Tact:Low-cost, Advanced Prosthetic Hand


In addition to the listed a few tools are required: phillips or flat head screw driver (depends on your type of screws), two needle nose pliers, superglue, and wire cutters.

For the 3D-printed components a Makerbot Replicator 2X was used, but any 3D-printer is capable of making these components. If you don’t have access to any, consider using a company such as Shapeways that will take files submitted online and mail you printed parts.

They  printed all components except for the spool at a resolution of 0.2 mm (200 microns) and 10% infill. This helps prints to be made more quickly while still strong enough. The spool should be printed at the finest resolution and highest infill that your printing device can produce. Total printing time for me took around 14 hours. Once you have all your parts ordered and 3D-printed components, you are ready to assemble!


All fingers including the thumb follow the same basic assembly structure and use the same components.

  1. First take your length of steel cable, tie a knot at one end, and dot it with glue to ensure it doesn’t slip. Take the spool and pull the cable through the smaller hole by the top of the part so that it starts on the outside diameter of the spool and pokes out on the inside of the spool diameter. Now pull the rest of the cable through until just the knot is left at the outside of the hole. Send the free end of the cable through the larger hole in the spool, beginning on the inside the diameter of the spool and exiting to the outer edge of the spool.
  2. Take a motor and press fit the spool onto the shaft of the motor. Ensure that you have lined up the flat part of the motor shaft with the flat part of the spool. If this is not aligned correctly you risk damaging the spool.
  3. Now take the motor housing piece. Insert two 6mm M2 screws into the small holes on either side of the larger opening. Push the motor/spool combination up through this larger hole and screw in the motor to the housing.
  4. Gather both the finger tip part and the linkage. Using an 12mm M2 screw and nut fasten the linkage into the slot in the finger tip part. Make sure it is loose enough to still rotate freely.
  5. Now take the lower portion of the finger and slide the linkage and finger combination inside of it. Watch the orientation. Screw the two finger pieces together through the remaining hole in the finger tip part with a 20mm M2 screw.
  6. Take the partially assembled motor housing and finger parts and affix the free end of the linkage to the appropriate hole in the motor housing using a 12mm M2 screw.
  7. Now affix the remaining hole in the lower portion of the finger to the remaining hole in the motor housing using a 20mm M2 screw.
  8.  Now route the length of cable remaining out of the inside of the motor housing and up through the hole in the cylindrical part of the lower finger piece. Take a wire crimp or tie a knot in the steel cable and add a dot of glue for strength.
  9.  Repeat this finger assembly process for all fingers and the thumb.

Thumb Assembly

  1. First find the servo and the servo holder printed piece. They should press fit together.
  2.  Next take the small part that mounts between the servo and the thumb and attach it to the corresponding hole in the thumb piece using a 6mm M2 screw.
  3. Now assemble the thumb bracket onto the servo using the two screws given with the thumb servo. Attach this assembly onto the front part of the hand containing the other four fingers with two 6mm M2 screws.

You have completed the mechanical build of the hand!


Source: instructables

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