Home built independent suspension?

[GeoTracker90]

Camber, camber, camber. Boy this seems to be a sticking point for a lot of people. I think that we really need to get an objective hold on this. For starters I've seen trailer axles with what appears to be no camber built into them and I've seen others where the bow in the axle for camber is quite easy to see. I know, the previous sentence is purely subjective and anecdotal. So where do the numbers need to be?

I presume that the toe value on a trailer should be as close to zero as possible. Now what about that dang camber? How much is really needed? And is it positive (top of the tire tilted in) or is it negative (top of the tire tilted out)? I'll do some looking in my two trailer design books tonight after work and see if it is mentioned in there.

One last coment about camber; I think that the amount of camber needed will change with the expected load rating of the trailer. For my little trailer I doubt if it will see more than 1500 lbs. of a load ever. How does this play into the equation?

Mike

 

[ntsqd]

I don't think camber is worth pursuing. You see unladen trailer axles with an arch in them. That is so that while loaded the tires sit flat on the ground.
If you want to go road racing with the trailer, then a camber curve would be worth looking into.
Also, if you have no built-in camber then one fixture will make both sides. I do not think that identical is achievable or worth anally pursuing. Within 1/16" isn't likely to be noticeable in towing traits.

FWIW I would not build the arms as has been consistently shown, with a bend in the one leg. Tube benders are a tool, not an obligation. If you put a bend in that tube it will flex in the bend and tear up the inner bushing at an accelerated rate as well as work the welds to failure. I would suggest geometry roughly like that in the attached pic.

 

[UK4X4]

"Do you have a build thread for your trailer? I'd love to check out some pictures of what you have accomplished."


just consolidated the diferent threads I had into 1

so you can see where I am...

camber......I would'nt worry about that unless you intend track racing it........

make straight ...if it looks like the tyres are bowing in....take some weight off...

 

[Grim Reaper]

Camber, camber, camber. Boy this seems to be a sticking point for a lot of people. I think that we really need to get an objective hold on this. Mike

Let me clarify why I wonder about any built in camber. The bushings and the the arms are going to twist just a little. I wonder if AT didn't account for this and put a little positive camber (top of the wheel out) into the design so that once it is loaded the come up to zero camber.

 

[Rezarf <><]

This thread is getting super cool!

Drew

 

[Martyn]

As Rezarf said the thread is getting interesting.

So far I think the communal engineering skills are phenomenal, and most of your ideas are very sound.

The project has evolved from a simple independent suspension project to something much more involved and complex, and costly.

The stage you are at now is the camber and toe in question, and the answer is complex because it makes a costly suspension very expensive, and may only give you a slight edge on performance.

AT offers a patented way to adjust toe in and camber but you have to understand our company philosophy to understand why we use it. Our goal is to produce the best off road trailers in the world. We spend one month out of every twelve doing R&D to improve our product, and we accept no compromises.

Introducing an adjustable suspension costs money, but if fits into our philosophy, and we can spread the R&D and design work over 2 to 3 years of production.

I'd balance out the expense against the benefit. I'd also see if my money was better spent making sure what I already have will be strong enough to withstand the punishment it will have to endure.

Our first attempt at trailing arms fell apart in the first 10 miles of prototyping. It’s hard approach perfection first time around.

 

[GeoTracker90]

Here is the most informative section I could find about camber in the book "Trailers: How To Design & Build, Volume 1 Basics." On page 105 M.M. Smith has Figure 4.10 that shows line drawings of two different trailers, one has the axle straight and the other shows the axle with NEGATIVE camber and the tops of the wheels tilted in. The caption reads:

Figure 4.10. Axles are typically "positive cambered" in the center to accommodate the addition of basic weight which generally brings the wheels and tires close to vertical. Additional loads can then bend the axxle as shown in B. This puts teh top of the wheel/tire closer to the trailer frame and upper fender down closer to the tire. These changwes must be accounted for when fenders are installed. Clearance problem areas to check:
1) Edge of fender/tire tread,
2) Top of Tire/underside of fender,
3) Body side /inside sidewall of tire,
4)Tire tread/fender brace.

 

[ntsqd]

At this point I believe that the little bit of twist induced into a trailing arm & bushings by the load would be insignificant to handling traits so long as the arm itself is torsionally stiff enough, which should be a by-product result of making it from tubing large enough to handle the other loads.
Which leaves deflection of the bushings and mfging tolerences. So some adjustability is a good idea.

Should there be a little camber in the loaded tire, the direction it will tilt is favorable to handling - just not so much to tire wear.

 

[GeoTracker90]

Well today I fired up the lathe and started working on the first aluminum puck that will center everything when it comes time to weld up the trailing arms. Turn down the OD to 2" to match the OD of the bushing shell - OK. Turn down a segment to fit inside the bushing shell, should be 1-1/2" like I set my calipers to. Zeroed me digital calipers so that I can see how much oversized it is and how much more material I need to remove. Finally I've reached the correct ID, but wait that looks a little too small. What the? Double check the calipers and DOH! I zeroed the calipers at 1-1/4" instead of the 1-1/2" that I needed. Well that sucked. I bet I don't make that mistake again for a while.

Sorry, no pictures of my failed manufacturing attempt.

 

[Metal Twister]

Hey guys Im really enjoying this thread. I havent built that many trailers, But I do build high end sand car frames and suspensions and they all use trailing arms. As far as toe in, we shoot for 3 degrees. By putting 3 degrees in the toe the cars track very true. 0 degrees would be fine but we are compensating for 500 horsepower and monster paddle tires that wants to spread our poly bushings open. Under load we are very close to 0 degrees.

We have our trailing arms set up at 0 degrees camber at ride height. With cars, especially long travel cars you need to compensate for the arc of the axle.(Transaxles) We build in a camber change above and below the ride height. That is done by kicking the outboard pivits foward of the inboard pivits 7 degrees. Another words the back bone or cross brace has 14 degree kick in the center with the ends positioned foward. We've exhausted solidworks on this and spent more time than you can imagine cycling these arms. When I build my next trailer I am going to use .120 wall 1 3/4" molly tube. Im going to fixture them up at 0 degrees toe. 0 degrees camber. I will use a mag laser and attach it to the backing plate mount and cycle it watching the laser on the wall 40 feet ahead. If the laser beam runs vertical and true thats going to be where I weld my pivots to the cross tube which is square with side rails and level. These are trailers... We can make it as high tech as we want. But old HeneryFord had this stuff all figured out back in the 20's. He set his rear ends up at 0 degrees and everthing on the front was set up at 7 degrees, Toe, camber, and caster. I just had to add my 2 cents. I will shut up now and go back to lurking. Thanks Bob :victory:

 

[UK4X4]

Metal twister..

".120 wall 3/4" molly tube"

Would this size tube be really strong enough to take a 1500lbs -2000lbs trailer weight over rough terrain ?

Especially using the trailing arm / airbag or spring type design ?

I know that most of the weight is absorbed in the vertical axle/spring frame.

But the twisting force on the assembly would be quite high as the hub would be about 6-8 " out from the edge of the spring.

I was looking at 2" box hrew..or similar

 

[Metal Twister]

Humm, I use .120 wall 1 1/2" molly on these. Ive built about 60 in the last year and a half. Not one failure of any kind. Its all in the design, material, and weldments. Do it right and you will have no problems. With our sand cars up until just a few cars ago all used nothing but 1.25" .120 wall molly on the arms. The forces you are talking about are absorbed by the bag and shock. The most torque is on the Poly bushings. I would use a good quality bushing and a molly insert with a 3/4" grade 8 bolt. Believe me on this, you wont have any problems. Honestly DOM or even 120 wall mild would work just fine. I just happen to have the molly laying around so I mise well use it up. Besides that, Molly is the new buzz word in the industry so Im really doing a cool thing here LOL. Feel free to contact me via phone or Pm me if I can answer any questions for you. You have got to be sure in your mind that its going to work before youll be able to relax and enjoy it. Relax and enjoy it!

 

[oldcj5guy]

I wouldn't suggest going with 3/4 molly .120 for the average joe. Chromoly isn't worth crap if you don't know what you are doing when you throw the weld down. Probably work good for you as it is what you use everyday.

I like the design that was thrown up with the square tubing, but I think I would probably have welded my other busing directly into the square tubing versus adding another piece in there. If you went with a design with a bend in one leg, flex inthe bent leg could be compensated for by using plate for the crosspiece between the legs attached at the bend point. This would keep the bend from being able to flex.

 

[Metal Twister]

I wouldn't suggest going with 3/4 molly .120 for the average joe. Chromoly isn't worth crap if you don't know what you are doing when you throw the weld down. Probably work good for you as it is what you use everyday.

Ok. Enjoy...

 

[ntsqd]

The wall thickness is fine IF the geometry of the arm is well designed. If it is not then 1/4" won't save you (or it). The key to that design type of arm working & surviving is that it be a truss not unlike truss bridges and pre-fab'd roofing components. The loads must be applied at the intersections - no mid-span loads allowed or it's doomed.

In something like a suspension arm 4130 is a waste unless post weld Normalization is done. If it isn't all you have is some fancy & expensive tubing held together by on-site castings, with all of the normal attributes that castings are known for being present. That is, unless those welds were done by the Oxy-fuel process since that is what 4130 was designed to be welded with. Given the rarity of that.....