Simone Giertz Builds Her Three
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Simone Giertz Builds Her Three

Jul 17, 2023

Sadly, it is quite common for dogs to lose legs. There are several reasons for that. Part of it is because most pet owners simply can't afford the kinds of limb-saving surgeries that doctors perform on people. Such surgeries are also a lower priority for dogs, because many of them can move around well on three legs. But Simone Giertz has a three-legged dog named Scraps that is developing mobility issues as she ages. Scraps is only three years old, so the problem is only going to get worse. To help Scraps live a long and happy life, Giertz built this robotic exoskeleton.

Giertz started by filming Scraps in slow motion as she ran in order to gain an understanding of her gait. That gave Giertz a vague idea for a motorized leg brace that would serve two functions. First, it would provide torque while Scraps extends her leg, which would reduce the muscle strength required to take a step. Second, it would act as a sort of spring cushion to eliminate strain when Scraps steps back down.

But before Giertz could even begin turning that idea into a prototype, she had to find out what kind of wearable Scraps would tolerate. While some dogs are fine with braces and harnesses, others are not. My own dog had to wear a leg brace for years after a hip removal and she hated it. So Giertz experimented with different styles to try and find one Scraps might want to wear. That proved to be difficult, as Scraps didn't like most of the traditional harnesses. But she accepted one particular type of brace and that gave Giertz a jumping-off point.

Giertz doesn't go into much detail about the electronics, but it appears that this exoskeleton utilizes a single brushless DC motor positioned next to the knee joint. Some sort of controller/driver board tells that when to rotate and when to act as a brake. That board includes Bluetooth connectivity so that Giertz can adjust the parameters and receive feedback data via her smartphone. She can, for example, increase the torque a little bit at a time as Scraps becomes accustomed to the exoskeleton. Power comes from a small hobby LiPo battery pack that is easy to swap out or charge.

Scraps seems okay with her new exoskeleton so far, but only time will tell if it is worthwhile in the long term.