[WIP] Realistic tatra 8x8

[Zerobricks]

Inspired by the release of the planetary hubs and the diff lock idea from Zetors I decided to create a proper, realistic Tatra 8x8 with the following goals:

• Use of planetary hubs - Keeping it realistic, so no portal ones
• No load bearing axles - Most other models used the same drive axle to also hold the half-axles in place which increased friction in the driveline
• Realistic steering setup - Using a smillar mechanism the real trucks use
• Differential locks on all wheels - Each axle has it's own diff lock + a central one

Here's what I came up with so far...

The concept uses the blue bevel gears to transfer the power to the half-axles without spinning the pivot axle. This also allows for wheels to turn at different speeds when cornering.

Once the power is transfered to the half-axles an additional gearing is used before the power is delivered to the wheel. Total gearing on half-axles alone is 1:9.

Differential locks work by locking one of the differential's output to the main drive axle. As mentioned before all 4 axles have lockable differentials along with the central differential.

 

Steering uses a couple of 9L links turned by the turntable acruated by an 8 tooth gear. This setup provides the front axles with slightly different steering angles.

The model will probably powered with 4 of the BuWizz motors. Total gear ratio is 1:21 which should give the model around 900-1000 Ncm torque.

I think the concept looks very promising so far and I will keep on building it virtually until I'm confident enough to order parts.

[keymaker]

Wow, it will be massive and heavy. Could you show some close ups of the mechanisms around diffs?

[Jurss]

I'm really afraid about that blue and tan gear connection. But this is not Your first build.

[Zerobricks]

9 hours ago, keymaker said:

Wow, it will be massive and heavy. Could you show some close ups of the mechanisms around diffs?

Sure, here's the gearing:

32 minutes ago, Jurss said:

I'm really afraid about that blue and tan gear connection. But this is not Your first build.

I tested it and when holding the wheel it will make the rim spin inside the wheel, haven't managed to make it slip for now. If it's going to be an issue there are thin bricks I can slide under the bevel gear to keep it from bending.

[Mechbuilds]

But a real tatra has offset on the axles.. But massive bonus points for no load bearing axles.

[Zerobricks]

2 minutes ago, Mechbuilds said:

But a real tatra has offset on the axles.. But massive bonus points for no load bearing axles.

Adding offset is easy, but the real ones have such small offset, it's negliable. Having no offset also makes the setup system more symmetrical.

[Mechbuilds]

i wonder how half a stud of offset would look like 

[1gor]

This is good concept, but it tooks also lots of space.

Looking forward 

[dpi2000]

Wa, be very expect for Tatra' differential locks... ；）

Edited October 5, 2021 by dpi2000

[MajklSpajkl]

This is fantastic!  I am looking forward to see this come to life!

My observation would be about schock absorbers. Do you have any space to add more? According to my experience first two axles need to bare with a large and heavy cabin - I used 3 pairs of hard springs on 1st and two pairs of hard springs on 2nd axle on my yellow Tatra as there was no way to get only one pair of springs to hold the heavy cabin. Of course it depends on what kind of body work you are going for.

Best regards.

[pleegwat]

7 hours ago, 1gor said:

This is good concept, but it tooks also lots of space.

I wonder if you could put the drive axle beside the differential instead of above it, saving vertical room.

[MajklSpajkl]

3 hours ago, pleegwat said:

I wonder if you could put the drive axle beside the differential instead of above it, saving vertical room.

I think getting the driving axle so high is actually a good thing. Not so easy to put the motors low in the chassis among all the suspension and steering mechanisms, so having the driving axle so high by default makes installing motors much easier. Besides, it is not that high and it's not like you need the space up there - it is an 8x8 trial truck, not a dump truck...

[Void_S]

Building the rear Tatra, the motors should be placed above the main drive shaft. Maybe on the sides of authentic model of V- shaped engine? 

[jorgeopesi]

I love tatras but I preffer them in smaller scale, but good luck with this big one.

[Zerobricks]

On 10/5/2021 at 2:44 PM, MajklSpajkl said:

This is fantastic!  I am looking forward to see this come to life!

My observation would be about schock absorbers. Do you have any space to add more? According to my experience first two axles need to bare with a large and heavy cabin - I used 3 pairs of hard springs on 1st and two pairs of hard springs on 2nd axle on my yellow Tatra as there was no way to get only one pair of springs to hold the heavy cabin. Of course it depends on what kind of body work you are going for.

Best regards.

Thanj you, Majkl. Regarding shock absorbers, I can easily fit more in parallel if needed, up to 3.

21 hours ago, pleegwat said:

I wonder if you could put the drive axle beside the differential instead of above it, saving vertical room.

Unfortunetaly the shock absorbers and steering mechanism get in the way. Besides having all the drive gears and central diff aligned simplifies the locking mechanism to a single axle.

[Legotekkrick]

Have u tried this concept of steering in a model? Looks like this could have a lot of play

[Zerobricks]

Unfortunately I don't have any time or motivation currently for realizing this model, I hope I find some soon though...

[HorcikDesigns]

Nice one. I have no idea how I missed this topic. Would it be possible to take a closer look to front wheel hub attachment? I am currently building something with very similar initial conditions, so I am looking for little bit of inspiration. :)

[Zerobricks]

1 hour ago, HorcikDesigns said:

Nice one. I have no idea how I missed this topic. Would it be possible to take a closer look to front wheel hub attachment? I am currently building something with very similar initial conditions, so I am looking for little bit of inspiration. :)

Here you go:

Each hub is attached with the 6L suspension arm which is sandwiched between 3 dog bones. This way there's nothing than slide apart and the half-axles can withstand a very high torque.

[HorcikDesigns]

@Zerobricks Thank you so much! 

[nervousman]

Looks like very interesting machine...

What kind of engine and how many will power this monster? 

Will it be something like "only 12 buwizz motors" again? :P

 

EDIT - i just realized, the posts are from  dec 2021 , not 22, so idea probably died?

Edited January 17, 2023 by nervousman

[Zerobricks]

Original idea was to use 4 BuWizz motors. But currently this model is on a hold.