The UnLimbited arm has arrived

Stephen's 1st build was for Isabella; it was also one of Team UnLimited's most complex builds to date as it was our first venture into building an arm. 

Isabella received a RIT arm; the RIT Arm is an adaptive device for people with an elbow but no wrist. It can be actuated by bending the residual elbow or via a bowden cable connected to a shoulder harness.

The RIT arm was originally developed by e-NABLE members at Rochester Institute of Technology in America; it is a "1st generation" open source assistive device and provides functional usage to the recipient.

e-NABLE's combined arm team are currently working on a new arm; however Team UnLimbited thought we would have a go at creating our own arm !

Following the build and delivery of the RIT arm to Isabella myself and Stephen discussed what we would like to improve :-

  • Total print time of the RIT arm came in at 44 hours; we wanted to reduce this.
  • The cuff for the upper arm is very bulky and while still relatively light it could be improved.
  • The forearm socket is also very bulky and also introduces the complexity of cup fitting for the residual forearm.
  • Potential problems of heat / sweat in the forearm socket, complexity of padding etc.
  • The front forearm requires a tube to interface the socket and the hand; we used a carbon fibre tube from a RC helicopter, but in many parts of the world where these devices could have the biggest impact this might be hard to source.
  • The RIT arm requires various screws and fasteners (if used with the original RIT hand) to be completed, again proving a challenge for people to source components.
  • We wanted to make building an arm easier. To help reduce the list of arm recipient who are waiting.

Stephen took inspiration from a post he saw on instagram of a picture of a girl using an arm adaptation made to fit Gyrobot's world famous Flexyhand.

The adaptation was developed by fellow e-NABLER Christian Silva and he has been having great success with it to date.

So with the development goals set, some inspiration from fellow e-NABLER's and our existing love of thermoforming (as seen in our reverse dovetail gauntlet design) we set out on designing the Unlimited arm.

As the design developed we kept re-printing parts, testing them, evolving the design, re-printing. Working as a team firing ideas and changes between us.

Given that neither of us had developed an arm there was a large amount of thinking, trial and error and more thinking involved ! Stephen had a unique insight into designing what was needed as a recipient himself, and spent many long evening and nights modelling, and remodelling the designs to achieve the best possible outcome.

We decided to cover all eventualities and build 2 devices, Stephen would build one at 100% and Drew at 110% that way we were sure that at least one would fit and let Isabella experiment with one and provide valuable feedback.

  • Colour scheme was to be same as before, pink, purple and green.
  • Phoenix hand to be used as this is what she had adapted to on her custom RIT we built her.

Drew asked Isabella's father Matt if they were any shapes / theme Isabella would like including; apparently starts and hearts would both be good.

Drew's arm was to be customised with colour inlays; this was done by modelling the inlay shapes in Fusion 360, printing them separately and then forming and super glueing them into position. By using inlays we wanted to see what was possible for people who have a printer with a single extruder; often people think this limits them to one colour, but that does not have to be the case with a little cleaver thinking.

Some pictures of Drew's design and build below.

And after final construction, the end result :-

Some picture of Stephen's design build below.

And after final construction, the end result :-

So with the arm's all built and ready for our first alpha test Stephen set off and delivered them both; the results can be seen below, it's fair to say we are over the moon with the results so far !

Team UnLimbited invent the reverse dovetail gauntlet

Following on from the development of the thermo-gauntlet by e-NABLE members and Team Unlimbited I mentioned to Stephen in one of our hangouts that it would be better if the dovetail on the gauntlet that allows the tension block to connect was raised up on a pillar. This would allow for the overall gauntlet shape to follow the contour of the forearm better without the dovetail deforming.


Stephen and I discussed a few ways this could be done, remembering we wanted to maintain easy printability and strength.

Later that day, Stephen sent me a picture of his interpretation of the initial idea; he had invented the reverse dovetail thermo-gauntlet !

By turning the dovetail joint around and making it less wide would allow for thermo-forming to have more material that could be formed while still leaving a connection for the tensioner box.

Steve also realised that the tensioner box could be customised to a different shape.

Steve Wood AKA Gyrobot also pointed out that the bottom of the tensioner block does not have to be flat and that lead to a few more different designs as well.

Steve and I wasted no time running a few off on our printers to validate the dovetail joint strength, position and little retaining notch used to clip the tension block on.

After a few little tweaks we were happy that the reverse dovetail gauntlet works well; the different shape now possible can be seen in the pictures below compared with the standard thermo-form gauntlet.

Team unlimited will be adopting this gauntlet in our devices for our recipients and we have already done so in both Mollie’s and Abbi’s device. Abbi reports the gauntlet fits much better and is more comfortable for her to wear, the increased comfort also helps with her grip strength when bending her wrist.

Team Unlimited are currently re-modeling the reverse dovetail gauntlet into Autodesk fusion 360 file format and it will be released back to the e-NABLE community for all to use.

Team UnLimbited Develop Simple Adaptive Grip Idea

Normally the fingers on an e-NABLE device all work together from the tensioner system. That is if one of the fingers grips an object, the tension created in the tendons prevents the other fingers from gripping any further; often resulting in a weak grip (one of the biggest issues with current devices)

For some time several e-NABLER’s have been experimenting with a way of achieving adaptive grip on devices. Adaptive grip allows a degree of independence in the individual finger actions, thus if one finger starts to grip the other fingers can still continue to move to help improve that grip. To date these excellent developments have been based on the use of a whipple tree design.

Myself and Stephen had built these devices but for reason unknown neither of us had managed to get the same level of adaptive grip as other people were able to re-produce.

Fellow e-NABLER from France Theirry Oquidam posted a picture of a rapor hand which he had wired the fingers 1&2 and 3&4 by lopping them through the tensioner pin and back to the other digit, creating a simple adaptive grip.

This idea sounded almost to simple to work, but Stephen and myself though its worth trying out. Stephen quickly created a 3 pin tension block to use on our Reverse Dovetail Gauntlet to test, at the same time we both created tension pins with a rounded internal surface to help the tendons move freely through them.

A quick print later and we gave this idea a test; and it worked really well. I'm sure a more complex Whipple tree gives a better adaptive grip, but given the simplicity with this Stephen and myself have decided to stick with this design for the moment.

To date both Mollie and Abbi have received devices with this modification for them to evaluate.

We look forward to their feedback and also releasing this back to the e-NABLE community for all to re-use / progress. For anyone who wants to test this out, the files are HERE.

UnLimbited Phoenix to RIT Adaptor

When Stephen started his 1st build for Isabella, which was to be a RIT arm he quickly discovered the extra components needed to make the standard RIT hand he did not have e.g. chicago screws. Stephen also wanted to use this build to road test further the Phoenix hand developed by Jason Bryant that is currently undergoing evaluation.

During one of our many Hangout conversations I suggested to Stephen that we could develop an adapter to allow the Phoenix to be retro-fitted on to the RIT arm; I quickly knocked up these very rough images on the train while on the way to see a client.

Stephen wasted no time and began developing the idea further and soon had a working idea.

Stephen then noticed that the adapter would interfere with the palm area, so he reduced the adapter size, enough to fit and be strong but not occupy the whole palm void; perhaps someone in the future could make use of this space :-) Stephen then added tendon paths and mounting point for the forearm.

So with all the basic elements taken care of Stephen sent me the files while he focused on the rest of Isabella's RIT arm and I printed off a test adapter to fit to a Phoenix hand I was building for Abbi Jillians,

Initial tests seem good, the fit was great and the adapter would click in around the wrist pin holes, I did notice the tendon holes did not quite line up, I provided this feedback to Stephen and demonstrated it by using Spaghetti :-)

Stephen's own testing had also determined that the tendon routing needed to change as the internal angles were to steep and impacting on the finger movement. After some modification and tweaking Stephen settled on the final version, he printed it ready for Isabella's arm.

Stephen also produced a mock up of what Isabella's RIT arm with Phoenix hand would look like, very cool indeed.

You can find out more about our work with Isabella in THESE blog posts. The Phoenix adapter files can be found HERE should anyone want to make use of them.