What I've noticed about all of these thermally based systems - this one, the earlier (and DIY capable) one made of fishing line, and heck, even shape memory alloys - they all seem to have relatively slow cycling rates for either the entire cycle, or one half of it.<p>It might take several seconds to contract or relax; or it's fast contracting, but slow to relax. Much of it I think has to do with the thermal mass of the fibers/material, and how it takes longer to relax because the heat is being dissipated slower. Perhaps this could be mitigated using an active cooling system, but that also adds more complexity and takes up more space.<p>Hopefully these issues can be overcome in time, as such muscles and fibers are simpler, relatively cheaper, and more compact than many other actuators.