Hi,I'm building a tricycle for 2 passengers as well as the rider.My main concern for the structure of the chassis is the junction between the rear and the bike frame. Both structures on their own withstand the weight when made out of aluminium, no need to go for steel. But what about that junction? Will aluminium have a propensity to buckle? should i used double tubing or a fork design? I suppose the shape and caliber of the tube also comes into play.Lastly, which of a tube or cylindrical rod is stronger?ThanksAddendum: I'm looking at aluminium because it's cheaper and for weight reduction in the vehicle.
ehter one may work well depending on what the wheel base is but i prefer steel as it is easyer to weld and and a gusset or two if you need to. aluminum can be hard to weld and un forgiving if you make a misstake.
I would make just the junction itself out of steel because alluminum tends to be VERY weak. I would weld the steel junction to the rest of the alluminum frame to make a strong trellis type of design.
You cannot weld steel to aluminum with traditional arc welding techniques. It can only be done with explosion or friction welding. I doubt either of these processes will be utilized on a trike frame as they would be cost prohibitive for low production runs. Are you an experienced aluminum welder, or will you be using one? If not, I'd suggest using steel tubing. Steel is much more forgiving during the welding process. It is stronger too; although on the downside, it is heavier. As for your design, it is very difficult to follow your description without a picture. I would be remiss to suggest something with my current, limited understanding. As far as tubing and solid rod are concerned, for the same weight, the tubing will be stronger because it has its mass located away from the center. This will give it much more structural rigidity to resist bending. Now solid rod of the same diameter is stronger than tube, but very heavy. I would think you should be able to use tubing for everything. Maybe thicker or even larger tubes for the areas of high stress concentration such as the area you ask about. If you go with the aluminum, good luck welding it. While it certainly can be done, it takes a great deal more experienced of a welder to perform this operation successfully.
