I read an article a few years ago about improving a hand car's balky performance by building a trailer with a pick-up roller, attaching it to the hand car, and wiring it into the main unit. This created an additional and much more reliable way for the current to reach the motor (instead of just the copper "slider" under the handcar itself). I tried it, and it really worked well for me ... especially when running through switches, where the hand car used to often come to a dead stop. Now it runs flawlessly around my entire layout.
The original article I read had modified a Mickey Mouse hand car, and they had constructed a mini ore car to pull behind it. Mine is a Santa hand car, so I made a little trailer full of presents, added a few colored lights, and finished it off with a Christmas tree and a snowman hitching a ride.
This was a fun project, and is now a favorite as it glides smoothly around the Christmas tree at this time of year! I thought you might like to see it.
