Introduction: Falcon Hand V1

Our first contribution to the E-nable community.

This hand is a research platform for the development of various 3d printed prosthetic ideas. Namely the Radial-Ulnar deviation controlled grip patterns, eliminated elastic cording/soft control cables, eliminated knot tying, minimized hardware, and a new tensioning idea.

This version of the Falcon hand is not intended to be fit for an actual patient AS-IS. Our hope is that these technologies work their way into already-accepted hand designs like the Cyborg Beast, Talon, and Flexy Hand.

Materials list:

1. Various dental elastics

2. 3X 3/16 in. by1/2 in. Chicago Screws

3. Acetone and a cotton swab

4. Printed parts from Thingiverse

5. (Optional but recommended)

6. Velcro straps that can be cut to length

Link to Thingiverse files:

Link to E-nable website:

Design and development credit: Dr. Adam Arabian, Sean Russell, and Barrett Estep.

Step 1: File Rotating Surfaces to Smooth Layering

Use a small file to smooth out the rotating surfaces of the fingers. Don't forget to file down the inside edge of the middle phalange, as shown. The more attention you put into this step, the better. Friction is this hand's worst enemy.

Step 2: Acetone Smoothing (ABS Printers Only)

If you printed in ABS:

Take a cotton swab, or similar tool, and apply acetone to the rotating surfaces. You may need to rub the swab gently against the part to work down any rough bits that the filing missed. I found that if the swab is well soaked, the acetone will flow onto the hinge and coat it very evenly, with little or no rubbing on your part. The goal here is to further eliminate the friction in the joints. Get the surfaces of the finger joints as well as on the palm.

Very important: the acetoned surfaces needs a good 10 minutes to completely harden.

Step 3: Drill Out Hinge Holes

When you are sure that the acetone has hardened completely.

Drill out the hinge pilot holes so that your filament stock turns smoothly within them. It should be a close enough fit that there is little to no play in the joint, but loose enough that the joint will roll under the force of gravity alone.

We use 1.75mm filament, and we found that a #48 drill bit (~1.92 mm) works quite well.

Step 4: Install Filament Hinges

Cut small segments of filament a little longer than the width of the finger. Use a soldering iron to fuse the ends of the filament flush with the sides of the finger. You can put a small piece of brass tubing over the end of your soldering iron to protect it if you want to keep it clean.

NOTE: When you do this for the first time, you may want to melt pin heads onto the filament but not fuse it to the sides of the finger. This will allow you to snip off the ends of the filament and replace/modify selective parts of the finger. Totally fusing the filament will result in greater strength and better aesthetics, but if these are not important to your build, don't do it.

Finish the two joints in each finger this way, and do all 4 fingers.

Step 5: Attach Elastic Bands

Stretch the elastic dental bands onto their anchors. We used light (1.8 oz) elastics for the each of these joints. It is difficult to get the bands to seat properly with your fingers alone, so it will help to take a narrow pointy tool to push them down into place. In the photo, I am using a small diamond grit needle file.

This completes the assembly for the finger modules.

Step 6: Snap Fingers Onto Palm Axles

Loop the proximal phalange onto the palm axle and pull it straight away from the palm, like the "pull-my-finger" trick. It might take more force than you'd expect. Do this for all 4 fingers.

Step 7: Beading Wire Prep

Cut a piece of .6mm beading wire to about a foot of length. We got a little container full of short lengths of small diameter aluminum tubing to use as crimps. Loop the wire through the crimp as shown, pull it tight and then pinch the crimp with needle nose pliers. Trim the excess so that it will fit in the end of the printed fingertip better.

Step 8: Thread the Fingers

The wire threads down through the fingers. Pull the wire tight so that the crimped end seats well in the fingertip.

Step 9: Install the Knuckle Slide Cover

This knuckle slide cover has the proximal anchors for the final set of elastic bands. The cover simply drops into slots on the back of the palm and is pushed forward into place. Be careful not to snap the small tabs on the bottom of the cover.

On this particular design, there is no way to prevent the slide cover from sliding back and coming out, you may want to figure something out. I would avoid methods of permanent attachment such as glue, as this limits almost all repairability. Filament pins of a sort would work well.

Step 10: Stretch Elastic Bands Onto Proximal Knuckle

We used a medium weight dental elastics for this step. Using a heavier elastic at this joint will cause it to close after the distal joints, resulting in a smooth curl.

Step 11: Thumb

Install the thumb with another filament hinge. I would recommend melting the ends of the filament so that there is a pin head on either end that can be snipped off for thumb removal.

Stretch an elastic band into place as with the rest of the fingers. Crimp the end of another length of bead wire and thread it through as you did with the other fingers.

Step 12: Gauntlet Attachment

Use 3/16 x 1/2 inch chicago screws to attach the Arch and Gauntlet. This will likely require some sanding to get the parts to rotate smoothly.

Once this is done, you can begin to thread the bead wire into the gauntlet. Notice that the wire travels from the palm along the outer channels of the gauntlet and then into the rotating crimpers. The wire threads straight through the center of the rotating crimpers and then they are given a partial turn to pinch the wire.

For the most useful grasps, the wires should be threaded such that Radial deviation (inward, rotating to the side that the thumb is on) pinches the thumb and forefinger. Ulnar deviation should curl the middle, ring, and pinky fingers (making the hand point). Reference the photos for a better idea.

This is the most tricky part of the build process. The rotating crimpers have two large flathead slots so that if one breaks (they are sort of fragile) you can use the other. Additionally the location of the beadwire through-hole prevents a centered slot.

This process requires some patience and finesse but once the wires are all threaded it becomes a simple process to tension the various fingers. Just use a flathead screwdriver to loosen the crimper and then give the beadwire a little tug in the appropriate direction with needle-nose pliers. Reference the photos for a better idea.

Step 13: Gel Tips

Putting set of gel tips on the fingers will improve the grip significantly.

Step 14: Snap Cover

Snap the cover over the gauntlet tensioners when all the fingers are moving properly. This protects them and improves aesthetics.