Schludermann said:
I use a trailer a lot around town and sometimes I transport a heavy load, usually like 50lbs or more, and it's a real drag.
I know what you mean about heavy loads and drag, though my loads (not including hte trailer, which in the case of the MkIV with the dog crate on it weighs around 50-ish lbs by itself) usually are in the 100-200lbs range (and sometimes quite wiggly). There's a link to this trailer in my signature, and links to the others in that thread.
In my case, for now, I depend on the 2WD power on the trike (or bike) to pull it, which is sufficient for doing this on the flats. But I've considered a number of ways to motorize a trailer.
The motor mounting I've most considered other than hubmotor (since mine are custom-built it's easy to work mounts for the motor in there, as I can't use single-ended axles anyway for the loads I carry) is simply to use rear wheels for both sides of the trailer, with single-speed freewheels on each one, and chain drive them from a brushed powerchair motor with gearbox (like I used on the early CrazyBike2 drivetrain; they have massive torque). This would let me get started from a stop, the time I most need extra power when hauling a load, and then when I get up to speeds beyond what I'd have the trailer assist geared for, the trailer wheels would freewheel and not ahve to worry about drag from the motors and chains.
Being 24v brushed motors, I could run them in series off a single "48v" pack and controller, and each would have the same current as the other, and same torque.
Or for more massive torque, in short bursts at least, I could run them in parallel off the same pack and controller, and each would have the current needed to do it's job.
Can't do either of those with brushless motors, would need individual controllers, but in that case torque would even itself out as each one pushed, shouldn't need anything fancy to prevent torque steer.
In my case, I would not get any braking from the trailer's motors, so I would need to use mechanical brakes on it instead, if I used the freewheeling wheels and chain drive to the powerchair motors.
But if I used hubmotors I could get regen braking (or even active EABS braking like on my trike's right rear wheel).
For throttle and brake I would probably use an adaptation of a kind of brake used on automotive trailers, where the car slows down and the trailer pushes on the hitch, compressing a braking control device in the tongue, activating the trailer's own brakes. As the compression decreases, the braking decreases, so the trailer doesnt' jerk the car around.
In this adaptation, if using regen braking, one might need to use a controller like the Phaserunner for brushless motors, that can control braking proportionally to the amount of braking control input, rather than like the typical ebike controller that just turns regen on or off to whatever it's maximum is.
Anyway, there are two ways to control throttle, using just the trailer itself--one is to use the same arrangment as for the brakes, but in reverse, so that a sufficient pull on the tongue from the bike would engage the motors, and the harder the pull the greater the motor output. There does need to be a dead zone between braking and throttle, though, or else the trailer will always be trying to push or to brake, when it's not necessary.
Since in my case I would prefer to only use the trailer motors to help at startup or when there is a steep enough slope to start dragging the trailer down, like going up a driveway/parking lot entrance, etc., I'd also probably put a speed sensor (perhaps a 555 timer type circuit) that once the speed gets above what the motors can help with the controller is disabled (or just the throttle), and only reenable ti when the speed drops below that point.
A second way throttle could be controlled is to use a speed sensor to send pulses to an op-amp circuit to integrate them into a voltage, so that the faster the bike goes, the faster the trailer goes too.
Catch with this one is that at zero speed startup, when having the trailer help at it's full capacity would be most helpful, you'd get zero help from it. But using the trailer tongue pull/push detection would give maximum throttle at this time, as the trailer lags behind the bike.
Can also combine the two using just a switch instead of proportional control on the tongue, which would turn off once you've gotten going, but then the speed control would keep it going just enough to keep up with the bike.
I haven't built or tested these ideas yet, but they should be fairly easy to implement, and then just fine-tune for the actual trailer/motors.
To simplify stuff you can use just one motor: there's no need for two motors, though it would give greater torque from a stop and be easier on the motors. Any off-center torque is something you can get used to easily enough, and learn it's handling characteristics.
