Skip to main content

Angel Arms


  The very first arm exoskeleton for kids with SMA I’ve discovered was Angel Arms. Designed by two biomedical engineering students Joseph Kissing and Brooks Schaefer at Grand Valley State University in Grand Rapids, Michigan was simple and beautiful piece of engineering. Its minimalist design use rubber bends to compensate hand weight thus allows less force to move.
  SMA – Spinal Muscular Atrophy is a neuromuscular disorder characterized by loss of motor neurons and progressive muscle wasting. Kids with SMA have very weak muscles and often couldn’t move their arms themselves. Thanks to initiatives like Angel Arms they can finally play, draw and throw a ball, but it’s still emerging field. There are medical companies that produce similar devices but they need a lot of measurements and custom fitting and can’t be ordered remotely because proper setup in their case is crucial and simply they doesn’t work if they’re misaligned. Moreover they need to be replaced multiple times during children growth and becomes too expensive for most parents.
  Low budget 3D printed Angel Arms open doors for frequent replacement on larger ones and general use for kids. This is really dirty cheap (unit for one hand weights less than 100g) and super easy to assembly. So can be 3D printed locally and made by parents themselves. Unfortunately it has also downsides. It’s difficult to mount, setup and operate. Even minor misalignment can prevent the device from working. I would suggest this for kids with milder SMA type (SMA3) as it can rally provide much fun for them. And for parents with basic mechanical skills as it need some of maintenance from time to time.

You can visit and download models from official Angel Arms source page here: https://www.patternspace.co/PatternSet/36

And here is one of polish users of Angel Arms printed by Golem 3D:





Comments

Post a Comment

Popular posts from this blog

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...
Post a Comment
Read more

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 a...
Post a Comment
Read more

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 prototyp...
Post a Comment
Read more