I built two electric bikes. I actually prefer them except for the range thing. Both were friction drive made with inexpensive scooter motors. No controller for me, just a simple household on off switch. I used the motor like a pulse jet. On to assist or cruise, off to slow down. It worked really well but the battery range problem haunted me. Yes i did have to peddle on the hills but even that was doable while comfortable seated with the assist from the engine.

At this time I keep one for a spare it has two 250 watt scooter motors against the rear wheel. One under the seat and one behind it. I use one for small hills and to cruise and kick the other in on larger hills. I can get about five miles range on two garden tractor batteries pulled in a trailer behind me.