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    Arm good

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    John Fenley

    by John Fenley

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    A master/slave system I built using potentiometers, servos, and an IFI robotics controller .

    I took this robot apart a couple of years ago, but I am re-building it for a class at my university.

    The shoulder rotation, elevation, and elbow joints are Expert Electronics SL820(shoulder elevation) or SL800(rotation and elbow) giant ball bearing servos. I don't have the original gripper as it broke. it was just a regular servo with a piece of balsa wood attached to the side, and one attached to the servo horn. I used epoxy to attach the wood.

    To create the arm structure I used coat hangars and welded them together. I melted holes in the servo horns to stick bits of wire through. I taped the 2 shoulder servos together, and taped the elbow servo and wrist servos to the previous arm segments.

    To create the master arm, I used pieces of wire coat hangars connected via 100K potentiometers using hose clamps. I had to flatten the side of the coat hangar so it wouldn't rotate. I wired it using telephone wire,(4 conductors, 4 signals) and 1 red power wire.

    I connected that to an old joystick connector. The robot controller I used(IFI Robotics) has a powered joystick input. All 4 axis of motion are sent to the microcontroller as numbers from 0 to 255.

    The microcontroller runs each input through a simple calibration program that knows the input values for the ends of motion of the master, and converts each number into another number from 0 to 255 that is used to set the position of each servo.