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How To Make A Tendon

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jlack1987 edited this page Jun 21, 2016 · 6 revisions

This page provides detailed directions for broken tendons that operate the fingers and thumb on Valkyie's hands.

Tendon-Actuator Routing

The following table/graphic show which forearm motors correspond to which finger,

Finger/Tendon Motor Location
Index F1
Pinky F2
Thumb Distal F3
Middle F4
Thumb Proximal F5

Tendon Lengths

Each forearm has slightly different tendon lengths. When replacing a tendon, make sure to use the length corresponding to the forearm you are working with. Each forearm contains a serial number. There will be a label on each forearm that designates the serial number for that particular forearm, and it should look something like 'v_h_xxx', where 'h' specifies that it is a forearm assembly and the 'xxx' is a 3 digit number. Once you have found your serial number, the following table will tell you the correct tendon lengths,

Table 1
Forearm Serial Number Thumb Distal Length(inches) Thumb Proximal Length(inches) Index Finger Length(inches) Middle Finger Length(inches) Pinky Finger Length(inches)
v_h_005 12.1 9.625 10.6 13.35 11.25
v_h_006 12.5 9.5 10.5 13.375 10.75
v_h_007 12.25 9.625 10.85 13.35 11.25
v_h_008 12.25 9.5 10.5 13.375 10.75
v_h_003 12 9.625 10.5 13.25 11.25
v_h_004 12.25 9.5 10.5 13.375 10.75

Tendon Making Protocol

You will need the following tools,

  • Sharp exacto blade
  • Hook nose forceps
  • 2-3" length of 32 gauge wire
  • Marker/Pen/Sharpie
  • Size 18 tapestry needle (0.05" diameter)
  • Scale

The following table lists key points/measurements that will be referenced later,

Actuator/Pulley Side Pin/Finger Termination Side
1.5" - a minimum to place tail marking X.X" - length of tendon(from Table 1) from end of larger eye loop (also B top of eye loop) to point "B"
1.5" - From tail mark to point "A" 0.25" - To points "A" and "C", point "A" is closer to the free end of the tendon
0.5" -From point "A" to point "B" 1.5" - From point "A" for tail mark
0.5" - From point "B" to point "C" -

  1. Mark tendon material with points A, B, C, and tail length,

  2. Thread tendon through eye of needle on the tail side

  3. Insert needle into point C and draw tendon tail all the way through, and carefully invert the loop,

  4. Insert needle into point A and draw tendon tail all the way through, carefully invert the loop.

  5. Using the wire, draw the tendon material point "B" back through point A such that it untwists the twist created in Step 4. Be sure to pull point "C" through the newly created eyelet.

  6. Again, using the wire, draw the tendon point "B" back through point C such that it untwists the twist created in Step 3.

  7. Hold the newly formed eye and pull on the non-tail side of the tendon to tighten, to snug the Brummel loops together. Do not pull excessively tight as to damage the woven pattern of the tendon.

  8. Insert the needle into the core of the tendon material near the bottom of the last Brummel eye.

  9. Draw the needle through the center and compress tendon braid to cover most of needle before allowing the need to protrude out of the core of the tendon.

  10. Draw needle all the way through and keep hold of the tail.

  11. Trim the tendon at the 1.5" tail mark at a steep angle

  12. Fray the end of the tail to reduce the transition for the tail bury

  13. Holding the eye, pull the tendon to bury the tail

  14. Repeat on the other end as necessary and measure from eye tip to eye tip

  15. Lubricate tendon with krytox

  16. For more detailed notes of eye brummel splicing, please see: animated knots

Now you have created a tendon, you can find instructions for replacing a broken tendon [here](How To Replace Finger Tendons)

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