e-NABLING R&D – Experimenting With Elastics



It’s R&D “Motivational Monday” again and we are excited to keep sharing some of the behind the scenes work that is going on in our research and development teams within our forums and Google+ groups!

We have a whole lot of e-NABLE volunteers that are working on getting our current designs printed and gifted to children and adults around the world, but we have just as many who are working on improving the designs for the future!

Here is another great article about some of the incredible collaboration and design work going on in the community!

e-NABLING R&D – Orthotic Rubber Band Hand
By Adam Kitz – WWU e-NABLE Intern/Volunteer

This week’s “Focus on R&D” design is brought to you by Jason Bryant, e-NABLE volunteer, researcher and teacher at Shandong University in China. His design is an amalgamation of the Raptor Reloaded hand (available on the e-Nable website) and the Falcon V1 hand designed by Dr Adam Arabian from Seattle Pacific University (available on thingiverse). The Falcon V1 was the first e-NABLE 3D printed hand prototype to use orthodontic rubber bands as opposed to the elastic cords that current devices use. Jason began work on his new design by looking at the differences between the rubber band and the elastic cord.

falcon v1

Jason, on his research: “I did a little testing and found that rubber bands can stretch to about 500% of their original length, while the nice elastic cord only stretches to 150%. So obviously the elastic cord is hitting its limit. This is more of a problem on the smaller hands, which have less elastic to stretch. That might also help explain why I had an elastic cord break before any of the rubber bands broke. The rubber bands still have stretch to spare even when the fingers are fully closed, so they’re not feeling the strain.”

Jason’s study helped to shed some light on one of the main problems with the elastic cord. Specifically, in smaller hands where there is not much elastic to stretch when the hand is being closed. The traditional elastic can make it difficult to fully close the hand due to its lack of elasticity. After finding that the rubber bands had nearly 5 times the stretch of the elastic cord, Jason designed a Raptor Reloaded hand with rubber bands in mind. His new design uses dental bands like the Falcon V1 to connect the joints of a Raptor Reloaded hand.

According to Jason: “At this point, I do have a few thoughts on the design. It seems to work pretty well. The dental elastic hand does not close as easily as the rubber band hand, but it does close easier than the elastic cord hand… One interesting thing is that the force is distributed differently. At the very beginning of the motion, the dental elastic hands require a little more force. However, that force doesn’t seem to increase much as I continue pushing the fingers closed. On the hand with elastic cord, it starts off very easy and linearly ramps up as you get closer to closing the fingers. This might be improved by experimenting with different lengths of elastic bands. The ones I got were 3/16, which I believe means they have a diameter of 3/16 of an inch. There are many other sizes, and I’m trying to get 1/4 now. If they are longer, then they won’t be stretched so much at their starting positions. That should make it easier to open the fingers for the full range of motion.”

In addition to the dental band hand being easier to close than the traditional elastic cord hand, the dental bands are also much easier to put on because there are no knots to tie. Jayson says, “The goal of the Falcon Hand team was to make something that can be put on with one hand. It’s not easy, but I managed to do that. That means that you can give your recipient a little bag of rubber bands, and they can fix any broken bands themselves.”


Despite these improvements from the standard Raptor Reloaded, Jason was still unhappy with the way the hand closed. The hand would close first at the fingers and at the palm last, making for an awkward and inorganic grip. In order to make the hand close more naturally, Jason began by tightening the bands by the fingertips and by adding two bars to the palm of the hand to change the angle at which the fingers are pulled. These two things together allow the hand to close in a much more natural way, making it easier to grab objects of all sizes. It also has a more organic finger shape and his Gripper Box design to aid in the adaptive grip.

You can watch the hand in action below!

Jason: “Perhaps I’m getting overly excited because I’m so impressed with the thing I made, but this feels like a significant improvement. I think this gives a small improvement both to picking up large objects and picking up small objects. Obviously that will require testing, starting with maker testing. This is still a test, not a new hand. If things go as well as I’m hoping, we’ll need to build a new hand from the ground up, not just hack off parts of the Raptor Reloaded and stick on new parts.”

If you would like to be a part of this research and development team, have a 3D printer and want to help beta test the design or have ideas on how to improve this design – please visit our Forum for the “Rubber Band Raptor Reloaded.”