Home built independent suspension?

[lowenbrau]

This is a great thread. I'm preparing to build a new, more rugged chassis for my Kamparoo and am following right along.

What is the design intent in making more than a couple inches of bag travel? Trailers don't 'articulate', or actually they articulate in relation to the tow vehicle freely even with no suspension. The only suspension required is as much as the shocks will allow on a big bump (very little) and enough to allow the trailer to be leveled in camp.

I've helped a couple buddies build their airbag-ed Land Cruisers and I am of the opinion that you want to choose a bag that will normally operate at 60- 75% of its capacity. Choosing a bag that is too strong and then under-inflating makes for lots of body roll.

 

[Martyn]

This is a great thread. I'm preparing to build a new, more rugged chassis for my Kamparoo and am following right along.

What is the design intent in making more than a couple inches of bag travel? Trailers don't 'articulate', or actually they articulate in relation to the tow vehicle freely even with no suspension. The only suspension required is as much as the shocks will allow on a big bump (very little) and enough to allow the trailer to be leveled in camp.

I've helped a couple buddies build their airbag-ed Land Cruisers and I am of the opinion that you want to choose a bag that will normally operate at 60- 75% of its capacity. Choosing a bag that is too strong and then under-inflating makes for lots of body roll.

Don't you think body roll is also a function of bag height ?

 

[ntsqd]

I see body roll as being a function of roll stiffness and CG height.

Without knowing too much about them it seems to me that a large air spring will have a much faster rising rate than will a smaller air spring. Depending on the design and placement of the air spring this could be favorable if it counteracts a falling rate linkage design, but could be a damper tuning disaster when coupled with a rising rate linkage design.

 

[Corbet]

No expert here but have been pondering a way to do this as well. I plan to start a trailer project this year as money allows

What about two separate 4-links. Each to act on its independent side of the trailer. The first problem I see it how to keep the "axle" from just pivoting on the bottom of each sides spring/airbag.

Just thinking outside the box.....Now I'll leave it to the experts to discuss and tell me how this won't or "could" work

 

[ntsqd]

No expert here but have been pondering a way to do this as well. I plan to start a trailer project this year as money allows

What about two separate 4-links. Each to act on its independent side of the trailer. The first problem I see it how to keep the "axle" from just pivoting on the bottom of each sides spring/airbag.

Just thinking outside the box.....Now I'll leave it to the experts to discuss and tell me how this won't or "could" work

What I'm picturing as a "4 link" would work, but your last sentence in the second paragraph throws me. Can you make some sort of drawing of what you are thinking of?

On the surface I'd guess that while it could and would work, it sounds like unnecessary complexity. Trailers have different suspension needs than passenger vehicles. Since their "articulation" happens at the coupler (rather than in the suspension), and for most there is no power being applied, the simpler the design the better. I suppose braking forces could force a more sophisticated design, but mostly observation and some experience have shown me that this does not have a huge influence.
Perhaps in higher speed uses divorcing the braking reaction force from a simple trailing arm would prevent brake dive and partial suspension lock-out. Might be a fun project, but I'm not convinced that there is fruit there worth the effort.

 

[lowenbrau]

No expert here but have been pondering a way to do this as well. I plan to start a trailer project this year as money allows

What about two separate 4-links. Each to act on its independent side of the trailer. The first problem I see it how to keep the "axle" from just pivoting on the bottom of each sides spring/airbag.

Just thinking outside the box.....Now I'll leave it to the experts to discuss and tell me how this won't or "could" work

I've had serious thoughts about a solid axle four link on bags. It would allow for leveling and varying load which are the primary advantages of bags. I've hauled leaf sprung solid axles over all kinds of rough terrain and I'm not sure independent suspension adds a ton of value. (I'd love to follow one up to Racetrack Playa to see the it in action) That being said, independent doesn't seem to be any more work to build than a four link.

 

[lowenbrau]

Don't you think body roll is also a function of bag height ?

Yes, exactly. If you get a bag that is designed for 5000 lbs at 100 psi and you put 500 lbs on it at 10 PSI it ranges through its full travel with every undulation. That works ok as long as the travel is being controlled by a shock absorber but as soon as you introduce a side hill or corner it'll keel way over. I'd want to calculate exactly the amount of required suspension and then choose the appropriate bag. I think two inches of travel at the bag is probably plenty. I'd rather not have to use a sway bar.

 

[Corbet]

What I'm picturing as a "4 link" would work, but your last sentence in the second paragraph throws me. Can you make some sort of drawing of what you are thinking of?

How would one keep the independent 4-links from acting like an inverted teeter-totter on the single air bag. Where as a traditional 4-linked axle would have to bags/wheels to balance out. Did that make more sense?

I've had serious thoughts about a solid axle four link on bags. It would allow for leveling and varying load which are the primary advantages of bags.

In the end this is the direction I will probably end up going.

 

[#686 Sahara]

Here's my first attempt that I had a friend design and install. Worked well for a while.

[/IMG]

[/IMG]

Then on our last jeep trip from Lone Pine to Bridgeport with very little time on black top it let me down all the way down. I guess the placement of the bag to far away from the wheel put to much twist on the heim and caused it to snap. We were north of Lee Vining by about 20 min so we called AAA to flat tow into town and then the dreaded call to the wife to drive 9 hrs with my work truck and the jeep trailer and pick me up. After alot of loving promises she was on her way.

[/IMG]

[/IMG]

[/IMG]

So I bought a new Miller welder and plasma and started my first fab project. Started with a 3500# blank trailer axle that I orderd from my local Rv shop and then started ordering brackets and tabs and this is what I ended up with.

[/IMG]

[/IMG]

[/IMG]

[/IMG]

[/IMG]

 

[Borrego60]

I like the new design,but how does it perform?

 

[Marcie's Disco]

Four link, heims, sway bar, limiting straps, air bags, Bilsteins....:Wow1: That is quite a trick set up you've assembled. Thing of beauty. If the performance is half as good as it's appearance...it's a win!

 

[ntsqd]

What I'm picturing as a "4 link" would work, but your last sentence in the second paragraph throws me. Can you make some sort of drawing of what you are thinking of?

How would one keep the independent 4-links from acting like an inverted teeter-totter on the single air bag. Where as a traditional 4-linked axle would have to bags/wheels to balance out. Did that make more sense?

Not really, no. First, which direction are you picturing the 4 links being oriented? Across the width of the trailer or aligned with the length of the trailer? Second, we are talking about truly independent suspension and not what Sahara posted above as his solution to the SRE failure that he had?

I've had serious thoughts about a solid axle four link on bags. It would allow for leveling and varying load which are the primary advantages of bags.

In the end this is the direction I will probably end up going.

Like what Sahara posted? In his original design I only saw two issues, the now obvious too small of an SRE, and I agree with his deduction that the air springs were too far inboard. Moving the spring (of any type) laterally as close to the tire as possible reduces but doesn't eliminate the torsional forces in the arm (induced camber). Moving the spring longitudinally as close to the tire as is possible reduces the bending forces on the arm. If you can buy an air spring with 20% more travel than you need the trailer to have (remember that it does not need wheel travel to articulate so the travel needs are much less than the tow rig) then mount it on the axle centerline.

For me, I don't know that I care too much about leveling the load while under way. Perhaps if I were dealing with leaf springs I might feel different. Just doesn't seem like the torsions change ride height much with different loadings.
From my perspective if you're starting from leaves and not going to eliminate the live axle (i.e. go to truly independent suspension) then you're money and time ahead to try removing all but the main leaf and installing the air springs between the axle and the frame. If the main leaf is light enough it will act first as an axle locator and second as a spring. If it is not, find one that is and try it. Could easily be that is all the is needed.

 

[gabepari]

[/IMG]

Might be just the effect of the camera lens, but it appears that all that welding on the top of the axle tube gave you a whole bunch of negative camber.

 

[lowenbrau]

From my perspective if you're starting from leaves and not going to eliminate the live axle (i.e. go to truly independent suspension) then you're money and time ahead to try removing all but the main leaf and installing the air springs between the axle and the frame. If the main leaf is light enough it will act first as an axle locator and second as a spring. If it is not, find one that is and try it. Could easily be that is all the is needed.

As long as the trailer doesn't have brakes, I completely agree. If it does have brakes, the same system might simply need an anti wrap bar.

Sahara, what did you do with the suspension you took out? It seems like it would be just fine with something other than SREs. (Are the cool kids still using johnnyjoints or is there something better now?)

 

[Corbet]

Not really, no. First, which direction are you picturing the 4 links being oriented? Across the width of the trailer or aligned with the length of the trailer? Second, we are talking about truly independent suspension and not what Sahara posted above as his solution to the SRE failure that he had?

#1 Independent, I've considered both but have not studied suspension design enough to resolve possible issues with either design. My main thought is that building a link system with adjustable rod ends could solve any alignment issues from welding by being able to adjust it back to proper alignment if necessary.

#2 I'll probably end up with Sahara's 2nd design for simplicity.

But I definitely want air bags to adjust for a wide range of trailer loads. As well as level it on site for RTT sleeping.