Now, this is really just a thought experiment by a bored engineer, but I'd like some ideas as to whether this concept would work in practice.

What I have in mind is a single-wheeled bike trailer, fitted with its own brake and wheel hub motor. It would function in a similar way to the over-run brake on car trailers:the trailer hitch is telescopic, and compressing it actuates the brake, but also with tension on the hitch controlling the motor's throttle. That way, the trailer would effectively 'follow' the acceleration/braking of the bicycle without greatly affecting it.

I think this principle would allow you to safely haul heavier loads than with a conventional trailer, since you are no longer relying on the bicycle's brakes for stopping, and saving the cyclist's legs a bit. In theory at least, multiple trailers could be coupled together as a road train, though this might lead to forward/backward oscillations as the trailers tried to follow each other. I'm surprised over-run brakes haven't really been done before though.

I think on a single-wheeled trailer you'll run into stability and volume limitations long before pedaling and braking become problems. That's just my gut feeling.

Something like: https://www.ihpva.org/projects/tstrike/electrailer.htm , only with hitch-controlled throttle? Hmmm... I think you'd run into feedback issues between the motor and the main bike. That is, you'd put tension on the hitch when you apply power, the trailer "senses" this and adds power, which reduces the tension on the hitch, which reduces the power, which puts tension on the hitch, which applies power... over and over again. Depending on the responsiveness of the throttle, it'd be annoying or dangerous.

I like the Bionx hub motors: they measure power input and add power in proportion to the pedaling power applied. They can also be set to regenerative braking.

Yeah I ran a quick mathematical model of it and it seems that there would be oscillations unless you had some form of a damper on the hitch. It would cause a little more force to be transferred to the bike but with the right amount of damping should make it more controllable.

Put a force meter in the hitch and feed it through a PD-controller to regulate the throttle/brake?

Since you are using a hub motor, could you use the regen as the brake? Maybe attach it directly to one of the brake levers on the bike?

Here is a link to a forum .

https://www.motoredbikes.com/forumdisplay.php?f=119

I would imagine it working something like that. You'd have a pair of load cells on the hitch and servo pulling the throttle and brake cable. Not as neat as an integrated controller but probably the simplest to arrange. Come to think of it, this idea would potentially work just as well with a two-wheeled trailer.