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/diy/ - Do It Yourself



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I have a friend who can't move his lower leg. His walking is reduced to an awkward shuffle that put loads of strain on him.

I want to come up with a sort of leg brace that, when he lifts up his thigh, it bends his knee, and when he puts his thigh down, it stretches the knee out, essentially mimicking the movement he can't do.

I figure this could be accomplished through some ingenious gear-and-strap system without the need for motors, but I'm not sure on the details. Any ideas, guys?
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Tell him to man up and follow a squats and oats routine.
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>>1210960
Yeah, because permanent damage can be fixed with that.

He was in a car accident.
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>>1210957
key is how does it know when to bend?
you need a reference
one option is keep the shin parallel to the body.
take a hint from how e.g. a desk lamp works.
consider a parallelogram. pick one pair of opposite sides. this is the thigh. one other side is the torso, side opposite is the shin.
now if you anchor the torso and adjust the angle between the torso and thigh to mimic lifting the leg you see the shin is kept parallel to the torso.

check out parallelogram 4 bar linkage.
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>>1210957
Have you considered that he walks like that because he literally cannot stretch his legs that far, and to force him to do so would be extremely painful for him?

Just checking. Don't put in a whole lot of work without knowing all the facts
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>>1210957
Build a motorized skateboard.
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>>1210997
It's not painful. The ligaments are busted.

>>1210995
Thanks, that's really helpful.
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>>1210957
Whatever you end up making, just make damn sure there's some physical barrier that prevents hyper extension. Like the actual hinges have that part built solidly and as one piece into their design.
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>>1211008
Thanks for reminding me of that scene in Iron Man 2 where the dude gets his back snapped by the suit.
Blech.
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>>1210957
Whatever you're planing to make will have to be electrically driven. What you've described can only work as a bi-stable system requiring muscle movements to extend and bend the knee(think of a light switch or a toggle switch that's springloaded. Without that activation the contraption will only work one way. It will bend up and the mechanism will hold it up, but your pal won't have the knee strength to activate enough leverage to spring the leg back down.
That being said, your best bet is a clutch system that you're gonna have to toy with and redesign several times.
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welcome to old age drink heavily
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>>1210995
An Exoskeleton That Acts Like a Wearable Chair

>https://www.wired.com/2015/03/exoskeleton-acts-like-wearable-chair/
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>>1210957
How's his ankle. Plantarflexion is pretty important for walking. Best solution would be a full AKO.
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>>1210957
I know it sounds relatively straightforward, but it isn't, unfortunately.

You would struggle to make anything meaningful without complex electronics. Anything that relied on physics alone would be difficult and probably heavy.
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>>1211034
Yeah, I was specifically thinking of that scene and was going to post a webm of it, but decided not to. As someone who has been wanting to make something like that since the 1980s after seeing the cargo lifter in Aliens I've always known there needs to be physical stops for shit like that. Which made the Iron Man scene feel retarded to me because there were no physical stops like that.

>>1211180
Pretty awesome actually.
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>>1211190
Lol what?? By electronics, do you mean hydraulics or servos or similar? I don't see how that would be easier and lighter than a simple mechanism, but I might've misunderstood something here. He would essentially have more pressure on his thigh muscles by moving this mechanism, but it surely wouldn't be actually heavy burden
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>>1210957
http://www.telegraph.co.uk/news/science/11388954/Bionic-leg-Golfer-becomes-first-to-wear-Bluetooth-brace-allowing-him-to-walk-cycle-and-tackle-the-stairs.html
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>>1211238
I think that's why it was included, to make Justin Hammer look like a moron.

Anyway the biggest issue with exoskeletons etc is power. We've been kinda stuck for a few years now when it comes to energy density.
All I want is Adam Jensen legs, is that so much to ask?
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>>1210957

This does sound like a rather unique case for which a passive solution would seem ideal.

Lets simplify, you want three rods, with two rotating joints on the same plane between them, with the bottom rod always pointing in the same direction as the top rod.

I'm no mechanical engineer, but this should be doable with some kind of belt drive (belt instead of chain, so he can simply pull the belt off the pully when he wants free movement).
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>>1210957

Maybe this would be of use to him?

http://www.cadencebiomedical.com
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>>1211335
A passive solution would be ideal in all cases but wouldn't work in this case because OP's cripple friend needs more than active step assistance. But then again, OP hasn't explained in detail exactly which movements have been compromised and by how much. I recommend seeing what a physiotherapist would prescribe and copying the design of that orthotic.

The main issue is that human gait is complicated and aperiodic, along with being highly variable in amplitude, which makes a mechanical system unsuitable. Passive AKOs are only used in cases where only one movement (either flexion or extension) is compromised, movement hasn't been severely hampered, or a strong amount of movement and control isn't required.

Back in grad school, I was working with the school to develop and cheap active assistance AKO, essentially what OP wanted, using position, FSR, EMG, and tri-axial linear acceleration data. This was used in conjunction with gait data from the kinesiology department to determine when to provide assistance.. By the time I left the project, we were able to get it to work with a well-paced gait on a flat surface. Deviate from that and there were issues with keeping up.

There is a reasonably documented passive ankle assist system I read about some time ago which used a clutch system which engaged beginning at heel strike and released stored energy for toe-off. That could be of interest.

The reason why there are bionics and stuff from Boston Dynamics that can do all sorts of crazy shit as apposed to exoskeletons, is that robots are pretty much completely closed systems so the PID loops can be very fine tuned. Hard to do when the inputs to the system are incredibly dynamic and noisy due to humans being a bitch to data-mine from.
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>>1211310
Not so much power, but noise. The government doesn't want noisy exosuits. All you need to do is add an engine for hydraulics and a few other things. It will be as noisy as a motor cycle, two stroke engine, forklift, or other such device depending on design and fuel type. The main problem is that they are not much more practical than things we already have that perform the same jobs.
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>>1210957
>WWAD?




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