15 ways we tried to destroy our myoelectric prosthesis during testing [Part1]

15th November 2021

Wonder how robust the Hero Arm is? To ensure our myoelectric prosthesis can be used in multiple environments and conditions, we have put it through its paces so you don’t have to.

In short, the Hero Arm has been… 

… and thrived.

Here’s how it fared in every test.
Dropped

The drop test is a simple one applied to all medical devices that can be picked up and moved around. It’s dropped onto a hard floor from around table height, 1m.

Crushed

The Hero Arm is made from nylon called PA12, one very commonly used in 3D printing. It’s an incredibly tough material that can take a lot of punishment.

This is the arm with 150 kg pressing down on it. Amazingly the frames were able to hold the weight without breaking.

Stretched

This is how we worked out what the Hero Arm can carry. First, we used our “universal testing machine”, a Lloyd instrument LRX, to apply loads to the hand in multiple orientations.

The system subjected the myoelectric prosthesis to mechanical shocks equivalent to 15 g, that’s a car crash at 30 mph if you stop in just over half a meter (1.5 ft). We did 3 shocks for each direction, up, down, left, right, front and back, so 18 total. The Hero Arm survived in full working order. 

Let it rain!

Although the Hero Arm isn’t waterproof, it still has to be safe to use in the real world, where things like rain showers and spilled drinks can lurk. So for “environmental” testing, we took the Hero Arm to a Product Assessment and Reliability Centre (PARC). There, we can use their accredited lab and get the advice of their expert staff. To simulate a rainy day, we put the Hero Arm in a rig that “rained” on it for 10 minutes (at a drip rate of 3 mm per minute, equivalent to 30 mm of rain falling). We checked that it didn’t cause anything dangerous (like an electric shock) during the test.

We had to open it up and dry it out, but the Hero Arm fully recovered.

To mimic spillages, we poured a pint of water over the hand, again checking for anything dangerous going wrong. Just as it did for the rain test, the Hero Arm came through unscathed.

Shaken

Generally, medical devices stay in hospitals. The ones taken outside, like the Hero Arm, have to meet additional criteria to account for having a more challenging life. This test is designed to mimic a life of hard-knocks.

Back at PARC, we strapped the Hero Arm to a shaker system.

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The system subjected the myoelectric prosthesis to mechanical shocks equivalent to 15 g, that’s a car crash at 30 mph if you stop in just over half a meter (1.5 ft). We did 3 shocks for each direction, up, down, left, right, front and back, so 18 total. The Hero Arm survived in full working order. 

Vibrated

This test is designed to mimic a lifetime of bumpy car rides. We used the same shaker system used for the shaking tests.

Clubbed – watch video

Being on the end of the arm, the hand is vulnerable to being knocked into all sorts of things. The wrist has to be strong enough to absorb those impacts. In this test, we strapped the Hero Arm into this rather macabre pendulum rig which swings the weight into the palm of the hand. We can work out the energy of the impact from the angle we drop the weight from. More than a few prototypes were “decapitated” before we landed on a design that could withstand a beating.

Run into the Ground – watch video!

We had to make sure everything that moves on the Hero Arm can keep going for the full life of the device. We have: 

This video clip shows a cycle test of our motors. The thing inside the motor block is in the Hero Arm. It’s being run continuously to simulate it’s whole life in a short amount of time as possible.

We’ve tested it, so you don’t have to. Please don’t try to recreate any of these at home! 

If you want to know how our myoelectric prosthesis was torched, cooked, frozen and destroyed in more ways, let us know! We’re always up for a smashing sequel.