Robson-Kanu opened the scoring for Swindon after 13 minutes with a goal from just inside the area beating the diving Steve Mildenhall, who was making another return to his old club.
Then on 18 minutes Swindon had the ball in the back of the net, but the whistle had already gone after a foul on Paynter. Cox took the penalty and made it 2-0.
Before half time Swindon were able to control the play for long periods, including having about 30 passes in a row.
The game seemed to be heading for a 2-0 win before just into injury time Timlim was fouled in the box. Simon Cox again took the penalty and made it 3-0.
Overall a good win for Swindon, who played really well. Swindon's next game is at home to Hereford, who are also in the relegation zone.