I didn’t see any indication that you have formal training in orthotics. If not, keep in mind that you are attaching your device to a human being, and it will likely be powerful enough to injure the person if something goes wrong. Motor controllers can fail in a way that the motor turns on unexpectedly, and of course, a programming error will likely resut in the same thing at some point in its development. So, you have to be pretty good at both biomedical engineering, and in designing ultra-reliable robotics. You’ve seen a need, and you are now hunting for a way to address that need, but you have chosen a very difficult project.
If you want to proceed, I suggest you abandon any idea of strapping anything onto anyone for now. Instead, focus on things that people sit on, or perhaps grab. E.g. there are chairs that will lift up the seat cushion to help a person get out of the chair. Of course, that is a problem that is already solved. But, perhaps you can find another.
I will mention a particular need I see, that is not yet met in the market. Personally, I have a muscle disorder and am easily fatigued. This is only a problem when I go to shopping malls, or to a county fair. I am not an invalid, so I don’t need medical grade equipment to get around. If an scooter occasionally gets stuck when it is used on the grass, I can deal with that. There are some relatively low cost mobility scooters out there, which are both very light (under 40 pounds), and low cost (around $400-$700). But, those cannot go over grass because the single drive wheel just spins in the grass. [ VEVOR Portable 3-Wheel Mobility Scooter for Seniors 12 Mile Range Max 330LBS | eBay or Robot or human? ]. There are other ones out there, that are both light-weight and can be used in grass, but those cost dramatically more. Engineering is not just about calculating forces, but also economics.
The ones with a single front power wheel, cannot go up hill, because all your weight transfers to the unpowered rear wheels. The one with rear-wheel power, really needs both wheels to be powered. Also, you really need larger wheels, such as ones made for hoverboards, that can go over grass. In fact, hoverboards have turned powerful BLDC motors into commodity items.
My bottom line recommendation is to start with something simpler, to help build your robotics skills. And choose something that doesn’t present a danger to its user until you gain the knowledge and experience to properly design a biomedical device.
