A-arm material

[Kare423]

Does anyone know if there is a composite material or lightweight metal for wich you could design into an A-arm for a baja vehicle? I am using double A-arms on the front suspension and I would like to change the upper A-arm to a lighter, but very durable material. The lower A-arm is 4130 Chromoly steel.

Any suggestions what to use?

Thanks!! My website:

http://www.geocities.com/kare6

 

[brad]

I don't want to say that it can't be done; however I have never seen it done.
You may be able to design a composite a-arm which can withstand the loads associated with it, but I would be concerned that it wouldn't provide sufficient stiffness for that application. A-arm stiffness is a very important parameter for the handling and performance.
Have you investigated using aluminum instead? That could provide a significant savings, and still give equivalent stiffness to the steel part.
Good luck,
Brad

 

[butelja]

If you are looking for light and stiff, then Beryllium is king. However, it it godawfully expensive, its dust is toxic to all things living, and possibly pyrophoric when in the form of powder or chips.

I like bradh's aluminum suggestion better.

 

[GregLocock]

I have had built chassis from carbon fibre, aluminium, and chrome moly, usually in the form of space frames, except for the carbon fibre, which was a mixture of cloth and tow over a foam core. The guy who built this makes carbon fibre motorbike frames for a living (Jim Cook, Melbourne, Australia)

Weight wise there is very little in it. The carbon fibre was the lightest, but not by 10%. For high stress components I prefer chrome moly, but generally I prefer MIG welded 6061. On problem with that is the softening at the joints - an A arm should be heat treated (and then straightend) after welding.

With an upper arm you are primarily chasing stiffness, not strength. Therefore carbon fibre would not be expected to be a particularly good choice - its strength is its main virtue. To us the difference is that 4 people on our team can MIG weld well enough to trust (not me), whereas we had to hire Jim to build a carbon fibre structure that we could not repair easily, if it broke, which admittedly it hasn't yet.

Cheers

Greg Locock

 

[WeaponEvo1]

I've designed many baja cars, and been around the competition for many years. I think your choice of material should be based upon what race (East, Midwest, or West) that you are competiting in. For an example, in the east race the chances for hitting a tree, rock, another car, or any ostacle with the a-arms of your suspension is extremly high because of the tracks that are used for the east event. In the east race i would use nothing but 4130N tubing(because of its high energy absorption) to give you at least a chance to save your suspension in the event of an impact of some sorts. In the midwest competition, the track is wide and smooth, and consists of just jumps, woops, and table tops. For the midwest you can run 6061 arms or carbon arms because the chances of hitting your suspension on something is close to nothing unless you have a REALLY bad driver. The west is the same type of aggressive track as the east, except it has a boatload more rocks, more like boulders. When it comes to carbon or any composites on a Baja car, don't forget about your cost report!, if you are very familiar with the many different types of manufacturing processes involve with composites then i'd say your good, but if you arn't it might bring you many problems when it comes time to cost out your suspension. One thing you might consider for a-arms would be to triangulate your shock mount rather than put it in bending(a tube across one of the arms), you can save a good amount of weight if you correctly triangulate forces (you'd be amazed actually).

Adam
Team Chemical Interaction
Wentworth Institute of Technology Mini-Baja

 

Hey-

Stick with 4130 tube. By the time you fabricate, or have fabricated composite control arms, your weight savings will not offset your loss of points because of cost.

I also made some ctrl arms for my GT5 Datsun, and found a significant weight savings by pressing spherical bearings into the pickup point rather than rod ends. I pressed Al in the ends, crimp, drill, and press the bearing. Super light. Good luck!