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 need 100kg payload but frictionless operation. Happily there are plenty of synthetic lines to choose from.

Bowden cables are chosen as a link between active and passive devices. The active devices with counterweights “collects” gravity energy and transmits it through cables to the passive device on the other side where the energy is used to compensate gravity force on child’s arm. Both devices should be in perfect balance and provide true “weightless effect” hard to get in rubber powered devices.

To be continued...

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