e-NABLE prosthetic hand

Contributed by
Martin van Wezel

For the Ulti-Evening of January 2016 we asked Ultimaker co-founder Erik de Bruijn and community member Martin van Wezel to share their knowledge about the e-NABLE project. e-NABLE is a platform for providing 3D printed hands to children in need. Accessible, cost effective, and colourful. All to improve their life, provide an aide that will give them more flexibility, boost their self-esteem. It is a platform of volunteers, some with medical background, some with a background in 3D design and printing, all with a drive to help people. During the Ulti-Evening Erik and Martin shared their tips for becoming involved in the e-NABLE project as a volunteer.

To get started with e-NABLE it is strongly recommended to print and assemble a Raptor or Raptor Reloaded hand before you sign up. This will give you a feel of what is needed, what materials to source, where to source them and which print settings to work with for your printer. And you will have a cool demo hand for your future projects.

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Materials needed

  • M3x8 mm countersink screws
  • M3x10 mm countersink screws
  • M3x30 mm screws
  • 4x Velcro with a width of 15 mm (2x strips of 70 mm, 2 strips of 230 mm)
  • 5x 300 mm kite string (preferably Dynema)
  • 5x 200 mm elastic string (round) with a diameter 1.5-2 mm
  • Craft foam (or medical foam if you can get it) with a thickness of 2 mm

Materials

Tools needed

  • Needle-nose pliers
  • Sidecut clippers
  • Philips Screwdriver
  • Flathead screwdriver
  • Exacto knife
  • Tweezers
  • Scissors
  • Soldering iron with cutting head
  • Beltpunch
  • Electric screwdriver with different bits (optional)
  • Thwack (optional - see tip 7)
  • Piece of tile (optional)
  • Threading loop (optional)

Tools

Printing

Get the files for the Raptor Reloaded here. This is the download file for a Raptor at 100% of the size. We recommend using the following settings for printing the Raptor:

  • Layer height: 0.15 - 0.2mm
  • Shell thickness: 0.8mm
  • Bottom/top thickness: 0.8mm
  • Fill density: 15% - 26%

When printing all parts at once, it is recommended to print with a brim of at least 5 lines. This keeps the small parts attached to the build plate and ensures the rounded corners of the fingers, gauntlet and palm don’t warp (which will cause assembly problems). Ensure, all parts are printed neatly (no meshing in top and bottom of the print - no delaminated layers).

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Assembling

  1. Clean all parts, remove brim and flashing, so parts are neat.
  2. Assemble all fingers with the 5 tips, 5 proximal planges, and small pins first.
  3. When the fingers are assembled, thread the elastic string through the fingers over the top.
  4. Take the 5 strands of elastic string and attach the strings to the bridge on the finger tips. Use 2 knots to fix them.
  5. Take the 5 strands of kite wire and thread through the bottom of the fingers. Attach them to the bridges on the tip by using 2 knots.

    Tip: Cutting the strands of kite wire is nearly impossible with scissors or clippers. It is recommended to use a soldering iron with a cutting blade instead. You can melt through the wire (no raffles) easily in no time. (use a tile as your cutting surface).

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  6. Connect the palm to the gauntlet using the thick pins and round caps. Make sure the pins are flush with the inside of the gauntlet. If not, clean the hole a little more.
  7. Connect the 4 fingers to the palm with the 2 large pins.
  8. Connect the 5th finger (or thumb) to the side of the palm with the medium pin.
  9. The fingers should be able to move freely. Therefore it's recommended to test the friction by shaking the hand with all the attached fingers. Ensure that:

    • No pins fall out.
    • All finger hinges hold move freely.

    Disassemble and clean the parts if required (use some sandpaper).

    Tip: In case pins should fall out, you can fix them with a small dot of superglue, or use the soldering iron to seal the pins in place.

  10. Pre-assemble the tensioner:

    • Take the tensioner block and insert 1 tensioner pin in the block.
    • Take a M3x30 mm screw and insert the screw for it to pull in the tensioner pin half way into the block.

    Repeat these steps for all remaining tensioner pins.

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  11. Attach the pre-assembled tensioner block to the gauntlet and insert the tensioner clip to keep it in place.
  12. Thread the elastic string through the palm and tie each string to the bridge on top of the palm.

    Tip: Threading the strings can be tedious, it is recommended to use a precision needle-nose pliers or a threading loop. A threading loop is essentially a piece of metal wire to which you can hook your string and either push or pull it through the required holes.

  13. Tie the strings tight enough so the fingers spring back when bending the 2 knots.
  14. Thread the kite string through the palm and tie to the holes in the tensioner pins.
  15. Tie them so they are tensioned when the wrist is in a neutral position 2 knots.

    Tip: A neutral position is achieved by putting the Raptor flat on a table keeping the fingertips ±10 mm above the table. This is achieved by putting a spacer (use the tile) underneath the finger tips when timing the knots.

  16. Test the hand by bending the wrist and releasing it again. All fingers should come back more or less simultaneously. If not, you can adjust the tension with a screwdriver. Als make sure none of the wires are slack. If this happens, you are better of un-tie and re-tie the strings.
  17. Take the 4 pieces of velcro of 70 mm and punch a 3mm hole in them with a belt-punch.
  18. Screw the velcro to the palm with the M3x8 mm (or 10mm) countersink screws.

    Tip: The palm has 7 drill holes. For your demo hand you want to use the ones closest to the edge. The other 3 holes are there to use when you need some customisation with the straps.

  19. Cut the foam to create a shape that can fit the inside of the palm and gauntlet.

    Tip: Always use a new blade! Alternatively, if you have access to a lasercutter, you can use this template and cut the foam.

  20. Add 2 strips of double sided tape to the foam shapes for them to stick neatly into the palm and gauntlet.
  21. Take the 2 pieces of velcro (270 mm) and thread them through the gauntlet.

You made yourself a Raptor! The result should look like this:

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Raptor versus Raptor Reloaded

The Raptor Reloaded is an improved version of the original Raptor hand. The original raptor can also be found here. The advantage of the Raptor Reloaded is the ease of assembly. The disadvantage is, it is not (yet) supported by the handomatic which makes it a little harder to establish the right sizing for your future projects. the original Raptor is supported by the handomatic. The assembly process is roughly the same. Great youtube video’s are shared on the assembly process.

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