Over the summer we had a rehab center for children with severe mental disabilities ask us to help them modify those little cars that the lucky kids drive around the neighborhood. We modified them with buttons on the steering wheel that the kids could push to make them go forward and made the seats better for them and made the steering remote controlled by a parent. We made the steering remote controlled by taking an old globe motor and having it turn the steering shaft with a couple little gears that we printed out. We had other designs with string and chain and stuff but the gears were by far the best solution. I'll try to find some pictures of it.
We're also printing out stuff to help prototype some new drivetrains we might want to use this next season.
edit: here's some of the cars during their photo shoot, we did like 4 of them.
http://imgur.com/a/rziev