I built a delta trike years ago using a Mini starter motor to drive one of the rear wheels.
We started off with a Sturmey 3 speed hub (with emery cloth glued to the shell) friction driving the rear wheel.
We then changed to driving a 3 speed built into the wheel. I think we usede a 7 tooth cog on the motor and a 42 tooth at the wheel
- it was a BMX chainring welded onto a Sturmey sprocket!
It worked for limited periods, but the motor got hot very quickly.
We welded the frame up on ours, but I had (and may still have) plans to build one based on a sheet of plywood, with only one little welding/brazing job neccesary at the front end.
Does the fan motor have it's own cooling fan?