[WIP] Lada Niva Trial Truck

[Bluehose]

I'm interrested on the traction subject. To my mind it only depend of balance, suspension work and tyres, and I wonder how good are these these tyres.

[2GodBDGlory]

2 hours ago, Bluehose said:

I'm interrested on the traction subject. To my mind it only depend of balance, suspension work and tyres, and I wonder how good are these these tyres.

Yeah, I agree that it's an odd issue.

Granted, I was testing on a slope of loose sand, which is a pretty worst-case scenario.

The center of gravity is worryingly high, which could have some impact on it, but the suspension was easily keeping all the wheels on the ground. These tires aren't the stickiest out there, but they are nice and big, with helpful lugs on them.

One thing I've done in the past on similar models is to stuff the tires with marbles, which adds lots of weight right where it's needed for maximum traction. I think that's not really purist enough to use for this race, though!

[2GodBDGlory]

Well, I've been grinding away at this for a bit now, and this is how it went:

I found by replacing the 11L axle in the gearbox with a new one, it started working again, and is still working fine. They might become kind of disposable in this application, but they last for a while at least!

Then, I spent a while creating more solid reinforcement for the 20:12 upgearing in the axles, but it still skipped, even when sandwiched directly between two half-beams! After that, I gave up on having that gearing, and eliminated it altogether, moving the ball joint back down to where it was before on the axle.

After eliminating that weak point, though, gears began skipping in the O-frames in the axles, so I swapped those gears for knob wheels, restoring the higher speed I lost when I eliminated that 20:12 gearing.

However, after making all these changes, I began getting issues like this on what seemed like routine, well-supported axle connections:

 

I think that's a sign that I have reached the limits of the Lego system... Anyways, at this point, the only choices open to me are to reduce the gear reduction earlier in the drivetrain, which isn't really possible, run the motors at lower voltage, or just drive conservatively (especially in low gear). I think that last option should be fine; I'll just need to be careful!

[Zerobricks]

My tips:

Since I see you need A LOT of torque, I would recommens combining planetary and portal hubs, or just use the planetary ones, they are much more compact, stronger and there are no axles to bend on the way to the wheels.

Secondly use a 7x11 frame with 28 gears, those are currently the strongest perependicular drivelines available (with exception of maybe yellow diff).

Third, split the driveline to left and right sides, so that you split the torque more evenly between 2 seperate systems.

FYI, just recently I made a project with 16 BW drive motors which produces way over 1500 Ncm of torque, so you can do A LOT if you know how to spread the load over multiple components.

Edited June 28, 2023 by Zerobricks

[2GodBDGlory]

1 hour ago, Zerobricks said:

My tips:

Since I see you need A LOT of torque, I would recommens combining planetary and portal hubs, or just use the planetary ones, they are much more compact, stronger and there are no axles to bend on the way to the wheels.

Secondly use a 7x11 frame with 28 gears, those are currently the strongest perependicular drivelines available (with exception of maybe yellow diff).

Third, split the driveline to left and right sides, so that you split the torque more evenly between 2 seperate systems.

FYI, just recently I made a project with 16 BW drive motors which produces way over 1500 Ncm of torque, so you can do A LOT if you know how to spread the load over multiple components.

Thanks for the advice! How would you recommend combining planetary and portal hubs? I've thought it would be a neat thing to do, but the lack of axle connections on the official hubs seems like it would have to make the hub far too wide for reasonable steering pivots. Unless you forego the official planetary hubs and use turntables or Power Miners wheels, but then you'd lose some strength.

Would you say that 28T gears in that bracing are more secure than even knob wheels? I find that somewhat hard to believe, though bevel gears are definitely smoother and preferable in that regard.

Strangely, though, I've finally reached a point in the project where everything is reinforced well enough that no gears are skipping, and axles and axle connectors have become the point of least resistance! Really, the correct way to fix this problem would be to move my reduction further down the line, probably swapping the 1:3 ratio I have in the portal hubs back to the 1:5 I started with, and then putting a good amount of reduction in the O-frame drive, keeping there from being high torque anywhere else in the model. The trouble here is that I really want to keep the gearbox I have in here, and it only just barely fits, so there isn't any option for me to decrease torque early on! I think I'm happy with where the model is now, because even though its ability to absorb torque is compromised, it's a compromise that allowed me to keep other features I wanted, such as its high power output and transmission, and large ground clearance.

[Zerobricks]

6 hours ago, 2GodBDGlory said:

Thanks for the advice! How would you recommend combining planetary and portal hubs? I've thought it would be a neat thing to do, but the lack of axle connections on the official hubs seems like it would have to make the hub far too wide for reasonable steering pivots. Unless you forego the official planetary hubs and use turntables or Power Miners wheels, but then you'd lose some strength.

 

It just so happens that the small female CV axle fits directly into the planetary hub, though with a very sligh offset :)

[gyenesvi]

I told you you're going to twist axles with that much torque :)

It's a tough cookie though, the overall model looks really big and heavy. I'd probably also try as you say, lot of down-gearing in the axles (12:28 at the (locked) diff and planetary hubs), and up-geared in the gearbox itself. I don't think more down-gearing is needed than that, it's going to be super slow with PF XL motors otherwise (Zero is thinking in Buwizz motors :) ), even with the gearing I propose it would be like 2x slower than the Zetros in low gear..

[2GodBDGlory]

5 hours ago, Zerobricks said:

It just so happens that the small female CV axle fits directly into the planetary hub, though with a very sligh offset :)

That's true; I've used that trick before, but I guess I would assume that it wouldn't hold up to extreme levels of torque, the 2L axle might not be long enough for the most convenient bracing of the portal gears. It is an option, though, and clever reinforcement could probably make it work!

4 hours ago, gyenesvi said:

I told you you're going to twist axles with that much torque :)

It's a tough cookie though, the overall model looks really big and heavy. I'd probably also try as you say, lot of down-gearing in the axles (12:28 at the (locked) diff and planetary hubs), and up-geared in the gearbox itself. I don't think more down-gearing is needed than that, it's going to be super slow with PF XL motors otherwise (Zero is thinking in Buwizz motors :) ), even with the gearing I propose it would be like 2x slower than the Zetros in low gear..

That is good advice, but I just don't see any way I can add upgearing earlier on, because my gearbox has extremely tight spacing and is dependent on gearing that works over a five stud space, which leaves the only options as 24:40 and 28:36, and I'm already maxed out with 40:24 gearing in high gear, and I really don't have room left to change the gearing! I may look into 56:8 gearing using large turntables, but that sounds a bit desperate and I doubt it'll work. Really at this point, I'd either have to remove the gearbox, which I'm rather attached to, or do some complete redesign of the chassis that makes more room for the gearbox, though I can't imagine how I'd do that!

Really I'm only breaking parts in low gear, and there is a fair bit of warning before they break (motors running while the wheels aren't turning!), so I think as long as I avoid using low gear as much as possible, and drive carefully while in it, I should be fine.

[gyenesvi]

8 minutes ago, 2GodBDGlory said:

That is good advice, but I just don't see any way I can add upgearing earlier on, because my gearbox has extremely tight spacing and is dependent on gearing that works over a five stud space, which leaves the only options as 24:40 and 28:36, and I'm already maxed out with 40:24 gearing in high gear, and I really don't have room left to change the gearing!

I did not mean doing more upgearing by changing anything. I just meant keeping the 40:24 upgearing as you have now in high gear (and the 28:36 in low gear).

 

[2GodBDGlory]

5 minutes ago, gyenesvi said:

I did not mean doing more upgearing by changing anything. I just meant keeping the 40:24 upgearing as you have now in high gear (and the 28:36 in low gear).

 

Oh, I see! (Thought the low gear is actually 24:40, but I think that's irrelevant :) )

However, the thing is that all of my axle twisting is happening before gear reduction, so I'm not sure how adding more gear reduction would change anything. I suppose it would make it less likely for the model itself to get into a situation where it wants to stall, on the logic that by making it really easy for the model to crawl over anything, the path of least resistance would always be to do the crawling, rather than break parts.

The question then, since I'm building this for a race, kind of comes down to how intense the terrain we're going to be going over will be! My feeling is that it might not be as intense as I built this for, and there might not really be any heavy-duty crawling, so I'd kind of like to keep my top speed up, but final drive and portal axle gear swaps are pretty easy mods to do, so I can change it as necessary when I know more about the course.

[gyenesvi]

56 minutes ago, 2GodBDGlory said:

However, the thing is that all of my axle twisting is happening before gear reduction, so I'm not sure how adding more gear reduction would change anything. I suppose it would make it less likely for the model itself to get into a situation where it wants to stall, on the logic that by making it really easy for the model to crawl over anything, the path of least resistance would always be to do the crawling, rather than break parts.

Indeed, that could be also happen, depending on the circumstances, like the weight of the model and the friction of the wheels. It might even spin the wheels under itself instead of getting stuck, if it's light enough for the friction, but that might not apply to your model, it seems heavy.

Quote

The question then, since I'm building this for a race, kind of comes down to how intense the terrain we're going to be going over will be! My feeling is that it might not be as intense as I built this for, and there might not really be any heavy-duty crawling, so I'd kind of like to keep my top speed up, but final drive and portal axle gear swaps are pretty easy mods to do, so I can change it as necessary when I know more about the course.

That's essential to know for a good competition build, because it's pretty hard to build something of a universal offroader from Lego, much easier something purpose-built. For lighter terrain, you might not need all that ground clearance and down-gearing, or even the gearbox. Maybe faster speed and the brute force of the 4 XL motors is just enough, and you can slow down with a proportional controller if needed here and there. That's what happened last year in the Buwizz camp, faster builds with more motors clearly had some advantage on the less challenging terrain (though they had problems with precision steering their fast vehicles).

BTW, I remember I managed to twist an axle a bit even with a single XL motor when I built a medium heavy offroader with large wheels and closed differentials and portal axles.. those motors are hard to stall..

Edited June 28, 2023 by gyenesvi

[2GodBDGlory]

Well, it's been a long struggle, but I think I'm finally done with this trial truck!

(I love this picture! No fancy camera or editing, just awesome nature and sunset lighting! It's currently my desktop background)

In the end I saw reason and realized that a mechanically cool but unreliable vehicle with a gearbox wouldn't be as fun to actually drive as a lame, single-speed one would be, so I converted to single-speed. The funny thing is that the gearbox itself seemed to work fine, but the only possible gearing that would fit and reduce torque enough to be safe was the maxed-out 40:24 ratio, leaving me no lower alternatives for the other gear. I also converted to knob wheels in the axles, which are stronger than the bevel gears I had, and then tried swapping my portal axles from 12:36 back to the 8:40 I had originally had to gain torque, but then I just shredded the carbon axles I was using to connect the 40T gear to the wheels and snapped the 8T gear on the other side, so I decided that much torque was intolerable.

I think what I really learned here is that if you want a vehicle with high torque, you must have the two axles running on separate systems, so a given wheel can never take more than half of the total torque. In this model, that's not the case, because it was designed for gearbox compatibility, and as a result, my total torque is quite a bit lower than I'd like, since adding more will break parts when applied to only one or two wheels. The upside of this is that I now have a lot of speed, so as long as the race course isn't overly hard I should be in good shape, but it's not like I have no torque at all, so I think I should be alright.

Anyways, my final function list is:

• 4WD with four PF XL-motors with 40:24 gearing in the chassis, 1:1 knob wheel gearing in the axles, and 12:36 gearing in the portal axles
• 
• 4WS with two independent PF L-motors (one on each axle), with parallel gear systems to spread out torque, and a rack with two pinions
• 
• Dual live-axle suspension with ball joints and 9.5L hard shock absorbers
• LED headlights, taillights, and running lights
• Custom 3D-printed battery pack housing three Lithium 18650 cells, for a total nominal voltage of 11.1V (Just above 12V at full charge!)
• 
• Mouldking 6.0 battery pack to run the steering motors and LEDs, allowing for easy proportional control from joysticks on a physical remote

Here's some more pictures from that shoot!

Spoiler

As usual, I've got more pictures at my Bricksafe: https://bricksafe.com/pages/2GodBDGlory/lada-niva