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Assembling

Having all those pieces everything I had to do was put them together. The prototype contains 3D printed parts in three different technologies: SLA , SLS and FDM on a pair with standardized parts and even sewed padding. Assembling was a bit like jigsaw but done same way as simulated in Fusion 360 design software and took about 20 minutes. Passive module (mounted on hand) weights 350g and is way too heavy to be mounted directly on corset. Moreover, most users will be in half sitting position with head support right behind them. Following advice of physiotherapy experts, orthopedists and parents I added simple tripod mount to be used with Manfrotto Mini Arm and mounted at the back of any chair. After first try-on (without counterweights) the feedback was very positive. The device follows natural arm movement and doesn’t lock in any position. Looks as if it’s indeed more resistant to misalignment than Magic and Angel Arms. The prototype padding could be better, ladder locks and
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Sewn prototype

The most important part of any device is that which interact with human the most. In computing it’s interface, in case of exoskeletons and orthopedics it’s padding attached to the body. The padding determines users comfort and experience with the product and if badly designed, poorly manufactured often leads to users aversion. It’s basic rule of all of us, especially the most gentle: children. I experimented with different types of padding and came to the conclusion that less is more. I mean by that it should be unnoticeable like everyday cloth, be soft and drain the moisture out. I feel more confident in hard surface modeling and got help with sewing from my grandma. I cut the template from cardboard and then from mesh fabric. Grandma added trimming and ribbons. Ladder locks were downloaded from GrabCAD rapid manufactured.
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The screw

Initially all the parts were intended to be printed on desktop 3D printer. This is good approach taken from e-Nable organization – they print prosthetic hands for kids out of charge. Beside being easily available everywhere around the world (thanks for printing services like eg. 3D Hubs) and being relatively cheap desktop 3D printing has its weakness: limited quality. While in most usual cases it’s not the problem (believe me, for most applications desktop printer quality is just great), in arm exoskeletons is one of main factors responsible for locking and jerky movement. Iteration after iteration it was clearly visible that I wouldn’t design another clone of 3D printed WREX. And it wouldn’t have been even possible… Always focused on users comfort and fun of wearing supportive exoskeleton I’ve been trying to keep it slick and friendly. That’s why I reduced number of components and screws to minimum. The less screws means other joining methods must be utilized and this is the reaso
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Battle for space

 Luckily we live a world with all the 3d printers and advanced manufacturing methods. Luckily, because the production of complex parts is a whole lot easier or even possible in some cases. I could not care much about convexity so important in molding since all the plastics are thought to be 3d printed. I came out from external shape, and when I tried to fit a pulley for the first time I was shocked how BIG it was! There wasn’t any space left for bearings! Even if it had been I couldn’t have use them because I want to save weight. Alternative option was Igus plastic bearings (compact and lightweight) but they need precise fit. Moreover I wasn’t sure if they would work on plastic. Things went even more complicated when I realized parts of that shapes printed on budget desktop printer would be too weak to bear the twisting forces. Thanks to CadXpert I had an opportunity to 3d print the most loaded parts from Tough Resin on SLA printer Form 2. The technology itself gives better accu
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Rocky road to refinement

 Days passed… Stuck hard to my design guidelines I was still away from even a tiny sketch of the device. I was sure the direction but the horizon was covered by haze. I could recognize the overall shape but unable to see in details. And the devil is in the details. Working with form is like sculpting in clay; early stages of process give more freedom in reshaping but often it’s double-edge sword: you end up a day devastated by endless versions of nothing. And there’s no place for shortcuts. You can go on with refinement and detailing ONLY after previous stage is done. Every missed step will be only magnified by the next ones. I experimented a little with double bar design similar to Magic Arms, but being still unsatisfied I came up with the idea of hiding whole positioning “drive train”. This is what I like! The devices that are hard to figure out how they actually work! I did one more design choice: to achieve 180 degrees of motion. Its unnecessary in orthopedic appli
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Deeper into mechanics

 Lets take a closer look into the mechanics of the device. First of all: how to transfer moment from distant counterweight to arm module? Simple answer: by cable.  OK, it’s just the beginning of “The Cable Story”. I don’t mean electric wire – the device had to be mechanical only, no motors allowed! Other type of cable is Bowden cable that transmits mechanical force or energy. In some aspects similar to double rod design but flexible . Flexibility means total freedom of placing active device – on the back of wheelchair, on tripod, under the bed. And saves space around passive device at the same time, so helps in achieving second goal – opportunity of mounting directly to corset. I was asking myself if it would work, it should, but thanks to rapid prototyping I could empirically test it. I speed-designed and 3d printed proof-of-concept prototype with 5mm bike derailleurs cables.  It works but bike metal cords are to stiff to be used in next prototypes. I didn’t n
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Design choices

  Recently I had opportunity to talk with two SMA child families and discuss issues in existing exoskeleton solutions. Before that, they mentioned rubber bands of Angel Arms and Magic Arms are difficult to setup, and change its characteristics over time. I came out with a new idea and wanted to verify it with them.   I prepared some generic images of concepts and ask the parents to choose the most comfortable in their opinion. I tried not to bias their decisions, and restrict myself to raw description. A-B test used with parents   They agreed elimination of rubber bands and separation active and passive modules were good starting point.   I did several design choices to follow: the device should be fully mechanical the device should be counterweight driven the active (counterweight) module should be separated from passive (exoskeleton) module passive device (exoskeleton) could be mounted to corset forearm axis should be always
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