. I just hope that it will work.

P.S. 2GodBDGlory: Civilian Tatra 815, mainly semi tractors and dumpers, had double tires while still they had swung halfaxles with some angle, though when loaded halfaxles straightened up. Same will be my case.

And if Tatra chassis will fail or it will be good only for showcase, I will redo it to normal live axles.

[bruh]

One thing I’m noticing, not sure if it is easily fixable, but the front axles are not in line with each other! One is a full stud farther forward than the other one. Dunno if you can fix that, but to me it seems like you eill have trouble building a symmetrical body.

[NV Lego technic]

Tatas have offset wheels it's one of their signature features

[AdamFMX]

As NV said, it is signature feature of Tatra chassis. It is in reality about 7-8 cm.

P.S. why quote button doesnt work?

Edited September 19, 2024 by AdamFMX

[bruh]

OK. I didn't know that they were actually offset. That's really interesting! 

Also, 

18 hours ago, AdamFMX said:

P.S. why quote button doesnt work?

it works for me. Also, are you hitting the "quote" button or the "+" multiquote symbol?

[AdamFMX]

Oh I tapped on +...