Sorry no update for a while, this one will be kinda long due to the scale of my breakthrough. Found reliable ways to produce both nichrome wrapped and regular twisted nylon muscles from 50lb mono filament. I was able to pair together numerous AAA batteries in order to get the amperage needed to contract a muscle quickly. I found I could contract about 10% in 30 seconds with 9 amps when weighted with about a pound.
My great breakthrough was getting multiple muscles working together because unshielded they could touch and create shorts. I first tried to insulate them with silicone conform coating purchased from amazon. But that failed because it restricted movement quite a lot but may be something I come back to.
I found that if I lined up non-wrapped and wrapped in an alternating pattern the non-wraps would insulate the wraps from each other while being heated by their neighbors. To keep the multiple strands at the same tension I put them under load and then 'tune' then until they all appear the right space apart. Following that I clamp them with a small piece of wood and seal them loosely in plastic wrap. I've included some pictures below. My first attempt was with 3 muscles and is a bit stubbier, my second is much longer and with 7 muscles.
More to come soon!