This summer I designed and built a hinged aluminum trailer lid for a local FJ40 owner (who hasn't succumbed to RME yet) and thought there might be some interest if I posted it here. His posts about this project can be found on expedition portal. You can see more pictures and comments there if you log in.
He purchased the trailer in immaculate condition. Rhino lined throughout, widened fenders, upgraded tires & wheels, water can storage. To say the least, he didn't want the lid to dishonor this beautiful trailer.
Before:
After:
Scott wanted the Canadian military trailer to be water & dust resistant, provide secure storage, and create a place for his RTT to mount for storage and use. After giving me those criteria and showing me a couple of online examples for reference, he left me to design and build it.
From the beginning, I was leaning towards aluminum over steel - both for corrosion resistance and weight. I knew that the RTT was going to come in around 150-200# without occupants, which forced me to build strength into the design rather than use higher tensile, but otherwise heavier, materials.
Drawing on some understanding of aviation and engineering, the triangulated truss was the best choice for the material and weight considerations. With it, I could span the trailer opening, allow the lid to bear a lot of weight, and keep the lid as light as possible.
The shorter truss to go across the width:
The longer truss which runs lengthwise:
I didn't have the software or the time to test the trusses and the materials for the best designs or least possible amount of material needed, so I was left to over-engineer the parts to where I was confident that they would hold up. Ideally, I would at least try some real world testing to see how much load one of the trusses could take before breaking, but again considering time and re$our$es, I just overbuilt.
My material choices for the web of the trusses was .1875" thick (3/16") Aluminum and .125" thick (1/8") for the flanges. The web will bear the load, while the flange is in place to keep the web, or truss, straight and vertical. As I designed, I took care to make sure the trusses would line up directly under the load bar mounting locations, as that's where the force and weight of the tent would rest. The trailer opening is very close to 6'x4' and I ended up with two full length trusses running front to back about 6" in from each side, and 7 shorter trusses running left to right, 3 of which lined up under load bar mounts.
The entire idea with the lid was that it consist of two main parts: The skeleton underneath with a skin over the top. Although the skin, once in place, would add tremendous strength and stability to the lid, I wanted the skeleton to be independently strong and stable enough to do the job - again with the overbuilding. I achieved this in two ways. First, by interlocking the trusses via simple slots just wide enough for the two pieces to fit.
I sent the design to be laser cut and was able to get all the components cut from one 4'x8' sheet with room for one extra truss as a spare. The laser tends to leave slag on the back side of the cut and they needed some cleaning up before I started fitting everything together.
Right from CNC cutting:
After some cleaning up:
The top edge of the trailer is close to 1" wide, so I used 1" square tube around the perimeter as the foundation for the lid. With a little cleaning in the slots to get them just wide enough, the parts dropped together easily. That was the easy part.
Dry fitting the laser cut parts:
More to come...
He purchased the trailer in immaculate condition. Rhino lined throughout, widened fenders, upgraded tires & wheels, water can storage. To say the least, he didn't want the lid to dishonor this beautiful trailer.
Before:
After:
Scott wanted the Canadian military trailer to be water & dust resistant, provide secure storage, and create a place for his RTT to mount for storage and use. After giving me those criteria and showing me a couple of online examples for reference, he left me to design and build it.
From the beginning, I was leaning towards aluminum over steel - both for corrosion resistance and weight. I knew that the RTT was going to come in around 150-200# without occupants, which forced me to build strength into the design rather than use higher tensile, but otherwise heavier, materials.
Drawing on some understanding of aviation and engineering, the triangulated truss was the best choice for the material and weight considerations. With it, I could span the trailer opening, allow the lid to bear a lot of weight, and keep the lid as light as possible.
The shorter truss to go across the width:
The longer truss which runs lengthwise:
I didn't have the software or the time to test the trusses and the materials for the best designs or least possible amount of material needed, so I was left to over-engineer the parts to where I was confident that they would hold up. Ideally, I would at least try some real world testing to see how much load one of the trusses could take before breaking, but again considering time and re$our$es, I just overbuilt.
My material choices for the web of the trusses was .1875" thick (3/16") Aluminum and .125" thick (1/8") for the flanges. The web will bear the load, while the flange is in place to keep the web, or truss, straight and vertical. As I designed, I took care to make sure the trusses would line up directly under the load bar mounting locations, as that's where the force and weight of the tent would rest. The trailer opening is very close to 6'x4' and I ended up with two full length trusses running front to back about 6" in from each side, and 7 shorter trusses running left to right, 3 of which lined up under load bar mounts.
The entire idea with the lid was that it consist of two main parts: The skeleton underneath with a skin over the top. Although the skin, once in place, would add tremendous strength and stability to the lid, I wanted the skeleton to be independently strong and stable enough to do the job - again with the overbuilding. I achieved this in two ways. First, by interlocking the trusses via simple slots just wide enough for the two pieces to fit.
I sent the design to be laser cut and was able to get all the components cut from one 4'x8' sheet with room for one extra truss as a spare. The laser tends to leave slag on the back side of the cut and they needed some cleaning up before I started fitting everything together.
Right from CNC cutting:
After some cleaning up:
The top edge of the trailer is close to 1" wide, so I used 1" square tube around the perimeter as the foundation for the lid. With a little cleaning in the slots to get them just wide enough, the parts dropped together easily. That was the easy part.
Dry fitting the laser cut parts:
More to come...
