Sun EZ3-AL 27 spd. aluminum recumbent with 3 disk brakes. Scooter drive train has centrifugal clutch and gearbox to chain final drive on a 16 in. bike wheel with a coaster hub. I may replace the trailer wheel with one I have that is the same but has a 3 speed hub. However I'm more likely to use the 3 speed wheel on a new trailer that's a little lighter, quieter and has a tongue/hitch combo that will attach to uprights and recumbents without leaving any hardware on the bikes when detached.
The high engine placement was fine for a scooter, but is not ideal as a non-leaning trailer. It works OK, but is top heavy. My earlier design in the other vid is better in this regard. This one wouldn't have needed such a beefy hitch if the engine was low and ahead of the trailer wheel. Draw a line from a high hitch on your seat post or seat back to the contact point of your trailer tire on the ground. Build as much of the weight of the trailer as far below that line as possible for pendulum effect to keep (or approach keeping) the trailer upright on its own, if possible. Unless balanced perfectly upright on its own, with trailer wheel co-planar with your hitch, you will still need a u-joint hitch; to allow pitch and yaw but not roll. A dog-walking, 1-wheel powered trailer can oscillate alarmingly, especially if top heavy (or even if too bottom heavy) unless you build rigid and precise roll constraint into the hitch. Also, a top heavy, roll constrained trailer will add to the likelihood of a rollover when cornering sharply. I can feel it happen in this relatively lightweight trailer.
This one was hastily built the day before I hauled it with me on vacation. Better versions will come when I get back to my workshop and take time to practice what I preach.
