Very strange
I tried this last year after watching RM, to be frank I did'nt think about the complexity of hard versus soft or combinations, I tried what was immediately at hand, which was;
Drill : was a cut off section of the wood used in a basic windbreak, about 300mm long. (broken section so tried it )
Base: basicially a bit of 1" by 2" pine I had, around 400mm long
Bow: shrug, branch off a tree growing from a stump in the garden.
String: paracord
After a few attempts, I made a few adjustments
Drill was reduced from about 300 to 200mm
string was made a LOT looser, friction drives it not tension
Upright and close works better.
This worked very well.....I still have the burn marks in my right thigh to prove it, (got careless showing the system to next door

and let the live end touch my leg.