One of my first ever robotic prototypes, developed during my sophomore year of college as part of an independent study program. I wanted to try my hand, at making a robotic manipulator, something that would have all the functionality of a mechanical claw, (such as the ones found on diving submarines) but with more adaptability for situations that require a little more finesse.
Since the goal of the design was to be used in industrial situations, gripping power and holding torque were my primary concerns. I settled on using DC gear motors (with internal worm gears for extra torque) which I could control via a series of simple switches. The design went through several revisions as I discovered newer, smaller, and better motors to base my prototype around.
The final design which would be built as a physical prototype uses a series of five small DC gear motors (apparently designed for use in Chinese vending machines) to control each of the three fingers, one for the wrist rotation, and one to operate a geared mechanism for changing the hand into 'claw' mode.
The prototype is constructed of laser cut Delrin acetal homopolyme resin parts and 3D printed ABS plastic components. When in 'hand' configuration, the third finger performs much like an opposable thumb, allowing the machine to grasp objects firmly or interact with common human-designed objects (doors, levers, knobs) more efficiently. When oriented into 'claw' mode, the machine can grasp and hold cylindrical objects with greater effectiveness, and perform tasks more commonly reserved for industrial robots. In both modes the fingers can curl up into a compact fist-like configuration to protect them when not in use.