Without the tote, it doubles as a bike trailer for my daughter's or son's 20" bmx's. One at a time though.
Not too shabby, I've seen a golf ball on a big screw, and a piece of pvc as a cap over to lead the trailer like a normal ball type trailer attachment, I really like the use of that satellite dish armature, it just makes the perfect bends for the job, and from having removed them from several roofs I did notice how sturdy that stuff really is. Never thought to save any of it instead of letting scrappers take it all instead! It's hard to say if pvc or steel is going to be stronger, I think the ball pivot would be a step up from the linkage that you figured out (quite well.) They seem to be more robust because the load is concentrated right within the area that the load with change its pull on, as in there are no parts to pry apart because the load and forces acting on it aren't playing so much on tension of multiple moving parts, it's concentrating it entirely into only one moving part that is extremely strong and conformed to a sphere (a very strong structural element with no catch points, the force against it is always a 90° tangent towards the center of the sphere which is heavily stabilized against axial load, at which point the weakest element is the actual strength of the post itself (and the density of the material that makes the sphere, worth considering if your sphere is soft enough to think about. Cheap steel obviously doesn't work as good as great steel so a tow ball is another one of those 'get what you pay for' things. That sphere is surrounded by yet another sphere (or close approximation) which is also heavily (or not) reinforced which the actual source of load is connected to.
With the stretched universal joint the axial load is no longer confined within a certain tolerance so the reinforcement must be higher as sheering forces are applied at a distance apart from center which creates the leverage that tears the hinge apart. The same idea would apply if you shortened the u-frames you used to make the joint then the actual strength of it would be higher against being pulled apart. If you fashion the axiis points farther away the system gets weaker unless overbuilt to compensate.
Sorry for getting off track, the idea is great but ultimately I could perceive you doing just as good a job with a better ability to tow with your bike that could take on 2 bikes, I say this because the company that made mine rated it for 100 pounds of child meat, I put more in it than that and did fine, although I didn't use children meat because they don't sell that at Walmart. Either way it worked and they just used a really heavy spring, I would imagine a towball would be a much better option just because of the way it handles things without having a significant number of failure points, and the ability to be really robust for the volume of material to do the job, it relies on little yet is very efficient and safe compared to more complex structures of joints.
