Old connection in Achilles tendon was damaged by extreme load during jump test. So I redesigned a bit the system. It was possible to use thicker bold, but there is problem with nuts. So I bought cheap tube wrench, cut it to smaller tubes.
Also, I bought some springs. But first tests show, that these springs are too weak.
There is steel tube inset and spring connected.
"Tendons" here are made of copper wire and it works in both ways, but practically, these tendons are like real ones and work only in tension or traction. White and red rubber bands are "power reserve" tendons- this give additional strength when getting up or jumping.