Most hands-free door ideas I have seen involve covering the handle in foil, taping it up, or shelling out for commercial step plates. Matthew Davis took a different route with a 3D-printed system that turns the knob itself, and it fits regular doorknobs rather than needing any replacement hardware. That seems like the right target to me, since it works with doors people already own.
The setup is refreshingly simple: a foot pedal, a doorknob housing, string, and a door guide. Pressing the pedal pulls the string, which rotates the doorknob and retracts the latch. The mechanism is installed on both the interior and exterior of the door, and the door gets opened from either side. A grey housing mounted on the doorframe carries the cord, and that housing appears to contain a pulley or spring mechanism. Everything is printed plastic.
Two details stand out to me. First, a bead on the string acts as a tensioner to adjust pedal height, a neat touch for fitting different users. Second, the maker deliberately designed it around as few extra parts as possible, even declining an inline spring to keep the count down. My own view is that the restraint pays off, since every added part is another thing to print and fail.
There is one open question worth flagging. The maker demonstrated it while wearing shoes, but it is unconfirmed whether the system works without them, and testing is planned. Anyone hoping to use it barefoot will want to wait for that answer. I also like that when someone warned the rigid mechanism could break on a knob that will not spin, the maker explained the doorknob bracket spins around the knob instead of breaking if pulled hard.
Project by Matthew Davis. Watch it on their YouTube channel: