Alright- with all of this "discussion" regarding metal strength to weight ratios- I have a trailer question- i am building a trailer and the lid will lift similiar to te attached youtube video. the lid is about 70lbs made of a wood frame and poly foam then covered in several layers of fiberglass cloth and epoxy resins. It will have raingutters on the sides for holding yakima racks and the racks must be able to hold bikes and paddling gear up to about 400lbs. Being concerned about weight what would be the minimum recommendation for mild steel that you would recommend for the Lifting arm? I know that the supporting arms can be and will be smaller since they are not taking the load from the screw actuator. And Bonus question what profile would you recommend for the Arms? The rear arms (one of which is the lifting arm) will be 45" and the front arms will be 43" the differnce is required to prevent the "rotation" form binding

thanks scott

I would suggest 2"x2" square tubing at 3/16" thickness might even go 1/4" to be safe. That pivot point looks like it will be under a lot of stress if you plan on motorizing it like the one in the video.

There is no way that I would trust a gutter mount rack system with even one bike. 400lbs is crazy if you care about your gear. Use the flat mounts and through bolt them instead. Or mount the tracks if you need them adjustable. I put the tracks on my jeep.

[img]http://www.joegorm.com/2010-1-4%20jeep%20amp%20and%20sub%20074%20(Large).jpg[/img]

For the metal, it depends on the profile. If you are using angle iron, I would go at least 1/8" if it's 1.5" or more on the sides. 1/4" if its less than that. If you use square tube, you can cut down on the weight and use maybe 13-15 gauge if it's about 1" or more square.