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How To Replace Finger Tendons

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jlack1987 edited this page Apr 28, 2016 · 46 revisions

If you do not already have a replacement tendon prepared, you can find instructions for creating new tendons [here](How To Make A Tendon)

Replacing Tendons

In order to replace a tendon, you will need the following tools:

  • M2.5, M2, M1.5, Torx 16 drivers
  • Straight and Curved Forceps
  • 10" draw wires

With these tools, the following steps will guide you in replacing a broken tendon,

  1. Remove glove (easiest to doff glove with thumb fully opposed).

  2. Remove shells using M2.5 driver.

  3. Open up Athena 2 side mount to expose APS side of finger actuators using an M2 driver.

  4. Remove the distal finger nail cover to expose the terminator pin,

  5. Remove the pin,

  6. Withdraw tendon from finger links.

  7. Identify which motor drives the tendon that needs to be replaced and remove the APS sensor of that actuator to expose the pulley.

  8. Remove the teflon disk using one or both forceps, being careful not to damage or deform the disk.

  9. Remove the three bolts that fix the pulley to the output of the actuator using the torx T6 driver.

  10. Free the tendon from the post and pull it out of the forearm.

  11. [Make a new tendon](How To Make A Tendon), make sure to properly lubricate it by rubbing krytox into the braid.

  12. Using a draw wire, pull the side of the tendon with the larger hole through the base of the finger down to the actuator housing.

  13. A pair of forceps can be used when the wire peeks through into the housing itself.

  14. Pull the tendon through and place the loop on the pulley post. Do not yet bolt down the pulley to the output.

  15. Using a draw wire, pull the distal side of the tendon through the finger links to the distal link. Note that the thumb proximal (motor 5) terminates on the dorsal side of the proximal link of the thumb

  16. Insert the terminator pin into the loop and straighten the finger to pull the tendon into the slot. You can turn the pull in order to take up any slack.

  17. Rotate the pulley around and bolt it to the output of the actuator. Be sure that the position is within the range of motion of the finger and not near the full open position (the actuator would react poorly if the forearm wakes up with an APS sensor reading out of range – it would likely result in another broken tendon). You may need to hold the finger in a flexed position to enable pulley rotation.

  18. Reinstall the teflon disk, again taking care not to damage or deform the disk. Position the disk so that it is offset in the cutout on the pulley, then slide it into place such that center hole of the disk is concentric with the pulley/magnet.

  19. Rotate the disk so that the flat or cut side of the disk is 180 degrees from the cutout on the pulley.

  20. Reinstall the APS sensor.

  21. Ensure that the pin is in place on the distal link. If it is the thumb proximal, add a dab of silicone/RTV at the pin to help hold it in place.

  22. Replace the distal finger nail cover. Be sure to hold it into place against the tension of the rubber band. If you do not, you risk stripping the fine threads that help keep the finger nail in place.

  23. Perform checkout. If the tendon length was changed significantly, a position recal may be required.

  24. Reinstall shells, done gloves, and voila. Done.

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