If you want a electric bike setup that isn't a permanent mount, then it seems to me like the simple, safer answer would be a trailer with the batts, and a motor that hooks over the axle of the rear wheels and on the seat. If you don't want to use the axles, then some sort of hook arrangement that slips over the frame tube to the axle would be needed. You'd hook, roll the motor forward, hook the seat tube, then tighten. The motor would then drive the tire with a friction drive. You'd need some sort of slide adjustment on the axle arms to allow the use on different tire diameters, but that will complicate it and make it heavier. Be better to design it to one tire diameter, and a single slide on the part that goes to the seat to adjust the motor to the tire. What you would wind up with is a motor pod that hangs behind the seat. Then you'd just need a throttle cable with a reusable nylon tie arrangement and a removable squeeze lever throttle to one of the handles on the handlebar.
The trailer could be very simple, just an aluminum shelf with bicycle wheels attached. If brakes on the trailer are a requirement, then an electric brake setup that has a lever attached on the opposite handle would be the way to go. That wouldn't need much juice, so the battery could supply that power even if it was too drained to run the motor. Worse comes to worse on that, you could attach a bike generator to the trailer that would be able to provide braking power, or a separate, dedicated lawn mower battery for the brakes. I don't know if they make electric bike brakes, if not you'd just need a servo that can pull a cable, then use regular bike brakes. You'd need a way to control the servo according to how strong you pull the brake pedal though, would do no good to have brakes that are either 100 percent on or 100 percent off.
Here's a rough sketch of what I'm suggesting. With this arrangement you could have an electric power system that could be moved from bike to bike in less than 5 minutes, without worrying about a setup that would cause an accident.
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The trailer could be very simple, just an aluminum shelf with bicycle wheels attached. If brakes on the trailer are a requirement, then an electric brake setup that has a lever attached on the opposite handle would be the way to go. That wouldn't need much juice, so the battery could supply that power even if it was too drained to run the motor. Worse comes to worse on that, you could attach a bike generator to the trailer that would be able to provide braking power, or a separate, dedicated lawn mower battery for the brakes. I don't know if they make electric bike brakes, if not you'd just need a servo that can pull a cable, then use regular bike brakes. You'd need a way to control the servo according to how strong you pull the brake pedal though, would do no good to have brakes that are either 100 percent on or 100 percent off.
Here's a rough sketch of what I'm suggesting. With this arrangement you could have an electric power system that could be moved from bike to bike in less than 5 minutes, without worrying about a setup that would cause an accident.
