My 9-year, soon to be 10-year old son suffers from Calvé-Perthes disease, causing his hip joint ball to degenerate, making it impossible for him to pedal in a circular motion, all he can do is pump forward with his good leg and backwards with his bad leg, but only for a short while.
We have recently bought a chinese bike with 20" wheels, with typical folding bike ergonomics, even though it's not a folding bike. It's been privately imported from China, and throttle-only operated.
The original 9,5 kg 24V 12Ah SLA battery has been substituted with a 6S 8000mAh LiPo battery pack from HobbyKing, weighing only 900 gram.
Before his disease broke out, we often went out cycling, with me giving him a push from time to time, but without him doing any work, it has become to hard for my shoulder.
Now we ride in fear that some nitpicking copper will stop us, confiscate the bike and give me a huge fine.
Legally he is restricted to a certified electric wheelchair doing max. 12kph on the sidewalk.
The bike he has now goes 21 kph on level asphalt with the 23V from the 6S LiPo pack, but is not good at climbing, as it's a ~180W brushed motor. As a cheap proof of concept, it has been perfect.
My dream is to convert a girls bike with 20" wheels to a stealth E-bike for him, but the components sure add up fast.