I would like to throw out a challenge: the brush switch isn't a very elegant solution and I would be interested in anyone coming up with a mechanical switch design (no microprocessor) that only switches on when the pendulum is in forward motion.
Watch video here to see pendulum operating: http://youtu.be/0fq7WYCsqCo
The switch that turns the motor on only when the pendulum is in forward motion is simply a zip tie with a conductive wire shrink wrapped on one side. The end of the conductive wire makes contact with my electrical contact plate (a piece of steel ruler) only when going in one direction. As the pendulum returns the zip tie makes contact with the plate, but not the wire (mostly true - it does often make momentary contact both ways but not enough to power the motor equally both ways).
Note the screw just holds the zip tie in a hole through the pendulum arm to keep it in place.
2nd Photo: shows a closeup of the arm and the pivot axle. I used pieces of a hollow fiberglass fishing pole for both. I epoxied the smaller axle pole inside the pendulum arm. The axle is supported by a bicycle spoke that goes through holes in both support poles(see first photo). There must be very little play in the axle as the contact between the switch and the switch plate is measured in a few millimeters.
3rd Photo: closeup of the motor and prop. I used a 500mAh lipo 2S battery to power the motor (7.4 volts).