Laying the First Domino

I recently began building the first prototype of the domino laying robot out of Technic LEGOs. They are a great tool to quickly build a working model. In this case I've started with linkage that will eject dominoes from the clip. It works similar to a piston powering a train wheel, only in reverse. 

After a domino is ejected out to the left it will travel down a curving chute, ending up vertical on the ground. At that point another linkage will push the domino out of the robot. This final push will move backward at the same speed the robot moves forward, causing the domino to stand still and giving it time to balance. 

The gear on the right side, which will spin to move the center piston left and right will be driven by continuous servo motor. Typically servo motors have a limited degree of motion and the robot controls which angle the motor is at at any given time. In the case of continuous servos, the programmer controls how fast the servo goes and the motor continues to spin. I purchased a medium continuous servo from Sparkfun to learn how to program one. 

I programmed it in a way very similar to the Potentiometer LED project from Snow Day Tinkering.The potentiometer defined a variable which told the servo how fast and in which direction to spin. Programming the servo was very simple and the PWM wire broke up easily into three separate wires to plug into the Arduino and breadboard. PWM stands for pulse-width modulation. The PWM wire is really three cables, 5V (red), ground (black), and signal (white). The signal cable controls how fast the motor goes by turning the servo on and off very rapidly with different intervals. For example to achieve 50% velocity the signal would alternate between on and off being off half the time and on the other half.