Strap compression mechanism

Just putting that out there, a quote from http://web.mit.edu/2.75/projects/DMD_2010_Al_Husseini.pdf:

However, since BVMs were designed for manual operation, their compressible outer surface is made from high-friction material to maintain hand-contact with minimal slippage. This eliminates the option of tightening a strap wrapped around the bag as a means of actuation. To avoid the problems associated with high surface friction, the two main candidates for actuation were a roller chain and cam compression.