VEX Precision Bionic Arm

This is a Precision Bionic Arm that was made with the VEX Construction System as well as other components. It is controlled via a VEX Cortex Microcontroller and the VEX Cortex Game Controller, using the two joysticks and twelve pushbutton switches to animate the arm in Azimuth, and Elevation as well as wrist and gripper and arm flexing control. The game controller is also used as a teaching pendant to train the arm movements using a motion script generation function that RECORDS the motions entered via the joystick from a known location, position and orientation (home) and then PLAYS them back again to reproduce the motion.

The VEX Construction System normally uses DC motors and RC Servo motors for animating robots but this robot arm uses 3D Printer stepper motors for animating the Azimuth Axis, Elevation Axis, Wrist, and Arm flexing. It does use a VEX motor for opening and closing the gripper on the VEX Claw sub-assembly. Each stepper motor is driven by the Sparkfun QuadStepper Board using a 12-Volt power supply. The main advantages of using stepper motors over standard DC or servo motors are that a stepper motor can be controlled very accurately using Open Loop control law, which is much simpler to use than standard PID Control law and does not require position feedback from a quadrature encoder. Stepper motors can also be micro-stepped in 1/2 step, 1/4 step, 1/16, step up to 1/256 step for very accurate positioning using modern 3D Printer stepper drivers.

All the firmware is written in Robot C which runs on the VEX Cortex to pulse each of the stepper motors as well as to decode and convert joystick positions and pushbuttons from the game controller to stepper motor commands. It also provides functions to HOME, RECORD and PLAY back motion scripts.

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