Android 12 Foot and Ankle Assembly

Android 12 Ankle and foot assembly.

This page is about Android 12’s ankle and foot assembly, check out the project index for the rest.

All of the parts will be 3D printed, so my initial work is to design the pieces in CAD. I’m using Autodesk 123D, which is free software. There is a YouTube video about this section, or scroll down for the pictures and words.

Here are the CAD drawings of the foot assembly. The toe section is hinged to the rest of the foot, there are four locating holes in the front of the main part which will hold the toe actuator module. This module will either be a servo or passive springs, so I’ve left it so I can design different variants and interchange them. The main foot is the same for right and left feet, the toes are different however.

There are three sets of horizontal mounting holes in the main foot part. The middle one is for the actual ankle joint, the rear one is for the servo driven tendon, and the front one is for a shock absorber as I mentioned in the initial thoughts page.

The soles of the feet are curved and will be covered with foam so the foot can comply with the ground. The idea being that I can lose a degree of freedom for the sideways tilt of the ankle. These pieces are separate and will be stuck face to face with the upper foot once they are made. I’ve made small pilot holes in both halves so that I can align them.

The next job is to 3D print the pieces, and then design the shin part. Once all the parts actually fit together I’ll publish the CAD source and STL files so you can print your own.

Here are some initial pictures of the 3D printed parts. The top surfaces are a bit messy due to some issues getting the right infill density which I sorted out while printing the soles, but they are mechanically very rigid due to having an internal honeycomb structure:

Here are some marginally better pictures of the assembly. I’ve stuck the soles and main foot parts together, and also glued foam to the bottom of the curved soles to make a compliant surface:

The next stage is the ankle joint and shin.