I just finished making two 1:6 scale electric wheelchairs, one for my sister [whose dolls use wheelchairs, as she does] and one for me. The photos below do not provide a true tutorial, but I think that they document my progress in enough detail that interested parties could figure out my process.
Making the motor housing





Making the seat




Making the joybox







Making the pillar for the chair






Putting on the footrest





All done!!!

Making the motor housing
Making the seat
Making the joybox
Making the pillar for the chair
Putting on the footrest
All done!!!