Off-roader Chassis Comparison

[Erik Leppen]

So I wanted to build something off-road. So I built a cool off-road chassis. Of course, I could have stopped there, but I wanted to explore other options. So now I have two off-road chassis. But this raises a problem. Which one to use! Both have their own pros and cons, and they seem to weigh up quite well. Which makes it all the much harder to choose.

This is version 1, which I will call the low version.

This is version 2, which I will call the tall version.

Both versions are intended to be used with the Power Puller tyres (8466), and both have four-wheel drive and four-wheel steering.

Both versions have the same vertical suspension travel and the strength seems to be the same as well.

The pros of each version:

Steering:

the tall version has much smoother steering.

the tall version has a smaller turning radius

the tall version steering does not depend on the suspension compression

the low version has the turning point inside the wheel, giving a smaller displacement of the wheel. Steering the tall version looks kinda ridiculous.

Drive

the tall version's drive train has much less friction

the tall version's drive train has a 3:1 reduction near the wheel

Suspension

the low version is much more stable. The tall version has much less resistance against pushing it sideways and I'm afraid it will "sag" sideways when more weight is added (because the body will not be very light I'm afraid).

the tall version's suspension has a linkage that makes it heavier when it is compressed more

Structure

the low version doesn't bend parts. In the tall version the 16L links are bent when suspension is compressed on one side.

the tall version looks cooler.

the low version is much lower, and therefore, needs much less space, which means much more room is left for other mechanisms.

the low version's frame could be adjusted so other mechanisms can be incorporated in the same space. In the tall version, the space is mostly taken by the moving parts and the structure.

the tall version is fully studless, which is more "in style" (but I might change the low version)

Wheels

the low version can attach the wheels with the deep side inwards. On the tall version, when the wheels are mounted with the deep side inwards, the tyres rub against the Unimog portal axle parts.

So... which version would you rather continue with, if you were planning to build a rather heavy body? For your convenience I have added a poll, but I will mainly look at replies offering valuable insights :)

Edited December 16, 2015 by Erik Leppen

[Technic Jim]

I personally like the look of the tall version and it has floating axles. I love floating axles-they're so cool! Also, how do you start a poll, do you need a certain rank?

[Jay Psi]

If I was building something for off-road use then the drivetrain and steering would be pretty high up my list of priorities - not much point in having a great chassis that goes nowhere. On that basis I would prefer the tall version, even though the bending of the 16L links could be problematic depending on how much they bend. Again, to me the addition if extra features would only be a benefit if I was satisfied with the performance of the "barebones" chassis in the first place.

I (think I?) have some experience of this type of sagging from modding my 41999 (PP, 2 x XL) - in my case it wasn't a big deal in practise but the body of your MOC will be a lot heavier by the sounds of things. Do you have any idea of how heavy the body will be at this stage? I assume it is guaranteed to be hundreds of grams, but would it get close to/beyond 500g?

Edited December 16, 2015 by Jay Psi

[Kaanere]

Also, how do you start a poll, do you need a certain rank?

Yes, you need to be a knight (500 posts).

[Blakbird]

The tall version has diagonal braces and is therefore better.

[Zerobricks]

Will it be motorized? lots of things depends on that... Also why did you built a studded chassis with old suspesnion parts, when you could have built a much sturdier, and compact studless one...

[Cumulonimbus]

The tall version is more impressive but I'm a bit concerned by using the steering links as a stressed element, especially in compression. These aren't the most rigid parts. It all depends on the loads (weight of the body, driving speed and roughness of the terrain) I guess.

For a big, possibly RC/PF vehicle, I would vote for the low version.

Edited December 16, 2015 by Cumulonimbus

[Rishab N]

The tall one looks impressive, but I prefer the neat and compact lower one

[JJ2]

I prefer the tall version because live axles are better under high stress.

if you are going to motorize it you will need to.

1st you need to change the -negative caster on the front axle to positive to improve bump steer and make it easier for the motor.

2nd the top links that you say bend when compressed can be fixed by connecting them with THIS piece to the axle.

Edited December 16, 2015 by JJ2

[Imanol BB]

I think the tall chasis has more advantages, because, it has the portal hubs, so there is less stress on more of the drivetrain pieces, it also has a larger and better suspension, but the low chassis is more robust and compact, but it may get more damage on the drivetrain, however, it all depends of the body, if it is too tall or heavy, the tall suspension will have some problems with stability, in that case the low chassis is better, but im thinking, what if you take the low chassis structure (that could also be studless) and put portal hubs and planetary rims, this would solve the problem of the stress on the parts, but you would still have the robust and compact chassis and enough stability for a big-heavy body, however, both chassis look very nice.

[nerdsforprez]

I think that a lot of it depends on what type of body you are adding. If you are going for looks, and it will be a full body, then likely it will have some weight, and therefore, the shorter version may work better. Nothing is more annoying than getting the power to weight ratio correct, steering correct, etc.... just to have the darn thing tip over all the time. Crawlers have to be able to maintain themselves at fairly extreme angles.

On the other hand, if you can get away with a minimalistic body, then I, like others prefer the taller version. But, only if it does not affect the center of gravity too much. Based on how high it is... I am afraid that the crawler will be tipping over too much...

[gmshades]

You could add a swaybar or 2 to the taller version to help from side to side sway.

[lcvisser]

I like the low version better. It has a clean an sturdy look that seems to be very suitable for a wide range of vehicles. The tall version looks like a chassis for one of those monster trucks. And unless you intend to build a monster truck, it would look out-of-place for most off-road vehicles. Also the "ridiculous steering" (your words ) would negatively affect the overall aesthetics of the vehicle (unless, I guess, it is going to be a monster truck). I'm also worried about the black links needing to handle the impact forces. I would be very worried about buckling or disconnecting form the ball joints.

[allanp]

It depends what you want to build. The "low" version is still very tall when you put the wheels on. The ridiculously tall version could only really be used for a monster truck for it to look right.

[Kristof]

As mentioned, with HIGH one you end up with crawler/monster truck thing, no matter what magic you do with the chasis. And personally I think some realistic looking off road jeep style car is more interesting than another crawler.

Also I think that if you place all the motors (multiple XL?, servo) and batteries on top of the high chasis, your stability is gone. That's why people mostly mount their motors directly to the live axles to bring the center of the mass down as much as possible.

All in all, I'd choose something lower, not necesarily the chasis you made though. Perhaps you could try incorporating live axles but keeping the height decent, like in some real off road trucks.

[2LegoOrNot2Lego...]

Also prefer the "second" one, sheer for the looks of it...

[Erik Leppen]

It looks like most people assumed a motorized version, akin to 9398. But I probably won't be doing that. There are many great crawlers already on the net, there seems little point in adding another one. I want to do something similar to 8070, where the driving is manual and auxiliary functions are motorized.

Anyhow, thanks for responding all, and also for voting! The votes seem to be pretty even! I decided to continue with a heavily modified version of the the tall version, with many changes for the better.

I changed the linkage for the suspension. The 9L links were not great (thanks Cumulonimbus for pointing this out), and the sagging problem was caused by the fact that the mounting points on the axle were only 6 studs apart and were very low. So I put the mounting points higher, and 10 studs apart, and there's no sagging now.

. I now used the new 1x5 suspension arms combined with the 2 x 4.8 beams with ball. The new mechanism also removed the need for the weird anti-sway bars, so these are removed as well. This automatically solved the bending-parts problem. I made the mounting points much higher on the axles, reducing the sway problem. Also, the mounting points were only 6 studs apart, I made that 10 studs, reducing the say problem further. Now, with the body on, it seems to work fine on flat terrain and won't sag when pushed sideways.

I also made the whole chassis 2 studs longer, so that I could create a space in the center that fits the battery box.

The tall version has diagonal braces and is therefore better.

You'd be surprised by the strength of the studded beam of the other version.

The tall version is more impressive but I'm a bit concerned by using the steering links as a stressed element, especially in compression.

Good point, I now found another solution. Will post picture later.

[Technyk32231]

The tall version has diagonal braces and is therefore better.

However, if those diagonal braces bend then they aren't doing much.

[Erik Leppen]

However, if those diagonal braces bend then they aren't doing much.

They are in tension (pull), not in compression (push). :)

[Lipko]

If it's a manual model, than I would go with the lower one. I made once manual model that was almost a crawler (http://www.brickshelf.com/cgi-bin/gallery.cgi?f=487752), but you just can't play with a pushing toy on rough terrain. The wheels can only climb over obstacles if they are driven. The only manual model I can imagine that works over terrain, is a trophy truck with strong negative chamber. Or maybe you just want a display model.

Edited December 20, 2015 by Lipko

[Andy D]

According to your assessment, the low version has more pros and fewer cons than the tall version. Therefore, low version gets my vote. Also the pros of stability and steering also swayed my vote.

Merry Christmas,

Andy D

[TheNextLegoDesinger]

I prefer the tall version because live axles are better under high stress.

if you are going to motorize it you will need to.

1st you need to change the -negative caster on the front axle to positive to improve bump steer and make it easier for the motor.

2nd the top links that you say bend when compressed can be fixed by connecting them with THIS piece to the axle.

you don't have to use a positive caster angle on crawler, yes it makes the bump steer better but it makes it harder for the motor (making a crawler with 4 wheel steering and positive caster at the moment). steering is much worse than with my negative caster crawlers wich had also 4wheel steering and 4 wheel drive