Depends where you count the start and end at. I had a few different ideas of how I might be able to control the wings best and that ended up being the most promising. From when I really started working on the designs until the first successful test? Probably sixteen months. But there was a lot of tinkering and recalibrating after that as well as actually physically adjusting to the new inputs. In a better world they could have been fantastic for prosthetics.