12v Wiper Motor electric bike idea - Connected to highest gear still managed to turn.

Greetings this is just a short video to show the wiper motor bike idea I have the wiper motor screwed in directly to the crank and I actually have the chain wheel connected to the rear gears, unfortunately my son trashed the gears on the bike so it is running incredibly lumpy, I just wanted to try it to see if it would actually turn the rear wheel which it obviously does, also worth noting that due to the derailure being essentially scrap it is in the second from highest gear so is giving the wiper motor a lot of work to do.
To cut a long story short I need to get to working bike with good gears.
The other issue is that effectively the motor will undo itself unless it is welded to the crank this is due to the fact that the thread is on the wrong way.