I’m working on a project to make inflatable sculptures that react to contact. The inflatable shapes are sewn together out of materials like umbrella fabric and ripstop nylon. Those fabrics block air well, and so a shape made of them can be inflated by a fan.
I am planning to have them react to contact by monitoring the speed of the fans that inflate them. If the inflated shape is pushed, the air pressure in it will increase, and escaping air will try to turn the fan backwards. This should show up as a decrease in fan speed, which I can detect with a microcontroller. The fans are computer cooling fans, so they already have speed sensors built into them. The speed sensors were originally intended to allow the computer that the fans cooled to detect fan failure and shut down gracefully.
I have a couple of inflatable shapes together, but I need a beefier 12V benchtop supply to run them. each fan draws 1.1A at 12V. That is a lot more than a normal computer fan, but these are high-volume server cooling fans, so they move a lot more air.