[Ryland]

As I was at work today, pulling a flat bed trailer, I got to thinking about what it would take to pull a trailer behind my electric car, my first thought was to plug in to the car and have a powered axle, then I got to thinking about the same idea only behind a gas car, of course at this point the batteries would be best as part of the trailer.
My thoughts for controls are along the same lines as the automatic brakes on some trailers, the hitch of the trailer extends and compresses and operates the brakes, a setup like this would work for throttle as well, only speed controllers can be programmed so instead of relying on mechanical dampening, the dampener and lag can be programmed in to off the shelf speed controllers, so a pull on the hitch will give the power source of the trailer a bit of throttle, a trailer like this could even be towed behind a bicycle if the throttle was sensitive enough, of course the braking is very important and with this type of set up could be easy because of regen braking with added mechanical braking for those times when you need to stop fast.
My first thought for building this is to build it off a golf cart, a two wheeled trailer could use just the rear end of the golf cart, for a bicycle a 4 wheeled trailer would be best because it wouldn't need to have tongue weight if it was set up like a wagon.
Big hold up is speed, my idea with a golf car would have a top speed of 30-40mph, weight should not be an issue because golf carts are designed to haul or people, so 600-800 pounds, plus the weight of the body, roof and the design of a golf cart having a low floor, that low floor being a weak point.
Another reference point is that Commuti-cars use a golf cart rear end and have a curb weight of 1,400 pounds or more plus the weight of cargo and two people, GEM Neighborhood electric vehicles come on a pickup version that can haul over half a ton with a total gross vehicle weight of 3,000 pounds fully loaded with people and cargo, again about 1,500 pounds of that is vehicle, so it seems to me that building a trailer that can power it's self for the most part, or assist at least and haul 1,000 pounds or more should be realistic, giving people with compact cars and light weight vehicles like bicycles, motorcycles and small electric cars a great deal of hauling capacity.