Champion Case Study: The Third Thumb

How to Extend Human Abilities with 3D Printing

When student designer Dani Clode presented her wearable device “The Third Thumb” at the Royal College of Art degree show, she couldn’t have imagined that it would become a global phenomenon. The Third Thumb is a 3D-printed motorised device that straps onto your hand and acts like a real thumb, which you control wirelessly via your foot. Since the project debuted this July, it has attracted huge media attention, a television show, and opened the dialogue about using prosthetics to extend human abilities rather than “fix” disabilities.

But rewind a few months back to the design and prototyping of The Third Thumb, in early 2017, and you see just how much effort, enthusiasm, and ultimately hope in a new technology went into making the project a success.

This is where our story, the collaboration between Dani and Champion 3D to manufacture “The Third Thumb”, begins.

“The Third Thumb” is controlled by a pressure sensor.

From Design to Reality

“The origin of the word ‘prosthesis’ means ’to add, put onto’; so not to fix or replace, but to extend,” Dani notes. This word origin forms the backbone and inspiration for “The Third Thumb”, a device that adds an extra ability to humans.

Although her product design master’s course offered a variety of prototyping techniques, Dani decided to use 3D printing because of its versatility of materials and speed, which brought her to 3DHubs.

Dani tried several hubs on the platform. For the first iterations of “The Third Thumb”, she used a flexible resin, but this material was expensive and did not offer the properties she required.

She soon discovered that Champion 3D offered flexible (TPU) plastics, which was the real connection. Flexible plastics are relatively affordable and come with different degrees of elasticity and toughness, so they were perfect for experimenting with “The Third Thumb”. The hub was also within walking distance to her so she could design and iterate quickly.

Making the Thumb — The Challenges

The main challenges in making “The Third Thumb” were creating a great 3D-printable model and finding exactly the right materials to mimic the behaviour of a real human thumb. Primarily, its natural rebound properties.

Dani using The Third Thumb to stack blocks.

How We Helped

Dani chose to work with Champion 3D because of the fast service, advice on how to design the model for optimal printability, 3D printing suggestions and tips, and because we took a real interest in the project. We learned through iteration and developed some best practices.

Over our collaboration, Dani modelled and tested over 30 successive versions of the thumb, all of which we printed in a flexible material called NinjaFlex, while fine-tuning the print settings.

Design iterations.

Modelling

Dani needed to design a functional piece that could move as naturally as a real thumb. Doing this with a flexible material was tricky.

Dani said, “It was tough modelling for a flexible material, just because when you’re working on the model, it looks so stiff and life-less and you really don’t know how it’s going to respond until you test it.

“My main inspiration was looking at living hinges on existing products. With the NinjaFlex, it was really about designing the material to move from one place to another. It flexes, but doesn’t really stretch, so you need to keep it mind that if you want something to bend, you need to have a pivot point but also somewhere for that material to move to, otherwise it won’t bend. The material will bend at the weakest point, so it’s just about incorporating that into your design. The fill of the print also plays a big role in how flexible it is, Champion 3D helped a lot with that.”

The Third Thumb used to play those tricky guitar chords.

Materials

We chose NinjaFlex as the best flexible filament for this project because of its elasticity and strength.

Filaflex could have worked, but wasn’t available in the Concrete Grey colour, which was part of Dani’s design. Also, Filaflex was softer and more rubber-like.

As Dani’s model was quite complex, the NinjaFlex made it easier to print, with less oozing at lower temperature. NinjaFlex has a polyurethane composition with a Shore hardness of 85A.

Find NinjaFlex filament here.

Machine requirements

We recommend printing flexible materials directly onto the glass of a cold print bed. As we progressed through the iterations, we also lowered the layer height of the model from 150 to 100 microns, which gave a good surface finish.

We used a 3D printer with a double-geared direct drive extruder, which pushes the material through the extruder on both sides. When using flexible materials, a Bowden system isn’t ideal. The best set up is to feed the material directly into the extruder from above, with the least amount of distance between the spool and the extruder, so the travel distance is minimal.

We chose an optimal print speed of 45 mm/sec and experimented with different infill densities, between 20 and 100%. Dani chose 60% infill density in the end, as it offered just the right level of squidginess to the model.

The printer feeding in NinjaFlex.

Local & Fast

Because Champion 3D was within walking distance to her, Dani could iterate the design fast. She would make minor adjustments to the model on a nightly basis and would send us the new files in the morning.

The perfect colour

Colour choice was an important part of the final design. Dani was specifically after the Concrete Grey offered by NinjaFlex.

Different iterations of the prototype.

The Right Price

We were able to offer 3D printing with flexible material, which is relatively inexpensive compared to resin (SLA) printing. Resins also mainly come in neutral colours, which restricts colour choice.

Champion 3D also offers a student discount, which further reduced the cost.


The Flextastic Result

The Third Thumb took at least five months to design, iterate, and prototype, but exceeded all expectations. So what was the secret to making The Third Thumb a global success? We believe it was all of these.

Good Modeller

Dani was a determined designer who asked a lot of questions about how 3D printers work, with regard to temperature, orientation, etc. She understood the capabilities of the machine and how the material prints. She was willing to adapt and refine her design quickly, given new information. She also prototyped the model successfully using Rhino, which can be challenging.

Flexible Materials

Our ultimate goal was to make the material work for us and make it act like a thumb. Not every print was successful, but we were both committed to making 3D printing technology work for this project.

Dani said, “3D printing is the perfect medium for this project, as it enables quick prototyping, customised designs for various hand sizes and one-off production.”

We will certainly print more in flexible materials in the future.

“It’s just cool”

Ultimately, “The Third Thumb” went viral because it was cool. It attracted interest from engineers, artists, designers, and all sorts of makers. 

Look out for the Daily Planet documentary on Discovery Canada, which takes you through exclusive interviews with Dani Clode and Champion 3D, as we manufactured this amazing project.

You can find out more about Dani Clode and her innovative design work here:
w: daniclodedesign.com
i: @daninkx

Need a 3D model or 3D printing? Find us here, and we will be happy to help: w: champion3D.com