Long Arm Of The Law Physics Home robotics, bubeleh. Build a working hydraulic arm with this excellent 66-piece kit from Pathfinders' Simple Machine series. Structure is die-cut plywood and the kit includes tubing, (3) syringes and glue. You'll need a ruler and scissors. The finished arm will be approx 13-1/2 tall and will reach out over 16 and rotate 90 on an 8-5/8' x 6-7/8 base. Comes with a 12-page manual and uses water. Beautiful, too. For ages 8+.

• Pathfinders Robotic arm

Pathfinders Robotic armPathfinders