25th November 2021
The follow-up you’ve all been waiting for! Here are more ways we tried to destroy our prosthetic device to no avail.
If you have missed the first part of this blog, here’s a recap of how we tried to destroy the Hero Arm. You can also read the outcomes for each test here.
In short, the Hero Arm has been…
The Hero Arm is designed to work safely up to 122°F to ensure it works on those sweltering days. Like many electronic devices, the limiting factor is the temperature the battery can safely work below. The Hero Arm has a safety shutdown to stop the battery from being used above its maximum temperature. At a test centre, we put the Hero Arm in a temperature chamber and cooked it overnight at 131°F. We checked that the shutdown triggered as expected and that the Hero Arm worked as expected after it cooled off a little.
We also have to consider that Hero Arms are shipped around the world. Packages can have a hard life in transit, so the Hero Arm had to survive being baked at 158°F for 6 hours while turned off, ready for shipping.
At the cold end of the spectrum, again, batteries are the limiting factor. We used the same chamber we used for cooking to test the Hero Arm at 14°F while switched on and a chilly -13°F when turned off ready for shipping.
It’s not enough to check that the prosthetic device works at the hottest and coldest temperatures. We also had to account for going from one to the other. This simulates someone walking from outside on a cold and dry winter day into a warm and humid building. The transition can cause problems, including moisture condensing on the inside of the device and getting all the electronics wet. This is one of the most challenging tests to do logistically. We had to control the temperature and humidity and change them rapidly. We actually ended up using two machines for this and transferred the Hero Arm between them quickly.
Electric motors, kettles turning on/off, the electricity in our homes all produce electronic “noise” that can disrupt other electronics from a distance. A lot of work goes on behind the scenes to make sure all our electronic gadgets don’t interfere with each other. Noise is especially a problem for myoelectric prosthetic arms like the Hero Arm. The EMG sensors measure tiny voltages generated by the user’s muscles, distinguishing those from the electronic “noise”. Testing this is difficult because the background noise is everywhere. As such, the test has to be conducted in an “anechoic chamber”, which is a fancy name for a room covered in foam triangles to prevent all the electrical noise from outside getting in. Sensitive instruments can then measure the noise from the Hero Arm and check it’s below the acceptable limit. We can also do the reverse and use equipment to broadcast a range of frequencies to show the Hero Arm is safe no matter what it comes across.
Static electricity can damage electronic devices like the Hero Arm, so the casing has to be a good insulator to stop this from happening. To ensure the Hero Arm can handle the electricity, it was zapped with 15,000 V.
Electricity can actually jump further at lower pressures, and pressure decreases with altitude. The highest city on earth is La Paz in Bolivia at 3,869m (12,694 ft). Most airliners pressurise the cabin to a level equivalent to an altitude of 2,400 m (8,000 ft). Back at the test site, we tested the Hero Arm in a chamber down to a pressure equivalent to 4,000 m (13,123 ft).
All electronic devices have to be flame retardant to prevent short-circuits causing big problems. It’s especially important for a prosthetic device like the Hero Arm. We’ve made sure all the materials have a flame-retardancy rating. Even the covers have been put to the torch.
All the tests the Hero Arm has been put through is to ensure it can handle life’s hard knocks. Please note all of these tests were done in controlled environments so don’t try them at home.
If you want to put the Hero Arm to the test and enjoy a free trial, register your information here.
Author – Jonathan Raines, Head of Research & Development at Open Bionics.