I designed and built this claw specifically for my high school’s remotely operated underwater vehicle (ROV). The claw is powered by a servo that has been multiplexed to open, close, and rotate the claw. The claw was built completely out of Legos. The servo somehow fit nicely in the Lego design (I don’t know how everything fits with Legos).

The differential gear design allows the power to be diverted to the rotation once the claw is fully closed. When the claw is open, the claw requires less force to close than to rotate. The power of the servo is therefore used to close the claw. Once the claw closes, the resistance of the open/close function exceeds that of rotation, and the power is transferred to the rotation of the claw. Once the servo’s direction is reversed, there is no more resistance in the open/close function. The claw then opens in its current state of rotational position. This is extremely useful for the ROV as there are tasks that may require the claw oriented sideways and other tasks that require the claw turned 90 degrees.

Driving the servo is an ATmega8 microcontroller. Timer/Counter1 has been set to phase and frequency correct mode the produce a 50 Hz PWM signal. The duration of the high signal determines the direction of the servo. Normally the high signal controls the position of a servo, but the potentiometer in the servo has been disconnected allowing it to continuously rotate. Posted below is the code used for the robotic claw. It is just the function that configures the registers to produce a 50 Hz PWM signal with a 1.0 ms high signal (stop servo).

Downloads

Servo Functions Code – Servo.h