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Dexter Robotic Arm by

Notes on IO from the Dexter electronics board:

There is a digital IO pin on the wite connectors in the upper right on the back of the motor board
make_ins("S", "GripperMotor", 1), //Digital output pin. 0 = off 1 = 5v

Another pin on that same connector is the PWM output pin.
make_ins("S", "EERoll", 512), //PWN pin. Integer range of 0-512

These pins are used to control a vacuum pick and place head at about 1 minutes in this video

# FPGA Connector Human / Description Eye Rotations* Current adjust
1 1 Base Shoulder rotate Counter
2 3? Pivot Shoulder lift Counter
3 2? End Elbow Counter R65/66 (tested)
4 4 Angle Wrist: Differential combination
DiffA1 is rotate, DIffA2 is lift
5 5 Rotate Clockwise
6 6 External (not used)

*eye rotation direction may be individual depending on the wiring of the motor and photodisks. To standardize, swap wires on the encoder to match the table.

Decreasing the value of the first resistor listed in the "Current adjust" to 220 ohms will max the driver current. Normal value is 5K11.

Common issue: Arm shakes after Calibration, especially joint 4 / 5. The DiffA2 disk doesn't go all the way around Joint 4 so it is easy for it to NOT be concentric with the joint.This can lead to variation over the rotational range and make getting a good calibration "eye" impossible no matter where the encoder sensor is positioned. Great care must be taken to place it in the correct location. This can appear as an issue with Joint 5 as they are intertwined.

For next generation diff, ensure end effector and Joint 5 encoder sensor are correctly oriented. If you are facing joint 2 (looking at the harmonic drive) then the end effector should be pointing to your right. The encoder sensor should be on the left.

Arm shakes after Calibration, ALL joints. Ensure the AdcCenters.txt file on Dexters share folder are correctly updated.

Known issues: Arm loses power, "droops" or simply doesn't move, especially Joints 2 / 3.

Modes: Keep will return to the last commanded position, which may not be the current position after a Follow.


To Calibrate
  1. Power on in the best version of home you can get.
  2. Calibrate
  3. Run "FindHome"
  4. Follow
  5. Put Dexter in dock
  6. RecordPark
  7. Move out of park to any position.
  8. Power off Dexter.

To use:

  1. Power on generally close to home
  2. Run "FindHome"
  3. Follow
  4. Put Dexter in the dock. You may notice it is a little difficult as Dexter isn't callibrated.
  5. SetPoint
  6. Take Dexter out of dock
  7. Home
  8. Wait until Dexter stops moving.
  9. Hit Done button on popup box (not in main UI)
  10. Dexter is now at the home you first set and is callibrated.

See also:

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