If you're trying to eliminate the human resistance in 2029
They always do things the hard way in movies - just use biological warfare.
Nerve gas would also work well. Also, in addition to targeting the human soldiers, the robots could target their food supply. Use biological warfare or herbicides against their crops, and starve them.
Anyway, I completely disagree with the premise of TFA. Legged robots are only expensive because of NRE. Once we get beyond custom one-off robots, and go to mass manufacturing, a legged robot should cost less than a car. Most families should be able to afford a robotic household servant. I would gladly pay $10k or even $50k for a robot that could prepare dinner, clear the table, wash the dishes, do laundry, vacuum, babysitting, etc.