2015-09-05 (Sa) Wrist Mounted Chording Keyboard

Making servo levers go around obstructions has been a good choice. Yesterday one servo arm was modified to go around the thumbboard and a folded keypad. On the other side of the keyboard a straight servo arm was hitting a pulley. The model for the straight servo arm was modified by adding a hollow half-circle to the shaft. Each step and a rotation can be seen in the image below.

Process and rotation of the modified servo arm

After modeling a print was made but it did not fit well so a second was made. The problem with the print was the hollow half-circle was too far from the servo. Even the second print was not corrected enough so a third was modeled to get a good fit.

Second attempt at a half-circle held over the first print

All the parts were assembled but the servos were not screwed into place. Servo testers were used to move the servos but synchronized movement could not be obtained. Arduino's demonstration program, which normally turns a servo according to a potentiometer, was modified to turn two continuous rotation servos in opposite directions. If this program was run with ordinary servos in the same configuration it would work similarly except the servos would not turn very far from center.

Using servos to move the keyboard made it obvious that all four levers were needed to get coordinated movement. One of the first draft offset arms was temporarily used as a lever to go around the thumbboard and definitely helped the motion. All assembled parts were held up to the forearm and tested for fit where it became obvious all the levers would need to be lengthened but only the final draft will need these longer servo levers. Shorter levers will be used until the other dimensions are set.

Offset lever going around thumbboard

Program to test servos wired back-to-back

Downloadable Files:
To do:
  • Wrist mount
    • Revise offset levers
      • Make holes in thumb board cylindrical instead of countersunk
      • Model hinge arm to go around thumbboard
      • Add built-in spacers
      • Connect servo arms
      • Lengthen servo arms
      • Round corners?
    • Integrate:
      • Controller
      • Servos
      • Enclosure for each controller
      • Limit switches
    • Debug
    • Test
    • Refine
    • Repeat
    • Activation switch
    • Route wires
  • Write instructions
    • Make diagram with everything labeled
    • Schematic

The rest of the posts for this project have been arranged by date.

First time here?

Completed projects from year 1.
Completed projects from year 2

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2015-09-02 (W)