Feb. 19, 2015 | By Alec

More and more people missing an hand or an arm are discovering the many benefits of a 3D printed prosthesis. Not only are these far more affordable than all traditionally-manufactured prosthetics available on the medical market, they're also far easier to customize and adjust. While this is an absolutely wonderful development, most of these are just plastic constructions with a mechanical grip. Simply flick your wrist up or downwards, and the fingers move inwards or outwards.

That’s why a new air-powered approach by Instructables user Mikey77 – who is known for his interesting and innovative 3D printing tips– is so interesting. He has developed a way to 3D print cheap and easy air-powered prosthetics that could, potentially, become a cheap alternative for bionic prothetics. Fortunately, he has shared a tutorial for making these, so you can try it yourself on a regular FDM 3D printer.

As Mikey explains, this is ‘an artificial muscle robot hand that could eventually be used as a prosthetic replacement for a human hand. The "bones" are 3d printed in PLA and the silicone rubber artificial muscles and skin were cast in 3d printed molds. While most makers are not likely to want do duplicate this hand, some of the techniques used here might be found to be useful for other kinds of robots and casting.’

While it is still work-in-progress – Mikey is currently working on adding an arm that will have room for more hand muscles to stabilize movement – the hand actual works, as you can see in the video below.

The trick? Silicone artificial muscles, 3D printed air vents and a vast number of 3D printed components. ‘They are powered by compressed air. This gives it a soft touch that is much more human friendly than most robot hands. The artificial muscles are also very inexpensive to produce compared to traditional gear motors and servos.’ Mikey says.

While most of this can be simply created in PLA using just about any FDM 3D printer (Mikey used a Makerbot Replicator 2 himself) and the STL files provided on his Instructable page, you will three other more unconventional components: pourable silicone and molds (Mikey advises Dragon Skin 20), robot neurons to control the hand and, most importantly, an air pressure controller.

While the first can simply be purchased online, the other two are construction projects in their own right. Especially the air pressure controller can be a bit tricky, but if you have a similar system laying around you’re good to go.

Otherwise, go to this page for more info on constructing one. Mikey constructed a model that is very friendly to 3D printed parts, previously using it to make a beautiful flower construction. ‘The pneumatic muscle controller consists of 13 solenoid valves and a 12 volt air compressor. It allows for the control of 11 muscles. They can be pressurized at 9 psi or a vacuum can be applied,’ Mikey writes. ‘If you just want to test some air muscles without a controller, a 60cc syringe with tubing works well. It can provide up to 30 psi.’

The finger design in a silicone casing.

While most of the parts can simply be 3D printed, the finger components need to be subsequently cast in a silicone to ensure that the robot finger has a soft touch. When properly following Mikey’s steps, you’ll have a three-muscle soft finger complete with air channels that will enable flexing. As for casting the silicone, Mikey relied on a very clever system of 3D printed mold that can be easily broken apart thanks to a series of break lines. Not only will these be very easy to use, they also ensure that the silicone retains all the necessary properties. A clever tip even for other projects!

Aside from that, it's a simple matter of assembling all the parts and silicone fingers to shape a hand. While Mikey has not yet provided the parts that will enable you to attach it to a wrist and make it an actual prosthetic, I suspect that the open-source parts on typical mechanical grip prosthetics will work perfectly here.

Mikey's air pressure controller - not exactly ready to wear on your person.

Finally, it's a matter of programming the hand to open and close its grip. Fortunately, Mikey has already provided the code for the circuit board for it, which you can simply copy and paste from his Instructable page. If done correctly, that will give you a hand with a proper, electronic gripping function that is far more affordable than all those servos that would otherwise be used. The only problem is that Mikey’s own air pressure controller isn’t exactly fit to wear on your wrist for now, but this is still a work-in-progress after all.

While Mikey is still trying to perfect his designs, he is also already speculating about follow-up projects. Among them are plants for whole prosthetic arms filled with high pressure valves that can easily open and close the grip, but perhaps most impressive is his plan for a foot prosthetic. These are notoriously difficult to make with an FDM 3D printer, as plastic has difficulty to support all that weight, but Mikey is optimistic. ‘One of the advantages of using air powered muscles is that it should be possible to design an air pump that fits in or on a shoe. This could be used to pressurize a small flat backpack tank while walking. This could keep a prosthetic hand and arm powered in a fairly unobtrusive way,’ he writes.

While nothing more than speculation for now, thanks to Mikey’s own 3D printing track record I would not be at all surprised if he shows up with a whole foot prosthetic in just a few months.

Posted in 3D Printing Applications

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