Dexter Robotic Arm by HDRobotic.com

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
https://ksr-video.imgix.net/assets/015/535/426/dc37c52a916cd8b678d7ee124daeea56_h264_high.mp4

*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.

• The stepper motor shafts on Joints 2 and 3 can easily slip inside the shaft to wave generator adapter part. Carefully remove the wave generator and adapter (often they will remove themselves!) and then mung the motor shaft with small end cutters or other available tool. Then apply a small amount of very high end epoxy (I used the metalized JB weld, #8276) to the inside of the adapter and carefully slid it back in. Take care not to push it too far in as that will cause binding. Let cure before moving.
• The adapter can also come loose from the wave generator. And that again causes the joint to loose traction and/or the wave generator to fall out. In this case, the solution is a bit of low viscosity super glue carefully applied between the adapter and inner hub of the wave generator. Be very careful to avoid getting any glue in the wave generator. Let sit.
  
  Be very careful re-inserting the wave generator.  It is best to try slightly different positions until you find one that slips in easily. However, it can be accidentally inserted such that the teeth are not evenly divided between the two nodes of the wave generator. In that case, the joint will jam up and you won't be able to "back drive" it. To fix it, you should be able to manually spin the motor shaft until the teeth pop over into the correct position. At that point, the joint may start working correctly again. Or the wave generator may be damaged.

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

FindHome:

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:

• STL files (more up to date than the OnShape link)
  https://www.dropbox.com/sh/5bdyhcyyrf3x53k/AAAagpOvq-TxkVKE1Ax-uodEa/STLs?dl=0&lst=
   

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