"Big Grey" 8x8 Trial Truck

[2GodBDGlory]

This model is my latest attempt at a performance-oriented Trial Truck, built in anticipation of another Ontario Truck-Trial get-together this summer. After my 4x4 Lada Niva was soundly beaten by @Teo LEGO Technic's very well-rounded Praga 6x6 last summer (And after I bought four more 107mm tires from @lmdesigner42), I figured I'd go for a full-bore 8x8! It ended up being huge, heavy, and fairly overengineered, but it seems to have been "good" overengineering, because it actually proved to be fairly trouble-free!

The functionality includes:

• Eight-wheel drive, with four PF XL motors
• Eight-wheel steering, with two PF L motors
• Two independent two-speed transmissions, with two PF M motors
• Very complex and, I think, unique, unsprung interlinked pendular bogie suspension

The drive motors were driven off my custom 3D-printed 3S Lithium battery, through a mid-range RC control board, while all the other motors (And LEDs) were controlled via a MouldKing 6.0 battery pack.

So, for some more detail:

Aesthetics:

Nothing complicated here, to keep weight down and durability up. It is my first use of DBG on such a large model, and I really like how it worked out! It looks pretty tough in this colour, I'd say. There were LEDs for headlights and taillights.

Spoiler

Drive:

I knew such a large model would need lots of power, so we've got four PF XL motors on a ~12V, high output control system! However, with great power can come great part attrition (As last year's Lada proved), so I did a few things to try to prevent that this time. First, I split the drivetrain into front and rear sections, with two motors on a bogie for the front two axles, and the other two on a rear bogie. Next, I made sure that my gearbox between them increased speed in both gears, to minimize part-destroying torque. The gear rations here were 36:12 (3:1) and 28:20 (7:5). This was followed by two parallel 16:16 gearings to get drive where I needed it, followed by a 12:28 bevel gearing, and some HD CV joints to get drive down to planetary hubs. This gearing seemed to work well, with a significant enough difference in speed between the two gears. Plus, I didn't break a single gear, which was really encouraging!

Spoiler

Gearbox: 

Given my split drivetrain, two gearboxes were required, one for the rear, and one for the front. Both were shifted by PF M motors through small linear actuators. This moved the whole assembly the XL motors were mounted on to slide it a stud between the two gears (36:12 and 28:20, as mentioned above). Shifting usually required wiggling the drive motors forward and backward, but that was acceptable, and having the extra speed available was really nice.

Spoiler

Steering:

Again, one steering motor wouldn't cut it here, so I used one PF L-motor for each block of axles. These were mounted transversely, and then used some bevel gears and universal/CV shafts to get drive to some medium linear actuators that were used for the actual steering. The front and rear steering was on different channels, so there were options for front-wheels steering, crab steering, and opposite-steering. The added maneuverability really helped with the long wheelbase, and being able to wiggle every wheel around a bit was really good when fighting for traction.

Spoiler

Suspension:

This is the one I'm afraid of trying to explain... So, let's think of it this way. The main modules with the XL motors on them were first set up like a typical interlinked pendular setup, so that tilting one to the right would tilt the other to the left, keeping the body at the midpoint between them. Additionally, these modules were linked end to end, so that if the one tipped forwards clockwise, the other would tip backwards counterclockwise, to keep the middle two axles always approximately next to each other in height. This way it could bend all four wheels to keep as many as possible in contact with the ground when going up a hill or over a log.

Beyond this, we had a separate set of interlinked pendular axles mounted onto those XL motor modules, with the front and rear axles in each module linked so that tilting one would tilt the other the opposite way.

This was very complicated, with lots of linkages and craziness going on, and there was definitely a lot of slack in it by the time everything was put together. Because of this, the body would always tilt to one side, which was annoying, but didn't seem to cause problems. I'm guessing a simpler system would offer comparable performance, without that level of slack, but this system did provide very good floatation!

Spoiler

More pictures at: https://bricksafe.com/pages/2GodBDGlory/8x8

Anyways, I was pleasantly surprised with the performance! I see why all the big European truck trial meets are full of 8x8s, though they are pretty repetitive to build! We'll see if I try improving on it in the future, but honestly, there's probably not much I can see a way to improve, other than maybe simplifying the suspension

[burak]

The body looks a bit generic but the internals are pretty clever. It would be interesting to see or hear how it performs in the upcoming competition. And I like the color very much, I wish there was more pieces available in DBG

[gyenesvi]

Good to see you going to the dark side :D DBG is a very nice color for trucks I think.

The linkage based suspension is really interesting for an 8x8 due to its superior flex capabilities. I have also wondered myself how it would be possible to implement such a one for wheels more than 4 without restricting the freedom of their flex movement too much. I think even for a 6x6 it is not trivial, and I like your approach of splitting it to front and rear sections and then typing the wheels in the individual sections further (even though I don't completely comprehend the linkage and what degrees of freedom it allows). I like the individual axle constructions as well, seem simple but robust :)

5 hours ago, burak said:

I wish there was more pieces available in DBG

I wonder what you are missing because I think DBG is a color with one of the highest part availability due to some recent sets like Zetros, Peugeot 9x8 and Jesko, even the Liebherr crane helped a bit.

[burak]

54 minutes ago, gyenesvi said:

I wonder what you are missing because I think DBG is a color with one of the highest part availability due to some recent sets like Zetros, Peugeot 9x8 and Jesko, even the Liebherr crane helped a bit.

You're right, the part variety has indeed gotten better in recent years. But I'm missing a few more types of mudguard panels in DBG, there's only the ones from the Peugeot. Granted mudguards are very specialized parts, but they make color swapping a certain set or MOC very difficult without compromising on the looks.

[Fluwoeb]

This is really neat @2GodBDGlory!
The Pendulum suspension has always intrigued me, and you did it very well for such a large model! I'd be interested to see how it performs at the truck trial meet!

I assume you have an ESC on board? But how did you translate the 3S lipo to a PF connector?

[Paul B Technic]

Wow, I am a big fan of this, looks great.

[2GodBDGlory]

12 hours ago, burak said:

The body looks a bit generic but the internals are pretty clever. It would be interesting to see or hear how it performs in the upcoming competition. And I like the color very much, I wish there was more pieces available in DBG

Thanks! I guess I never mentioned it, but the "competition" had actually taken place before I posted this. In the end, the only people who showed up were @lmdesigner42 and I, so it was more of just a hangout/test drive than an actual competition, but it was lots of fun, and I was impressed with the performance! I do love the DBG on this truck

6 hours ago, gyenesvi said:

Good to see you going to the dark side :D DBG is a very nice color for trucks I think.

The linkage based suspension is really interesting for an 8x8 due to its superior flex capabilities. I have also wondered myself how it would be possible to implement such a one for wheels more than 4 without restricting the freedom of their flex movement too much. I think even for a 6x6 it is not trivial, and I like your approach of splitting it to front and rear sections and then typing the wheels in the individual sections further (even though I don't completely comprehend the linkage and what degrees of freedom it allows). I like the individual axle constructions as well, seem simple but robust :)

I wonder what you are missing because I think DBG is a color with one of the highest part availability due to some recent sets like Zetros, Peugeot 9x8 and Jesko, even the Liebherr crane helped a bit.

Hehe! This stretched my DBG collection pretty far as it was, so I doubt you'll see it too often in the future, but I did really like the look.

I really do think this suspension performed well, and splitting front and rear seemed to work nicely. If you take a look at this old model here: https://www.sheepo.es/2011/04/truck-trial-lizard-8x8.html, you'll see what I think is probably a fairly ideal design for an 8x8 suspension. Mine was very similar, but somewhat more complicated, in that the entire front assembly could tilt side-to-side while the entire rear assembly tilted the other way, but I think that extra complication was probably unnecessary.

3 hours ago, Fluwoeb said:

This is really neat @2GodBDGlory!
The Pendulum suspension has always intrigued me, and you did it very well for such a large model! I'd be interested to see how it performs at the truck trial meet!

I assume you have an ESC on board? But how did you translate the 3S lipo to a PF connector?

The suspension was sure complicated to figure out! As mentioned above, the meet had already happened when I posted the topic (though I didn't mention it for whatever reason), but I think performance was above expectations! It didn't really end up being a competition, but it was fun to get together.

So, this RC system is a bit different than the hobby RC things other people on here are doing. It started with this mid-range, ~$80 RC car my brother got, which had a brushed motor capable of about 50 km/h. Anyways, I found that I could buy replacement parts for it cheaply, so I bought a complete electronic system from it, and used it in Lego models for a while. I've now phased out most of those components, so all I'm left with is the original car's all-in-one circuit board and controller. Because the original car was only using a brushed motor, it's pretty trivial to run PF motors off of it. The big downside is that the steering system is some weird 5-wire system, because the "servo" module in the original car just had a DC motor and a rotation sensor in one housing to act as a servo, so it's impossible to use a GeekServo with it (Well, probably not strictly impossible, but certainly inconvenient!) Plus, the original car only ran 9.6V, and after I applied 12V, the steering circuit fried. Luckily the drive still works fine!

3 hours ago, Paul B Technic said:

Wow, I am a big fan of this, looks great.

Thanks!

Edited July 30, 2024 by 2GodBDGlory