by wattsworth » Sun Jun 07, 2009 10:51 am
The total weight of this frame & suspension design in ultralight teardrop size would be about 200# using 12" wheels, schedule 40 pipe, and 3/16" wall 2x3" square tube for the frame. What can I say, I overbuild things and like safety factors over 4 above yield to account for fatigue and any other loads I forgot. I'm also quite particular about quality full-penetration welds and fully closing the tubes via welding to ensure no moist air can condense inside the frame and start rust from the inside out ... where you can't see it doing its damage.
Certainly using drawn over mandrel (DOM) tube and thinner square tube would save perhaps 40# -- and add a lot of TIG welding. If I had the TIG stuff, I'd think about 4130 aircraft tubing. But, I'm limited to stick welding at the moment and build accordingly.
The forward axle connection to the tongue (apex of axle triangle) is a 1/2" tie-rod end between two brackets so the anchoring bolt is in double-shear. The tie-rod end is threaded into a rod at the apex of the axle triangle. Yes, I have a lathe to turn such items, but resort to a hand tap for the last bit.
The as-built trailer in the picture is destined for an enclosed trailer for a couple of very special bicycles (velomobiles) my dad wanted. I built the trailer ... he will build the box. It has a 10' tongue and is 68" between the coil-over towers. It tips the scales at 212# as pictured -- about half of that is unsprung axle, wheels, & hubs.
This design would be about 10% lighter than the Harbor Feight trailer option, despite the large safety factors and fairly thick-wall tubes. It also has adjustable suspension intended for lighter loads, and shock absorbers. At the end of the suspension travel there are rubber bumpers too.
Now, on to my light teardrop build....