The carboard prototype made me notice that the base of the spine was not rigid enough to support the weight and lever forces acting on the foot. I decided to redesign it a little bit to add a support for a second vertebrae and still have room for the electronics below:
I made the notches in opposition to each other so they could counter the torque of the arm.
I struggled to keep these shapes in the available workspace of my 3018 and i had to disable the end switches to gain a few mm of travel.
I'm also using 5mm plywood this time (retailer was out of 3.6mm)
Unfortunately, i made another rookie mistake in the cuts set-up : i didn't add any tabs and put the two legs too close too each other, and my part broke off before the end of the path... I managed to salvage the part by cutting the leftover with a handsaw.
Another irritating issue is the quality of the plywood i used : that micron-thick plated s..t peels as soons as it is being cut , leaving ugly scorch on the edges...
In the end ,the foot needed a little trim to fit to the tip of the leg but the assembly seems promising! I was really worried by the way it would work in real life, but so far so good. It gives me more confidence in my use of blender for the mechanical design !
I also cut the parts for the head and did another dry assembly to have a feel on its volume :