In the photo, you may see the only bicycle in the world to be fitted with Meccano!
Revolutionworks.co, Filwood, Bristol, makes very small battery-driven motors, attached to the seat-post via a gap cut in the mudguard. I found it sprayed water and mud all over the bike, so I made that scrap-Meccano device, backed with plastic sheet. I tested it one afternoon, riding round the Downs through every available puddle - there were plenty! - and hey! It works!