Quantity   Component name
1 × 1/2″ Ball Caster With 1/2″ Metal Ball from Pololu.
1 × 270-Point Breadboard From Pololu.
1 × 4 x AA Battery Holder with On/Off Switch
1 × Adafruit Trinket – Mini Microcontroller – 5V Logic From Adafruit.com
1 × HC-SR04 Ultrasonic Range Finder Can be found at Robotshop.com or Hobbyking
2 × FS90R Continuous Rotation Micro Servos Can be found at Robotshop.com or Hobbyking
6 × Jumper Wires The number of wires depends on what you want to do.