Building an 8x8 - Suspension and Drivetrain Options

[Tommy R]

Hey y'all,

I'm about to venture on my next scale build and this time it'll be an 8x8 inspired by European Trials Trucks. Before I start cutting metal, I want to determine what kind of suspension I want to run....and there are several options! I'd like to ask for thoughts from those of you who have experience building multi-axle offroad rigs. What I'm mainly concerned about is the suspension you chose to use, as well as the axles. What did you use for your build and why? Any regrets or suggestions?

FYI, my chassis will be 3/4" steel square tube that I will split into C channel so the overall chassis can be any width I choose.


AXLE OPTIONS
The way I see it, there are 3 axles to seriously consider: Axial, TLT, and Tamiya Semi axles. My plan is to use 4 TLT axles (2 steering, 2 fixed) due to their narrower width and the fact that I already have them! The width should look pretty scale under a Tamiya Globeliner or maybe a Bruder body. I've seen some nice Axial-based 8x8 and 6x6 rigs, but most utilize a wide homebuilt cab and I'd prefer not to do that. Are there other reasons I should consider a different axle other than the TLTs?


SUSPENSION OPTIONS
Like I said, there are several suspension options. It seems about half the builds I see use coilovers and half use leafs. I'm partial to leafs for such a truck because I think it's a bit more realistic, but I'm open to suggestions and will consider all possibilities. Here's a few of the ones I'm considering. If you have others, please post up!

1. Walking Beam - A coilover or leaf setup that incorporates some rather unique linkage and a central pivot between the axles which are both mounted to the same beam. A picture is worth a thousand words, right?


2. Bogie(?) - Best I can tell, a "Bogie" suspension is comparable to an inverted leaf spring version of a walking beam setup. It uses control arms, leafs, and a separate control arms for the axles. Best I can tell, this is how Tamiya sells their Semi kits with tandem rear axles. In the pic below I would attach the spring ends to the axle to act as an upper link.
[/URL]

3. Leaf Spring - Just like you would imagine. Each axle would have it's own hanger and shackle. Just imagine this done 4 times. ;)
[/URL]

4. Coilovers - A typical 4 link triangulated system with coilovers supporting the weight. I'm not so sure these are very realistic, but should yield a ton of suspension travel and would be pretty easy. I don't really think I need to provide pics of this setup, do I?


So there you have it. I realize there are pretty much infinite numbers of multi-axle suspensions, but these are the ones I'm most seriously considering. I'm interested in hearing everyone's thoughts. What suspension did you choose and why? What aspects of it did you like or dislike? Any suggestions for a builder who hasn't built a multi-axle rig before?

Thanks,
Tommy

[Tommy R]

Post holiday weekend bumpity bump!

[engineerjoe]

I've never built a 8x8 or 6x6 but I am familiar with the different types of suspension. (I'm at work right now so I couldn't see the pics either)

For racing or high speeds a bogie or 4-link system is going to work best. The nice thing about the 4-link on this type of truck is you can move the links around or even backwards (lowers forwards, uppers backwards) to control axlesteer with the short links.

For crawling, a walking beam may be the best setup. It won't allow the heavy, tall truck body to roll on off camber sections because there is no jounce. Plus you could save weight because you'd only need half the shocks.

maybe some sort of hybrid suspension would work too, like a walking beam with a shock between the two ends of the beam for jounce travel.

So were you planning on having the front two axles be the steering ones? or the front and the rear axle?

[Tommy R]

My rig will be primarily a low speed crawler. I want it to have realistic suspension travel. I could just link it with coilovers and make it act like a centipede, but that's not what I'm after. And I plan on having both front axles steer and the rear axles will be locked out straight.

I'm not sure how a walking beam axle setup would help reduce the chances of a rollover due to less jounce, though. Since each beam is independently suspended, it should still be able to roll and move like a conventional setup, right? Maybe I'm missing something or perhaps I have an incorrect understanding of a walking beam suspension?

I'm currently leaning toward a bogie setup where two axles will share a common pair of leaf springs. I think it's a variation of what the Tamiya Semi RC trucks use, but I need to check out a close-up pic to verify it is what I think it is.

[2500hdon37s]

id go walking beam, and use some blackwell axles hooked to an axial tranny with a holmes hobbies hand wound motor for the tourqe to spin the extra 2 tires

[Difuser]

Tommy look for the build edge540 did on Warcrc. He didn't do a walking beam it was all independent 4 links. He paid he'll getting it all driven and still is having issues with the second axle and blowing cvd's due to bind and turning radius

[BigSki]

I gave a lot of thought to the type of rear suspension when I started my 6x6 last year. I immediately eliminated the walking beam design because it is for more of a on road rig, it doesn't allow very much 'cross up' between the 2 rear axles. I looked at a bunch of old 2 1/2T. military trucks and really liked their suspension, it's similar to the second pic that you have posted. The leaf springs just floated in a pocket on the axle housing, allowing some decent suspension flex, but it was more complicated than what I wanted to build.

I stopped by a construction site (after hours) and I started to check out how the huge Volvo 6x6 dump truck suspensions worked, as they have a bunch of rear wheel travel. It was very similar to a 3 link suspension, so I decided to just use the tried and true 4 link on my 6x6's rear suspension. I'm extremely happy with the amount of flex I get and one axles movement doesn't have much effect on how the other axle moves. I feel like it's the simplest and most rugged suspension for a 6x6 scaler.

Go over to scale4x4 and do a search, there have been some outstanding 6x6 and 8x8 builds going on over there with a bunch of ideas on suspension design. I saw one that used Tamiya TA-01 sub-assemblies for independent suspension like the Tatra uses.

[Tommy R]

Originally Posted by 2500hdon37s

id go walking beam, and use some blackwell axles hooked to an axial tranny with a holmes hobbies hand wound motor for the tourqe to spin the extra 2 tires

You lost me at Blackwell axles. I'm doing this on somewhat of a budget so nothing too radical for me, although I admit Blackwells would be cool! I've got nearly all my axle stuff already (TLTs), an Axial trans, and will likely just use a 45T or 55T motor for lots of low end grunt. I want it to be realistic and that means no real wheel speed....just like a trials truck.

Originally Posted by Difuser

Tommy look for the build edge540 did on Warcrc. He didn't do a walking beam it was all independent 4 links. He paid he'll getting it all driven and still is having issues with the second axle and blowing cvd's due to bind and turning radius

I've seen his build and while it's impressive, it's not what I want. That thing articulates like mad, but I'm after a more realistic performance and that means only marginal suspension travel. So I'm pretty sure I want to run leafs, but I wonder why some people choose the suspension they run. Maybe it was easier to build/fabricate? Maybe they already had the parts? Maybe it suited their style of build better?

[Tommy R]

Originally Posted by BigSki

I gave a lot of thought to the type of rear suspension when I started my 6x6 last year. I immediately eliminated the walking beam design because it is for more of a on road rig, it doesn't allow very much 'cross up' between the 2 rear axles. I looked at a bunch of old 2 1/2T. military trucks and really liked their suspension, it's similar to the second pic that you have posted. The leaf springs just floated in a pocket on the axle housing, allowing some decent suspension flex, but it was more complicated than what I wanted to build.

I stopped by a construction site (after hours) and I started to check out how the huge Volvo 6x6 dump truck suspensions worked, as they have a bunch of rear wheel travel. It was very similar to a 3 link suspension, so I decided to just use the tried and true 4 link on my 6x6's rear suspension. I'm extremely happy with the amount of flex I get and one axles movement doesn't have much effect on how the other axle moves. I feel like it's the simplest and most rugged suspension for a 6x6 scaler.

Go over to scale4x4 and do a search, there have been some outstanding 6x6 and 8x8 builds going on over there with a bunch of ideas on suspension design. I saw one that used Tamiya TA-01 sub-assemblies for independent suspension like the Tatra uses.

Thanks, man! Good stuff. I'd like to check out you build. I'll search for it, but if you have a link, please feel free to share it. I've definitely spent some time on scale4x4 and did indeed see some great builds, but didn't see a lot behind why some folks chose certain suspensions. I'll head back over there and do some more research, but ultimately I may end up posting these questions over there, as well.

[engineerjoe]

Originally Posted by Tommy R

I'm not sure how a walking beam axle setup would help reduce the chances of a rollover due to less jounce, though. Since each beam is independently suspended, it should still be able to roll and move like a conventional setup, right? Maybe I'm missing something or perhaps I have an incorrect understanding of a walking beam suspension?

I'm currently leaning toward a bogie setup where two axles will share a common pair of leaf springs. I think it's a variation of what the Tamiya Semi RC trucks use, but I need to check out a close-up pic to verify it is what I think it is.

Okay, I'm home and see the pics.
My idea of a walking beam is like the first pic minus the leafs and with a coilover on the end of each beam. The reason it wouldn't roll as easy is because when there is equal pressure on the two wheels on the same beam, the suspension doesn't flex.

The bogie setup you have a pic of would work well but it'd take a bunch of leaf spring tuning to get right.

[Tommy R]

I think I've decided what I want to do. I'm going to run a setup from the Tamiya Semi trucks. Like this:


However, I may change a few things in order to get it to perform more like a trials truck instead of an 18 wheeler on the street. I will likely make my own control arms and modify or change the leafs in order to get reasonable articulation out of it. Again, I don't want it to flex like mad! I want it to flex in a realistic, true-to-life manner....and from what I've seen, I think this setup may be just what I was looking for.