Robot type thing for older person?

[la79al]

My FIL was an auto mechanic before a series of injuries/illnesses. He still loves tinkering with things but really doesn't have the strength, etc that he used to. I was thinking that some kind of robot type thing would be fun for him. I was looking at something like a soda can robot. I figured he could build it and then have fun demonstrating to my 4 year old nephew. Does anyone have any similar suggestions? It really can't have a million pieces because I just don't think he would be able to handle them.