How To Make Hanging Cots and Bunks for Kids Beds in Camper Van Over Front Seats
I've designed some cots that hang over the front seats of the van. They were designed primarily for kids but they can easily hold 200 lbs and span the width of the van.
The cot could be built as a folding or non-folding cot. For simplicities sake I went with non-folding first just to get something that is functional. I designed a folding frame that collapses into a stick (still the full length of the cot, but easier to store.
DESIGN INSPIRATION
NON-FOLDING COT BUILD
When I started designing, I assumed that the fabric would need to be super tight to create a flat surface. First, that is virtually impossible. Second, cots are actually more comfortable when the fabric is a bit loose and can sag such that it confirms to your body shape, like a hammock. I've used cots that are stretched very tight, and they are initially comfortable, but feel hard after a while and become uncomfortable during the night. Cots that are a little loose and you can sink into are more comfortable, but there's a limit there too.
Materials
Frame - This structural framing tube is plenty strong for a kids cot. It is 1.08in OD zinc plated steel tube and has a 1/16in wall. There are many different connectors available.
Corner Brackets
For a non folding cot, these corner brackets can be used. They are nice because they have a generous radius, which is friendlier when moving these around inside a van.
Fabric
I used a heavy duty mesh because it's what I had. You can use any strong fabric. The mesh is comfortable, because the fabric can stretch and conform locally.
Frame Design
The frame consists of 4 pieces of tube and 4 corner brackets. The overall dimensions that I wanted was 63in by 26in. Each corner bracket takes up about 2in of length, so the tube pieces were cut like this:
2X 59in long
2X 22in long
To attach the side and end tubes, I used these corner brackets. They were convenient to use, and the rounded edges make them user-friendly inside the van. No sharp corners to grab or scratch things.
The corner brackets bolt together with 2 screws and captive nuts.
The frame is completely assembled and laid out on the fabric to take measurements and cut to fit the frame.
Enough fabric was used to completely wrap around the frame, creating 2 layers. The intention with the dual layers is that a piece of foam can be placed between the layers for insulation.
Fiberglass rods were used to spread the load of the lacing. The easiest source for fiberglass rods that are long enough were kid's bike flags.
The fiberglass rods were cut to the length of the frame. This was conveniently right at the base of the flag.
Pass the fiberglass rod into the hem.
Lace the ends of the fabric together. Punch holes in the fabric next to the fiberglass rod such that the paracord can thread through around the fiberglass rod. I started lacing from the inside out since it seemed easier.
Sew velcro onto the ends. I wanted the ends to be easy to open and close to make it easy to remove the material from the cot frame, and easy to slip some foam in between.
Loops of paracord at the corners to attach the hanging straps.
Hanging the cots in the van cab.
The passenger's seat folds down flat, or it could lean back. The driver's seat is leaned back. I used basic but heavy-duty tie-down straps with strong steel buckles (don't use cast buckle straps, because the buckle could break). I removed some of the hooks from the straps where they attach to the cots, and left the hooks at the top so they can easily be hung and removed. Setting up and taking down is far faster than setting up a tent.
The kids love it and like sleeping in them. They say it's comfortable and they sleep well. Even an adult can sleep on the lower one and it's pretty comfortable. Far more comfortable than sleeping in the front seats.
Sleeping on cots is colder than a mattress, because the cot provides 0 insulation, and even a sleeping bag will compress underneath, voiding the insulative value of the sleeping bag underneath. That's why I made these double layer. A foam pad can be slipped between the layers for insulation that doesn't get compressed and won't slide around.
FOLDING COTS BUILD
Folding Cot Materials
These brackets can be used for a folding cot. The ends could hinge on one side and snap into place on the other.
The end pieces could also hinge in the center. Bolt or weld this hinge to the outside of the end bars. When open, the hinge overcenters and the bars stay opened.
Frame Design
CARBON FIBER TUBES FOR LIGHTER WEIGHT
Although the cots are not very heavy and can be easily moved around together, any significant decrease in the weight would improve the maneuverability and set up inside the tight spaces of the van. Carbon fiber is the obvious lightest candidate for replacing the steel tubes. However, a steel tube of the same dimensions as a carbon fiber tube will be stronger than the carbon fiber tube. The advantage of carbon fiber is the ability to increase the diameter or wall thickness to increase the amount of material in a structurally beneficial way to make the part stronger while still lower weight than steel.
The long side tubes can't be simply replaced with a carbon fiber tube of the same OD and wall thickness, because they will flex more and can't support as much load. The carbon tubes would need a larger wall thickness. A short piece of steel tube could be used as a coupler between the end fitting and the ID of a larger-diameter carbon fiber tube.
The shorter end tubes don't see a lot of load, so these can be replaced with a tube of similar dimensions to the steel tubes.
The steel tubes
1.08in (27.43mm) OD
0.065in (1.65mm) Wall thickness
0.95in (24.13mm) ID
Weight per foot = 0.71lbs per foot
Long tube = 59in = 3.49 lbs
Short tube = 22in = 1.30 lbs
Carbon Fiber Tubes for ends
27mm (1.063in) OD
1mm (0.039in) Wall thickness
25mm ID
Weight per foot = 0.09 lbs
Short tube = 22in = 0.165 lbs
Weight savings vs steel = (1.3*2)-(0.165*2) = 2.27 lbs per cot = 4.54 lbs for both cots
Cost = $25 per 1m tube = $100 to replace all 4 tubes to save 4.54 lbs of weight. Is that really worth it?
Carbon Fiber Tubes for long sides
1.04in (26.42mm) OD
Weight per foot = 0.19 lbs per foot
Long tube = 59in = 0.93 lbs
Weight savings vs steel = (3.49*2)-(0.93*2) = 5.12 lbs per cot = 10.24 lbs for both cots
Cost = $25 per 1ft tube = $500 to replace all 4 tubes to save 10.24 lbs of weight. Is that really worth it?
Total weight savings by switching to carbon fiber tubes is 14.78 lbs at a cost of $600. Not really worth it, especially not for the side pieces.
To be continued...
