Been watching, but was not sure if you were worried about breaking the cord or the wooden arms!
If your trials with Venetian blind cord are successful, but you think that you need even more strength then you might consider one of the "exotic" cords used on racing yachts - spectra, dyneema, vectran, kevlar, etc.
For example, 3mm spectra has about double the breaking strength of 3mm polyester venetian blind cord and much less stretch.
Donaghys Superspeed (Spectraspeed) Rope, $1.65 | Whitworths Marine
But it is extremely difficult to cut without a hot knife.