Biped, Experiment 001

I would like to build a cheap, lightweight biped robot. To make it "Fun", i have set the limitation that i can not have any actuators mounted on the legs, they have to be mounted in the torso.

So i started FreeCAD and went to work, first i want to try out how to control the leg using fishing wires as tendons.

And into my Ender 5 Pro it went. Then it was time for assembly.

If you note the rectangular cut outs in the lower leg (at the ancle) my plan was to have the wires go out there and then connect to the loops on the foot. 

Turns out, this was a horrible idea. The wires lifted the lower leg into the air, disconnecting it from the half-sphere at the foot when the wires was tensioned. I had half expected this and had already added holes a secondary mounting option.

This worked much better, now the half sphere and lower leg was forced together instead of apart.

I Used 0.6 mm fishing wire and it was a pain to attach to the loops, i will defenitely redesign the wire attachment on the foot. In the future I will attach it through a 0.65 mm hole and some glue instead of trying to make a knot in a loop.

The "haf-ball" foot joint worked better than expected. 

When the lower and upper leg was attached, there was no room left inside the leg for the wires to pass through the lower leg all the way to the top. So i took them out through the back side of the big hole in the lower leg. This was also a bad idea as this caused the foot actuation to pull on the lower leg casing it to retract.

I tried to resolve this by adding some shrink tube, but it only made it marginally better, mostly because there was no extra space inside the legs, so when the leg got retracted the tube got compressed preventing the wires from running smoothly inside. 

Action list for next version Experiment 002

1. Move kneeJoint so wires can pass all the way throgh lower leg
2. Open up lower leg on the backside
3. Remove loops in foot with "hole attachment" for wires.
4. Improve spacing inside legs, allow for better wire flow / cable management

FreeCAD model available here: https://gitlab.com/maidenOne/RoboticRavings/-/tree/master/Experiment001