This Saturday I hacked together a foot pedal device that allows the user to turn a door knob or door handle without touching it with their hands. I decided at the beginning of the design process that this hands-free door unlatching device should not require mechanical modifications to the door (i.e. no drilling holes in the door) and should be easily adaptable to any door knob and handle geometry. If you have a 3D printer, this device can be made and installed on any door for less than $5. 

A hose clamp is used a the door knob to adjust to any size of door knob diameter. If connecting to a door handle, a smaller diameter hose clamp could be used. I put the clamp strap in a 1/2in vinyl tube to prevent the strap from scratching the door handle and to protect the user from sharp edges in the event that they need to turn the handle to open the door. The rope is tied around the hose clamp screw using a square knot.

The foot pedal assembly consists of two 3D printed parts. The foot pedal slides up and down the rail plate. Three adhesive picture frame strips are used to attach the rail plate to the door. The rope is tied to the hook feature of the foot pedal. A petroleum jelly lubricant was applied to the contact surfaces between the foot pedal and rail plate to reduce friction and prevent binding.

I included a 0.25mm clearance between the foot pedal and rail plate slide feature in the 3D model. This ensured that the foot pedal would slide on the rail plate without much friction. The 3D printed parts still had more friction than I would have liked. On the next revision, I will use a 0.5mm clearance. 

The parts printed in less than six hours at 30% infill and 0.6mm wall thickness. No support material is required. 

By itself, the foot pedal door unlatch device is not hands free on the pull side of the door without the custom forearm door pull. Unfortunately, adhesive picture frame strips are not strong enough to secure the forearm door pull to the door; a screw or bolted connection to the door is required.

I am pleasantly surprised with the simplicity and flexibility of the final foot pedal door unlatch design. The adhesive picture frame strips enable it to be mounted on any type of flat surface (e.g. wood, glass, metal). The string length can be easily adjusted for any type of door knob or handle geometry. Using the spring of the door knob or handle to return the foot pedal to the top position reduces the foot pedal assembly complexity and part count.

The next unsolved hands-free door challenge is a forearm door hook for the push side of the door. For doors that do not automatically close when you go through them, a pull hook is needed on the push side of the door to pull the door shut after passing through from the pull side. At the moment, I am imagining a modified version of the forearm door pull that I modeled previously (https://hackaday.io/project/170412-hands-free/log/174912-3d-printed-forearm-door-pull).