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

 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

 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