Custom frame building advice

[Kodin]

After buying a motor, starting the wheel build, and starting a custom rear swing-arm fabrication, (Using the plasma cut parts from Barent's Farfle V2 kit), I'm thinking I might as well go for broke and build up a recumbent trike from scratch while I'm at it. I'm going to make the swing arm to spec for the V2100 so it can be swapped over if I really feel like it, but I'll get more bang for my buck with a vehicle that's low to the ground due to at least half the wind resistance.

Here's my question:

Speccing materials for the frame, and short of trial-and-error destructive testing of various steel profiles, how do I know what profile size, wall thickness, and length of tube, (probably square or rectangular,) will take a certain amount of weight or force without bending? Are there handy online calculators for this sort of thing? Reference books? I'd rather not completely over-build the frame. My TIG skills suck and my machine can't do A/C, and my MIG machine is badass, so I'm sticking with something like A36 (or equivalent) steel for everything.

Thanks for any advice,
-Kodin-

 

[Kodin]

OK, here's one...

https://www.easycalculation.com/engineering/mechanical/deflection-hollow-rectangular-beams.php

 

[Drunkskunk]

Calculators like that are realy only good if you have the engineering background to have done it yourself first, and then use it as a shortcut. There is far more to design than what that calc can account for. For example, it lumps all Ferrous alloys into one type: Steel.

It might help you optimize a design to use it, butdon't count on it for much.

4130 CroMoly is a far better steel for bike frames than A36. it's very weldable, and has almost twice the yield strength, and 25% better strength to weight. 0.065" wall tubing is thicker than usually needed for a bicycle, but still light and easy to weld with a MIG. A thinner wall might require TIG.