Future Project, help wanted!

Alright, so some friends of mine approached me and asked me to build the a bicycle trailer that they can carry their son, Dan in.  Dan is about 35 years old and mentally handicapped.  The trailer is going to have to be strong enough to carry him, light enough to be towed, and safe.

I've been kicking several ideas around for the last week and playing around on Sketchup.  Here's what I've come up with.  Remember, these are JUST ideas at this point, I really don't know much about bicycle trailers but I'm learning a lot along the way, and would love to hear it if anyone has any suggestions.

First sketches:













Real rough.  As you can see from the next few sketches, a lot has changed.  Kicked around a few more ideas, and discarded a few others.

Small tires, with a stroller version. Will be using bike tires, so this is moot.



Seat suspension. Probably won't be doing this.



Extended frame for adding a basket or carrying stuff.



Rollbar / pushbar for stroller.



Stroller, with detachable tongue / attachable caster wheel. Tongue stows under trailer.



Other pics.





Keep in mind these are just design ideas... The trailer will likely be skinnier (this model has a 3' wide frame, will probably cut that down to 2') and change a bunch while building. Sounds like they really want me to build it, so I will, but there are a few other projects on the table and a few other things to iron out here first. May start on it over spring break, we'll just have to wait and see. 


Current things we have decided on: 

Bicycle wheels for sure.  Probably 16", as I've read the smaller tires handle cornering forces better?

Low side mount tongue.

Some type of platform off the back to mount a basket or case of some sorts.

Fenders for the pull bicycles- Store bought.

Fenders for the trailer- going to try hand making them out of aluminum sheet, but no cover on the outside.

Rotomolded racing seat from JEGS, with a 5 pt harness.

Leg board most likely also hand made by me out of aluminum sheet.


Things they seem to maybe want:

Seat suspension

Stroller castor / removable tongue

Powedercoated frame.



There you have it.  I want to try and keep very little weight on the tongue, so the seat position will likely move back.  The axles will be 5/8" rod welded to the top of the frame crossbar to lower the center of gravity more.  I will probably have to build some type of bracket behind the seat to mount the safety harness too as well.

Anything I'm missing?  Or, I know I'm missing about thirteen hundred things, wanna enlighten me on a few?!