In addition to the sonar and PIR , we are adding in a VL53LOX laser distance sensor. These look very good on paper. 2m range and millimetre accuracy @£10 price point. 2 of these on a hammer bot I would imagine would guarantee a "hit now something is there" detector. Obvs the walls would trigger it but cheaper than the $200 lidar modules like chomp has VL53L0X