> accelerate the HDD to its own speed in those 2 ms (maybe it's not realistic, though not obvious to me)
You need to conserve the momentum and kinetic energy, so assuming an elastic collision you're going to accelerate the PC to about half the speed of roomba[1] so you're looking at closer to 25G. With the plastic bumper, you're not getting anywhere near an elastic collision and your contact time is probably a lot longer than .002 due to the deflection. I would not worry too much about this.
You need to conserve the momentum and kinetic energy, so assuming an elastic collision you're going to accelerate the PC to about half the speed of roomba[1] so you're looking at closer to 25G. With the plastic bumper, you're not getting anywhere near an elastic collision and your contact time is probably a lot longer than .002 due to the deflection. I would not worry too much about this.
http://www.convertalot.com/elastic_collision_calculator.html